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INFORMATIONAL
Internet Engineering Task Force (IETF)                  E. Grossman, Ed.
Request for Comments: 8578                                         DOLBY
Category: Informational                                         May 2019
ISSN: 2070-1721


                   Deterministic Networking Use Cases

Abstract

   This document presents use cases for diverse industries that have in
   common a need for "deterministic flows".  "Deterministic" in this
   context means that such flows provide guaranteed bandwidth, bounded
   latency, and other properties germane to the transport of time-
   sensitive data.  These use cases differ notably in their network
   topologies and specific desired behavior, providing as a group broad
   industry context for Deterministic Networking (DetNet).  For each use
   case, this document will identify the use case, identify
   representative solutions used today, and describe potential
   improvements that DetNet can enable.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Not all documents
   approved by the IESG are candidates for any level of Internet
   Standard; see Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc8578.















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Copyright Notice

   Copyright (c) 2019 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1. Introduction ....................................................6
   2. Pro Audio and Video .............................................7
      2.1. Use Case Description .......................................7
           2.1.1. Uninterrupted Stream Playback .......................8
           2.1.2. Synchronized Stream Playback ........................9
           2.1.3. Sound Reinforcement .................................9
           2.1.4. Secure Transmission ................................10
                  2.1.4.1. Safety ....................................10
      2.2. Pro Audio Today ...........................................10
      2.3. Pro Audio in the Future ...................................10
           2.3.1. Layer 3 Interconnecting Layer 2 Islands ............10
           2.3.2. High-Reliability Stream Paths ......................11
           2.3.3. Integration of Reserved Streams into IT Networks ...11
           2.3.4. Use of Unused Reservations by Best-Effort Traffic ..11
           2.3.5. Traffic Segregation ................................11
                  2.3.5.1. Packet-Forwarding Rules, VLANs,
                           and Subnets ...............................12
                  2.3.5.2. Multicast Addressing (IPv4 and IPv6) ......12
           2.3.6. Latency Optimization by a Central Controller .......12
           2.3.7. Reduced Device Costs due to Reduced Buffer Memory ..13
      2.4. Pro Audio Requests to the IETF ............................13
   3. Electrical Utilities ...........................................14
      3.1. Use Case Description ......................................14
           3.1.1. Transmission Use Cases .............................14
                  3.1.1.1. Protection ................................14
                  3.1.1.2. Intra-substation Process Bus
                           Communications ............................21
                  3.1.1.3. Wide-Area Monitoring and Control Systems ..23
                  3.1.1.4. WAN Engineering Guidelines
                           Requirement Classification ................25




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           3.1.2. Generation Use Case ................................26
                  3.1.2.1. Control of the Generated Power ............26
                  3.1.2.2. Control of the Generation Infrastructure ..27
           3.1.3. Distribution Use Case ..............................32
                  3.1.3.1. Fault Location, Isolation, and
                           Service Restoration (FLISR) ...............32
      3.2. Electrical Utilities Today ................................33
           3.2.1. Current Security Practices and Their Limitations ...34
      3.3. Electrical Utilities in the Future ........................35
           3.3.1. Migration to Packet-Switched Networks ..............36
           3.3.2. Telecommunications Trends ..........................37
                  3.3.2.1. General Telecommunications Requirements ...37
                  3.3.2.2. Specific Network Topologies of
                           Smart-Grid Applications ...................38
                  3.3.2.3. Precision Time Protocol ...................38
           3.3.3. Security Trends in Utility Networks ................39
      3.4. Electrical Utilities Requests to the IETF .................41
   4. Building Automation Systems (BASs) .............................41
      4.1. Use Case Description ......................................41
      4.2. BASs Today ................................................42
           4.2.1. BAS Architecture ...................................42
           4.2.2. BAS Deployment Model ...............................44
           4.2.3. Use Cases for Field Networks .......................45
                  4.2.3.1. Environmental Monitoring ..................45
                  4.2.3.2. Fire Detection ............................46
                  4.2.3.3. Feedback Control ..........................46
           4.2.4. BAS Security Considerations ........................46
      4.3. BASs in the Future ........................................46
      4.4. BAS Requests to the IETF ..................................47
   5. Wireless for Industrial Applications ...........................47
      5.1. Use Case Description ......................................47
           5.1.1. Network Convergence Using 6TiSCH ...................48
           5.1.2. Common Protocol Development for 6TiSCH .............48
      5.2. Wireless Industrial Today .................................49
      5.3. Wireless Industrial in the Future .........................49
           5.3.1. Unified Wireless Networks and Management ...........49
                  5.3.1.1. PCE and 6TiSCH ARQ Retries ................51
           5.3.2. Schedule Management by a PCE .......................52
                  5.3.2.1. PCE Commands and 6TiSCH CoAP Requests .....52
                  5.3.2.2. 6TiSCH IP Interface .......................54
           5.3.3. 6TiSCH Security Considerations .....................54
      5.4. Wireless Industrial Requests to the IETF ..................54









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   6. Cellular Radio .................................................54
      6.1. Use Case Description ......................................54
           6.1.1. Network Architecture ...............................54
           6.1.2. Delay Constraints ..................................55
           6.1.3. Time-Synchronization Constraints ...................57
           6.1.4. Transport-Loss Constraints .........................59
           6.1.5. Cellular Radio Network Security Considerations .....60
      6.2. Cellular Radio Networks Today .............................60
           6.2.1. Fronthaul ..........................................60
           6.2.2. Midhaul and Backhaul ...............................60
      6.3. Cellular Radio Networks in the Future .....................61
      6.4. Cellular Radio Networks Requests to the IETF ..............64
   7. Industrial Machine to Machine (M2M) ............................64
      7.1. Use Case Description ......................................64
      7.2. Industrial M2M Communications Today .......................66
           7.2.1. Transport Parameters ...............................66
           7.2.2. Stream Creation and Destruction ....................67
      7.3. Industrial M2M in the Future ..............................67
      7.4. Industrial M2M Requests to the IETF .......................67
   8. Mining Industry ................................................68
      8.1. Use Case Description ......................................68
      8.2. Mining Industry Today .....................................68
      8.3. Mining Industry in the Future .............................69
      8.4. Mining Industry Requests to the IETF ......................70
   9. Private Blockchain .............................................70
      9.1. Use Case Description ......................................70
           9.1.1. Blockchain Operation ...............................71
           9.1.2. Blockchain Network Architecture ....................71
           9.1.3. Blockchain Security Considerations .................72
      9.2. Private Blockchain Today ..................................72
      9.3. Private Blockchain in the Future ..........................72
      9.4. Private Blockchain Requests to the IETF ...................72
   10. Network Slicing ...............................................73
      10.1. Use Case Description .....................................73
      10.2. DetNet Applied to Network Slicing ........................73
           10.2.1. Resource Isolation across Slices ..................73
           10.2.2. Deterministic Services within Slices ..............74
      10.3. A Network Slicing Use Case Example - 5G Bearer Network ...74
      10.4. Non-5G Applications of Network Slicing ...................75
      10.5. Limitations of DetNet in Network Slicing .................75
      10.6. Network Slicing Today and in the Future ..................75
      10.7. Network Slicing Requests to the IETF .....................75
   11. Use Case Common Themes ........................................76
      11.1. Unified, Standards-Based Networks ........................76
           11.1.1. Extensions to Ethernet ............................76
           11.1.2. Centrally Administered Networks ...................76
           11.1.3. Standardized Data-Flow Information Models .........76




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           11.1.4. Layer 2 and Layer 3 Integration ...................76
           11.1.5. IPv4 Considerations ...............................76
           11.1.6. Guaranteed End-to-End Delivery ....................77
           11.1.7. Replacement for Multiple Proprietary
                   Deterministic Networks ............................77
           11.1.8. Mix of Deterministic and Best-Effort Traffic ......77
           11.1.9. Unused Reserved Bandwidth to Be Available
                   to Best-Effort Traffic ............................77
           11.1.10. Lower-Cost, Multi-Vendor Solutions ...............77
      11.2. Scalable Size ............................................78
           11.2.1. Scalable Number of Flows ..........................78
      11.3. Scalable Timing Parameters and Accuracy ..................78
           11.3.1. Bounded Latency ...................................78
           11.3.2. Low Latency .......................................78
           11.3.3. Bounded Jitter (Latency Variation) ................79
           11.3.4. Symmetrical Path Delays ...........................79
      11.4. High Reliability and Availability ........................79
      11.5. Security .................................................79
      11.6. Deterministic Flows ......................................79
   12. Security Considerations .......................................80
   13. IANA Considerations ...........................................80
   14. Informative References ........................................80
   Appendix A. Use Cases Explicitly Out of Scope for DetNet ..........90
     A.1. DetNet Scope Limitations ...................................90
     A.2. Internet-Based Applications ................................90
       A.2.1. Use Case Description ...................................91
         A.2.1.1. Media Content Delivery .............................91
         A.2.1.2. Online Gaming ......................................91
         A.2.1.3. Virtual Reality ....................................91
       A.2.2. Internet-Based Applications Today ......................91
       A.2.3. Internet-Based Applications in the Future ..............91
       A.2.4. Internet-Based Applications Requests to the IETF .......92
     A.3. Pro Audio and Video - Digital Rights Management (DRM) ......92
     A.4. Pro Audio and Video - Link Aggregation .....................92
     A.5. Pro Audio and Video - Deterministic Time to Establish
          Streaming ..................................................93
   Acknowledgments ...................................................93
   Contributors ......................................................95
   Author's Address ..................................................97












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1.  Introduction

   This memo documents use cases for diverse industries that require
   deterministic flows over multi-hop paths.  Deterministic Networking
   (DetNet) flows can be established from either a Layer 2 or Layer 3
   (IP) interface, and such flows can coexist on an IP network with
   best-effort traffic.  DetNet also provides for highly reliable flows
   through provision for redundant paths.

   The DetNet use cases explicitly do not suggest any specific design
   for DetNet architecture or protocols; these are topics for other
   DetNet documents.

   The DetNet use cases, as originally submitted, explicitly were not
   considered by the DetNet Working Group (WG) to be concrete
   requirements.  The DetNet WG and Design Team considered these use
   cases, identifying which of their elements could be feasibly
   implemented within the charter of DetNet; as a result, certain
   originally submitted use cases (or elements thereof) were moved to
   Appendix A ("Use Cases Explicitly Out of Scope for DetNet") of this
   document.

   This document provides context regarding DetNet design decisions.  It
   also serves a long-lived purpose of helping those learning (or new
   to) DetNet understand the types of applications that can be supported
   by DetNet.  It also allows those WG contributors who are users to
   ensure that their concerns are addressed by the WG; for them, this
   document (1) covers their contributions and (2) provides a long-term
   reference regarding the problems that they expect will be served by
   the technology, in terms of the short-term deliverables and also as
   the technology evolves in the future.

   This document has served as a "yardstick" against which proposed
   DetNet designs can be measured, answering the question "To what
   extent does a proposed design satisfy these various use cases?"

   The industries covered by the use cases in this document are

   o  professional audio and video (Section 2)

   o  electrical utilities (Section 3)

   o  building automation systems (BASs) (Section 4)

   o  wireless for industrial applications (Section 5)

   o  cellular radio (Section 6)




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   o  industrial machine to machine (M2M) (Section 7)

   o  mining (Section 8)

   o  private blockchain (Section 9)

   o  network slicing (Section 10)

   For each use case, the following questions are answered:

   o  What is the use case?

   o  How is it addressed today?

   o  How should it be addressed in the future?

   o  What should the IETF deliver to enable this use case?

   The level of detail in each use case is intended to be sufficient to
   express the relevant elements of the use case but no more than that.

   DetNet does not directly address clock distribution or time
   synchronization; these are considered to be part of the overall
   design and implementation of a time-sensitive network, using existing
   (or future) time-specific protocols (such as [IEEE-8021AS] and/or
   [RFC5905]).

   Section 11 enumerates the set of common properties implied by these
   use cases.

2.  Pro Audio and Video

2.1.  Use Case Description

   The professional audio and video industry ("ProAV") includes:

   o  Music and film content creation

   o  Broadcast

   o  Cinema

   o  Live sound

   o  Public address, media, and emergency systems at large venues
      (e.g., airports, stadiums, churches, theme parks)





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   These industries have already transitioned audio and video signals
   from analog to digital.  However, the digital interconnect systems
   remain primarily point to point, with a single signal or a small
   number of signals per link, interconnected with purpose-built
   hardware.

   These industries are now transitioning to packet-based
   infrastructures to reduce cost, increase routing flexibility, and
   integrate with existing IT infrastructures.

   Today, ProAV applications have no way to establish deterministic
   flows from a standards-based Layer 3 (IP) interface; this is a
   fundamental limitation of the use cases described here.  Today,
   deterministic flows can be created within standards-based Layer 2
   LANs (e.g., using IEEE 802.1 TSN ("TSN" stands for "Time-Sensitive
   Networking")); however, these flows are not routable via IP and thus
   are not effective for distribution over wider areas (for example,
   broadcast events that span wide geographical areas).

   It would be highly desirable if such flows could be routed over the
   open Internet; however, solutions of more-limited scope (e.g.,
   enterprise networks) would still provide substantial improvements.

   The following sections describe specific ProAV use cases.

2.1.1.  Uninterrupted Stream Playback

   Transmitting audio and video streams for live playback is unlike
   common file transfer in that uninterrupted stream playback in the
   presence of network errors cannot be achieved by retrying the
   transmission; by the time the missing or corrupt packet has been
   identified, it is too late to execute a retry operation.  Buffering
   can be used to provide enough delay to allow time for one or more
   retries; however, this is not an effective solution in applications
   where large delays (latencies) are not acceptable (as discussed
   below).

   Streams with guaranteed bandwidth can eliminate congestion on the
   network as a cause of transmission errors that would lead to playback
   interruption.  The use of redundant paths can further mitigate
   transmission errors and thereby provide greater stream reliability.

   Additional techniques, such as Forward Error Correction (FEC), can
   also be used to improve stream reliability.







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2.1.2.  Synchronized Stream Playback

   Latency in this context is the time between when a signal is
   initially sent over a stream and when it is received.  A common
   example in ProAV is time-synchronizing audio and video when they take
   separate paths through the playback system.  In this case, the
   latency of both the audio stream and the video stream must be bounded
   and consistent if the sound is to remain matched to the movement in
   the video.  A common tolerance for audio/video synchronization is one
   National Television System Committee (NTSC) video frame (about
   33 ms); to maintain the audience's perception of correct lip-sync,
   the latency needs to be consistent within some reasonable tolerance
   -- for example, 10%.

   A common architecture for synchronizing multiple streams that have
   different paths through the network (and thus potentially different
   latencies) enables measurement of the latency of each path and has
   the data sinks (for example, speakers) delay (buffer) all packets on
   all but the slowest path.  Each packet of each stream is assigned a
   presentation time that is based on the longest required delay.  This
   implies that all sinks must maintain a common time reference of
   sufficient accuracy, which can be achieved by various techniques.

   This type of architecture is commonly implemented using a central
   controller that determines path delays and arbitrates buffering
   delays.

2.1.3.  Sound Reinforcement

   Consider the latency (delay) between the time when a person speaks
   into a microphone and when their voice emerges from the speaker.  If
   this delay is longer than about 10-15 ms, it is noticeable and can
   make a sound-reinforcement system unusable (see slide 6 of
   [SRP_LATENCY]).  (If you have ever tried to speak in the presence of
   a delayed echo of your voice, you might be familiar with this
   experience.)

   Note that the 15 ms latency bound includes all parts of the signal
   path -- not just the network -- so the network latency must be
   significantly less than 15 ms.

   In some cases, local performers must perform in synchrony with a
   remote broadcast.  In such cases, the latencies of the broadcast
   stream and the local performer must be adjusted to match each other,
   with a worst case of one video frame (33 ms for NTSC video).






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   In cases where audio phase is a consideration -- for example,
   beam-forming using multiple speakers -- latency can be in the 10 us
   range (one audio sample at 96 kHz).

2.1.4.  Secure Transmission

2.1.4.1.  Safety

   Professional audio systems can include amplifiers that are capable of
   generating hundreds or thousands of watts of audio power.  If used
   incorrectly, such amplifiers can cause hearing damage to those in the
   vicinity.  Apart from the usual care required by the systems
   operators to prevent such incidents, the network traffic that
   controls these devices must be secured (as with any sensitive
   application traffic).

2.2.  Pro Audio Today

   Some proprietary systems have been created that enable deterministic
   streams at Layer 3; however, they are "engineered networks" that
   require careful configuration to operate and often require that the
   system be over-provisioned.  Also, it is implied that all devices on
   the network voluntarily play by the rules of that network.  To enable
   these industries to successfully transition to an interoperable
   multi-vendor packet-based infrastructure requires effective open
   standards.  Establishing relevant IETF standards is a crucial factor.

2.3.  Pro Audio in the Future

2.3.1.  Layer 3 Interconnecting Layer 2 Islands

   It would be valuable to enable IP to connect multiple Layer 2 LANs.

   As an example, ESPN constructed a state-of-the-art 194,000 sq. ft.,
   $125-million broadcast studio called "Digital Center 2" (DC2).  The
   DC2 network is capable of handling 46 Tbps of throughput with 60,000
   simultaneous signals.  Inside the facility are 1,100 miles of fiber
   feeding four audio control rooms (see [ESPN_DC2]).

   In designing DC2, they replaced as much point-to-point technology as
   they could with packet-based technology.  They constructed seven
   individual studios using Layer 2 LANs (using IEEE 802.1 TSN) that
   were entirely effective at routing audio within the LANs.  However,
   to interconnect these Layer 2 LAN islands together, they ended up
   using dedicated paths in a custom SDN (Software-Defined Networking)
   router because there is no standards-based routing solution
   available.




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2.3.2.  High-Reliability Stream Paths

   On-air and other live media streams are often backed up with
   redundant links that seamlessly act to deliver the content when the
   primary link fails for any reason.  In point-to-point systems, this
   redundancy is provided by an additional point-to-point link; the
   analogous requirement in a packet-based system is to provide an
   alternate path through the network such that no individual link can
   bring down the system.

2.3.3.  Integration of Reserved Streams into IT Networks

   A commonly cited goal of moving to a packet-based media
   infrastructure is that costs can be reduced by using off-the-shelf,
   commodity-network hardware.  In addition, economy of scale can be
   realized by combining media infrastructure with IT infrastructure.
   In keeping with these goals, stream-reservation technology should be
   compatible with existing protocols and should not compromise the use
   of the network for best-effort (non-time-sensitive) traffic.

2.3.4.  Use of Unused Reservations by Best-Effort Traffic

   In cases where stream bandwidth is reserved but not currently used
   (or is underutilized), that bandwidth must be available to
   best-effort (i.e., non-time-sensitive) traffic.  For example, a
   single stream may be "nailed up" (reserved) for specific media
   content that needs to be presented at different times of the day,
   ensuring timely delivery of that content, yet in between those times
   the full bandwidth of the network can be utilized for best-effort
   tasks such as file transfers.

   This also addresses a concern of IT network administrators that are
   considering adding reserved-bandwidth traffic to their networks that
   "users will reserve large quantities of bandwidth and then never
   unreserve it even though they are not using it, and soon the network
   will have no bandwidth left."

2.3.5.  Traffic Segregation

   Sink devices may be low-cost devices with limited processing power.
   In order to not overwhelm the CPUs in these devices, it is important
   to limit the amount of traffic that these devices must process.

   As an example, consider the use of individual seat speakers in a
   cinema.  These speakers are typically required to be cost reduced,
   since the quantities in a single theater can reach hundreds of seats.
   Discovery protocols alone in a 1,000-seat theater can generate enough
   broadcast traffic to overwhelm a low-powered CPU.  Thus, an



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   installation like this will benefit greatly from some type of traffic
   segregation that can define groups of seats to reduce traffic within
   each group.  All seats in the theater must still be able to
   communicate with a central controller.

   There are many techniques that can be used to support this feature,
   including (but not limited to) the following examples.

2.3.5.1.  Packet-Forwarding Rules, VLANs, and Subnets

   Packet-forwarding rules can be used to eliminate some extraneous
   streaming traffic from reaching potentially low-powered sink devices;
   however, there may be other types of broadcast traffic that should be
   eliminated via other means -- for example, VLANs or IP subnets.

2.3.5.2.  Multicast Addressing (IPv4 and IPv6)

   Multicast addressing is commonly used to keep bandwidth utilization
   of shared links to a minimum.

   Because Layer 2 bridges by design forward Media Access Control (MAC)
   addresses, it is important that a multicast MAC address only be
   associated with one stream.  This will prevent reservations from
   forwarding packets from one stream down a path that has no interested
   sinks simply because there is another stream on that same path that
   shares the same multicast MAC address.

   In other words, since each multicast MAC address can represent 32
   different IPv4 multicast addresses, there must be a process in place
   to make sure that any given multicast MAC address is only associated
   with exactly one IPv4 multicast address.  Requiring the use of IPv6
   addresses could help in this regard, due to the much larger address
   range of IPv6; however, due to the continued prevalence of IPv4
   installations, solutions that are effective for IPv4 installations
   would be practical in many more use cases.

2.3.6.  Latency Optimization by a Central Controller

   A central network controller might also perform optimizations based
   on the individual path delays; for example, sinks that are closer to
   the source can inform the controller that they can accept greater
   latency, since they will be buffering packets to match presentation
   times of sinks that are farther away.  The controller might then move
   a stream reservation on a short path to a longer path in order to
   free up bandwidth for other critical streams on that short path.  See
   slides 3-5 of [SRP_LATENCY].





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   Additional optimization can be achieved in cases where sinks have
   differing latency requirements; for example, at a live outdoor
   concert, the speaker sinks have stricter latency requirements than
   the recording-hardware sinks.  See slide 7 of [SRP_LATENCY].

2.3.7.  Reduced Device Costs due to Reduced Buffer Memory

   Device costs can be reduced in a system with guaranteed reservations
   with a small bounded latency due to the reduced requirements for
   buffering (i.e., memory) on sink devices.  For example, a theme park
   might broadcast a live event across the globe via a Layer 3 protocol.
   In such cases, the size of the buffers required is defined by the
   worst-case latency and jitter values of the worst-case segment of the
   end-to-end network path.  For example, on today's open Internet, the
   latency is typically unacceptable for audio and video streaming
   without many seconds of buffering.  In such scenarios, a single
   gateway device at the local network that receives the feed from the
   remote site would provide the expensive buffering required to mask
   the latency and jitter issues associated with long-distance delivery.
   Sink devices in the local location would have no additional buffering
   requirements, and thus no additional costs, beyond those required for
   delivery of local content.  The sink device would be receiving
   packets identical to those sent by the source and would be unaware of
   any latency or jitter issues along the path.

2.4.  Pro Audio Requests to the IETF

   o  Layer 3 routing on top of Audio Video Bridging (AVB) (and/or other
      high-QoS (Quality of Service) networks)

   o  Content delivery with bounded, lowest possible latency

   o  IntServ and DiffServ integration with AVB (where practical)

   o  Single network for A/V and IT traffic

   o  Standards-based, interoperable, multi-vendor solutions

   o  IT-department-friendly networks

   o  Enterprise-wide networks (e.g., the size of San Francisco but not
      the whole Internet (yet...))









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3.  Electrical Utilities

3.1.  Use Case Description

   Many systems that an electrical utility deploys today rely on high
   availability and deterministic behavior of the underlying networks.
   Presented here are use cases for transmission, generation, and
   distribution, including key timing and reliability metrics.  In
   addition, security issues and industry trends that affect the
   architecture of next-generation utility networks are discussed.

3.1.1.  Transmission Use Cases

3.1.1.1.  Protection

   "Protection" means not only the protection of human operators but
   also the protection of the electrical equipment and the preservation
   of the stability and frequency of the grid.  If a fault occurs in the
   transmission or distribution of electricity, then severe damage can
   occur to human operators, electrical equipment, and the grid itself,
   leading to blackouts.

   Communication links, in conjunction with protection relays, are used
   to selectively isolate faults on high-voltage lines, transformers,
   reactors, and other important electrical equipment.  The role of the
   teleprotection system is to selectively disconnect a faulty part by
   transferring command signals within the shortest possible time.

3.1.1.1.1.  Key Criteria

   The key criteria for measuring teleprotection performance are command
   transmission time, dependability, and security.  These criteria are
   defined by International Electrotechnical Commission (IEC)
   Standard 60834 [IEC-60834] as follows:

   o  Transmission time (speed): The time between the moment when a
      state change occurs at the transmitter input and the moment of the
      corresponding change at the receiver output, including propagation
      delay.  The overall operating time for a teleprotection system is
      the sum of (1) the time required to initiate the command at the
      transmitting end, (2) the propagation delay over the network
      (including equipment), and (3) the time required to make the
      necessary selections and decisions at the receiving end, including
      any additional delay due to a noisy environment.







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   o  Dependability: The ability to issue and receive valid commands in
      the presence of interference and/or noise, by minimizing the
      Probability of Missing Commands (PMC).  Dependability targets are
      typically set for a specific Bit Error Rate (BER) level.

   o  Security: The ability to prevent false tripping due to a noisy
      environment, by minimizing the Probability of Unwanted Commands
      (PUC).  Security targets are also set for a specific BER level.

   Additional elements of the teleprotection system that impact its
   performance include:

   o  Network bandwidth

   o  Failure recovery capacity (aka resiliency)

3.1.1.1.2.  Fault Detection and Clearance Timing

   Most power-line equipment can tolerate short circuits or faults for
   up to approximately five power cycles before sustaining irreversible
   damage or affecting other segments in the network.  This translates
   to a total fault clearance time of 100 ms.  As a safety precaution,
   however, the actual operation time of protection systems is limited
   to 70-80% of this period, including fault recognition time, command
   transmission time, and line breaker switching time.

   Some system components, such as large electromechanical switches,
   require a particularly long time to operate and take up the majority
   of the total clearance time, leaving only a 10 ms window for the
   telecommunications part of the protection scheme, independent of the
   distance of travel.  Given the sensitivity of the issue, new
   networks impose requirements that are even more stringent: IEC
   Standard 61850-5:2013 [IEC-61850-5:2013] limits the transfer time for
   protection messages to 1/4-1/2 cycle or 4-8 ms (for 60 Hz lines) for
   messages considered the most critical.
















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3.1.1.1.3.  Symmetric Channel Delay

   Teleprotection channels that are differential must be synchronous;
   this means that any delays on the transmit and receive paths must
   match each other.  Ideally, teleprotection systems support zero
   asymmetric delay; typical legacy relays can tolerate delay
   discrepancies of up to 750 us.

   Some tools available for lowering delay variation below this
   threshold are as follows:

   o  For legacy systems using Time-Division Multiplexing (TDM), jitter
      buffers at the multiplexers on each end of the line can be used to
      offset delay variation by queuing sent and received packets.  The
      length of the queues must balance the need to regulate the rate of
      transmission with the need to limit overall delay, as larger
      buffers result in increased latency.

   o  For jitter-prone IP networks, traffic management tools can ensure
      that the teleprotection signals receive the highest transmission
      priority to minimize jitter.

   o  Standard packet-based synchronization technologies, such as the
      IEEE 1588-2008 Precision Time Protocol (PTP) [IEEE-1588] and
      synchronous Ethernet (syncE) [syncE], can help keep networks
      stable by maintaining a highly accurate clock source on the
      various network devices.
























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3.1.1.1.4.  Teleprotection Network Requirements

   Table 1 captures the main network metrics.  (These metrics are based
   on IEC Standard 61850-5:2013 [IEC-61850-5:2013].)

   +---------------------------------+---------------------------------+
   |    Teleprotection Requirement   |            Attribute            |
   +---------------------------------+---------------------------------+
   |      One-way maximum delay      |             4-10 ms             |
   |                                 |                                 |
   |    Asymmetric delay required    |               Yes               |
   |                                 |                                 |
   |          Maximum jitter         |   Less than 250 us (750 us for  |
   |                                 |           legacy IEDs)          |
   |                                 |                                 |
   |             Topology            |     Point to point, point to    |
   |                                 |            multipoint           |
   |                                 |                                 |
   |           Availability          |             99.9999%            |
   |                                 |                                 |
   |     Precise timing required     |               Yes               |
   |                                 |                                 |
   |  Recovery time on node failure  |    Less than 50 ms - hitless    |
   |                                 |                                 |
   |      Performance management     |          Yes; mandatory         |
   |                                 |                                 |
   |            Redundancy           |               Yes               |
   |                                 |                                 |
   |           Packet loss           |            0.1% to 1%           |
   +---------------------------------+---------------------------------+

               Table 1: Teleprotection Network Requirements



















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3.1.1.1.5.  Inter-trip Protection Scheme

   "Inter-tripping" is the signal-controlled tripping of a circuit
   breaker to complete the isolation of a circuit or piece of apparatus
   in concert with the tripping of other circuit breakers.

   +---------------------------------+---------------------------------+
   |      Inter-trip Protection      |            Attribute            |
   |           Requirement           |                                 |
   +---------------------------------+---------------------------------+
   |      One-way maximum delay      |               5 ms              |
   |                                 |                                 |
   |    Asymmetric delay required    |                No               |
   |                                 |                                 |
   |          Maximum jitter         |           Not critical          |
   |                                 |                                 |
   |             Topology            |     Point to point, point to    |
   |                                 |            multipoint           |
   |                                 |                                 |
   |            Bandwidth            |             64 kbps             |
   |                                 |                                 |
   |           Availability          |             99.9999%            |
   |                                 |                                 |
   |     Precise timing required     |               Yes               |
   |                                 |                                 |
   |  Recovery time on node failure  |    Less than 50 ms - hitless    |
   |                                 |                                 |
   |      Performance management     |          Yes; mandatory         |
   |                                 |                                 |
   |            Redundancy           |               Yes               |
   |                                 |                                 |
   |           Packet loss           |               0.1%              |
   +---------------------------------+---------------------------------+

            Table 2: Inter-trip Protection Network Requirements

3.1.1.1.6.  Current Differential Protection Scheme

   Current differential protection is commonly used for line protection
   and is typically used to protect parallel circuits.  At both ends of
   the lines, the current is measured by the differential relays; both
   relays will trip the circuit breaker if the current going into the
   line does not equal the current going out of the line.  This type of
   protection scheme assumes that some form of communication is present
   between the relays at both ends of the line, to allow both relays to
   compare measured current values.  Line differential protection
   schemes assume that the telecommunications delay between both relays
   is very low -- often as low as 5 ms.  Moreover, as those systems are



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   often not time-synchronized, they also assume that the delay over
   symmetric telecommunications paths is constant; this allows the
   comparison of current measurement values taken at exactly the
   same time.

   +---------------------------------+---------------------------------+
   | Current Differential Protection |            Attribute            |
   |           Requirement           |                                 |
   +---------------------------------+---------------------------------+
   |      One-way maximum delay      |               5 ms              |
   |                                 |                                 |
   |    Asymmetric delay required    |               Yes               |
   |                                 |                                 |
   |          Maximum jitter         |   Less than 250 us (750 us for  |
   |                                 |           legacy IEDs)          |
   |                                 |                                 |
   |             Topology            |     Point to point, point to    |
   |                                 |            multipoint           |
   |                                 |                                 |
   |            Bandwidth            |             64 kbps             |
   |                                 |                                 |
   |           Availability          |             99.9999%            |
   |                                 |                                 |
   |     Precise timing required     |               Yes               |
   |                                 |                                 |
   |  Recovery time on node failure  |    Less than 50 ms - hitless    |
   |                                 |                                 |
   |      Performance management     |          Yes; mandatory         |
   |                                 |                                 |
   |            Redundancy           |               Yes               |
   |                                 |                                 |
   |           Packet loss           |               0.1%              |
   +---------------------------------+---------------------------------+

             Table 3: Current Differential Protection Metrics
















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3.1.1.1.7.  Distance Protection Scheme

   The distance (impedance relay) protection scheme is based on voltage
   and current measurements.  The network metrics are similar (but not
   identical) to the metrics for current differential protection.

   +---------------------------------+---------------------------------+
   | Distance Protection Requirement |            Attribute            |
   +---------------------------------+---------------------------------+
   |      One-way maximum delay      |               5 ms              |
   |                                 |                                 |
   |    Asymmetric delay required    |                No               |
   |                                 |                                 |
   |          Maximum jitter         |           Not critical          |
   |                                 |                                 |
   |             Topology            |     Point to point, point to    |
   |                                 |            multipoint           |
   |                                 |                                 |
   |            Bandwidth            |             64 kbps             |
   |                                 |                                 |
   |           Availability          |             99.9999%            |
   |                                 |                                 |
   |     Precise timing required     |               Yes               |
   |                                 |                                 |
   |  Recovery time on node failure  |    Less than 50 ms - hitless    |
   |                                 |                                 |
   |      Performance management     |          Yes; mandatory         |
   |                                 |                                 |
   |            Redundancy           |               Yes               |
   |                                 |                                 |
   |           Packet loss           |               0.1%              |
   +---------------------------------+---------------------------------+

                 Table 4: Distance Protection Requirements

3.1.1.1.8.  Inter-substation Protection Signaling

   This use case describes the exchange of sampled values and/or GOOSE
   (Generic Object Oriented Substation Events) messages between
   Intelligent Electronic Devices (IEDs) in two substations for
   protection and tripping coordination.  The two IEDs are in
   master-slave mode.

   The Current Transformer or Voltage Transformer (CT/VT) in one
   substation sends the sampled analog voltage or current value to the
   Merging Unit (MU) over hard wire.  The MU sends the time-synchronized
   sampled values (as specified by IEC 61850-9-2:2011
   [IEC-61850-9-2:2011]) to the slave IED.  The slave IED forwards the



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   information to the master IED in the other substation.  The master
   IED makes the determination (for example, based on sampled value
   differentials) to send a trip command to the originating IED.  Once
   the slave IED/relay receives the GOOSE message containing the command
   to trip the breaker, it opens the breaker.  It then sends a
   confirmation message back to the master.  All data exchanges between
   IEDs are through sampled values and/or GOOSE messages.

   +---------------------------------+---------------------------------+
   |   Inter-substation Protection   |            Attribute            |
   |           Requirement           |                                 |
   +---------------------------------+---------------------------------+
   |      One-way maximum delay      |               5 ms              |
   |                                 |                                 |
   |    Asymmetric delay required    |                No               |
   |                                 |                                 |
   |          Maximum jitter         |           Not critical          |
   |                                 |                                 |
   |             Topology            |     Point to point, point to    |
   |                                 |            multipoint           |
   |                                 |                                 |
   |            Bandwidth            |             64 kbps             |
   |                                 |                                 |
   |           Availability          |             99.9999%            |
   |                                 |                                 |
   |     Precise timing required     |               Yes               |
   |                                 |                                 |
   |  Recovery time on node failure  |    Less than 50 ms - hitless    |
   |                                 |                                 |
   |      Performance management     |          Yes; mandatory         |
   |                                 |                                 |
   |            Redundancy           |               Yes               |
   |                                 |                                 |
   |           Packet loss           |                1%               |
   +---------------------------------+---------------------------------+

             Table 5: Inter-substation Protection Requirements

3.1.1.2.  Intra-substation Process Bus Communications

   This use case describes the data flow from the CT/VT to the IEDs in
   the substation via the MU.  The CT/VT in the substation sends the
   analog voltage or current values to the MU over hard wire.  The MU
   converts the analog values into digital format (typically
   time-synchronized sampled values as specified by IEC 61850-9-2:2011
   [IEC-61850-9-2:2011]) and sends them to the IEDs in the substation.
   The Global Positioning System (GPS) Master Clock can send 1PPS or
   IRIG-B format to the MU through a serial port or IEEE 1588 protocol



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   via a network.  1PPS (One Pulse Per Second) is an electrical signal
   that has a width of less than 1 second and a sharply rising or
   abruptly falling edge that accurately repeats once per second.  1PPS
   signals are output by radio beacons, frequency standards, other types
   of precision oscillators, and some GPS receivers.  IRIG (Inter-Range
   Instrumentation Group) time codes are standard formats for
   transferring timing information.  Atomic frequency standards and GPS
   receivers designed for precision timing are often equipped with an
   IRIG output.  Process bus communication using IEC 61850-9-2:2011
   [IEC-61850-9-2:2011] simplifies connectivity within the substation,
   removes the requirement for multiple serial connections, and removes
   the slow serial-bus architectures that are typically used.  This also
   ensures increased flexibility and increased speed with the use of
   multicast messaging between multiple devices.

   +---------------------------------+---------------------------------+
   |   Intra-substation Protection   |            Attribute            |
   |           Requirement           |                                 |
   +---------------------------------+---------------------------------+
   |      One-way maximum delay      |               5 ms              |
   |                                 |                                 |
   |    Asymmetric delay required    |                No               |
   |                                 |                                 |
   |          Maximum jitter         |           Not critical          |
   |                                 |                                 |
   |             Topology            |     Point to point, point to    |
   |                                 |            multipoint           |
   |                                 |                                 |
   |            Bandwidth            |             64 kbps             |
   |                                 |                                 |
   |           Availability          |             99.9999%            |
   |                                 |                                 |
   |     Precise timing required     |               Yes               |
   |                                 |                                 |
   |  Recovery time on node failure  |    Less than 50 ms - hitless    |
   |                                 |                                 |
   |      Performance management     |          Yes; mandatory         |
   |                                 |                                 |
   |            Redundancy           |            Yes or No            |
   |                                 |                                 |
   |           Packet loss           |               0.1%              |
   +---------------------------------+---------------------------------+

             Table 6: Intra-substation Protection Requirements







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3.1.1.3.  Wide-Area Monitoring and Control Systems

   The application of synchrophasor measurement data from Phasor
   Measurement Units (PMUs) to wide-area monitoring and control systems
   promises to provide important new capabilities for improving system
   stability.  Access to PMU data enables more-timely situational
   awareness over larger portions of the grid than what has been
   possible historically with normal SCADA (Supervisory Control and Data
   Acquisition) data.  Handling the volume and the real-time nature of
   synchrophasor data presents unique challenges for existing
   application architectures.  The Wide-Area Management System (WAMS)
   makes it possible for the condition of the bulk power system to be
   observed and understood in real time so that protective,
   preventative, or corrective action can be taken.  Because of the very
   high sampling rate of measurements and the strict requirement for
   time synchronization of the samples, the WAMS has stringent
   telecommunications requirements in an IP network, as captured in
   Table 7:

































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   +---------------------------------+---------------------------------+
   |         WAMS Requirement        |            Attribute            |
   +---------------------------------+---------------------------------+
   |      One-way maximum delay      |              50 ms              |
   |                                 |                                 |
   |    Asymmetric delay required    |                No               |
   |                                 |                                 |
   |          Maximum jitter         |           Not critical          |
   |                                 |                                 |
   |             Topology            |     Point to point, point to    |
   |                                 |    multipoint, multipoint to    |
   |                                 |            multipoint           |
   |                                 |                                 |
   |            Bandwidth            |             100 kbps            |
   |                                 |                                 |
   |           Availability          |             99.9999%            |
   |                                 |                                 |
   |     Precise timing required     |               Yes               |
   |                                 |                                 |
   |  Recovery time on node failure  |    Less than 50 ms - hitless    |
   |                                 |                                 |
   |      Performance management     |          Yes; mandatory         |
   |                                 |                                 |
   |            Redundancy           |               Yes               |
   |                                 |                                 |
   |           Packet loss           |                1%               |
   |                                 |                                 |
   |     Consecutive packet loss     |     At least one packet per     |
   |                                 |    application cycle must be    |
   |                                 |            received.            |
   +---------------------------------+---------------------------------+

             Table 7: WAMS Special Communication Requirements


















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3.1.1.4.  WAN Engineering Guidelines Requirement Classification

   The IEC has published a technical report (TR) that offers guidelines
   on how to define and deploy Wide-Area Networks (WANs) for the
   interconnection of electric substations, generation plants, and SCADA
   operation centers.  IEC TR 61850-90-12:2015 [IEC-61850-90-12:2015]
   provides four classes of WAN communication requirements, as
   summarized in Table 8:

   +----------------+-----------+----------+----------+----------------+
   |      WAN       |  Class WA | Class WB | Class WC |    Class WD    |
   |  Requirement   |           |          |          |                |
   +----------------+-----------+----------+----------+----------------+
   |  Application   |    EHV    | HV (High |    MV    |    General-    |
   |     field      |  (Extra-  | Voltage) | (Medium  |    purpose     |
   |                |    High   |          | Voltage) |                |
   |                |  Voltage) |          |          |                |
   |                |           |          |          |                |
   |    Latency     |    5 ms   |  10 ms   |  100 ms  |    >100 ms     |
   |                |           |          |          |                |
   |     Jitter     |   10 us   |  100 us  |   1 ms   |     10 ms      |
   |                |           |          |          |                |
   |    Latency     |   100 us  |   1 ms   |  10 ms   |     100 ms     |
   |   asymmetry    |           |          |          |                |
   |                |           |          |          |                |
   | Time accuracy  |    1 us   |  10 us   |  100 us  |  10 to 100 ms  |
   |                |           |          |          |                |
   |      BER       |  10^-7 to | 10^-5 to |  10^-3   |                |
   |                |   10^-6   |  10^-4   |          |                |
   |                |           |          |          |                |
   | Unavailability |  10^-7 to | 10^-5 to |  10^-3   |                |
   |                |   10^-6   |  10^-4   |          |                |
   |                |           |          |          |                |
   | Recovery delay |    Zero   |  50 ms   |   5 s    |      50 s      |
   |                |           |          |          |                |
   | Cybersecurity  | Extremely |   High   |  Medium  |     Medium     |
   |                |    high   |          |          |                |
   +----------------+-----------+----------+----------+----------------+

             Table 8: Communication Requirements (Courtesy of
                         IEC TR 61850-90-12:2015)










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3.1.2.  Generation Use Case

   Energy generation systems are complex infrastructures that require
   control of both the generated power and the generation
   infrastructure.

3.1.2.1.  Control of the Generated Power

   The electrical power generation frequency must be maintained within a
   very narrow band.  Deviations from the acceptable frequency range are
   detected, and the required signals are sent to the power plants for
   frequency regulation.

   Automatic Generation Control (AGC) is a system for adjusting the
   power output of generators at different power plants, in response to
   changes in the load.

   +---------------------------------+---------------------------------+
   |     FCAG (Frequency Control     |            Attribute            |
   |      Automatic Generation)      |                                 |
   |           Requirement           |                                 |
   +---------------------------------+---------------------------------+
   |      One-way maximum delay      |              500 ms             |
   |                                 |                                 |
   |    Asymmetric delay required    |                No               |
   |                                 |                                 |
   |          Maximum jitter         |           Not critical          |
   |                                 |                                 |
   |             Topology            |          Point to point         |
   |                                 |                                 |
   |            Bandwidth            |             20 kbps             |
   |                                 |                                 |
   |           Availability          |             99.999%             |
   |                                 |                                 |
   |     Precise timing required     |               Yes               |
   |                                 |                                 |
   |  Recovery time on node failure  |               N/A               |
   |                                 |                                 |
   |      Performance management     |          Yes; mandatory         |
   |                                 |                                 |
   |            Redundancy           |               Yes               |
   |                                 |                                 |
   |           Packet loss           |                1%               |
   +---------------------------------+---------------------------------+

                 Table 9: FCAG Communication Requirements





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3.1.2.2.  Control of the Generation Infrastructure

   The control of the generation infrastructure combines requirements
   from industrial automation systems and energy generation systems.
   This section describes the use case for control of the generation
   infrastructure of a wind turbine.

   Figure 1 presents the subsystems that operate a wind turbine.

                       |
                       |
                       |  +-----------------+
                       |  |   +----+        |
                       |  |   |WTRM| WGEN   |
                  WROT x==|===|    |        |
                       |  |   +----+    WCNV|
                       |  |WNAC             |
                       |  +---+---WYAW---+--+
                       |      |          |
                       |      |          |        +----+
                              |WTRF      |        |WMET|
                              |          |        |    |
                       Wind Turbine      |        +--+-+
                       Controller        |           |
                         WTUR |          |           |
                         WREP |          |           |
                         WSLG |          |           |
                         WALG |     WTOW |           |

                  Figure 1: Wind Turbine Control Network

   The subsystems shown in Figure 1 include the following:

   o  WROT (rotor control)

   o  WNAC (nacelle control) (nacelle: housing containing the generator)

   o  WTRM (transmission control)

   o  WGEN (generator)

   o  WYAW (yaw controller) (of the tower head)

   o  WCNV (in-turbine power converter)

   o  WTRF (wind turbine transformer information)





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   o  WMET (external meteorological station providing real-time
      information to the tower's controllers)

   o  WTUR (wind turbine general information)

   o  WREP (wind turbine report information)

   o  WSLG (wind turbine state log information)

   o  WALG (wind turbine analog log information)

   o  WTOW (wind turbine tower information)

   Traffic characteristics relevant to the network planning and
   dimensioning process in a wind turbine scenario are listed below.
   The values in this section are based mainly on the relevant
   references [Ahm14] and [Spe09].  Each logical node (Figure 1) is a
   part of the metering network and produces analog measurements and
   status information that must comply with their respective data-rate
   constraints.

   +-----------+--------+----------+-----------+-----------+-----------+
   | Subsystem | Sensor |  Analog  | Data Rate |   Status  | Data Rate |
   |           | Count  |  Sample  | (bytes/s) |   Sample  | (bytes/s) |
   |           |        |  Count   |           |   Count   |           |
   +-----------+--------+----------+-----------+-----------+-----------+
   |    WROT   |   14   |    9     |    642    |     5     |     10    |
   |           |        |          |           |           |           |
   |    WTRM   |   18   |    10    |    2828   |     8     |     16    |
   |           |        |          |           |           |           |
   |    WGEN   |   14   |    12    |   73764   |     2     |     4     |
   |           |        |          |           |           |           |
   |    WCNV   |   14   |    12    |   74060   |     2     |     4     |
   |           |        |          |           |           |           |
   |    WTRF   |   12   |    5     |   73740   |     2     |     4     |
   |           |        |          |           |           |           |
   |    WNAC   |   12   |    9     |    112    |     3     |     6     |
   |           |        |          |           |           |           |
   |    WYAW   |   7    |    8     |    220    |     4     |     8     |
   |           |        |          |           |           |           |
   |    WTOW   |   4    |    1     |     8     |     3     |     6     |
   |           |        |          |           |           |           |
   |    WMET   |   7    |    7     |    228    |     -     |     -     |
   +-----------+--------+----------+-----------+-----------+-----------+

               Table 10: Wind Turbine Data-Rate Constraints





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   QoS constraints for different services are presented in Table 11.
   These constraints are defined by IEEE Standard 1646 [IEEE-1646] and
   IEC Standard 61400 Part 25 [IEC-61400-25].

   +---------------------+---------+-------------+---------------------+
   |       Service       | Latency | Reliability |   Packet Loss Rate  |
   +---------------------+---------+-------------+---------------------+
   |  Analog measurement |  16 ms  |    99.99%   |        <10^-6       |
   |                     |         |             |                     |
   |  Status information |  16 ms  |    99.99%   |        <10^-6       |
   |                     |         |             |                     |
   |  Protection traffic |   4 ms  |   100.00%   |        <10^-9       |
   |                     |         |             |                     |
   |    Reporting and    |   1 s   |    99.99%   |        <10^-6       |
   |       logging       |         |             |                     |
   |                     |         |             |                     |
   |  Video surveillance |   1 s   |    99.00%   |     No specific     |
   |                     |         |             |     requirement     |
   |                     |         |             |                     |
   | Internet connection |  60 min |    99.00%   |     No specific     |
   |                     |         |             |     requirement     |
   |                     |         |             |                     |
   |   Control traffic   |  16 ms  |   100.00%   |        <10^-9       |
   |                     |         |             |                     |
   |     Data polling    |  16 ms  |    99.99%   |        <10^-6       |
   +---------------------+---------+-------------+---------------------+

        Table 11: Wind Turbine Reliability and Latency Constraints

3.1.2.2.1.  Intra-domain Network Considerations

   A wind turbine is composed of a large set of subsystems, including
   sensors and actuators that require time-critical operation.  The
   reliability and latency constraints of these different subsystems are
   shown in Table 11.  These subsystems are connected to an intra-domain
   network that is used to monitor and control the operation of the
   turbine and connect it to the SCADA subsystems.  The different
   components are interconnected using fiber optics, industrial buses,
   industrial Ethernet, EtherCAT [EtherCAT], or a combination thereof.
   Industrial signaling and control protocols such as Modbus [MODBUS],
   PROFIBUS [PROFIBUS], PROFINET [PROFINET], and EtherCAT are used
   directly on top of the Layer 2 transport or encapsulated over TCP/IP.

   The data collected from the sensors and condition-monitoring systems
   is multiplexed onto fiber cables for transmission to the base of the
   tower and to remote control centers.  The turbine controller
   continuously monitors the condition of the wind turbine and collects




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   statistics on its operation.  This controller also manages a large
   number of switches, hydraulic pumps, valves, and motors within the
   wind turbine.

   There is usually a controller at the bottom of the tower and also in
   the nacelle.  The communication between these two controllers usually
   takes place using fiber optics instead of copper links.  Sometimes, a
   third controller is installed in the hub of the rotor and manages the
   pitch of the blades.  That unit usually communicates with the nacelle
   unit using serial communications.

3.1.2.2.2.  Inter-domain Network Considerations

   A remote control center belonging to a grid operator regulates the
   power output, enables remote actuation, and monitors the health of
   one or more wind parks in tandem.  It connects to the local control
   center in a wind park over the Internet (Figure 2) via firewalls at
   both ends.  The Autonomous System (AS) path between the local control
   center and the wind park typically involves several ISPs at different
   tiers.  For example, a remote control center in Denmark can regulate
   a wind park in Greece over the normal public AS path between the two
   locations.

   +--------------+
   |              |
   |              |
   | Wind Park #1 +----+
   |              |    |      XXXXXX
   |              |    |      X    XXXXXXXX           +----------------+
   +--------------+    |   XXXX    X      XXXXX       |                |
                       +---+                XXX       | Remote Control |
                           XXX    Internet       +----+     Center     |
                       +----+X                XXX     |                |
   +--------------+    |    XXXXXXX             XX    |                |
   |              |    |          XX     XXXXXXX      +----------------+
   |              |    |            XXXXX
   | Wind Park #2 +----+
   |              |
   |              |
   +--------------+

                Figure 2: Wind Turbine Control via Internet

   The remote control center is part of the SCADA system, setting the
   desired power output to the wind park and reading back the result
   once the new power output level has been set.  Traffic between the
   remote control center and the wind park typically consists of
   protocols like IEC 60870-5-104 [IEC-60870-5-104], OPC XML-Data Access



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   (XML-DA) [OPCXML], Modbus [MODBUS], and SNMP [RFC3411].  At the time
   of this writing, traffic flows between the remote control center and
   the wind park are best effort.  QoS requirements are not strict, so
   no Service Level Agreements (SLAs) or service-provisioning mechanisms
   (e.g., VPNs) are employed.  In the case of such events as equipment
   failure, tolerance for alarm delay is on the order of minutes, due to
   redundant systems already in place.

   Future use cases will require bounded latency, bounded jitter, and
   extraordinarily low packet loss for inter-domain traffic flows due to
   the softwarization and virtualization of core wind-park equipment
   (e.g., switches, firewalls, and SCADA server components).  These
   factors will create opportunities for service providers to install
   new services and dynamically manage them from remote locations.  For
   example, to enable failover of a local SCADA server, a SCADA server
   in another wind-park site (under the administrative control of the
   same operator) could be utilized temporarily (Figure 3).  In that
   case, local traffic would be forwarded to the remote SCADA server,
   and existing intra-domain QoS and timing parameters would have to be
   met for inter-domain traffic flows.

   +--------------+
   |              |
   |              |
   | Wind Park #1 +----+
   |              |    |      XXXXXX
   |              |    |      X    XXXXXXXX           +----------------+
   +--------------+    |   XXXX           XXXXX       |                |
                       +---+      Operator-   XXX     | Remote Control |
                           XXX    Administered   +----+     Center     |
                       +----+X    WAN         XXX     |                |
   +--------------+    |    XXXXXXX             XX    |                |
   |              |    |          XX     XXXXXXX      +----------------+
   |              |    |            XXXXX
   | Wind Park #2 +----+
   |              |
   |              |
   +--------------+

       Figure 3: Wind Turbine Control via Operator-Administered WAN











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3.1.3.  Distribution Use Case

3.1.3.1.  Fault Location, Isolation, and Service Restoration (FLISR)

   "Fault Location, Isolation, and Service Restoration (FLISR)" refers
   to the ability to automatically locate the fault, isolate the fault,
   and restore service in the distribution network.  This will likely
   be the first widespread application of distributed intelligence in
   the grid.

   The static power-switch status (open/closed) in the network dictates
   the power flow to secondary substations.  Reconfiguring the network
   in the event of a fault is typically done manually on site to
   energize/de-energize alternate paths.  Automating the operation of
   substation switchgear allows the flow of power to be altered
   automatically under fault conditions.

   FLISR can be managed centrally from a Distribution Management System
   (DMS) or executed locally through distributed control via intelligent
   switches and fault sensors.































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   +---------------------------------+---------------------------------+
   |        FLISR Requirement        |            Attribute            |
   +---------------------------------+---------------------------------+
   |      One-way maximum delay      |              80 ms              |
   |                                 |                                 |
   |    Asymmetric delay required    |                No               |
   |                                 |                                 |
   |          Maximum jitter         |              40 ms              |
   |                                 |                                 |
   |             Topology            |     Point to point, point to    |
   |                                 |    multipoint, multipoint to    |
   |                                 |            multipoint           |
   |                                 |                                 |
   |            Bandwidth            |             64 kbps             |
   |                                 |                                 |
   |           Availability          |             99.9999%            |
   |                                 |                                 |
   |     Precise timing required     |               Yes               |
   |                                 |                                 |
   |  Recovery time on node failure  |    Depends on customer impact   |
   |                                 |                                 |
   |      Performance management     |          Yes; mandatory         |
   |                                 |                                 |
   |            Redundancy           |               Yes               |
   |                                 |                                 |
   |           Packet loss           |               0.1%              |
   +---------------------------------+---------------------------------+

                Table 12: FLISR Communication Requirements

3.2.  Electrical Utilities Today

   Many utilities still rely on complex environments consisting of
   multiple application-specific proprietary networks, including TDM
   networks.

   In this kind of environment, there is no mixing of Operation
   Technology (OT) and IT applications on the same network, and
   information is siloed between operational areas.

   Specific calibration of the full chain is required; this is costly.

   This kind of environment prevents utility operations from realizing
   operational efficiency benefits, visibility, and functional
   integration of operational information across grid applications and
   data networks.





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   In addition, there are many security-related issues, as discussed in
   the following section.

3.2.1.  Current Security Practices and Their Limitations

   Grid-monitoring and control devices are already targets for cyber
   attacks, and legacy telecommunications protocols have many intrinsic
   network-related vulnerabilities.  For example, the Distributed
   Network Protocol (DNP3) [IEEE-1815], Modbus, PROFIBUS/PROFINET, and
   other protocols are designed around a common paradigm of "request and
   respond".  Each protocol is designed for a master device such as an
   HMI (Human-Machine Interface) system to send commands to subordinate
   slave devices to perform data retrieval (reading inputs) or control
   functions (writing to outputs).  Because many of these protocols lack
   authentication, encryption, or other basic security measures, they
   are prone to network-based attacks, allowing a malicious actor or
   attacker to utilize the request-and-respond system as a mechanism for
   functionality similar to command and control.  Specific security
   concerns common to most industrial-control protocols (including
   utility telecommunications protocols) include the following:

   o  Network or transport errors (e.g., malformed packets or excessive
      latency) can cause protocol failure.

   o  Protocol commands may be available that are capable of forcing
      slave devices into inoperable states, including powering devices
      off, forcing them into a listen-only state, or disabling alarming.

   o  Protocol commands may be available that are capable of
      interrupting processes (e.g., restarting communications).

   o  Protocol commands may be available that are capable of clearing,
      erasing, or resetting diagnostic information such as counters and
      diagnostic registers.

   o  Protocol commands may be available that are capable of requesting
      sensitive information about the controllers, their configurations,
      or other need-to-know information.

   o  Most protocols are application-layer protocols transported over
      TCP; it is therefore easy to transport commands over non-standard
      ports or inject commands into authorized traffic flows.

   o  Protocol commands may be available that are capable of
      broadcasting messages to many devices at once (i.e., a
      potential DoS).





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   o  Protocol commands may be available that will query the device
      network to obtain defined points and their values (i.e., perform a
      configuration scan).

   o  Protocol commands may be available that will list all available
      function codes (i.e., perform a function scan).

   These inherent vulnerabilities, along with increasing connectivity
   between IT and OT networks, make network-based attacks very feasible.
   By injecting malicious protocol commands, an attacker could take
   control over the target process.  Altering legitimate protocol
   traffic can also alter information about a process and disrupt the
   legitimate controls that are in place over that process.  A
   man-in-the-middle attack could result in (1) improper control over a
   process and (2) misrepresentation of data that is sent back to
   operator consoles.

3.3.  Electrical Utilities in the Future

   The business and technology trends that are sweeping the utility
   industry will drastically transform the utility business from the way
   it has been for many decades.  At the core of many of these changes
   is a drive to modernize the electrical grid with an integrated
   telecommunications infrastructure.  However, interoperability
   concerns, legacy networks, disparate tools, and stringent security
   requirements all add complexity to the grid's transformation.  Given
   the range and diversity of the requirements that should be addressed
   by the next-generation telecommunications infrastructure, utilities
   need to adopt a holistic architectural approach to integrate the
   electrical grid with digital telecommunications across the entire
   power delivery chain.

   The key to modernizing grid telecommunications is to provide a
   common, adaptable, multi-service network infrastructure for the
   entire utility organization.  Such a network serves as the platform
   for current capabilities while enabling future expansion of the
   network to accommodate new applications and services.

   To meet this diverse set of requirements both today and in the
   future, the next-generation utility telecommunications network will
   be based on an open-standards-based IP architecture.  An end-to-end
   IP architecture takes advantage of nearly three decades of IP
   technology development, facilitating interoperability and device
   management across disparate networks and devices, as has already been
   demonstrated in many mission-critical and highly secure networks.






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   IPv6 is seen as a future telecommunications technology for the smart
   grid; the IEC and different national committees have mandated a
   specific ad hoc group (AHG8) to define the strategy for migration to
   IPv6 for all the IEC Technical Committee 57 (TC 57) power automation
   standards.  The AHG8 has finalized its work on the migration
   strategy, and IEC TR 62357-200:2015 [IEC-62357-200:2015] has been
   issued.

   Cloud-based SCADA systems will control and monitor the critical and
   non-critical subsystems of generation systems -- for example, wind
   parks.

3.3.1.  Migration to Packet-Switched Networks

   Throughout the world, utilities are increasingly planning for a
   future based on smart-grid applications requiring advanced
   telecommunications systems.  Many of these applications utilize
   packet connectivity for communicating information and control signals
   across the utility's WAN, made possible by technologies such as
   Multiprotocol Label Switching (MPLS).  The data that traverses the
   utility WAN includes:

   o  Grid monitoring, control, and protection data

   o  Non-control grid data (e.g., asset data for condition monitoring)

   o  Data (e.g., voice and video) related to physical safety and
      security

   o  Remote worker access to corporate applications (voice, maps,
      schematics, etc.)

   o  Field area network Backhaul for smart metering

   o  Distribution-grid management

   o  Enterprise traffic (email, collaboration tools, business
      applications)

   WANs support this wide variety of traffic to and from substations,
   the transmission and distribution grid, and generation sites; between
   control centers; and between work locations and data centers.  To
   maintain this rapidly expanding set of applications, many utilities
   are taking steps to evolve present TDM-based and frame relay
   infrastructures to packet systems.  Packet-based networks are
   designed to provide greater functionalities and higher levels of
   service for applications, while continuing to deliver reliability and
   deterministic (real-time) traffic support.



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3.3.2.  Telecommunications Trends

   These general telecommunications topics are provided in addition to
   the use cases that have been addressed so far.  These include both
   current and future telecommunications-related topics that should be
   factored into the network architecture and design.

3.3.2.1.  General Telecommunications Requirements

   o  IP connectivity everywhere

   o  Monitoring services everywhere, and from different remote centers

   o  Moving services to a virtual data center

   o  Unified access to applications/information from the corporate
      network

   o  Unified services

   o  Unified communications solutions

   o  Mix of fiber and microwave technologies - obsolescence of the
      Synchronous Optical Network / Synchronous Digital Hierarchy
      (SONET/SDH) or TDM

   o  Standardizing grid telecommunications protocols to open standards,
      to ensure interoperability

   o  Reliable telecommunications for transmission and distribution
      substations

   o  IEEE 1588 time-synchronization client/server capabilities

   o  Integration of multicast design

   o  Mapping of QoS requirements

   o  Enabling future network expansion

   o  Substation network resilience

   o  Fast convergence design

   o  Scalable headend design

   o  Defining SLAs and enabling SLA monitoring




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   o  Integration of 3G/4G technologies and future technologies

   o  Ethernet connectivity for station bus architecture

   o  Ethernet connectivity for process bus architecture

   o  Protection, teleprotection, and PMUs on IP

3.3.2.2.  Specific Network Topologies of Smart-Grid Applications

   Utilities often have very large private telecommunications networks
   that can cover an entire territory/country.  Until now, the main
   purposes of these networks have been to (1) support transmission
   network monitoring, control, and automation, (2) support remote
   control of generation sites, and (3) provide FCAPS (Fault,
   Configuration, Accounting, Performance, and Security) services from
   centralized network operation centers.

   Going forward, one network will support the operation and maintenance
   of electrical networks (generation, transmission, and distribution),
   voice and data services for tens of thousands of employees and for
   exchanges with neighboring interconnections, and administrative
   services.  To meet those requirements, a utility may deploy several
   physical networks leveraging different technologies across the
   country -- for instance, an optical network and a microwave network.
   Each protection and automation system between two points has two
   telecommunications circuits, one on each network.  Path diversity
   between two substations is key.  Regardless of the event type
   (hurricane, ice storm, etc.), one path needs to stay available so the
   system can still operate.

   In the optical network, signals are transmitted over more than tens
   of thousands of circuits using fiber optic links, microwave links,
   and telephone cables.  This network is the nervous system of the
   utility's power transmission operations.  The optical network
   represents tens of thousands of kilometers of cable deployed along
   the power lines, with individual runs as long as 280 km.

3.3.2.3.  Precision Time Protocol

   Some utilities do not use GPS clocks in generation substations.  One
   of the main reasons is that some of the generation plants are 30 to
   50 meters deep underground and the GPS signal can be weak and
   unreliable.  Instead, atomic clocks are used.  Clocks are
   synchronized amongst each other.  Rubidium clocks provide clock and
   1 ms timestamps for IRIG-B.





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   Some companies plan to transition to PTP [IEEE-1588], distributing
   the synchronization signal over the IP/MPLS network.  PTP provides a
   mechanism for synchronizing the clocks of participating nodes to a
   high degree of accuracy and precision.

   PTP operates based on the following assumptions:

   o  The network eliminates cyclic forwarding of PTP messages within
      each communication path (e.g., by using a spanning tree protocol).

   o  PTP is tolerant of an occasional missed message, duplicated
      message, or message that arrived out of order.  However, PTP
      assumes that such impairments are relatively rare.

   o  As designed, PTP expects a multicast communication model; however,
      PTP also supports a unicast communication model as long as the
      behavior of the protocol is preserved.

   o  Like all message-based time transfer protocols, PTP time accuracy
      is degraded by delay asymmetry in the paths taken by event
      messages.  PTP cannot detect asymmetry, but if such delays are
      known a priori, time values can be adjusted to correct for
      asymmetry.

   The use of PTP for power automation is defined in
   IEC/IEEE 61850-9-3:2016 [IEC-IEEE-61850-9-3:2016].  It is based on
   Annex B of IEC 62439-3:2016 [IEC-62439-3:2016], which offers the
   support of redundant attachment of clocks to Parallel Redundancy
   Protocol (PRP) and High-availability Seamless Redundancy (HSR)
   networks.

3.3.3.  Security Trends in Utility Networks

   Although advanced telecommunications networks can assist in
   transforming the energy industry by playing a critical role in
   maintaining high levels of reliability, performance, and
   manageability, they also introduce the need for an integrated
   security infrastructure.  Many of the technologies being deployed to
   support smart-grid projects such as smart meters and sensors can
   increase the vulnerability of the grid to attack.  Top security
   concerns for utilities migrating to an intelligent smart-grid
   telecommunications platform center on the following trends:

   o  Integration of distributed energy resources

   o  Proliferation of digital devices to enable management, automation,
      protection, and control




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   o  Regulatory mandates to comply with standards for critical
      infrastructure protection

   o  Migration to new systems for outage management, distribution
      automation, condition-based maintenance, load forecasting, and
      smart metering

   o  Demand for new levels of customer service and energy management

   This development of a diverse set of networks to support the
   integration of microgrids, open-access energy competition, and the
   use of network-controlled devices is driving the need for a converged
   security infrastructure for all participants in the smart grid,
   including utilities, energy service providers, large commercial and
   industrial customers, and residential customers.  Securing the assets
   of electric power delivery systems (from the control center to the
   substation, to the feeders and down to customer meters) requires an
   end-to-end security infrastructure that protects the myriad of
   telecommunications assets used to operate, monitor, and control power
   flow and measurement.

   "Cybersecurity" refers to all the security issues in automation and
   telecommunications that affect any functions related to the operation
   of the electric power systems.  Specifically, it involves the
   concepts of:

   o  Integrity: data cannot be altered undetectably

   o  Authenticity (data origin authentication): the telecommunications
      parties involved must be validated as genuine

   o  Authorization: only requests and commands from authorized users
      can be accepted by the system

   o  Confidentiality: data must not be accessible to any
      unauthenticated users

   When designing and deploying new smart-grid devices and
   telecommunications systems, it is imperative to understand the
   various impacts of these new components under a variety of attack
   situations on the power grid.  The consequences of a cyber attack on
   the grid telecommunications network can be catastrophic.  This is why
   security for the smart grid is not just an ad hoc feature or product;
   it's a complete framework integrating both physical and cybersecurity
   requirements and covering the entire smart-grid networks from
   generation to distribution.  Security has therefore become one of the
   main foundations of the utility telecom network architecture and must
   be considered at every layer with a defense-in-depth approach.



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   Migrating to IP-based protocols is key to addressing these challenges
   for two reasons:

   o  IP enables a rich set of features and capabilities to enhance the
      security posture.

   o  IP is based on open standards; this allows interoperability
      between different vendors and products, driving down the costs
      associated with implementing security solutions in OT networks.

   Securing OT telecommunications over packet-switched IP networks
   follows the same principles that are foundational for securing the IT
   infrastructure, i.e., consideration must be given to (1) enforcing
   electronic access control for both person-to-machine and machine-to-
   machine communications and (2) providing the appropriate levels of
   data privacy, device and platform integrity, and threat detection and
   mitigation.

3.4.  Electrical Utilities Requests to the IETF

   o  Mixed Layer 2 and Layer 3 topologies

   o  Deterministic behavior

   o  Bounded latency and jitter

   o  Tight feedback intervals

   o  High availability, low recovery time

   o  Redundancy, low packet loss

   o  Precise timing

   o  Centralized computing of deterministic paths

   o  Distributed configuration (may also be useful)

4.  Building Automation Systems (BASs)

4.1.  Use Case Description

   A BAS manages equipment and sensors in a building for improving
   residents' comfort, reducing energy consumption, and responding to
   failures and emergencies.  For example, the BAS measures the
   temperature of a room using sensors and then controls the HVAC
   (heating, ventilating, and air conditioning) to maintain a set
   temperature and minimize energy consumption.



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   A BAS primarily performs the following functions:

   o  Periodically measures states of devices -- for example, humidity
      and illuminance of rooms, open/close state of doors, fan speed.

   o  Stores the measured data.

   o  Provides the measured data to BAS operators.

   o  Generates alarms for abnormal state of devices.

   o  Controls devices (e.g., turns room lights off at 10:00 PM).

4.2.  BASs Today

4.2.1.  BAS Architecture

   A typical present-day BAS architecture is shown in Figure 4.

                          +----------------------------+
                          |                            |
                          |       BMS        HMI       |
                          |        |          |        |
                          |  +----------------------+  |
                          |  |  Management Network  |  |
                          |  +----------------------+  |
                          |        |          |        |
                          |        LC         LC       |
                          |        |          |        |
                          |  +----------------------+  |
                          |  |     Field Network    |  |
                          |  +----------------------+  |
                          |     |     |     |     |    |
                          |    Dev   Dev   Dev   Dev   |
                          |                            |
                          +----------------------------+

                          BMS: Building Management Server
                          HMI: Human-Machine Interface
                          LC: Local Controller

                        Figure 4: BAS Architecture

   There are typically two layers of a network in a BAS.  The upper
   layer is called the management network, and the lower layer is called
   the field network.  In management networks, an IP-based communication
   protocol is used, while in field networks, non-IP-based communication




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   protocols ("field protocols") are mainly used.  Field networks have
   specific timing requirements, whereas management networks can be best
   effort.

   An HMI is typically a desktop PC used by operators to monitor and
   display device states, send device control commands to Local
   Controllers (LCs), and configure building schedules (for example,
   "turn off all room lights in the building at 10:00 PM").

   A building management server (BMS) performs the following operations.

   o  Collects and stores device states from LCs at regular intervals.

   o  Sends control values to LCs according to a building schedule.

   o  Sends an alarm signal to operators if it detects abnormal device
      states.

   The BMS and HMI communicate with LCs via IP-based "management
   protocols" (see standards [BACnet-IP] and [KNX]).

   An LC is typically a Programmable Logic Controller (PLC) that is
   connected to several tens or hundreds of devices using "field
   protocols".  An LC performs the following kinds of operations:

   o  Measures device states and provides the information to a BMS
      or HMI.

   o  Sends control values to devices, unilaterally or as part of a
      feedback control loop.

   At the time of this writing, many field protocols are in use; some
   are standards-based protocols, and others are proprietary (see
   standards [LonTalk], [MODBUS], [PROFIBUS], and [FL-net]).  The result
   is that BASs have multiple MAC/PHY modules and interfaces.  This
   makes BASs more expensive and slower to develop and can result in
   "vendor lock-in" with multiple types of management applications.














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4.2.2.  BAS Deployment Model

   An example BAS for medium or large buildings is shown in Figure 5.
   The physical layout spans multiple floors and includes a monitoring
   room where the BAS management entities are located.  Each floor will
   have one or more LCs, depending on the number of devices connected to
   the field network.

               +--------------------------------------------------+
               |                                          Floor 3 |
               |     +----LC~~~~+~~~~~+~~~~~+                     |
               |     |          |     |     |                     |
               |     |         Dev   Dev   Dev                    |
               |     |                                            |
               |---  |  ------------------------------------------|
               |     |                                    Floor 2 |
               |     +----LC~~~~+~~~~~+~~~~~+  Field Network      |
               |     |          |     |     |                     |
               |     |         Dev   Dev   Dev                    |
               |     |                                            |
               |---  |  ------------------------------------------|
               |     |                                    Floor 1 |
               |     +----LC~~~~+~~~~~+~~~~~+   +-----------------|
               |     |          |     |     |   | Monitoring Room |
               |     |         Dev   Dev   Dev  |                 |
               |     |                          |    BMS   HMI    |
               |     |   Management Network     |     |     |     |
               |     +--------------------------------+-----+     |
               |                                |                 |
               +--------------------------------------------------+

         Figure 5: BAS Deployment Model for Medium/Large Buildings

   Each LC is connected to the monitoring room via the management
   network, and the management functions are performed within the
   building.  In most cases, Fast Ethernet (e.g., 100BASE-T) is used for
   the management network.  Since the management network is not a
   real-time network, the use of Ethernet without QoS is sufficient for
   today's deployments.

   Many physical interfaces used in field networks have specific timing
   requirements -- for example, RS232C and RS485.  Thus, if a field
   network is to be replaced with an Ethernet or wireless network, such
   networks must support time-critical deterministic flows.







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   Figure 6 shows another deployment model, in which the management
   system is hosted remotely.  This model is becoming popular for small
   offices and residential buildings, in which a standalone monitoring
   system is not cost effective.

                                                     +---------------+
                                                     | Remote Center |
                                                     |               |
                                                     |  BMS     HMI  |
            +------------------------------------+   |   |       |   |
            |                            Floor 2 |   |   +---+---+   |
            |    +----LC~~~~+~~~~~+ Field Network|   |       |       |
            |    |          |     |              |   |     Router    |
            |    |         Dev   Dev             |   +-------|-------+
            |    |                               |           |
            |--- | ------------------------------|           |
            |    |                       Floor 1 |           |
            |    +----LC~~~~+~~~~~+              |           |
            |    |          |     |              |           |
            |    |         Dev   Dev             |           |
            |    |                               |           |
            |    |   Management Network          |     WAN   |
            |    +------------------------Router-------------+
            |                                    |
            +------------------------------------+

              Figure 6: Deployment Model for Small Buildings

   Some interoperability is possible in today's management networks but
   is not possible in today's field networks due to their non-IP-based
   design.

4.2.3.  Use Cases for Field Networks

   Below are use cases for environmental monitoring, fire detection, and
   feedback control, and their implications for field network
   performance.

4.2.3.1.  Environmental Monitoring

   The BMS polls each LC at a maximum measurement interval of 100 ms
   (for example, to draw a historical chart of 1-second granularity with
   a 10x sampling interval) and then performs the operations as
   specified by the operator.  Each LC needs to measure each of its
   several hundred sensors once per measurement interval.  Latency is
   not critical in this scenario as long as all sensor value
   measurements are completed within the measurement interval.
   Availability is expected to be 99.999%.



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4.2.3.2.  Fire Detection

   On detection of a fire, the BMS must stop the HVAC, close the fire
   shutters, turn on the fire sprinklers, send an alarm, etc.  There are
   typically tens of fire sensors per LC that the BMS needs to manage.
   In this scenario, the measurement interval is 10-50 ms, the
   communication delay is 10 ms, and the availability must be 99.9999%.

4.2.3.3.  Feedback Control

   BASs utilize feedback control in various ways; the most time-critical
   is control of DC motors, which require a short feedback interval
   (1-5 ms) with low communication delay (10 ms) and jitter (1 ms).  The
   feedback interval depends on the characteristics of the device and on
   the requirements for the control values.  There are typically tens of
   feedback sensors per LC.

   Communication delay is expected to be less than 10 ms and jitter less
   than 1 ms, while the availability must be 99.9999%.

4.2.4.  BAS Security Considerations

   When BAS field networks were developed, it was assumed that the field
   networks would always be physically isolated from external networks;
   therefore, security was not a concern.  In today's world, many BASs
   are managed remotely and are thus connected to shared IP networks;
   therefore, security is a definite concern.  Note, however, that
   security features are not currently available in the majority of BAS
   field network deployments.

   The management network, being an IP-based network, has the protocols
   available to enable network security, but in practice many BASs do
   not implement even such available security features as device
   authentication or encryption for data in transit.

4.3.  BASs in the Future

   In the future, lower energy consumption and environmental monitoring
   that is more fine-grained will emerge; these will require more
   sensors and devices, thus requiring larger and more-complex building
   networks.

   Building networks will be connected to or converged with other
   networks (enterprise networks, home networks, and the Internet).

   Therefore, better facilities for network management, control,
   reliability, and security are critical in order to improve resident
   and operator convenience and comfort.  For example, the ability to



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   monitor and control building devices via the Internet would enable
   (for example) control of room lights or HVAC from a resident's
   desktop PC or phone application.

4.4.  BAS Requests to the IETF

   The community would like to see an interoperable protocol
   specification that can satisfy the timing, security, availability,
   and QoS constraints described above, such that the resulting
   converged network can replace the disparate field networks.  Ideally,
   this connectivity could extend to the open Internet.

   This would imply an architecture that can guarantee

   o  Low communication delays (from <10 ms to 100 ms in a network of
      several hundred devices)

   o  Low jitter (<1 ms)

   o  Tight feedback intervals (1-10 ms)

   o  High network availability (up to 99.9999%)

   o  Availability of network data in disaster scenarios

   o  Authentication between management devices and field devices (both
      local and remote)

   o  Integrity and data origin authentication of communication data
      between management devices and field devices

   o  Confidentiality of data when communicated to a remote device

5.  Wireless for Industrial Applications

5.1.  Use Case Description

   Wireless networks are useful for industrial applications -- for
   example, (1) when portable, fast-moving, or rotating objects are
   involved and (2) for the resource-constrained devices found in the
   Internet of Things (IoT).

   Such network-connected sensors, actuators, control loops, etc.
   typically require that the underlying network support real-time QoS,
   as well as such specific network properties as reliability,
   redundancy, and security.





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   These networks may also contain very large numbers of devices -- for
   example, for factories, "big data" acquisition, and the IoT.  Given
   the large numbers of devices installed and the potential
   pervasiveness of the IoT, this is a huge and very cost-sensitive
   market such that small cost reductions can save large amounts of
   money.

5.1.1.  Network Convergence Using 6TiSCH

   Some wireless network technologies support real-time QoS and are thus
   useful for these kinds of networks, but others do not.

   This use case focuses on one specific wireless network technology
   that provides the required deterministic QoS: "IPv6 over the TSCH
   mode of IEEE 802.15.4e" (6TiSCH, where "TSCH" stands for
   "Time-Slotted Channel Hopping"; see [Arch-for-6TiSCH], [IEEE-802154],
   and [RFC7554]).

   There are other deterministic wireless buses and networks available
   today; however, they are incompatible with each other and with IP
   traffic (for example, see [ISA100] and [WirelessHART]).

   Thus, the primary goal of this use case is to apply 6TiSCH as a
   converged IP-based and standards-based wireless network for
   industrial applications, i.e., to replace multiple proprietary and/or
   incompatible wireless networking and wireless network management
   standards.

5.1.2.  Common Protocol Development for 6TiSCH

   Today, there are a number of protocols required by 6TiSCH that are
   still in development.  Another goal of this use case is to highlight
   the ways in which these "missing" protocols share goals in common
   with DetNet.  Thus, it is possible that some of the protocol
   technology developed for DetNet will also be applicable to 6TiSCH.

   These protocol goals are identified here, along with their
   relationship to DetNet.  It is likely that ultimately the resulting
   protocols will not be identical but will share design principles that
   contribute to the efficiency of enabling both DetNet and 6TiSCH.

   One such commonality is that -- although on a different time scale --
   in both TSN [IEEE-8021TSNTG] and TSCH, a packet that crosses the
   network from node to node follows a precise schedule, as does a train
   that leaves intermediate stations at precise times along its path.
   This kind of operation reduces collisions, saves energy, and enables
   engineering of the network for deterministic properties.




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   Another commonality is remote monitoring and scheduling management of
   a TSCH network by a Path Computation Element (PCE) and Network
   Management Entity (NME).  The PCE and NME manage timeslots and device
   resources in a manner that minimizes the interaction with, and the
   load placed on, resource-constrained devices.  For example, a tiny
   IoT device may have just enough buffers to store one or a few IPv6
   packets; it will have limited bandwidth between peers such that it
   can maintain only a small amount of peer information, and it will not
   be able to store many packets waiting to be forwarded.  It is
   advantageous, then, for the IoT device to only be required to carry
   out the specific behavior assigned to it by the PCE and NME (as
   opposed to maintaining its own IP stack, for example).

   It is possible that there will be some peer-to-peer communication;
   for example, the PCE may communicate only indirectly with some
   devices in order to enable hierarchical configuration of the system.

   6TiSCH depends on [PCE] and [DetNet-Arch].

   6TiSCH also depends on the fact that DetNet will maintain consistency
   with [IEEE-8021TSNTG].

5.2.  Wireless Industrial Today

   Today, industrial wireless technology ("wireless industrial") is
   accomplished using multiple deterministic wireless networks that are
   incompatible with each other and with IP traffic.

   6TiSCH is not yet fully specified, so it cannot be used in today's
   applications.

5.3.  Wireless Industrial in the Future

5.3.1.  Unified Wireless Networks and Management

   DetNet and 6TiSCH together can enable converged transport of
   deterministic and best-effort traffic flows between real-time
   industrial devices and WANs via IP routing.  A high-level view of
   this type of basic network is shown in Figure 7.












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               ---+-------- ............ ------------
                  |      External Network       |
                  |                          +-----+
               +-----+                       | NME |
               |     | LLN Border            |     |
               |     | Router                +-----+
               +-----+
             o    o   o
      o     o   o     o
         o   o LLN   o    o     o
            o   o   o       o
                    o

      LLN: Low-Power and Lossy Network

                      Figure 7: Basic 6TiSCH Network

   Figure 8 shows a backbone router federating multiple synchronized
   6TiSCH subnets into a single subnet connected to the external
   network.

                  ---+-------- ............ ------------
                     |      External Network       |
                     |                          +-----+
                     |             +-----+      | NME |
                  +-----+          |  +-----+   |     |
                  |     | Router   |  | PCE |   +-----+
                  |     |          +--|     |
                  +-----+             +-----+
                     |                   |
                     | Subnet Backbone   |
               +--------------------+------------------+
               |                    |                  |
            +-----+             +-----+             +-----+
            |     | Backbone    |     | Backbone    |     | Backbone
       o    |     | Router      |     | Router      |     | Router
            +-----+             +-----+             +-----+
       o                  o                   o                 o   o
           o    o   o         o   o  o   o         o  o   o    o
      o             o        o  LLN      o      o         o      o
         o   o    o      o      o o     o  o   o    o    o     o

                     Figure 8: Extended 6TiSCH Network








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   The backbone router must ensure end-to-end deterministic behavior
   between the LLN and the backbone.  This should be accomplished in
   conformance with the work done in [DetNet-Arch] with respect to
   Layer 3 aspects of deterministic networks that span multiple Layer 2
   domains.

   The PCE must compute a deterministic path end to end across the TSCH
   network and IEEE 802.1 TSN Ethernet backbone, and DetNet protocols
   are expected to enable end-to-end deterministic forwarding.

5.3.1.1.  PCE and 6TiSCH ARQ Retries

   6TiSCH uses the Automatic Repeat reQuest (ARQ) mechanism
   [IEEE-802154] to provide higher reliability of packet delivery.  ARQ
   is related to Packet Replication and Elimination (PRE) because there
   are two independent paths for packets to arrive at the destination.
   If an expected packet does not arrive on one path, then it checks for
   the packet on the second path.

   Although to date this mechanism is only used by wireless networks,
   this technique might be appropriate for DetNet, and aspects of the
   enabling protocol could therefore be co-developed.

   For example, in Figure 9, a track is laid out from a field device in
   a 6TiSCH network to an IoT gateway that is located on an IEEE 802.1
   TSN backbone.

                     +-----+
                     | IoT |
                     | G/W |
                     +-----+
                        ^  <---- Elimination
                       | |
        Track Branch   | |
               +-------+ +--------+ Subnet Backbone
               |                  |
            +--|--+            +--|--+
            |  |  | Backbone   |  |  | Backbone
       o    |  |  | Router     |  |  | Router
            +--/--+            +--|--+
       o     /    o     o---o----/       o
           o    o---o--/   o      o   o  o   o
      o     \  /     o               o   LLN    o
         o   v  <---- Replication
             o

                     Figure 9: 6TiSCH Network with PRE




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   In ARQ, the replication function in the field device sends a copy of
   each packet over two different branches, and the PCE schedules each
   hop of both branches so that the two copies arrive in due time at the
   gateway.  In the case of a loss on one branch, one hopes that the
   other copy of the packet will still arrive within the allocated time.
   If two copies make it to the IoT gateway, the elimination function in
   the gateway ignores the extra packet and presents only one copy to
   upper layers.

   At each 6TiSCH hop along the track, the PCE may schedule more than
   one timeslot for a packet, so as to support Layer 2 retries (ARQ).

   At the time of this writing, a deployment's TSCH track does not
   necessarily support PRE but is systematically multipath.  This means
   that a track is scheduled so as to ensure that each hop has at least
   two forwarding solutions.  The forwarding decision will be to try the
   preferred solution and use the other solution in the case of Layer 2
   transmission failure as detected by ARQ.

5.3.2.  Schedule Management by a PCE

   A common feature of 6TiSCH and DetNet is actions taken by a PCE when
   configuring paths through the network.  Specifically, what is needed
   is a protocol and data model that the PCE will use to get/set the
   relevant configuration from/to the devices, as well as perform
   operations on the devices.  Specifically, both DetNet and 6TiSCH need
   to develop a protocol (and associated data model) that the PCE can
   use to (1) get/set the relevant configuration from/to the devices and
   (2) perform operations on the devices.  These could be initially
   developed by DetNet, with consideration for their reuse by 6TiSCH.
   The remainder of this section provides a bit more context from the
   6TiSCH side.

5.3.2.1.  PCE Commands and 6TiSCH CoAP Requests

   The 6TiSCH device does not expect to place the request for bandwidth
   between itself and another device in the network.  Rather, an
   operation control system invoked through a human interface specifies
   the traffic requirements and the end nodes (in terms of latency and
   reliability).  Based on this information, the PCE must compute a path
   between the end nodes and provision the network with per-flow state
   that describes the per-hop operation for a given packet, the
   corresponding timeslots, the flow identification that enables
   recognizing that a certain packet belongs to a certain path, etc.

   For a static configuration that serves a certain purpose for a long
   period of time, it is expected that a node will be provisioned in one
   shot with a full schedule, i.e., a schedule that defines the behavior



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   of the node with respect to all data flows through that node. 6TiSCH
   expects that the programming of the schedule will be done over the
   Constrained Application Protocol (CoAP) as discussed in
   [CoAP-6TiSCH].

   6TiSCH expects that the PCE commands will be mapped back and forth
   into CoAP by a gateway function at the edge of the 6TiSCH network.
   For instance, it is possible that a mapping entity on the backbone
   transforms a non-CoAP protocol such as the Path Computation Element
   Communication Protocol (PCEP) into the RESTful interfaces that the
   6TiSCH devices support.  This architecture will be refined to comply
   with DetNet [DetNet-Arch] when the work is formalized.  Related
   information about 6TiSCH can be found in [Interface-6TiSCH-6top] and
   [RFC6550] ("RPL: IPv6 Routing Protocol for Low-Power and Lossy
   Networks").

   A protocol may be used to update the state in the devices during
   runtime -- for example, if it appears that a path through the network
   has ceased to perform as expected, but in 6TiSCH that flow was not
   designed and no protocol was selected.  DetNet should define the
   appropriate end-to-end protocols to be used in that case.  The
   implication is that these state updates take place once the system is
   configured and running, i.e., they are not limited to the initial
   communication of the configuration of the system.

   A "slotFrame" is the base object that a PCE would manipulate to
   program a schedule into an LLN node [Arch-for-6TiSCH].

   The PCE should read energy data from devices and compute paths that
   will implement policies on how energy in devices is consumed -- for
   instance, to ensure that the spent energy does not exceed the
   available energy over a period of time.  Note that this statement
   implies that an extensible protocol for communicating device
   information to the PCE and enabling the PCE to act on it will be part
   of the DetNet architecture; however, for subnets with specific
   protocols (e.g., CoAP), a gateway may be required.

   6TiSCH devices can discover their neighbors over the radio using a
   mechanism such as beacons, but even though the neighbor information
   is available in the 6TiSCH interface data model, 6TiSCH does not
   describe a protocol to proactively push the neighbor information to a
   PCE.  DetNet should define such a protocol; one possible design
   alternative is that it could operate over CoAP.  Alternatively, it
   could be converted to/from CoAP by a gateway.  Such a protocol could
   carry multiple metrics -- for example, metrics similar to those used
   for RPL operations [RFC6551].





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5.3.2.2.  6TiSCH IP Interface

   Protocol translation between the TSCH MAC layer and IP is
   accomplished via the "6top" sublayer [Sublayer-6TiSCH-6top].  The
   6top data model and management interfaces are further discussed in
   [Interface-6TiSCH-6top] and [CoAP-6TiSCH].

   An IP packet that is sent along a 6TiSCH path uses a differentiated
   services Per-Hop Behavior Group (PHB) called "deterministic
   forwarding", as described in [Det-Fwd-PHB].

5.3.3.  6TiSCH Security Considerations

   In addition to the classical requirements for protection of control
   signaling, it must be noted that 6TiSCH networks operate on limited
   resources that can be depleted rapidly in a DoS attack on the system
   -- for instance, by placing a rogue device in the network or by
   obtaining management control and setting up unexpected additional
   paths.

5.4.  Wireless Industrial Requests to the IETF

   6TiSCH depends on DetNet to define:

   o  Configuration (state) and operations for deterministic paths

   o  End-to-end protocols for deterministic forwarding (tagging, IP)

   o  A protocol for PRE

6.  Cellular Radio

6.1.  Use Case Description

   This use case describes the application of deterministic networking
   in the context of cellular telecom transport networks.  Important
   elements include time synchronization, clock distribution, and ways
   to establish time-sensitive streams for both Layer 2 and Layer 3
   user-plane traffic.

6.1.1.  Network Architecture

   Figure 10 illustrates a 3GPP-defined cellular network architecture
   typical at the time of this writing.  The architecture includes
   "Fronthaul", "Midhaul", and "Backhaul" network segments.  The
   "Fronthaul" is the network connecting base stations (Baseband Units
   (BBUs)) to the Remote Radio Heads (RRHs) (also referred to here as
   "antennas").  The "Midhaul" is the network that interconnects base



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   stations (or small-cell sites).  The "Backhaul" is the network or
   links connecting the radio base station sites to the network
   controller/gateway sites (i.e., the core of the 3GPP cellular
   network).

              Y (RRHs (antennas))
               \
           Y__  \.--.                   .--.         +------+
              \_(    `.     +---+     _(    `.       | 3GPP |
       Y------( Front- )----|eNB|----( Back-  )------| core |
             ( `  .haul )   +---+   ( ` .haul) )     | netw |
             /`--(___.-'      \      `--(___.-'      +------+
          Y_/     /            \.--.       \
               Y_/            _(Mid-`.      \
                             (   haul )      \
                            ( `  .  )  )      \
                             `--(___.-'\_____+---+    (small-cell sites)
                                   \         |SCe|__Y
                                  +---+      +---+
                               Y__|eNB|__Y
                                  +---+
                                Y_/   \_Y ("local" radios)

        Figure 10: Generic 3GPP-Based Cellular Network Architecture

   In Figure 10, "eNB" ("E-UTRAN Node B") is the hardware that is
   connected to the mobile phone network and enables the mobile phone
   network to communicate with mobile handsets [TS36300].  ("E-UTRAN"
   stands for "Evolved Universal Terrestrial Radio Access Network".)

6.1.2.  Delay Constraints

   The available processing time for Fronthaul networking overhead is
   limited to the available time after the baseband processing of the
   radio frame has completed.  For example, in Long Term Evolution (LTE)
   radio, 3 ms is allocated for the processing of a radio frame, but
   typically the baseband processing uses most of it, allowing only a
   small fraction to be used by the Fronthaul network.  In this example,
   out of 3 ms, the maximum time allocated to the Fronthaul network for
   one-way delay is 250 us, and the existing specification [NGMN-Fronth]
   specifies a maximum delay of only 100 us.  This ultimately determines
   the distance the RRHs can be located from the base stations (e.g.,
   100 us equals roughly 20 km of optical fiber-based transport).
   Allocation options regarding the available time budget between
   processing and transport are currently undergoing heavy discussion in
   the mobile industry.





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   For packet-based transport, the allocated transport time between the
   RRH and the BBU is consumed by node processing, buffering, and
   distance-incurred delay.  An example of the allocated transport time
   is 100 us (from the Common Public Radio Interface [CPRI]).

   The baseband processing time and the available "delay budget" for the
   Fronthaul is likely to change in the forthcoming "5G" due to reduced
   radio round-trip times and other architectural and service
   requirements [NGMN].

   The transport time budget, as noted above, places limitations on the
   distance that RRHs can be located from base stations (i.e., the link
   length).  In the above analysis, it is assumed that the entire
   transport time budget is available for link propagation delay.
   However, the transport time budget can be broken down into three
   components: scheduling/queuing delay, transmission delay, and link
   propagation delay.  Using today's Fronthaul networking technology,
   the queuing, scheduling, and transmission components might become the
   dominant factors in the total transport time, rather than the link
   propagation delay.  This is especially true in cases where the
   Fronthaul link is relatively short and is shared among multiple
   Fronthaul flows -- for example, in indoor and small-cell networks,
   massive Multiple Input Multiple Output (MIMO) antenna networks, and
   split Fronthaul architectures.

   DetNet technology can improve Fronthaul networks by controlling and
   reducing the time required for the queuing, scheduling, and
   transmission operations by properly assigning network resources, thus
   (1) leaving more of the transport time budget available for link
   propagation and (2) enabling longer link lengths.  However, link
   length is usually a predetermined parameter and is not a controllable
   network parameter, since RRH and BBU sites are usually located in
   predetermined locations.  However, the number of antennas in an RRH
   site might increase -- for example, by adding more antennas,
   increasing the MIMO capability of the network, or adding support for
   massive MIMO.  This means increasing the number of Fronthaul flows
   sharing the same Fronthaul link.  DetNet can now control the
   bandwidth assignment of the Fronthaul link and the scheduling of
   Fronthaul packets over this link and can provide adequate buffer
   provisioning for each flow to reduce the packet loss rate.

   Another way in which DetNet technology can aid Fronthaul networks is
   by providing effective isolation between flows -- for example,
   between flows originating in different slices within a network-sliced
   5G network.  Note, however, that this isolation applies to DetNet
   flows for which resources have been preallocated, i.e., it does not
   apply to best-effort flows within a DetNet.  DetNet technology can
   also dynamically control the bandwidth-assignment, scheduling, and



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   packet-forwarding decisions, as well as the buffer provisioning of
   the Fronthaul flows to guarantee the end-to-end delay of the
   Fronthaul packets and minimize the packet loss rate.

   [METIS] documents the fundamental challenges as well as overall
   technical goals of the future 5G mobile and wireless systems as the
   starting point.  These future systems should support much higher data
   volumes and rates and significantly lower end-to-end latency for 100x
   more connected devices (at cost and energy-consumption levels similar
   to today's systems).

   For Midhaul connections, delay constraints are driven by inter-site
   radio functions such as Coordinated Multi-Point (CoMP) processing
   (see [CoMP]).  CoMP reception and transmission constitute a framework
   in which multiple geographically distributed antenna nodes cooperate
   to improve performance for the users served in the common cooperation
   area.  The design principle of CoMP is to extend single-cell-to-
   multi-UE (User Equipment) transmission to a multi-cell-to-multi-UE
   transmission via cooperation among base stations.

   CoMP has delay-sensitive performance parameters: "Midhaul latency"
   and "CSI (Channel State Information) reporting and accuracy".  The
   essential feature of CoMP is signaling between eNBs, so Midhaul
   latency is the dominating limitation of CoMP performance.  Generally,
   CoMP can benefit from coordinated scheduling (either distributed or
   centralized) of different cells if the signaling delay between eNBs
   is within 1-10 ms.  This delay requirement is both rigid and
   absolute, because any uncertainty in delay will degrade performance
   significantly.

   Inter-site CoMP is one of the key requirements for 5G and is also a
   goal for 4.5G network architectures.

6.1.3.  Time-Synchronization Constraints

   Fronthaul time-synchronization requirements are given by [TS25104],
   [TS36104], [TS36211], and [TS36133].  These can be summarized for the
   3GPP LTE-based networks as:

   Delay accuracy:
      +-8 ns (i.e., +-1/32 Tc, where Tc is the Universal Mobile
      Telecommunications System (UMTS) Chip time of 1/3.84 MHz),
      resulting in a round-trip accuracy of +-16 ns.  The value is this
      low in order to meet the 3GPP Timing Alignment Error (TAE)
      measurement requirements.  Note that performance guarantees of
      low-nanosecond values such as these are considered to be below the
      DetNet layer -- it is assumed that the underlying implementation
      (e.g., the hardware) will provide sufficient support (e.g.,



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      buffering) to enable this level of accuracy.  These values are
      maintained in the use case to give an indication of the overall
      application.

   TAE:
      TAE is problematic for Fronthaul networks and must be minimized.
      If the transport network cannot guarantee TAE levels that are low
      enough, then additional buffering has to be introduced at the
      edges of the network to buffer out the jitter.  Buffering is not
      desirable, as it reduces the total available delay budget.

      Packet Delay Variation (PDV) requirements can be derived from TAE
      measurements for packet-based Fronthaul networks.

      *  For MIMO or TX diversity transmissions, at each carrier
         frequency, TAE measurements shall not exceed 65 ns (i.e.,
         1/4 Tc).

      *  For intra-band contiguous carrier aggregation, with or without
         MIMO or TX diversity, TAE measurements shall not exceed 130 ns
         (i.e., 1/2 Tc).

      *  For intra-band non-contiguous carrier aggregation, with or
         without MIMO or TX diversity, TAE measurements shall not exceed
         260 ns (i.e., 1 Tc).

      *  For inter-band carrier aggregation, with or without MIMO or TX
         diversity, TAE measurements shall not exceed 260 ns.

   Transport link contribution to radio frequency errors:
      +-2 PPB.  This value is considered to be "available" for the
      Fronthaul link out of the total 50 PPB budget reserved for the
      radio interface.  Note that the transport link contributes to
      radio frequency errors for the following reason: at the time of
      this writing, Fronthaul communication is direct communication from
      the radio unit to the RRH.  The RRH is essentially a passive
      device (e.g., without buffering).  The transport drives the
      antenna directly by feeding it with samples, and everything the
      transport adds will be introduced to the radio "as is".  So, if
      the transport causes any additional frequency errors, the errors
      will show up immediately on the radio as well.  Note that
      performance guarantees of low-nanosecond values such as these are
      considered to be below the DetNet layer -- it is assumed that the
      underlying implementation (e.g., the hardware) will provide
      sufficient support to enable this level of performance.  These
      values are maintained in the use case to give an indication of the
      overall application.




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   The above-listed time-synchronization requirements are difficult to
   meet with point-to-point connected networks and are more difficult to
   meet when the network includes multiple hops.  It is expected that
   networks must include buffering at the ends of the connections as
   imposed by the jitter requirements, since trying to meet the jitter
   requirements in every intermediate node is likely to be too costly.
   However, every measure to reduce jitter and delay on the path makes
   it easier to meet the end-to-end requirements.

   In order to meet the timing requirements, both senders and receivers
   must remain time synchronized, demanding very accurate clock
   distribution -- for example, support for IEEE 1588 transparent clocks
   or boundary clocks in every intermediate node.

   In cellular networks from the LTE radio era onward, phase
   synchronization is needed in addition to frequency synchronization
   [TS36300] [TS23401].  Time constraints are also important due to
   their impact on packet loss.  If a packet is delivered too late, then
   the packet may be dropped by the host.

6.1.4.  Transport-Loss Constraints

   Fronthaul and Midhaul networks assume that transport is almost
   error free.  Errors can cause a reset of the radio interfaces, in
   turn causing reduced throughput or broken radio connectivity for
   mobile customers.

   For packetized Fronthaul and Midhaul connections, packet loss may be
   caused by BER, congestion, or network failure scenarios.  Different
   Fronthaul "functional splits" are being considered by 3GPP, requiring
   strict Frame Loss Ratio (FLR) guarantees.  As one example (referring
   to the legacy CPRI split, which is option 8 in 3GPP), lower-layer
   splits may imply an FLR of less than 10^-7 for data traffic and less
   than 10^-6 for control and management traffic.

   Many of the tools available for eliminating packet loss for Fronthaul
   and Midhaul networks have serious challenges; for example,
   retransmitting lost packets or using FEC to circumvent bit errors (or
   both) is practically impossible, due to the additional delay
   incurred.  Using redundant streams for better guarantees of delivery
   is also practically impossible in many cases, due to high bandwidth
   requirements for Fronthaul and Midhaul networks.  Protection
   switching is also a candidate, but at the time of this writing,
   available technologies for the path switch are too slow to avoid a
   reset of mobile interfaces.






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   It is assumed that Fronthaul links are symmetric.  All Fronthaul
   streams (i.e., those carrying radio data) have equal priority and
   cannot delay or preempt each other.

   All of this implies that it is up to the network to guarantee that
   each time-sensitive flow meets its schedule.

6.1.5.  Cellular Radio Network Security Considerations

   Establishing time-sensitive streams in the network entails reserving
   networking resources for long periods of time.  It is important that
   these reservation requests be authenticated to prevent malicious
   reservation attempts from hostile nodes (or accidental
   misconfiguration).  This is particularly important in the case where
   the reservation requests span administrative domains.  Furthermore,
   the reservation information itself should be digitally signed to
   reduce the risk of a legitimate node pushing a stale or hostile
   configuration into another networking node.

   Note: This is considered important for the security policy of the
   network but does not affect the core DetNet architecture and design.

6.2.  Cellular Radio Networks Today

6.2.1.  Fronthaul

   Today's Fronthaul networks typically consist of:

   o  Dedicated point-to-point fiber connection (common)

   o  Proprietary protocols and framings

   o  Custom equipment and no real networking

   At the time of this writing, solutions for Fronthaul are direct
   optical cables or Wavelength-Division Multiplexing (WDM) connections.

6.2.2.  Midhaul and Backhaul

   Today's Midhaul and Backhaul networks typically consist of:

   o  Mostly normal IP networks, MPLS-TP, etc.

   o  Clock distribution and synchronization using IEEE 1588 and syncE

   Telecommunications networks in the Midhaul and Backhaul are already
   heading towards transport networks where precise time-synchronization
   support is one of the basic building blocks.  In order to meet



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   bandwidth and cost requirements, most transport networks have already
   transitioned to all-IP packet-based networks; however, highly
   accurate clock distribution has become a challenge.

   In the past, Midhaul and Backhaul connections were typically based on
   TDM and provided frequency-synchronization capabilities as a part of
   the transport media.  More recently, other technologies such as GPS
   or syncE [syncE] have been used.

   Ethernet, IP/MPLS [RFC3031], and pseudowires (as described in
   [RFC3985] ("Pseudo Wire Emulation Edge-to-Edge (PWE3) Architecture")
   for legacy transport support)) have become popular tools for building
   and managing new all-IP Radio Access Networks (RANs)
   [SR-IP-RAN-Use-Case].  Although various timing and synchronization
   optimizations have already been proposed and implemented, including
   PTP enhancements [IEEE-1588] (see also [Timing-over-MPLS] and
   [RFC8169]), these solutions are not necessarily sufficient for the
   forthcoming RAN architectures, nor do they guarantee the more
   stringent time-synchronization requirements such as [CPRI].

   Existing solutions for TDM over IP include those discussed in
   [RFC4553], [RFC5086], and [RFC5087]; [MEF8] addresses TDM over
   Ethernet transports.

6.3.  Cellular Radio Networks in the Future

   Future cellular radio networks will be based on a mix of different
   xHaul networks (xHaul = Fronthaul, Midhaul, and Backhaul), and future
   transport networks should be able to support all of them
   simultaneously.  It is already envisioned today that:

   o  Not all "cellular radio network" traffic will be IP; for example,
      some will remain at Layer 2 (e.g., Ethernet based).  DetNet
      solutions must address all traffic types (Layer 2 and Layer 3)
      with the same tools and allow their transport simultaneously.

   o  All types of xHaul networks will need some types of DetNet
      solutions.  For example, with the advent of 5G, some Backhaul
      traffic will also have DetNet requirements (for example, traffic
      belonging to time-critical 5G applications).

   o  Different functional splits between the base stations and the
      on-site units could coexist on the same Fronthaul and Backhaul
      network.







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   Future cellular radio networks should contain the following:

   o  Unified standards-based transport protocols and standard
      networking equipment that can make use of underlying deterministic
      link-layer services

   o  Unified and standards-based network management systems and
      protocols in all parts of the network (including Fronthaul)

   New RAN deployment models and architectures may require TSN services
   with strict requirements on other parts of the network that
   previously were not considered to be packetized at all.  Time and
   synchronization support are already topical for Backhaul and Midhaul
   packet networks [MEF22.1.1] and are also becoming a real issue for
   Fronthaul networks.  Specifically, in Fronthaul networks, the timing
   and synchronization requirements can be extreme for packet-based
   technologies -- for example, on the order of a PDV of +-20 ns or less
   and frequency accuracy of +-0.002 PPM [Fronthaul].

   The actual transport protocols and/or solutions for establishing
   required transport "circuits" (pinned-down paths) for Fronthaul
   traffic are still undefined.  Those protocols are likely to include
   (but are not limited to) solutions directly over Ethernet, over IP,
   and using MPLS/pseudowire transport.

   Interesting and important work for TSN has been done for Ethernet
   [IEEE-8021TSNTG]; this work specifies the use of PTP [IEEE-1588] in
   the context of IEEE 802.1D and IEEE 802.1Q.  [IEEE-8021AS] specifies
   a Layer 2 time-synchronizing service, and other specifications such
   as IEEE 1722 [IEEE-1722] specify Ethernet-based Layer 2 transport for
   time-sensitive streams.

   However, even these Ethernet TSN features may not be sufficient for
   Fronthaul traffic.  Therefore, having specific profiles that take
   Fronthaul requirements into account is desirable [IEEE-8021CM].

   New promising work seeks to enable the transport of time-sensitive
   Fronthaul streams in Ethernet bridged networks [IEEE-8021CM].
   Analogous to IEEE 1722, standardization efforts in the IEEE 1914.3
   Task Force [IEEE-19143] to define the Layer 2 transport encapsulation
   format for transporting Radio over Ethernet (RoE) are ongoing.

   As mentioned in Section 6.1.2, 5G communications will provide one of
   the most challenging cases for delay-sensitive networking.  In order
   to meet the challenges of ultra-low latency and ultra-high
   throughput, 3GPP has studied various functional splits for 5G, i.e.,
   physical decomposition of the 5G "gNodeB" base station and deployment
   of its functional blocks in different locations [TR38801].



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   These splits are numbered from split option 1 (dual connectivity, a
   split in which the radio resource control is centralized and other
   radio stack layers are in distributed units) to split option 8 (a
   PHY-RF split in which RF functionality is in a distributed unit and
   the rest of the radio stack is in the centralized unit), with each
   intermediate split having its own data-rate and delay requirements.
   Packetized versions of different splits have been proposed, including
   enhanced CPRI (eCPRI) [eCPRI] and RoE (as previously noted).  Both
   provide Ethernet encapsulations, and eCPRI is also capable of IP
   encapsulation.

   All-IP RANs and xHaul networks would benefit from time
   synchronization and time-sensitive transport services.  Although
   Ethernet appears to be the unifying technology for the transport,
   there is still a disconnect when it comes to providing Layer 3
   services.  The protocol stack typically has a number of layers below
   Ethernet Layer 2 that might be "visible" to Layer 3.  In a fairly
   common scenario, on top of the lowest-layer (optical) transport is
   the first (lowest) Ethernet layer, then one or more layers of MPLS,
   pseudowires, and/or other tunneling protocols, and finally one or
   more Ethernet layers that are visible to Layer 3.

   Although there exist technologies for establishing circuits through
   the routed and switched networks (especially in the MPLS/PWE space),
   there is still no way to signal the time-synchronization and
   time-sensitive stream requirements/reservations for Layer 3 flows in
   a way that addresses the entire transport stack, including the
   Ethernet layers that need to be configured.

   Furthermore, not all "user-plane" traffic will be IP.  Therefore, the
   solution in question also must address the use cases where the
   user-plane traffic is on a different layer (for example, Ethernet
   frames).


















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6.4.  Cellular Radio Networks Requests to the IETF

   A standard for data-plane transport specifications that is:

   o  Unified among all xHauls (meaning that different flows with
      diverse DetNet requirements can coexist in the same network and
      traverse the same nodes without interfering with each other)

   o  Deployed in a highly deterministic network environment

   o  Capable of supporting multiple functional splits simultaneously,
      including existing Backhaul and CPRI Fronthaul, and (potentially)
      new modes as defined, for example, in 3GPP; these goals can be
      supported by the existing DetNet use case "common themes"
      (Section 11); of special note are Sections 11.1.8 ("Mix of
      Deterministic and Best-Effort Traffic"), 11.3.1 ("Bounded
      Latency"), 11.3.2 ("Low Latency"), 11.3.4 ("Symmetrical Path
      Delays"), and 11.6 ("Deterministic Flows")

   o  Capable of supporting network slicing and multi-tenancy; these
      goals can be supported by the same DetNet themes noted above

   o  Capable of transporting both in-band and out-of-band control
      traffic (e.g., Operations, Administration, and Maintenance (OAM)
      information)

   o  Deployable over multiple data-link technologies (e.g., IEEE 802.3,
      mmWave)

   A standard for data-flow information models that is:

   o  Aware of the time sensitivity and constraints of the target
      networking environment

   o  Aware of underlying deterministic networking services (e.g., on
      the Ethernet layer)

7.  Industrial Machine to Machine (M2M)

7.1.  Use Case Description

   "Industrial automation" in general refers to automation of
   manufacturing, quality control, and material processing.  This M2M
   use case focuses on machine units on a plant floor that periodically
   exchange data with upstream or downstream machine modules and/or a
   supervisory controller within a LAN.





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   PLCs are the "actors" in M2M communications.  Communication between
   PLCs, and between PLCs and the supervisory PLC (S-PLC), is achieved
   via critical control/data streams (Figure 11).

              S (Sensor)
               \                                  +-----+
         PLC__  \.--.                   .--.   ---| MES |
              \_(    `.               _(    `./   +-----+
       A------( Local  )-------------(  L2    )
             (      Net )           (      Net )    +-------+
             /`--(___.-'             `--(___.-' ----| S-PLC |
          S_/     /       PLC   .--. /              +-------+
               A_/           \_(    `.
            (Actuator)       (  Local )
                            (       Net )
                             /`--(___.-'\
                            /       \    A
                           S         A

      Figure 11: Current Generic Industrial M2M Network Architecture

   This use case focuses on PLC-related communications; communication to
   Manufacturing Execution Systems (MESs) are not addressed.

   This use case covers only critical control/data streams; non-critical
   traffic between industrial automation applications (such as
   communication of state, configuration, setup, and database
   communication) is adequately served by prioritizing techniques
   available at the time of this writing.  Such traffic can use up to
   80% of the total bandwidth required.  There is also a subset of
   non-time-critical traffic that must be reliable even though it is not
   time sensitive.

   In this use case, deterministic networking is primarily needed to
   provide end-to-end delivery of M2M messages within specific timing
   constraints -- for example, in closed-loop automation control.
   Today, this level of determinism is provided by proprietary
   networking technologies.  In addition, standard networking
   technologies are used to connect the local network to remote
   industrial automation sites, e.g., over an enterprise or metro
   network that also carries other types of traffic.  Therefore, flows
   that should be forwarded with deterministic guarantees need to be
   sustained, regardless of the amount of other flows in those networks.








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7.2.  Industrial M2M Communications Today

   Today, proprietary networks fulfill the needed timing and
   availability for M2M networks.

   The network topologies used today by industrial automation are
   similar to those used by telecom networks: daisy chain, ring,
   hub-and-spoke, and "comb" (a subset of daisy chain).

   PLC-related control/data streams are transmitted periodically and
   carry either a preconfigured payload or a payload configured during
   runtime.

   Some industrial applications require time synchronization at the end
   nodes.  For such time-coordinated PLCs, accuracy of 1 us is required.
   Even in the case of "non-time-coordinated" PLCs, time synchronization
   may be needed, e.g., for timestamping of sensor data.

   Industrial-network scenarios require advanced security solutions.  At
   the time of this writing, many industrial production networks are
   physically separated.  Filtering policies that are typically enforced
   in firewalls are used to prevent critical flows from being leaked
   outside a domain.

7.2.1.  Transport Parameters

   The cycle time defines the frequency of message(s) between industrial
   actors.  The cycle time is application dependent, in the range of
   1-100 ms for critical control/data streams.

   Because industrial applications assume that deterministic transport
   will be used for critical control-data-stream parameters (instead of
   having to define latency and delay-variation parameters), it is
   sufficient to fulfill requirements regarding the upper bound of
   latency (maximum latency).  The underlying networking infrastructure
   must ensure a maximum end-to-end message delivery time in the range
   of 100 us to 50 ms, depending on the control-loop application.

   The bandwidth requirements of control/data streams are usually
   calculated directly from the bytes-per-cycle parameter of the control
   loop.  For PLC-to-PLC communication, one can expect 2-32 streams with
   packet sizes in the range of 100-700 bytes.  For S-PLC-to-PLC
   communication, the number of streams is higher -- up to 256 streams.
   Usually, no more than 20% of available bandwidth is used for
   critical control/data streams.  In today's networks, 1 Gbps links
   are commonly used.





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   Most PLC control loops are rather tolerant of packet loss; however,
   critical control/data streams accept a loss of no more than one
   packet per consecutive communication cycle (i.e., if a packet gets
   lost in cycle "n", then the next cycle ("n+1") must be lossless).
   After the loss of two or more consecutive packets, the network may be
   considered to be "down" by the application.

   As network downtime may impact the whole production system, the
   required network availability is rather high (99.999%).

   Based on the above parameters, some form of redundancy will be
   required for M2M communications; however, any individual solution
   depends on several parameters, including cycle time and
   delivery time.

7.2.2.  Stream Creation and Destruction

   In an industrial environment, critical control/data streams are
   created rather infrequently, on the order of ~10 times per
   day/week/month.  Most of these critical control/data streams get
   created at machine startup; however, flexibility is also needed
   during runtime -- for example, when adding or removing a machine.  As
   production systems become more flexible going forward, there will be
   a significant increase in the rate at which streams are created,
   changed, and destroyed.

7.3.  Industrial M2M in the Future

   We foresee a converged IP-standards-based network with deterministic
   properties that can satisfy the timing, security, and reliability
   constraints described above.  Today's proprietary networks could then
   be interfaced to such a network via gateways; alternatively, in the
   case of new installations, devices could be connected directly to the
   converged network.

   For this use case, time-synchronization accuracy on the order of 1 us
   is expected.

7.4.  Industrial M2M Requests to the IETF

   o  Converged IP-based network

   o  Deterministic behavior (bounded latency and jitter)

   o  High availability (presumably through redundancy) (99.999%)

   o  Low message delivery time (100 us to 50 ms)




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   o  Low packet loss (with a bounded number of consecutive lost
      packets)

   o  Security (e.g., preventing critical flows from being leaked
      between physically separated networks)

8.  Mining Industry

8.1.  Use Case Description

   The mining industry is highly dependent on networks to monitor and
   control their systems, in both open-pit and underground extraction as
   well as in transport and refining processes.  In order to reduce
   risks and increase operational efficiency in mining operations, the
   location of operators has been relocated (as much as possible) from
   the extraction site to remote control and monitoring sites.

   In the case of open-pit mining, autonomous trucks are used to
   transport the raw materials from the open pit to the refining factory
   where the final product (e.g., copper) is obtained.  Although the
   operation is autonomous, the tracks are remotely monitored from a
   central facility.

   In pit mines, the monitoring of the tailings or mine dumps is
   critical in order to minimize environmental pollution.  In the past,
   monitoring was conducted through manual inspection of preinstalled
   dataloggers.  Cabling is not typically used in such scenarios, due to
   its high cost and complex deployment requirements.  At the time of
   this writing, wireless technologies are being employed to monitor
   these cases permanently.  Slopes are also monitored in order to
   anticipate possible mine collapse.  Due to the unstable terrain,
   cable maintenance is costly and complex; hence, wireless technologies
   are employed.

   In the case of underground monitoring, autonomous vehicles with
   extraction tools travel independently through the tunnels, but their
   operational tasks (such as excavation, stone-breaking, and transport)
   are controlled remotely from a central facility.  This generates
   upstream video and feedback traffic plus downstream actuator-control
   traffic.

8.2.  Mining Industry Today

   At the time of this writing, the mining industry uses a
   packet-switched architecture supported by high-speed Ethernet.
   However, in order to comply with requirements regarding delay and
   packet loss, the network bandwidth is overestimated.  This results in
   very low efficiency in terms of resource usage.



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   QoS is implemented at the routers to separate video, management,
   monitoring, and process-control traffic for each stream.

   Since mobility is involved in this process, the connections between
   the backbone and the mobile devices (e.g., trucks, trains, and
   excavators) are implemented using a wireless link.  These links are
   based on IEEE 802.11 [IEEE-80211] for open-pit mining and "leaky
   feeder" communications for underground mining.  (A "leaky feeder"
   communication system consists of a coaxial cable, run along tunnels,
   that emits and receives radio waves, functioning as an extended
   antenna.  The cable is "leaky" in that it has gaps or slots in its
   outer conductor to allow the radio signal to leak into or out of the
   cable along its entire length.)

   Lately, in pit mines the use of Low-Power WAN (LPWAN) technologies
   has been extended: tailings, slopes, and mine dumps are monitored by
   battery-powered dataloggers that make use of robust long-range radio
   technologies.  Reliability is usually ensured through retransmissions
   at Layer 2.  Gateways or concentrators act as bridges, forwarding the
   data to the backbone Ethernet network.  Deterministic requirements
   are biased towards reliability rather than latency, as events are
   triggered slowly or can be anticipated in advance.

   At the mineral-processing stage, conveyor belts and refining
   processes are controlled by a SCADA system that provides an
   in-factory delay-constrained networking environment.

   At the time of this writing, voice communications are served by a
   redundant trunking infrastructure, independent from data networks.

8.3.  Mining Industry in the Future

   Mining operations and management are converging towards a combination
   of autonomous operation and teleoperation of transport and extraction
   machines.  This means that video, audio, monitoring, and process-
   control traffic will increase dramatically.  Ideally, all activities
   at the mine will rely on network infrastructure.

   Wireless for open-pit mining is already a reality with LPWAN
   technologies; it is expected to evolve to more-advanced LPWAN
   technologies, such as those based on LTE, to increase last-hop
   reliability or novel LPWAN flavors with deterministic access.

   One area in which DetNet can improve this use case is in the wired
   networks that make up the "backbone network" of the system.  These
   networks connect many wireless Access Points (APs) together.  The
   mobile machines (which are connected to the network via wireless)




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   transition from one AP to the next as they move about.  A
   deterministic, reliable, low-latency backbone can enable these
   transitions to be more reliable.

   Connections that extend all the way from the base stations to the
   machinery via a mix of wired and wireless hops would also be
   beneficial -- for example, to improve the responsiveness of digging
   machines to remote control.  However, to guarantee deterministic
   performance of a DetNet, the end-to-end underlying network must be
   deterministic.  Thus, for this use case, if a deterministic wireless
   transport is integrated with a wire-based DetNet network, it could
   create the desired wired plus wireless end-to-end deterministic
   network.

8.4.  Mining Industry Requests to the IETF

   o  Improved bandwidth efficiency

   o  Very low delay, to enable machine teleoperation

   o  Dedicated bandwidth usage for high-resolution video streams

   o  Predictable delay, to enable real-time monitoring

   o  Potential for constructing a unified DetNet network over a
      combination of wired and deterministic wireless links

9.  Private Blockchain

9.1.  Use Case Description

   Blockchain was created with Bitcoin as a "public" blockchain on the
   open Internet; however, blockchain has also spread far beyond its
   original host into various industries, such as smart manufacturing,
   logistics, security, legal rights, and others.  In these industries,
   blockchain runs in designated and carefully managed networks in which
   deterministic networking requirements could be addressed by DetNet.
   Such implementations are referred to as "private" blockchain.

   The sole distinction between public and private blockchain is defined
   by who is allowed to participate in the network, execute the
   consensus protocol, and maintain the shared ledger.

   Today's networks manage the traffic from blockchain on a best-effort
   basis, but blockchain operation could be made much more efficient if
   deterministic networking services were available to minimize latency
   and packet loss in the network.




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9.1.1.  Blockchain Operation

   A "block" runs as a container of a batch of primary items (e.g.,
   transactions, property records).  The blocks are chained in such a
   way that the hash of the previous block works as the pointer to the
   header of the new block.  Confirmation of each block requires a
   consensus mechanism.  When an item arrives at a blockchain node, the
   latter broadcasts this item to the rest of the nodes, which receive
   it, verify it, and put it in the ongoing block.  The block
   confirmation process begins as the number of items reaches the
   predefined block capacity, at which time the node broadcasts its
   proved block to the rest of the nodes, to be verified and chained.
   The result is that block N+1 of each chain transitively vouches for
   blocks N and previous of that chain.

9.1.2.  Blockchain Network Architecture

   Blockchain node communication and coordination are achieved mainly
   through frequent point-to-multipoint communication; however,
   persistent point-to-point connections are used to transport both the
   items and the blocks to the other nodes.  For example, consider the
   following implementation.

   When a node is initiated, it first requests the other nodes'
   addresses from a specific entity, such as DNS.  The node then creates
   persistent connections with each of the other nodes.  If a node
   confirms an item, it sends the item to the other nodes via these
   persistent connections.

   As a new block in a node is completed and is proven by the
   surrounding nodes, it propagates towards its neighbor nodes.  When
   node A receives a block, it verifies it and then sends an invite
   message to its neighbor B.  Neighbor B checks to see if the
   designated block is available and responds to A if it is unavailable;
   A then sends the complete block to B.  B repeats the process (as was
   done by A) to start the next round of block propagation.

   The challenge of blockchain network operation is not overall data
   rates, since the volume from both the block and the item stays
   between hundreds of bytes and a couple of megabytes per second;
   rather, the challenge is in transporting the blocks with minimum
   latency to maximize the efficiency of the blockchain consensus
   process.  The efficiency of differing implementations of the
   consensus process may be affected to a differing degree by the
   latency (and variation of latency) of the network.






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9.1.3.  Blockchain Security Considerations

   Security is crucial to blockchain applications; at the time of this
   writing, blockchain systems address security issues mainly at the
   application level, where cryptography as well as hash-based consensus
   play a leading role in preventing both double-spending and malicious
   service attacks.  However, there is concern that in the proposed use
   case for a private blockchain network that is dependent on
   deterministic properties the network could be vulnerable to delays
   and other specific attacks against determinism, as these delays and
   attacks could interrupt service.

9.2.  Private Blockchain Today

   Today, private blockchain runs in Layer 2 or Layer 3 VPNs, generally
   without guaranteed determinism.  The industry players are starting to
   realize that improving determinism in their blockchain networks could
   improve the performance of their service, but at present these goals
   are not being met.

9.3.  Private Blockchain in the Future

   Blockchain system performance can be greatly improved through
   deterministic networking services, primarily because low latency
   would accelerate the consensus process.  It would be valuable to be
   able to design a private blockchain network with the following
   properties:

   o  Transport of point-to-multipoint traffic in a coordinated network
      architecture rather than at the application layer (which typically
      uses point-to-point connections)

   o  Guaranteed transport latency

   o  Reduced packet loss (to the point where delay incurred by packet
      retransmissions would be negligible)

9.4.  Private Blockchain Requests to the IETF

   o  Layer 2 and Layer 3 multicast of blockchain traffic

   o  Item and block delivery with bounded, low latency and negligible
      packet loss

   o  Coexistence of blockchain and IT traffic in a single network

   o  Ability to scale the network by distributing the centralized
      control of the network across multiple control entities



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10.  Network Slicing

10.1.  Use Case Description

   Network slicing divides one physical network infrastructure into
   multiple logical networks.  Each slice, which corresponds to a
   logical network, uses resources and network functions independently
   from each other.  Network slicing provides flexibility of resource
   allocation and service quality customization.

   Future services will demand network performance with a wide variety
   of characteristics such as high data rate, low latency, low loss
   rate, security, and many other parameters.  Ideally, every service
   would have its own physical network satisfying its particular
   performance requirements; however, that would be prohibitively
   expensive.  Network slicing can provide a customized slice for a
   single service, and multiple slices can share the same physical
   network.  This method can optimize performance for the service at
   lower cost, and the flexibility of setting up and releasing the
   slices also allows the user to allocate network resources
   dynamically.

   Unlike the other use cases presented here, network slicing is not a
   specific application that depends on specific deterministic
   properties; rather, it is introduced as an area of networking to
   which DetNet might be applicable.

10.2.  DetNet Applied to Network Slicing

10.2.1.  Resource Isolation across Slices

   One of the requirements discussed for network slicing is the "hard"
   separation of various users' deterministic performance.  That is, it
   should be impossible for activity, lack of activity, or changes in
   activity of one or more users to have any appreciable effect on the
   deterministic performance parameters of any other slices.  Typical
   techniques used today, which share a physical network among users, do
   not offer this level of isolation.  DetNet can supply point-to-point
   or point-to-multipoint paths that offer a user bandwidth and latency
   guarantees that cannot be affected by other users' data traffic.
   Thus, DetNet is a powerful tool when reliability and low latency are
   required in network slicing.









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10.2.2.  Deterministic Services within Slices

   Slices may need to provide services with DetNet-type performance
   guarantees; note, however, that a system can be implemented to
   provide such services in more than one way.  For example, the slice
   itself might be implemented using DetNet, and thus the slice can
   provide service guarantees and isolation to its users without any
   particular DetNet awareness on the part of the users' applications.
   Alternatively, a "non-DetNet-aware" slice may host an application
   that itself implements DetNet services and thus can enjoy similar
   service guarantees.

10.3.  A Network Slicing Use Case Example - 5G Bearer Network

   Network slicing is a core feature of 5G as defined in 3GPP.  The
   system architecture for 5G is under development at the time of this
   writing [TS23501].  A network slice in a mobile network is a complete
   logical network, including RANs and Core Networks (CNs).  It provides
   telecommunications services and network capabilities, which may vary
   from slice to slice.  A 5G bearer network is a typical use case for
   network slicing; for example, consider three 5G service scenarios:
   eMBB, URLLC, and mMTC.

   o  eMBB (Enhanced Mobile Broadband) focuses on services characterized
      by high data rates, such as high-definition video, Virtual Reality
      (VR), augmented reality, and fixed mobile convergence.

   o  URLLC (Ultra-Reliable and Low Latency Communications) focuses on
      latency-sensitive services, such as self-driving vehicles, remote
      surgery, or drone control.

   o  mMTC (massive Machine Type Communications) focuses on services
      that have high connection-density requirements, such as those
      typically used in smart-city and smart-agriculture scenarios.

   A 5G bearer network could use DetNet to provide hard resource
   isolation across slices and within a given slice.  For example,
   consider Slice-A and Slice-B, with DetNet used to transit services
   URLLC-A and URLLC-B over them.  Without DetNet, URLLC-A and URLLC-B
   would compete for bandwidth resources, and latency and reliability
   requirements would not be guaranteed.  With DetNet, URLLC-A and
   URLLC-B have separate bandwidth reservations; there is no resource
   conflict between them, as though they were in different physical
   networks.







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10.4.  Non-5G Applications of Network Slicing

   Although the operation of services not related to 5G is not part of
   the 5G network slicing definition and scope, network slicing is
   likely to become a preferred approach for providing various services
   across a shared physical infrastructure.  Examples include providing
   services for electrical utilities and pro audio via slices.  Use
   cases like these could become more common once the work for the 5G CN
   evolves to include wired as well as wireless access.

10.5.  Limitations of DetNet in Network Slicing

   DetNet cannot cover every network slicing use case.  One issue is
   that DetNet is a point-to-point or point-to-multipoint technology;
   however, network slicing ultimately needs multipoint-to-multipoint
   guarantees.  Another issue is that the number of flows that can be
   carried by DetNet is limited by DetNet scalability; flow aggregation
   and queuing management modification may help address this issue.
   Additional work and discussion are needed to address these topics.

10.6.  Network Slicing Today and in the Future

   Network slicing has promise in terms of satisfying many requirements
   of future network deployment scenarios, but it is still a collection
   of ideas and analyses without a specific technical solution.  DetNet
   is one of various technologies that could potentially be used in
   network slicing, along with, for example, Flex-E and segment routing.
   For more information, please see the IETF 99 Network Slicing BoF
   session agenda and materials as provided in [IETF99-netslicing-BoF].

10.7.  Network Slicing Requests to the IETF

   o  Isolation from other flows through queuing management

   o  Service quality customization and guarantees

   o  Security














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11.  Use Case Common Themes

   This section summarizes the expected properties of a DetNet network,
   based on the use cases as described in this document.

11.1.  Unified, Standards-Based Networks

11.1.1.  Extensions to Ethernet

   A DetNet network is not "a new kind of network" -- it is based on
   extensions to existing Ethernet standards, including elements of
   IEEE 802.1 TSN and related standards.  Presumably, it will be
   possible to run DetNet over other underlying transports besides
   Ethernet, but Ethernet is explicitly supported.

11.1.2.  Centrally Administered Networks

   In general, a DetNet network is not expected to be "plug and play";
   rather, some type of centralized network configuration and control
   system is expected.  Such a system may be in a single central
   location, or it may be distributed across multiple control entities
   that function together as a unified control system for the network.
   However, the ability to "hot swap" components (e.g., due to
   malfunction) is similar enough to "plug and play" that this kind of
   behavior may be expected in DetNet networks, depending on the
   implementation.

11.1.3.  Standardized Data-Flow Information Models

   Data-flow information models to be used with DetNet networks are to
   be specified by DetNet.

11.1.4.  Layer 2 and Layer 3 Integration

   A DetNet network is intended to integrate between Layer 2 (bridged)
   network(s) (e.g., an AVB/TSN LAN) and Layer 3 (routed) network(s)
   (e.g., using IP-based protocols).  One example of this is making
   AVB/TSN-type deterministic performance available from Layer 3
   applications, e.g., using RTP.  Another example is connecting two
   AVB/TSN LANs ("islands") together through a standard router.

11.1.5.  IPv4 Considerations

   This document explicitly does not specify any particular
   implementation or protocol; however, it has been observed that
   various use cases (and their associated industries) described herein
   are explicitly based on IPv4 (as opposed to IPv6), and it is not
   considered practical to expect such implementations to migrate to



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   IPv6 in order to use DetNet.  Thus, the expectation is that even if
   not every feature of DetNet is available in an IPv4 context, at least
   some of the significant benefits (such as guaranteed end-to-end
   delivery and low latency) will be available.

11.1.6.  Guaranteed End-to-End Delivery

   Packets in a DetNet flow are guaranteed not to be dropped by the
   network due to congestion.  However, the network may drop packets for
   intended reasons, e.g., per security measures.  Similarly,
   best-effort traffic on a DetNet is subject to being dropped (as on a
   non-DetNet IP network).  Also note that this guarantee applies to
   actions taken by DetNet protocol software and does not provide any
   guarantee against lower-level errors such as media errors or checksum
   errors.

11.1.7.  Replacement for Multiple Proprietary Deterministic Networks

   There are many proprietary non-interoperable deterministic Ethernet-
   based networks available; DetNet is intended to provide an
   open-standards-based alternative to such networks.

11.1.8.  Mix of Deterministic and Best-Effort Traffic

   DetNet is intended to support the coexistence of time-sensitive
   operational (OT) traffic and informational (IT) traffic on the same
   ("unified") network.

11.1.9.  Unused Reserved Bandwidth to Be Available to Best-Effort
         Traffic

   If bandwidth reservations are made for a stream but the associated
   bandwidth is not used at any point in time, that bandwidth is made
   available on the network for best-effort traffic.  If the owner of
   the reserved stream then starts transmitting again, the bandwidth is
   no longer available for best-effort traffic; this occurs on a
   moment-to-moment basis.  Note that such "temporarily available"
   bandwidth is not available for time-sensitive traffic, which must
   have its own reservation.

11.1.10.  Lower-Cost, Multi-Vendor Solutions

   The DetNet network specifications are intended to enable an ecosystem
   in which multiple vendors can create interoperable products, thus
   promoting device diversity and potentially higher numbers of each
   device manufactured, promoting cost reduction and cost competition





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   among vendors.  In other words, vendors should be able to create
   DetNet networks at lower cost and with greater diversity of available
   devices than existing proprietary networks.

11.2.  Scalable Size

   DetNet networks range in size from very small (e.g., inside a single
   industrial machine) to very large (e.g., a utility-grid network
   spanning a whole country and involving many "hops" over various kinds
   of links -- for example, radio repeaters, microwave links, or fiber
   optic links).  However, recall that the scope of DetNet is confined
   to networks that are centrally administered and thereby explicitly
   excludes unbounded decentralized networks such as the Internet.

11.2.1.  Scalable Number of Flows

   The number of flows in a given network application can potentially be
   large and can potentially grow faster than the number of nodes and
   hops, so the network should provide a sufficient (perhaps
   configurable) maximum number of flows for any given application.

11.3.  Scalable Timing Parameters and Accuracy

11.3.1.  Bounded Latency

   DetNet data-flow information models are expected to provide means to
   configure the network that include parameters for querying network
   path latency, requesting bounded latency for a given stream,
   requesting worst-case maximum and/or minimum latency for a given path
   or stream, and so on.  It is expected that the network may not be
   able to provide a given requested service level; if this is indeed
   the case, the network control system should reply that the requested
   services are not available (as opposed to accepting the parameter but
   then not delivering the desired behavior).

11.3.2.  Low Latency

   Various applications may state that they require "extremely low
   latency"; however, depending on the application, "extremely low" may
   imply very different latency bounds.  For example, "low latency"
   across a utility-grid network is a different order of magnitude of
   latency values compared to "low latency" in a motor control loop in a
   small machine.  It is intended that the mechanisms for specifying
   desired latency include wide ranges and that architecturally there is
   nothing to prevent arbitrarily low latencies from being implemented
   in a given network.





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11.3.3.  Bounded Jitter (Latency Variation)

   As with the other latency-related elements noted above, parameters
   that can determine or request permitted variations in latency should
   be available.

11.3.4.  Symmetrical Path Delays

   Some applications would like to specify that the transit delay time
   values be equal for both the transmit path and the return path.

11.4.  High Reliability and Availability

   Reliability is of critical importance to many DetNet applications,
   because the consequences of failure can be extraordinarily high in
   terms of cost and even human life.  DetNet-based systems are expected
   to be implemented with essentially arbitrarily high availability --
   for example, 99.9999% uptime (where 99.9999 means "six nines") or
   even 12 nines.  DetNet designs should not make any assumptions about
   the level of reliability and availability that may be required of a
   given system and should define parameters for communicating these
   kinds of metrics within the network.

   A strategy used by DetNet for providing such extraordinarily high
   levels of reliability is to provide redundant paths so that a system
   can seamlessly switch between the paths while maintaining its
   required level of performance.

11.5.  Security

   Security is of critical importance to many DetNet applications.  A
   DetNet network must have the ability to be made secure against device
   failures, attackers, misbehaving devices, and so on.  In a DetNet
   network, the data traffic is expected to be time sensitive; thus, in
   addition to arriving with the data content as intended, the data must
   also arrive at the expected time.  This may present "new" security
   challenges to implementers and must be addressed accordingly.  There
   are other security implications, including (but not limited to) the
   change in attack surface presented by PRE.

11.6.  Deterministic Flows

   Reserved-bandwidth data flows must be isolated from each other and
   from best-effort traffic, so that even if the network is saturated
   with best-effort (and/or reserved-bandwidth) traffic, the configured
   flows are not adversely affected.





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12.  Security Considerations

   This document covers a number of representative applications and
   network scenarios that are expected to make use of DetNet
   technologies.  Each of the potential DetNet use cases will have
   security considerations from both the use-specific perspective and
   the DetNet technology perspective.  While some use-specific security
   considerations are discussed above, a more comprehensive discussion
   of such considerations is captured in [DetNet-Security]
   ("Deterministic Networking (DetNet) Security Considerations").
   Readers are encouraged to review [DetNet-Security] to gain a more
   complete understanding of DetNet-related security considerations.

13.  IANA Considerations

   This document has no IANA actions.

14.  Informative References

   [Ahm14]    Ahmed, M. and R. Kim, "Communication Network Architectures
              for Smart-Wind Power Farms", Energies 2014, pp. 3900-3921,
              DOI 10.3390/en7063900, June 2014.

   [Arch-for-6TiSCH]
              Thubert, P., Ed., "An Architecture for IPv6 over the TSCH
              mode of IEEE 802.15.4", Work in Progress,
              draft-ietf-6tisch-architecture-20, March 2019.

   [BACnet-IP]
              ASHRAE, "Annex J to ANSI/ASHRAE 135-1995 - BACnet/IP",
              January 1999, <http://www.bacnet.org/Addenda/
              Add-1995-135a.pdf>.

   [BAS-DetNet]
              Kaneko, Y. and S. Das, "Building Automation Use Cases and
              Requirements for Deterministic Networking", Work in
              Progress, draft-bas-usecase-detnet-00, October 2015.

   [CoAP-6TiSCH]
              Sudhaakar, R., Ed. and P. Zand, "6TiSCH Resource
              Management and Interaction using CoAP", Work in Progress,
              draft-ietf-6tisch-coap-03, March 2015.

   [CoMP]     NGMN Alliance, "RAN EVOLUTION PROJECT COMP EVALUATION AND
              ENHANCEMENT", VERSION 2.0, NGMN Alliance, March 2015,
              <https://www.ngmn.org/fileadmin/user_upload/
              NGMN_RANEV_D3_CoMP_Evaluation_and_Enhancement_v2.0.pdf>.




Grossman                      Informational                    [Page 80]


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   [Content_Protection]
              Olsen, D., "1722a Content Protection", April 2012,
              <http://grouper.ieee.org/groups/1722/contributions/2012/
              avtp_dolsen_1722a_content_protection.pdf>.

   [CPRI]     CPRI Cooperation, "Common Public Radio Interface (CPRI);
              Interface Specification", CPRI Specification V6.1,
              July 2014, <http://www.cpri.info/downloads/
              CPRI_v_6_1_2014-07-01.pdf>.

   [DCI]      Digital Cinema Initiatives, LLC, "DCI Specification,
              Version 1.3", June 2018, <https://www.dcimovies.com/>.

   [Det-Fwd-PHB]
              Shah, S. and P. Thubert, "Deterministic Forwarding PHB",
              Work in Progress,
              draft-svshah-tsvwg-deterministic-forwarding-04,
              August 2015.

   [DetNet-6TiSCH]
              Thubert, P., Ed., "6TiSCH requirements for DetNet", Work
              in Progress, draft-thubert-6tisch-4detnet-01, June 2015.

   [DetNet-Arch]
              Finn, N., Thubert, P., Varga, B., and J. Farkas,
              "Deterministic Networking Architecture", Work in Progress,
              draft-ietf-detnet-architecture-13, May 2019.

   [DetNet-Audio-Reqs]
              Gunther, C., Ed. and E. Grossman, Ed., "Deterministic
              Networking Professional Audio Requirements", Work in
              Progress, draft-gunther-detnet-proaudio-req-01,
              March 2015.

   [DetNet-Mobile]
              Zha, Y., "Deterministic Networking Use Case in Mobile
              Network", Work in Progress, draft-zha-detnet-use-case-00,
              July 2015.

   [DetNet-RAN]
              Korhonen, J., "Deterministic networking for radio
              access networks", Work in Progress,
              draft-korhonen-detnet-telreq-00, May 2015.








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   [DetNet-Security]
              Mizrahi, T., Grossman, E., Ed., Hacker, A., Das, S.,
              Dowdell, J., Austad, H., Stanton, K., and N. Finn,
              "Deterministic Networking (DetNet) Security
              Considerations", Work in Progress,
              draft-ietf-detnet-security-04, March 2019.

   [DetNet-Util-Reqs]
              Wetterwald, P. and J. Raymond, "Deterministic Networking
              Uitilities requirements", Work in Progress,
              draft-wetterwald-detnet-utilities-reqs-02, June 2015.

   [eCPRI]    IEEE Standards Association, "Common Public Radio
              Interface: eCPRI Interface Specification V1.2", June 2018,
              <http://www.cpri.info/>.

   [ESPN_DC2] Daley, D., "ESPN's DC2 Scales AVB Large", SVG News,
              June 2014, <https://sportsvideo.org/main/blog/2014/06/
              espns-dc2-scales-avb-large>.

   [EtherCAT] "EtherCAT Technology Group",
              <https://www.ethercat.org/default.htm>.

   [FL-net]   Japan Electrical Manufacturers Association, "JEMA 1479 -
              English Edition", September 2012,
              <https://www.jema-net.or.jp/Japanese/standard/opcn/pdf/
              JEM_1479e(20120927).pdf>.

   [Fronthaul]
              Chen, D. and T. Mustala, "Ethernet Fronthaul
              Considerations", IEEE 1904.3, February 2015,
              <http://www.ieee1904.org/3/meeting_archive/2015/02/
              tf3_1502_chen_1.pdf>.

   [IEC-60834]
              International Electrotechnical Commission, "Teleprotection
              equipment of power systems - Performance and testing",
              IEC 60834, October 1999.

   [IEC-60870-5-104]
              International Electrotechnical Commission, "Telecontrol
              equipment and systems - Part 5-104: Transmission protocols
              - Network access for IEC 60870-5-101 using standard
              transport profiles", IEC 60870-5-104, June 2006.







Grossman                      Informational                    [Page 82]


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   [IEC-61400-25]
              International Electrotechnical Commission, "Communications
              for monitoring and control of wind power plants",
              IEC 61400-25, June 2013.

   [IEC-61850-5:2013]
              International Electrotechnical Commission, "Communication
              networks and systems for power utility automation -
              Part 5: Communication requirements for functions and
              device models", IEC 61850-5, January 2013.

   [IEC-61850-9-2:2011]
              International Electrotechnical Commission, "Communication
              networks and systems for power utility automation -
              Part 9-2: Specific communication service mapping (SCSM) -
              Sampled values over ISO/IEC 8802-3", IEC 61850-9-2,
              September 2011.

   [IEC-61850-90-12:2015]
              International Electrotechnical Commission, "Communication
              networks and systems for power utility automation -
              Part 90-12: Wide area network engineering guidelines",
              IEC TR 61850-90-12, July 2015.

   [IEC-62357-200:2015]
              International Electrotechnical Commission, "Power systems
              management and associated information exchange - Part 200:
              Guidelines for migration from Internet Protocol version 4
              (IPv4) to Internet Protocol version 6 (IPv6)",
              IEC 62357-200:2015, July 2015.

   [IEC-62439-3:2016]
              International Electrotechnical Commission, "Industrial
              communication networks - High availability automation
              networks - Part 3: Parallel Redundancy Protocol (PRP) and
              High-availability Seamless Redundancy (HSR)", March 2016.

   [IEC-IEEE-61850-9-3:2016]
              International Electrotechnical Commission, "Communication
              networks and systems for power utility automation -
              Part 9-3: Precision time protocol profile for power
              utility automation", IEC 61850-9-3, May 2016.

   [IEEE-1588]
              IEEE, "IEEE Standard for a Precision Clock Synchronization
              Protocol for Networked Measurement and Control Systems",
              IEEE Standard 1588, <https://standards.ieee.org/findstds/
              standard/1588-2008.html>.



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   [IEEE-1646]
              IEEE, "IEEE Standard Communication Delivery Time
              Performance Requirements for Electric Power Substation
              Automation", IEEE Standard 1646,
              <https://standards.ieee.org/standard/1646-2004.html>.

   [IEEE-1722]
              IEEE, "IEEE Standard for a Transport Protocol for
              Time-Sensitive Applications in Bridged Local Area
              Networks", IEEE Standard 1722,
              <https://standards.ieee.org/findstds/
              standard/1722-2016.html>.

   [IEEE-1815]
              IEEE Standards Association, "IEEE Standard for Electric
              Power Systems Communications-Distributed Network Protocol
              (DNP3)", IEEE Standard 1815, <https://ieeexplore.ieee.org/
              servlet/opac?punumber=6327576>.

   [IEEE-19143]
              IEEE Standards Association, "IEEE Standard for Radio over
              Ethernet Encapsulations and Mappings", IEEE 1914.3,
              <https://standards.ieee.org/develop/project/1914.3.html>.

   [IEEE-80211]
              IEEE Standard for Information technology, "IEEE Std.
              802.11, Telecommunications and information exchange
              between systems--Local and metropolitan area networks--
              Specific requirements - Part 11: Wireless LAN Medium
              Access Control (MAC) and Physical Layer (PHY)
              Specifications",
              <https://standards.ieee.org/standard/802_11-2016.html>.

   [IEEE-802154]
              IEEE Standard for Information technology, "IEEE Std.
              802.15.4, Part 15.4: Wireless Medium Access Control (MAC)
              and Physical Layer (PHY) Specifications for Low Rate
              Wireless Personal Area Networks (WPANs)",
              <https://standards.ieee.org/standard/802_15_4-2015.html>.

   [IEEE-8021AS]
              IEEE, "IEEE Standard for Local and Metropolitan Area
              Networks - Timing and Synchronization for Time-Sensitive
              Applications in Bridged Local Area Networks",
              IEEE 802.1AS,
              <http://www.ieee802.org/1/pages/802.1as.html>.





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   [IEEE-8021CM]
              "IEEE Standard for Local and metropolitan area networks -
              Time-Sensitive Networking for Fronthaul", IEEE
              Standard 802.1CM,
              <https://standards.ieee.org/standard/802_1CM-2018.html>.

   [IEEE-8021TSNTG]
              IEEE Standards Association, "IEEE 802.1 Time-Sensitive
              Networking Task Group",
              <http://www.ieee802.org/1/pages/avbridges.html>.

   [IETF99-netslicing-BoF]
              "Network Slicing (netslicing) BoF", IETF 99, Prague,
              July 2017, <https://datatracker.ietf.org/meeting/99/
              materials/slides-99-netslicing-chairs-netslicing-bof-04>.

   [Interface-6TiSCH-6top]
              Wang, Q., Ed. and X. Vilajosana, "6TiSCH Operation
              Sublayer (6top) Interface", Work in Progress,
              draft-ietf-6tisch-6top-interface-04, July 2015.

   [ISA100]   ISA/ANSI, "ISA100, Wireless Systems for Automation",
              <https://www.isa.org/isa100/>.

   [KNX]      KNX Association, "ISO/IEC 14543-3 - KNX", November 2006.

   [LonTalk]  Echelon Corp., "LonTalk(R) Protocol Specification
              Version 3.0", 1994, <http://www.enerlon.com/JobAids/
              Lontalk%20Protocol%20Spec.pdf>.

   [MailingList-6TiSCH]
              IETF, "6TiSCH Mailing List",
              <https://mailarchive.ietf.org/arch/browse/6tisch/>.

   [MEF22.1.1]
              Metro Ethernet Forum, "Mobile Backhaul Phase 2 Amendment 1
              -- Small Cells", MEF 22.1.1, July 2014,
              <http://www.mef.net/Assets/Technical_Specifications/PDF/
              MEF_22.1.1.pdf>.

   [MEF8]     Metro Ethernet Forum, "Implementation Agreement for the
              Emulation of PDH Circuits over Metro Ethernet Networks",
              MEF 8, October 2004, <https://www.mef.net/
              Assets/Technical_Specifications/PDF/MEF_8.pdf>.







Grossman                      Informational                    [Page 85]


RFC 8578                    DetNet Use Cases                    May 2019


   [METIS]    METIS, "Scenarios, requirements and KPIs for 5G mobile and
              wireless system", Document Number ICT-317669-METIS/D1.1,
              April 2013, <https://metis2020.com/wp-content/
              uploads/deliverables/METIS_D1.1_v1.pdf>.

   [MODBUS]   Modbus Organization, Inc., "MODBUS Application Protocol
              Specification", April 2012,
              <http://www.modbus.org/specs.php>.

   [NGMN]     NGMN Alliance, "5G White Paper", NGMN 5G White Paper v1.0,
              February 2015, <https://www.ngmn.org/fileadmin/ngmn/
              content/downloads/Technical/2015/
              NGMN_5G_White_Paper_V1_0.pdf>.

   [NGMN-Fronth]
              NGMN Alliance, "Fronthaul Requirements for C-RAN",
              March 2015, <https://www.ngmn.org/fileadmin/user_upload/
              NGMN_RANEV_D1_C-RAN_Fronthaul_Requirements_v1.0.pdf>.

   [OPCXML]   OPC Foundation, "OPC Data Access (OPC DA) Specification",
              <http://www.opcti.com/opc-da-specification.aspx>.

   [PCE]      IETF, "Path Computation Element",
              <https://datatracker.ietf.org/doc/charter-ietf-pce/>.

   [PROFIBUS] IEC, "PROFIBUS Standard - DP Specification (IEC 61158
              Type 3)", <https://www.profibus.com/>.

   [PROFINET] "PROFINET Technology",
              <https://us.profinet.com/technology/profinet/>.

   [RFC3031]  Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
              Label Switching Architecture", RFC 3031,
              DOI 10.17487/RFC3031, January 2001,
              <https://www.rfc-editor.org/info/rfc3031>.

   [RFC3411]  Harrington, D., Presuhn, R., and B. Wijnen, "An
              Architecture for Describing Simple Network Management
              Protocol (SNMP) Management Frameworks", STD 62, RFC 3411,
              DOI 10.17487/RFC3411, December 2002,
              <https://www.rfc-editor.org/info/rfc3411>.

   [RFC3985]  Bryant, S., Ed. and P. Pate, Ed., "Pseudo Wire Emulation
              Edge-to-Edge (PWE3) Architecture", RFC 3985,
              DOI 10.17487/RFC3985, March 2005,
              <https://www.rfc-editor.org/info/rfc3985>.





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   [RFC4553]  Vainshtein, A., Ed. and YJ. Stein, Ed., "Structure-
              Agnostic Time Division Multiplexing (TDM) over Packet
              (SAToP)", RFC 4553, DOI 10.17487/RFC4553, June 2006,
              <https://www.rfc-editor.org/info/rfc4553>.

   [RFC5086]  Vainshtein, A., Ed., Sasson, I., Metz, E., Frost, T., and
              P. Pate, "Structure-Aware Time Division Multiplexed (TDM)
              Circuit Emulation Service over Packet Switched Network
              (CESoPSN)", RFC 5086, DOI 10.17487/RFC5086, December 2007,
              <https://www.rfc-editor.org/info/rfc5086>.

   [RFC5087]  Stein, Y(J)., Shashoua, R., Insler, R., and M. Anavi,
              "Time Division Multiplexing over IP (TDMoIP)", RFC 5087,
              DOI 10.17487/RFC5087, December 2007,
              <https://www.rfc-editor.org/info/rfc5087>.

   [RFC5905]  Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch,
              "Network Time Protocol Version 4: Protocol and Algorithms
              Specification", RFC 5905, DOI 10.17487/RFC5905, June 2010,
              <https://www.rfc-editor.org/info/rfc5905>.

   [RFC6550]  Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J.,
              Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur,
              JP., and R. Alexander, "RPL: IPv6 Routing Protocol for
              Low-Power and Lossy Networks", RFC 6550,
              DOI 10.17487/RFC6550, March 2012,
              <https://www.rfc-editor.org/info/rfc6550>.

   [RFC6551]  Vasseur, JP., Ed., Kim, M., Ed., Pister, K., Dejean, N.,
              and D. Barthel, "Routing Metrics Used for Path Calculation
              in Low-Power and Lossy Networks", RFC 6551,
              DOI 10.17487/RFC6551, March 2012,
              <https://www.rfc-editor.org/info/rfc6551>.

   [RFC7554]  Watteyne, T., Ed., Palattella, M., and L. Grieco, "Using
              IEEE 802.15.4e Time-Slotted Channel Hopping (TSCH) in the
              Internet of Things (IoT): Problem Statement", RFC 7554,
              DOI 10.17487/RFC7554, May 2015,
              <https://www.rfc-editor.org/info/rfc7554>.

   [RFC8169]  Mirsky, G., Ruffini, S., Gray, E., Drake, J., Bryant, S.,
              and A. Vainshtein, "Residence Time Measurement in MPLS
              Networks", RFC 8169, DOI 10.17487/RFC8169, May 2017,
              <https://www.rfc-editor.org/info/rfc8169>.







Grossman                      Informational                    [Page 87]


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   [Spe09]    Barbosa, R., Sadre, R., and A. Pras, "A First Look into
              SCADA Network Traffic", IP Network Operations and
              Management Symposium, DOI 10.1109/NOMS.2012.6211945,
              June 2012, <https://ieeexplore.ieee.org/document/6211945>.

   [SR-IP-RAN-Use-Case]
              Khasnabish, B., Hu, F., and L. Contreras, "Segment
              Routing in IP RAN use case", Work in Progress,
              draft-kh-spring-ip-ran-use-case-02, November 2014.

   [SRP_LATENCY]
              Gunther, C., "Specifying SRP Acceptable Latency",
              March 2014, <http://www.ieee802.org/1/files/public/
              docs2014/cc-cgunther-acceptable-latency-0314-v01.pdf>.

   [Sublayer-6TiSCH-6top]
              Wang, Q., Ed. and X. Vilajosana, "6TiSCH Operation
              Sublayer (6top)", Work in Progress,
              draft-wang-6tisch-6top-sublayer-04, November 2015.

   [syncE]    International Telecommunication Union, "Timing and
              synchronization aspects in packet networks", ITU-T
              Recommendation G.8261, August 2013,
              <https://www.itu.int/rec/T-REC-G.8261>.

   [Timing-over-MPLS]
              Davari, S., Oren, A., Bhatia, M., Roberts, P., and L.
              Montini, "Transporting Timing messages over MPLS
              Networks", Work in Progress,
              draft-ietf-tictoc-1588overmpls-07, October 2015.

   [TR38801]  3GPP, "Study on new radio access technology: Radio access
              architecture and interfaces (Release 14)", 3GPP TR 38.801,
              April 2017,
              <https://portal.3gpp.org/desktopmodules/Specifications/
              SpecificationDetails.aspx?specificationId=3056>.

   [TS23401]  3GPP, "General Packet Radio Service (GPRS) enhancements
              for Evolved Universal Terrestrial Radio Access Network
              (E-UTRAN) access (Release 16)", 3GPP TS 23.401,
              March 2019, <https://portal.3gpp.org/
              desktopmodules/ Specifications/
              SpecificationDetails.aspx?specificationId=849>.

   [TS23501]  3GPP, "System architecture for the 5G System (5GS)
              (Release 15)", 3GPP TS 23.501, March 2019,
              <https://portal.3gpp.org/desktopmodules/Specifications/
              SpecificationDetails.aspx?specificationId=3144>.



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   [TS25104]  3GPP, "Base Station (BS) radio transmission and reception
              (FDD) (Release 16)", 3GPP TS 25.104, January 2019,
              <https://portal.3gpp.org/desktopmodules/Specifications/
              SpecificationDetails.aspx?specificationId=1154>.

   [TS36104]  3GPP, "Evolved Universal Terrestrial Radio Access
              (E-UTRA); Base Station (BS) radio transmission and
              reception (Release 16)", 3GPP TS 36.104, January 2019,
              <https://portal.3gpp.org/desktopmodules/Specifications/
              SpecificationDetails.aspx?specificationId=2412>.

   [TS36133]  3GPP, "Evolved Universal Terrestrial Radio Access
              (E-UTRA); Requirements for support of radio resource
              management (Release 16)", 3GPP TS 36.133, January 2019,
              <https://portal.3gpp.org/desktopmodules/Specifications/
              SpecificationDetails.aspx?specificationId=2420>.

   [TS36211]  3GPP, "Evolved Universal Terrestrial Radio Access
              (E-UTRA); Physical channels and modulation (Release 15)",
              3GPP TS 36.211, January 2019,
              <https://portal.3gpp.org/desktopmodules/Specifications/
              SpecificationDetails.aspx?specificationId=2425>.

   [TS36300]  3GPP, "Evolved Universal Terrestrial Radio Access (E-UTRA)
              and Evolved Universal Terrestrial Radio Access Network
              (E-UTRAN); Overall description; Stage 2 (Release 15)",
              3GPP TS 36.300, January 2019,
              <https://portal.3gpp.org/desktopmodules/Specifications/
              SpecificationDetails.aspx?specificationId=2430>.

   [WirelessHART]
              International Electrotechnical Commission, "Industrial
              networks - Wireless communication network and
              communication profiles - WirelessHART(TM)",
              IEC 62591:2016, March 2016.
















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Appendix A.  Use Cases Explicitly Out of Scope for DetNet

   This appendix contains text regarding use cases that have been
   determined to be outside the scope of the present DetNet work.

A.1.  DetNet Scope Limitations

   The scope of DetNet is deliberately limited to specific use cases
   that are consistent with the WG charter, subject to the
   interpretation of the WG.  At the time that the DetNet use cases were
   solicited and provided by the authors, the scope of DetNet was not
   clearly defined.  As the scope has been clarified, certain use cases
   have been determined to be outside the scope of the present DetNet
   work.  Text regarding these use cases was moved to this appendix to
   clarify that they will not be supported by the DetNet work.

   The text was moved to this appendix based on the following
   "exclusion" principles.  Please note that as an alternative to moving
   all such text to this appendix some text has been modified in situ to
   reflect these same principles.

   The following principles have been established to clarify the scope
   of the present DetNet work.

   o  The scope of networks addressed by DetNet is limited to networks
      that can be centrally controlled, i.e., an "enterprise" (aka
      "corporate") network.  This explicitly excludes "the open
      Internet".

   o  Maintaining time synchronization across a DetNet network is
      crucial to its operation; however, DetNet assumes that time is to
      be maintained using other means.  One example would be PTP
      [IEEE-1588].  A use case may state the accuracy and reliability
      that it expects from the DetNet network as part of a whole system;
      however, it is understood that such timing properties are not
      guaranteed by DetNet itself.  At the time of this writing, two
      open questions remain: (1) whether DetNet protocols will include a
      way for an application to communicate expectations regarding such
      timing properties to the network and (2) if so, whether those
      properties would likely have a material effect on network
      performance as a result.

A.2.  Internet-Based Applications

   There are many applications that communicate over the open Internet
   that could benefit from guaranteed delivery and bounded latency.
   However, as noted above, all such applications, when run over the
   open Internet, are out of scope for DetNet.  These same applications



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   may be in scope when run in constrained environments, i.e., within a
   centrally controlled DetNet network.  The following are some examples
   of such applications.

A.2.1.  Use Case Description

A.2.1.1.  Media Content Delivery

   Media content delivery continues to be an important use of the
   Internet, yet users often experience poor-quality audio and video due
   to the delay and jitter inherent in today's Internet.

A.2.1.2.  Online Gaming

   Online gaming is a significant part of the gaming market; however,
   latency can degrade the end user's experience.  For example, "First
   Person Shooter" (FPS) games are highly delay sensitive.

A.2.1.3.  Virtual Reality

   VR has many commercial applications, including real estate
   presentations, remote medical procedures, and so on.  Low latency is
   critical to interacting with the virtual world, because perceptual
   delays can cause motion sickness.

A.2.2.  Internet-Based Applications Today

   Internet service today is by definition "best effort", with no
   guarantees regarding delivery or bandwidth.

A.2.3.  Internet-Based Applications in the Future

   One should be able to play Internet videos without glitches and play
   Internet games without lag.

   For online gaming, the desired maximum allowance for round-trip delay
   is typically 100 ms.  However, it may be less for specific types of
   games; for example, for FPS games, the maximum delay should be 50 ms.
   Transport delay is the dominant part, with a budget of 5-20 ms.

   For VR, a maximum delay of 1-10 ms is needed; if doing remote VR, the
   total network delay budget is 1-5 ms.

   Flow identification can be used for gaming and VR, i.e., it can
   recognize a critical flow and provide appropriate latency bounds.






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A.2.4.  Internet-Based Applications Requests to the IETF

   o  Unified control and management protocols that handle time-critical
      data flows

   o  An application-aware flow-filtering mechanism that recognizes
      time-critical flows without doing 5-tuple matching

   o  A unified control plane that provides low-latency service on
      Layer 3 without changing the data plane

   o  An OAM system and protocols that can help provide service
      provisioning that is sensitive to end-to-end delays

A.3.  Pro Audio and Video - Digital Rights Management (DRM)

   The following text was moved to this appendix because this
   information is considered a link-layer topic for which DetNet is not
   directly responsible.

   Digital Rights Management (DRM) is very important to the audio and
   video industries.  Whenever protected content is introduced into a
   network, there are DRM concerns that must be taken into account (see
   [Content_Protection]).  Many aspects of DRM are outside the scope of
   network technology; however, there are cases when a secure link
   supporting authentication and encryption is required by content
   owners to carry their audio or video content when it is outside their
   own secure environment (for example, see [DCI]).

   As an example, two such techniques are Digital Transmission Content
   Protection (DTCP) and High-bandwidth Digital Content Protection
   (HDCP).  HDCP content is not approved for retransmission within any
   other type of DRM, while DTCP content may be retransmitted under
   HDCP.  Therefore, if the source of a stream is outside of the network
   and it uses HDCP, it is only allowed to be placed on the network with
   that same type of protection (i.e., HDCP).

A.4.  Pro Audio and Video - Link Aggregation

   Note: The term "link aggregation" is used here as defined by the text
   in the following paragraph, i.e., not following a more common
   network-industry definition.

   For transmitting streams that require more bandwidth than a single
   link in the target network can support, link aggregation is a
   technique for combining (aggregating) the bandwidth available on
   multiple physical links to create a single logical link that provides




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   the required bandwidth.  However, if aggregation is to be used, the
   network controller (or equivalent) must be able to determine the
   maximum latency of any path through the aggregate link.

A.5.  Pro Audio and Video - Deterministic Time to Establish Streaming

   The DetNet WG decided that guidelines for establishing a
   deterministic time to establish stream startup are not within the
   scope of DetNet.  If the bounded timing for establishing or
   re-establishing streams is required in a given use case, it is up to
   the application/system to achieve it.

Acknowledgments

   Pro audio (Section 2)

      As also acknowledged in [DetNet-Audio-Reqs], the editor would like
      to acknowledge the help of the following individuals and the
      companies they represent.

         Jeff Koftinoff, Meyer Sound
         Jouni Korhonen, Associate Technical Director, Broadcom
         Pascal Thubert, CTAO, Cisco
         Kieran Tyrrell, Sienda New Media Technologies GmbH

   Utility telecom (Section 3)

      Information regarding utility telecom was derived from
      [DetNet-Util-Reqs].  As in that document, the following
      individuals are acknowledged here.

         Faramarz Maghsoodlou, Ph.D., IoT Connected Industries
            and Energy Practice, Cisco
         Pascal Thubert, CTAO, Cisco

      The wind power generation use case has been extracted from the
      study of wind parks conducted within the 5GPPP VirtuWind Project.
      The project is funded by the European Union's Horizon 2020
      research and innovation programme under grant agreement No. 671648
      (VirtuWind).

   Building automation systems (Section 4)

      Please see [BAS-DetNet].







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   Wireless for industrial applications (Section 5)

      See [DetNet-6TiSCH].

      [DetNet-6TiSCH] derives from the 6TiSCH architecture, which is the
      result of multiple interactions -- in particular, during the
      6TiSCH (bi)weekly interim call, relayed through the 6TiSCH mailing
      list at the IETF [MailingList-6TiSCH].

      As also acknowledged in [DetNet-6TiSCH], the editor wishes to
      thank Kris Pister, Thomas Watteyne, Xavier Vilajosana, Qin Wang,
      Tom Phinney, Robert Assimiti, Michael Richardson, Zhuo Chen,
      Malisa Vucinic, Alfredo Grieco, Martin Turon, Dominique Barthel,
      Elvis Vogli, Guillaume Gaillard, Herman Storey, Maria Rita
      Palattella, Nicola Accettura, Patrick Wetterwald, Pouria Zand,
      Raghuram Sudhaakar, and Shitanshu Shah for their participation and
      various contributions.

   Cellular radio (Section 6)

      See [DetNet-RAN].

   Internet applications and CoMP (Section 6)

      As also acknowledged in [DetNet-Mobile], authored by Yiyong Zha,
      the editor would like to thank the following people for their
      reviews, suggestions, comments, and proposed text: Jing Huang,
      Junru Lin, Lehong Niu, and Oliver Huang.

   Industrial Machine to Machine (M2M) (Section 7)

      The editor would like to thank Feng Chen and Marcel Kiessling for
      their comments and suggestions.

   Mining industry (Section 8)

      This text was written by Diego Dujovne, who worked in conjunction
      with Xavier Vilajosana.

   Private blockchain (Section 9)

      This text was written by Daniel Huang.

   Network slicing (Section 10)

      This text was written by Xuesong Geng, who would like to
      acknowledge Norm Finn and Mach Chen for their useful comments.




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Contributors

   RFC 7322 ("RFC Style Guide") generally limits the number of authors
   listed on the front page of a document to five individuals -- far
   fewer than the 19 individuals listed below, who also made important
   contributions to this document.  The editor wishes to thank and
   acknowledge each of the following authors for contributing text to
   this document.  See also the Acknowledgments section.

      Craig Gunther (Harman International)
      10653 South River Front Parkway
      South Jordan, UT  84095
      United States of America
      Phone: +1 801 568 7675
      Email: craig.gunther@harman.com

      Pascal Thubert (Cisco Systems, Inc.)
      Building D, 45 Allee des Ormes - BP1200
      Mougins - Sophia Antipolis  06254
      France
      Phone: +33 4 97 23 26 34
      Email: pthubert@cisco.com

      Patrick Wetterwald (Cisco Systems)
      45 Allee des Ormes
      Mougins  06250
      France
      Phone: +33 4 97 23 26 36
      Email: pwetterw@cisco.com

      Jean Raymond (Hydro-Quebec)
      1500 University
      Montreal, Quebec  H3A 3S7
      Canada
      Phone: +1 514 840 3000
      Email: raymond.jean@hydro.qc.ca

      Jouni Korhonen (Broadcom Corporation)
      3151 Zanker Road
      San Jose, CA  95134
      United States of America
      Email: jouni.nospam@gmail.com

      Yu Kaneko (Toshiba)
      1 Komukai-Toshiba-cho
      Saiwai-ku, Kasasaki-shi, Kanagawa
      Japan
      Email: yu1.kaneko@toshiba.co.jp



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      Subir Das (Vencore Labs)
      150 Mount Airy Road
      Basking Ridge, NJ  07920
      United States of America
      Email: sdas@appcomsci.com

      Balazs Varga (Ericsson)
      Konyves Kalman krt. 11/B
      Budapest  1097
      Hungary
      Email: balazs.a.varga@ericsson.com

      Janos Farkas (Ericsson)
      Konyves Kalman krt. 11/B
      Budapest  1097
      Hungary
      Email: janos.farkas@ericsson.com

      Franz-Josef Goetz (Siemens)
      Gleiwitzerstr. 555
      Nurnberg  90475
      Germany
      Email: franz-josef.goetz@siemens.com

      Juergen Schmitt (Siemens)
      Gleiwitzerstr. 555
      Nurnberg  90475
      Germany
      Email: juergen.jues.schmitt@siemens.com

      Xavier Vilajosana (Worldsensing)
      483 Arago
      Barcelona, Catalonia  08013
      Spain
      Email: xvilajosana@worldsensing.com

      Toktam Mahmoodi (King's College London)
      Strand, London  WC2R 2LS
      United Kingdom
      Email: toktam.mahmoodi@kcl.ac.uk

      Spiros Spirou (Intracom Telecom)
      19.7 km Markopoulou Ave.
      Peania, Attiki  19002
      Greece
      Email: spiros.spirou@gmail.com





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      Petra Vizarreta (Technical University of Munich)
      Maxvorstadt, Arcisstrasse 21
      Munich  80333
      Germany
      Email: petra.stojsavljevic@tum.de

      Daniel Huang (ZTE Corporation, Inc.)
      No. 50 Software Avenue
      Nanjing, Jiangsu  210012
      China
      Email: huang.guangping@zte.com.cn

      Xuesong Geng (Huawei Technologies)
      Email: gengxuesong@huawei.com

      Diego Dujovne (Universidad Diego Portales)
      Email: diego.dujovne@mail.udp.cl

      Maik Seewald (Cisco Systems)
      Email: maseewal@cisco.com

Author's Address

   Ethan Grossman (editor)
   Dolby Laboratories, Inc.
   1275 Market Street
   San Francisco, CA  94103
   United States of America

   Phone: +1 415 645 4726
   Email: ethan.grossman@dolby.com
   URI:   http://www.dolby.com



















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