RFC 6660

Encoding Three Pre-Congestion Notification (PCN) States in the IP Header Using a Single Diffserv Codepoint (DSCP), July 2012

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RFC 5696
B. Briscoe
T. Moncaster
M. Menth
pcn (tsv)

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DOI:  https://doi.org/10.17487/RFC6660

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The objective of Pre-Congestion Notification (PCN) is to protect the quality of service (QoS) of inelastic flows within a Diffserv domain. The overall rate of PCN-traffic is metered on every link in the PCN- domain, and PCN-packets are appropriately marked when certain configured rates are exceeded. Egress nodes pass information about these PCN-marks to Decision Points that then decide whether to admit or block new flow requests or to terminate some already admitted flows during serious pre-congestion.

This document specifies how PCN-marks are to be encoded into the IP header by reusing the Explicit Congestion Notification (ECN) codepoints within a PCN-domain. The PCN wire protocol for non-IP protocol headers will need to be defined elsewhere. Nonetheless, this document clarifies the PCN encoding for MPLS in an informational appendix. The encoding for IP provides for up to three different PCN marking states using a single Diffserv codepoint (DSCP): not-marked (NM), threshold-marked (ThM), and excess-traffic-marked (ETM). Hence, it is called the 3-in-1 PCN encoding. This document obsoletes RFC 5696. [STANDARDS-TRACK]

For the definition of Status, see RFC 2026.

For the definition of Stream, see RFC 8729.

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