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RFC 4867, "RTP Payload Format and File Storage Format for the Adaptive Multi-Rate (AMR) and Adaptive Multi-Rate Wideband (AMR-WB) Audio Codecs", April 2007

Source of RFC: avt (rai)
See Also: RFC 4867w/ inline errata

Errata ID: 4349
Status: Verified
Type: Technical
Publication Format(s) : TEXT

Reported By: Thomas Belling
Date Reported: 2015-04-27
Verifier Name: Ben Campbell
Date Verified: 2016-05-25

Section 8.1 says:

      mode-set: Restricts the active codec mode set to a subset of all
               modes, for example, to be able to support transport
               channels such as GSM networks in gateway use cases.
               Possible values are a comma separated list of modes from
               the set: 0,...,7 (see Table 1a [2]).  The SID frame type
               8 and NO_DATA (frame type 15) are never included in the
               mode set, but can always be used.  If mode-set is
               specified, it MUST be abided, and frames encoded with
               modes outside of the subset MUST NOT be sent in any RTP
               payload or used in codec mode requests.  If not present,
               all codec modes are allowed for the payload type.

It should say:

      mode-set: Restricts the active codec mode set to a subset of all
               modes, for example, to be able to support transport
               channels such as GSM networks in gateway use cases.
               Possible values are a comma separated list of modes from
               the set: 0,...,7 (see Table 1a [2]).  The SID frame type
               8 and NO_DATA (frame type 15) are never included in the
               mode set, but can always be used.  If mode-set is
               specified, it MUST be abided, i.e. frames encoded with
               modes outside of the subset MUST NOT be sent in any RTP
               payload and codec mode requests MUST only use modes
               within the mode-set or CMR=15. If the mode-set parameter
               is not present, then all codec modes are allowed for the
               payload type.

Notes:

The existing text rules out that CMR=15 is used when a mode-set has been negotiated. However, this contradicts a statement in .clause 4.3.1 that if a terminal has no preference in which mode to receive, it SHOULD set CMR=15 in all its outbound payloads.

This erratum has been discussed and endorsed by the 3GPP SA4 group before submission to IETF.

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