RFC 3261, "SIP: Session Initiation Protocol", June 2002

Errata ID: 3237
Status: Held for Document Update
Type: Editorial
Publication Format(s) : TEXT
Reported By: Kevin P. Fleming
Date Reported: 2012-05-31
Held for Document Update by: Robert Sparks

Section 8.1.3.5 says:

   In all of the above cases, the request is retried by creating a new
   request with the appropriate modifications.  This new request
   constitutes a new transaction and SHOULD have the same value of the
   Call-ID, To, and From of the previous request, but the CSeq should
   contain a new sequence number that is one higher than the previous.

It should say:

   In all of the above cases, the request is retried by creating a new 
   request with the appropriate modifications.  This new request 
   constitutes a new transaction and SHOULD have the same value of the 
   Call-ID, To, and From of the previous request, but the CSeq SHOULD 
   contain a new sequence number that is one higher than the previous.

Notes:

We have had one implementor claim that they are not required to increment CSeq when retrying the request because the RFC says 'should' and not 'SHOULD'. Based on current IETF discussions, though, these should probably be changed to MUST anyway, but that's a much more substantive change throughout the whole RFC.

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