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

Errata ID: 2910
Status: Rejected
Type: Technical
Publication Format(s) : TEXT
Reported By: Iñaki Baz Castillo
Date Reported: 2011-08-02
Rejected by: Robert Sparks
Date Rejected: 2011-11-04

Section Table 2 says:

      Header field          where   proxy ACK BYE CAN INV OPT REG
      ___________________________________________________________
      Contact                1xx           -   -   -   o   -   -

It should say:

      Header field          where   proxy ACK BYE CAN INV OPT REG
      ___________________________________________________________
      Contact                1xx           -   -   -   m   -   -

Notes:

RFC 3261 says:

Section 12.1: "Dialogs are created through the generation of non-failure responses to requests with specific methods. Within this specification, only 2xx and 101-199 responses with a To tag, where the request was INVITE, will establish a dialog."

Section 12.1.1: "When a UAS responds to a request with a response that establishes a dialog (such as a 2xx to INVITE), the UAS MUST copy all Record-Route header field values from the request into the response [...]. The UAS MUST add a Contact header field to the response."

So it's clear that a 1xx response to an INVITE creates a dialog and then it MUST contain a Contact header and mirrored Record-Route headers.

However Table 2 (page 162) says:

Header field where proxy ACK BYE CAN INV OPT REG
___________________________________________________________
Contact 1xx - - - o - -
Record-Route 2xx,18x mr - o o o o -

Obviously Record-Route is optional since in the absence of a proxy doing record-routing, such header will not be present. However Contact header should appear as mandatory (m) for 1xx responses for INVITE rather than optional (o).
--VERIFIER NOTES--
1xx also includes 100 Trying, which cannot establish a Dialog. Contact is not mandatory in 100 Trying responses.

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