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

Note: This RFC has been updated by RFC 3265, RFC 3853, RFC 4320, RFC 4916, RFC 5393, RFC 5621, RFC 5626, RFC 5630, RFC 5922, RFC 5954, RFC 6026, RFC 6141, RFC 6665, RFC 6878, RFC 7462, RFC 7463, RFC 8217, RFC 8591, RFC 8760, RFC 8898, RFC 8996

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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