Multiple SIP Reason Header Field Values

Internet Engineering Task Force (IETF)                         R. Sparks
Request for Comments: 9366                                    March 2023
Updates: 3326
Category: Standards Track
ISSN: 2070-1721


                Multiple SIP Reason Header Field Values

Abstract

   The SIP Reason header field as defined in RFC 3326 allows only one
   Reason value per protocol value.  Experience with more recently
   defined protocols shows it is useful to allow multiple values with
   the same protocol value.  This document updates RFC 3326 to allow
   multiple values for an indicated registered protocol when that
   protocol defines what the presence of multiple values means.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc9366.

Copyright Notice

   Copyright (c) 2023 IETF Trust and the persons identified as the
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Table of Contents

   1.  Introduction
   2.  Conventions
   3.  Update to RFC 3326
   4.  Security Considerations
   5.  IANA Considerations
   6.  References
     6.1.  Normative References
     6.2.  Informative References
   Acknowledgments
   Author's Address

1.  Introduction

   The SIP Reason header field as defined in RFC 3326 allows only one
   Reason value per protocol value.  Experience with more recently
   defined protocols shows it is useful to allow multiple values with
   the same protocol value [STIRREASONS].  This document updates RFC
   3326 to allow multiple values for an indicated registered protocol
   when that protocol defines what the presence of multiple values
   means.  It does not change the requirement in RFC 3326 restricting
   the header field contents to one value per protocol for those
   protocols that do not define what multiple values mean.

2.  Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  Update to RFC 3326

   The last paragraph of Section 2 of [RFC3326] is replaced as follows:

   OLD:

   |  A SIP message MAY contain more than one Reason value (i.e.,
   |  multiple Reason lines), but all of them MUST have different
   |  protocol values (e.g., one SIP and another Q.850).  An
   |  implementation is free to ignore Reason values that it does not
   |  understand.

   NEW:

   |  A SIP message MAY contain more than one Reason value (i.e.,
   |  multiple Reason lines).  If the registered protocol for the Reason
   |  value specifies what it means for multiple values to occur in one
   |  message, more than one value for that protocol MAY be present.
   |  Otherwise, there MUST be only one value per protocol provided
   |  (e.g., one SIP and another Q.850).  An implementation is free to
   |  ignore Reason values that it does not understand.

4.  Security Considerations

   This document adds no security considerations to the use of SIP.  The
   security considerations in [RFC3326] and those in any registered
   protocols used in Reason header field values should be considered.

5.  IANA Considerations

   This document has no IANA actions.

6.  References

6.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC3326]  Schulzrinne, H., Oran, D., and G. Camarillo, "The Reason
              Header Field for the Session Initiation Protocol (SIP)",
              RFC 3326, DOI 10.17487/RFC3326, December 2002,
              <https://www.rfc-editor.org/info/rfc3326>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

6.2.  Informative References

   [STIRREASONS]
              Wendt, C., "Identity Header Errors Handling for STIR",
              Work in Progress, Internet-Draft, draft-ietf-stir-
              identity-header-errors-handling-08, 25 February 2023,
              <https://datatracker.ietf.org/doc/html/draft-ietf-stir-
              identity-header-errors-handling-08>.

Acknowledgments

   This text is based on discussions at a STIR Working Group interim
   meeting.  Jean Mahoney and Russ Housley provided suggestions that
   vastly improved the first attempts at assembling these words.
   Christer Holmberg, Dale Worley, Brian Rosen, Chris Wendt, and Paul
   Kyzivat provided constructive discussion during SIPCORE Working Group
   adoption.

Author's Address

   Robert Sparks
   Email: rjsparks@nostrum.com