The Internet Assigned Number Authority (IANA) Header Field Parameter Registry for the Session Initiation Protocol (SIP)
RFC 3968

Network Working Group                                       G. Camarillo
Request for Comments: 3968                                      Ericsson
Updates: 3427                                              December 2004
BCP: 98
Category: Best Current Practice

             The Internet Assigned Number Authority (IANA)
                  Header Field Parameter Registry for
                 the Session Initiation Protocol (SIP)

Status of This Memo

   This document specifies an Internet Best Current Practices for the
   Internet Community, and requests discussion and suggestions for
   improvements.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2004).

Abstract

   This document creates an Internet Assigned Number Authority (IANA)
   registry for the Session Initiation Protocol (SIP) header field
   parameters and parameter values.  It also lists the already existing
   parameters and parameter values to be used as the initial entries for
   this registry.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  2
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  2
   3.  Use of the Registry  . . . . . . . . . . . . . . . . . . . . .  2
   4.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  3
       4.1.  Header Field Parameters Sub-Registry . . . . . . . . . .  3
       4.2.  Registration Policy for SIP Header Field Parameters. . .  6
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . .  7
   6.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .  7
   7.  Normative References . . . . . . . . . . . . . . . . . . . . .  7
       Author's Address . . . . . . . . . . . . . . . . . . . . . . .  7
       Full Copyright Statement . . . . . . . . . . . . . . . . . . .  8

Camarillo                Best Current Practice                  [Page 1]
RFC 3968                 SIP Parameter Registry            December 2004

1.  Introduction

   RFC 3261 [3] allows new header field parameters and new parameter
   values to be defined.  However, RFC 3261 omitted an IANA registry for
   them.  This document creates such a registry.

   RFC 3427 [4] documents the process to extend SIP.  This document
   updates RFC 3427 by specifying how to define and register new SIP
   header field parameters and parameter values.

2.  Terminology

   In this document, the key words "MUST", "MUST NOT", "REQUIRED",
   "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT
   RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as
   described in BCP 14, RFC 2119 [1] and indicate requirement levels for
   compliant implementations.

3.  Use of the Registry

   SIP header field parameters and parameter values MUST be documented
   in an RFC in order to be registered by IANA.  This documentation MUST
   fully explain the syntax, intended usage, and semantics of the
   parameter or parameter value.  The intent of this requirement is to
   assure interoperability between independent implementations, and to
   prevent accidental namespace collisions between implementations of
   dissimilar features.

      Note that this registry, unlike other protocol registries, only
      deals with parameters and parameter values defined in RFCs (i.e.,
      it lacks a vendor-extension tree).  RFC 3427 [4] documents
      concerns with regards to new SIP extensions which may damage
      security, greatly increase the complexity of the protocol, or
      both.  New parameters and parameter values need to be documented
      in RFCs as a result of these concerns.

   RFCs defining SIP header field parameters or parameter values MUST
   register them with IANA as described below.

   Registered SIP header field parameters and parameter values are to be
   considered "reserved words".  In order to preserve interoperability,
   registered parameters and parameter values MUST be used in a manner
   consistent with that described in their defining RFC.
   Implementations MUST NOT utilize "private" or "locally defined" SIP
   header field parameters or parameter values that conflict with
   registered parameters.

Camarillo                Best Current Practice                  [Page 2]
RFC 3968                 SIP Parameter Registry            December 2004

      Note that although unregistered SIP header field parameters and
      parameter values may be used in implementations, developers are
      cautioned that usage of such parameters is risky.  New SIP header
      field parameters and parameter values may be registered at any