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The Internet Assigned Number Authority (IANA) Uniform Resource Identifier (URI) Parameter Registry for the Session Initiation Protocol (SIP)

The information below is for an old version of the document that is already published as an RFC.
Document Type
This is an older version of an Internet-Draft that was ultimately published as RFC 3969.
Author Gonzalo Camarillo
Last updated 2015-10-14 (Latest revision 2004-06-17)
RFC stream Internet Engineering Task Force (IETF)
Intended RFC status Best Current Practice
Additional resources Mailing list discussion
Stream WG state (None)
Document shepherd (None)
IESG IESG state Became RFC 3969 (Best Current Practice)
Action Holders
Consensus boilerplate Unknown
Telechat date (None)
Responsible AD Allison J. Mankin
Send notices to,
Internet Engineering Task Force                                   SIP WG
Internet Draft                                              G. Camarillo
June 16, 2004
Expires: December 2004

        The Internet Assigned Number Authority (IANA) Universal
      Resource Identifier (URI) Parameter Registry for the Session
                       Initiation Protocol (SIP)


   By submitting this Internet-Draft, I certify that any applicable
   patent or other IPR claims of which I am aware have been disclosed,
   and any of which I become aware will be disclosed, in accordance with
   RFC 3668.

   Internet-Drafts are working documents of the Internet Engineering
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   The list of current Internet-Drafts can be accessed at

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   This document creates an IANA registry for SIP and SIPS URI
   parameters, and their values. It also lists the already existing
   parameters to be used as initial values for that registry.

G. Camarillo                                                  [Page 1]

Internet Draft                    SIP                      June 16, 2004

                           Table of Contents

   1          Introduction ........................................    3
   2          Terminology .........................................    3
   3          Use of the Registry .................................    3
   4          IANA Considerations .................................    4
   4.1        SIP and SIPS URI Parameters Sub-Registry ............    4
   4.2        Registration Policy for SIP and SIPS URI Parameters .    5
   5          Security Considerations .............................    5
   6          Acknowledgements ....................................    5
   7          Authors' Addresses ..................................    5
   8          Normative References ................................    6
   9          Informative References ..............................    6

G. Camarillo                                                  [Page 2]

Internet Draft                    SIP                      June 16, 2004

1 Introduction

   RFC3261 [1] allows new SIP URI and SIPS URI parameters, and new
   parameter values to be defined. However, RFC3261 omitted an IANA
   registry for them. This document creates such a registry.

   RFC 3427 [2] documents the process to extend SIP. This document
   updates RFC 3427 by specifying how to define and register new SIP and
   SIP URI parameters and their values.

2 Terminology

   In this document, the key words "MUST", "MUST NOT", "REQUIRED",
   and "OPTIONAL" are to be interpreted as described in RFC 2119 [3] and
   indicate requirement levels for compliant SIP implementations.

3 Use of the Registry

   SIP and SIPS URI parameters and values for these parameters MUST be
   documented in a standards-track RFC in order to be registered by
   IANA. This documentation MUST fully explain the syntax, intended
   usage, and semantics of the parameter. The intent of this requirement
   is to assure inetroperability 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 [2]
        documents concerns with regards to new SIP extensions which
        may be damaging towards 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 URI, SIPS URI parameters, or parameter values MUST
   register them with IANA as described below.

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

        Note that although unregistered SIP and SIPS URI parameters
        may be used in implementations, developers are cautioned

G. Camarillo                                                  [Page 3]

Internet Draft                    SIP                      June 16, 2004

        that usage of such parameters is risky. New SIP and SIPS
        URI parameters and new values for them may be registered at
        any time, and there is no assurance that these new
        registered URI parameters will not conflict with
        unregistered parameters currently in use.

   Some SIP and SIPS URI parameters only accept a set of predefined
   parameter values. For example, a parameter indicating the transport
   protocol in use may only accept as valid values the predefined tokens
   TCP, UDP, and SCTP. Registering all parameter values for all SIP and
   SIPS URI parameters of this type would require a large number of
   subregistries. Instead, we have chosen to register URI parameter
   values by reference. That is, the entry in the URI parameter registry
   for a given URI parameter contains references to the RFCs defining
   new values of the parameter. References to RFCs defining parameter
   values appear in brackets in the registry.

   So, the SIP and SIPS URI parameter registry contains a column that
   indicates whether or not each parameter only accepts a set of
   predefined values. Implementers of parameters with a "yes" in that
   column need to find all the valid parameter values in the RFCs
   provided as references.

4 IANA Considerations

   Section 27 of RFC 3261 [1] creates an IANA registry for method names,
   header field names, warning codes, status codes, and option tags.
   This specification instructs the IANA to create a new sub-registry

        o SIP/SIPS URI Parameters

4.1 SIP and SIPS URI Parameters Sub-Registry

   New SIP and SIPS URI parameters and new parameter values are
   registered by the IANA. When registering a new SIP or SIPS parameter
   or a new value for a parameter, the following information MUST be

        o Name of the parameter.

        o Whether the parameter only accepts a set of predefined values.

        o Reference to the RFC defining the parameter and to any RFC
          that defines new values for the parameter. References to RFCs
          defining parameter values appear in brackets in the registry.

   Table 1 contains the initial values for this sub-registry.

G. Camarillo                                                  [Page 4]

Internet Draft                    SIP                      June 16, 2004

               Parameter Name  Predefined Values  Reference
               comp                   Yes         RFC 3486
               lr                      No         RFC 3261
               maddr                   No         RFC 3261
               method                 Yes         RFC 3261
               transport              Yes         RFC 3261
               ttl                     No         RFC 3261
               user                   Yes         RFC 3261

   Table 1: IANA SIP and SIPS URI parameter sub-registry

   Note that any given parameter name is registered both as a SIP and as
   a SIPS URI parameter. Still, some parameters may not apply to one of
   the schemes. We have chosen to register any parameter as both SIP and
   SIPS URI parameter anyway to avoid having two parameters with the
   same name, one applicable to SIP URIs and one to SIPS URIs, but with
   different semantics. Implementors are urged to read the parameter
   specifications for a detailed description of the semantics of any

4.2 Registration Policy for SIP and SIPS URI Parameters

   As per the terminology in RFC 2434 [4], the registration policy for
   SIP and SIPS URI parameters shall be "Specification Required".

   For the purposes of this registry, the parameter for which IANA
   registration is requested MUST be defined by a standards-track RFC.

5 Security Considerations

   There are no security considerations associated to this document.

6 Acknowledgements

   Jonathan Rosenberg, Henning Schulzrinne, Rohan Mahy, Dean Willis, and
   Allison Mankin provided useful comments.

7 Authors' Addresses

   Gonzalo Camarillo
   Advanced Signalling Research Lab.
   FIN-02420 Jorvas
   electronic mail:

G. Camarillo                                                  [Page 5]

Internet Draft                    SIP                      June 16, 2004

8 Normative References

   [1] J. Rosenberg, H. Schulzrinne, G. Camarillo, A. R. Johnston, J.
   Peterson, R. Sparks, M. Handley, and E. Schooler, "SIP: session
   initiation protocol," RFC 3261, Internet Engineering Task Force, June

   [2] A. Mankin, S. Bradner, R. Mahy, D. Willis, J. Ott, and B. Rosen,
   "Change process for the session initiation protocol (SIP)," RFC 3427,
   Internet Engineering Task Force, Dec. 2002.

   [3] S. Bradner, "Key words for use in RFCs to indicate requirement
   levels," RFC 2119, Internet Engineering Task Force, Mar. 1997.

   [4] T. Narten and H. Alvestrand, "Guidelines for writing an IANA
   considerations section in RFCs," RFC 2434, Internet Engineering Task
   Force, Oct. 1998.

9 Informative References

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G. Camarillo                                                  [Page 6]

Internet Draft                    SIP                      June 16, 2004

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G. Camarillo                                                  [Page 7]