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Versions: 00 01

Sipcore Working Group                                      A. Allen, Ed.
Internet-Draft                                                Blackberry
Intended status: Informational                              July 3, 2014
Expires: January 4, 2015


 Internet Assigned Numbers Authority (IANA) Registration of the Session
        Initiation Protocol (SIP) Feature-Capability indicators
             draft-allen-sipcore-sip-tree-cap-indicators-01

Abstract

   This document registers with IANA the SIP Feature-Capability
   indicators in the "SIP Feature-Capability Indicator Registration
   Tree" of the IANA "Proxy-Feature Feature-Capability Indicator Trees"
   registry for use with the SIP Feature-Caps header field.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on January 4, 2015.

Copyright Notice

   Copyright (c) 2014 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.



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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3

   2.  Motivation . . . . . . . . . . . . . . . . . . . . . . . . . .  3

   3.  SIP Feature-Capability indicators  . . . . . . . . . . . . . .  4

   4.  Security Considerations  . . . . . . . . . . . . . . . . . . .  5

   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  5
     5.1.  Audio  . . . . . . . . . . . . . . . . . . . . . . . . . .  5
     5.2.  Application  . . . . . . . . . . . . . . . . . . . . . . .  6
     5.3.  Data . . . . . . . . . . . . . . . . . . . . . . . . . . .  7
     5.4.  Control  . . . . . . . . . . . . . . . . . . . . . . . . .  7
     5.5.  Video  . . . . . . . . . . . . . . . . . . . . . . . . . .  8
     5.6.  Text . . . . . . . . . . . . . . . . . . . . . . . . . . .  9
     5.7.  Duplex . . . . . . . . . . . . . . . . . . . . . . . . . .  9
     5.8.  Description  . . . . . . . . . . . . . . . . . . . . . . . 11
     5.9.  Event Packages . . . . . . . . . . . . . . . . . . . . . . 11
     5.10. Priority . . . . . . . . . . . . . . . . . . . . . . . . . 12
     5.11. Methods  . . . . . . . . . . . . . . . . . . . . . . . . . 13
     5.12. Extensions . . . . . . . . . . . . . . . . . . . . . . . . 14
     5.13. Schemes  . . . . . . . . . . . . . . . . . . . . . . . . . 15
     5.14. Is Focus . . . . . . . . . . . . . . . . . . . . . . . . . 15
     5.15. Message  . . . . . . . . . . . . . . . . . . . . . . . . . 16
     5.16. Interactive Connectivity Establishment . . . . . . . . . . 17
     5.17. Application Subtype  . . . . . . . . . . . . . . . . . . . 17
     5.18. Fax  . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

   6.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 19

   7.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 19
     7.1.  Normative References . . . . . . . . . . . . . . . . . . . 19
     7.2.  Informative References . . . . . . . . . . . . . . . . . . 20

   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 21














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1.  Introduction

   RFC 6809 [1] specifies the SIP Feature-Caps header field thst conveys
   feature-capability indicators that are used to indicate support of
   features and capabilities for SIP entities that are not represented
   by the Uniform Resource Identifier (URI) of the Contact header field.
   RFC 6809 [1] also creates a new IANA registry, "Proxy-Feature
   Feature-Capability Indicator Trees", for registering feature-
   capability indicators including a SIP feature-capability indicator
   tree for registering SIP feature-capability indicators that is
   similar to the media feature tag SIP tree defined in RFC 3840 [2].
   This document populates this SIP tree with some feature-capability
   indicators that are based upon those already defined in RFC 3840 [2],
   RFC 4569 [3], RFC 5768 [4], RFC 5688 [5] and RFC 6913 [6].


2.  Motivation

   SIP sessions often involve intermediaries (typically acting as
   B2BUAs) that in addition to forwarding SIP requests and responses can
   also act as UAs to perform more complex manipulations of the session.
   Examples of such intermediaries include IP PBXs (Internet Protocol
   Private Brance Exchanges), Telephony Call Feature Application Servers
   and Session Transfer Anchor Points.  Often the manipulations of the
   session by the intermediary are initiated by one of the UAs in the
   session sending a request (such as REFER request) to the intermediary
   to for example transfer the session or create a conference.
   Additionally UAs may also need to subscribe to events related to the
   session with the intermediary accepting such subscritions and
   providing the notification of event state changes.

   Typically such functionality has been achieved by sending such REFER
   and SUBSCRIBE requests within the established dialog for the session,
   with the intermediary then intercepting and processing the REFER or
   SUBSCRIBE request rather than forwarding it to the remote UAS.
   However such dialog reuse has been problematic and RFC 6665 [7] has
   deprecated dialog reuse (except for legacy interoperability).
   However, in order to avoid reusing the same dialog as the session and
   achieve equivalent functionality when interacting with intermediaries
   using for instance REFER request requires that the UA obtain the
   Globally Routable User Agent URI (GRUU) of the intermediary and also
   know that the intermediary supports the relevant capabilities such as
   the required SIP methods (i.e.  REFER) as well as the needed SIP
   extensions, (such as target dialog extension specified in RFC 4538 in
   [8]).

   Typically B2BUAs have acted as two UAs back-to-back with the Contact
   URI being the URI of the B2BUA.  However this means that GRUU of the



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   UA is overwritten by the B2BUA and the meaning of the Contact header
   field parameters becomes obscure.  Do the Contact header field
   parameters reflect the capabilities of the Contact address (i.e the
   B2BUA) or do they reflect the capabilities of the remote UA?  If they
   relect the capabilities of the B2BUA then the identfication of the
   capabilities of the remote UA have been lost.  If they reflect the
   capabilities of the remote UA then they falsely identify that the
   B2BUA contact address has the capabilities of the remote UA.

   Another use case for B2BUAs is in control of Application Level
   Gateways (ALGs).  These ALGs are controlled by SIP intermediaries
   that act as routing B2BUs and perform media functions such as IP
   address translation, transcoding, and media policing.  Such ALGs may
   only support some media types while blocking others.  It is useful if
   the media types that are allowed can be communciated to other
   entities in the SIP signaling so that fruitless attempts to establish
   sessions with media types that will not be allowed are not attempted.

   What is needed is a way for intermediaries to pass the remote UA's
   contact address and capabilities transparently in the Contact header
   field while being able to indicate their own contact address (i.e
   GRUU) and associated capabilities to the UA.

   RFC 6809 [1] provides that addresses of intermediaries can be
   communicated as a value of an associated feature-capability indicator
   so it would be appropriate to define feature capability indicators as
   part of the global tree to communicate the GRUU of the intermediary
   and hence this is outside the scope of this document.  The feature-
   capability indicators for communicating SIP related capabilities (e.g
   supported SIP Methods and extensions) though need to be registered in
   the SIP tree.


3.  SIP Feature-Capability indicators

   The following media feature tags from RFC 3840 [2]", RFC 4569 [3],
   RFC 5768 [4], RFC 5688 [5] and RFC 6913 [6] are considered to be
   useful to also be defined as Feature-Capability indicators:
      sip.audio
      sip.application
      sip.data
      sip.control
      sip.video
      sip.text
      sip.duplex
      sip.description





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      sip.events
      sip.priority
      sip.methods
      sip.extensions
      sip.schemes
      sip.isfocus
      sip.message
      sip.ice
      sip.app-subtype
      sip.fax

   The following media feature tags from RFC 3840 [2], RFC 4235 [9] and
   RFC 5626 [10] are NOT considered to be useful to be defined as
   Feature-Capability indicators:
      sip.automata
      sip.class
      sip.mobility
      sip.actor
      sip.byeless
      sip.rendering
      sip.instance


4.  Security Considerations

   The security considerations in RFC 3840 [2] and RFC 6809 [1] apply to
   the use of Feature-capability indicators in the SIP tree.


5.  IANA Considerations

   This specification registers the following new feature-capability
   indicators in the SIP tree per the procedures defined in RFC 6809
   [10].


5.1.  Audio


      Feature-capability indicator name: sip.audio

      ASN.1 Identifier: 1

      Descrition:
      This Feature-capability indicator indicates that the intermediary
      supports audio as a streaming media type.





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      Feature-capability indicator specification reference: RFC 3840
      [2].

      Additional information:

         Values appropriate for use with this Feature-Capability
         indicator: Boolean.

         This Feature-Capability indicator is most useful in a
         communications application for describing the capabilities of a
         network intermediary, such as an IP-PBX or conference bridge.

         Examples of typical use: An IP PBX indicating that it is
         capable of accepting and initiating sessions with audio as a
         streaming media type.

         Security Considerations: Security considerations for this
         Feature-capability indicator are discussed in RFC 6809 [1] and
         RFC 3840 [2].


5.2.  Application


      Feature-capability indicator name: sip.application

      ASN.1 Identifier: 2

      Descrition:
      This Feature-capability indicator indicates that the intermediary
      supports application as a streaming media type.

      Feature-capability indicator specification reference: RFC 3840
      [2].

      Additional information:

         Values appropriate for use with this Feature-Capability
         indicator: Boolean.

         This Feature-Capability indicator is most useful in a
         communications application for describing the capabilities of a
         network intermediary, such as an IP-PBX or conference bridge.

         Examples of typical use: An IP PBX indicating that it is
         capable of accepting and initiating sessions with a media
         control application.




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         Security Considerations: Security considerations for this
         Feature-capability indicator are discussed in RFC 6809 [1] and
         RFC 3840 [2].


5.3.  Data




      Feature-capability indicator name: sip.data

      ASN.1 Identifier: 1

      Descrition:
      This Feature-capability indicator indicates that the intermediary
      supports data as a streaming media type.

      Feature-capability indicator specification reference: RFC 3840
      [2].

      Additional information:

         Values appropriate for use with this Feature-Capability
         indicator: Boolean.

         This Feature-Capability indicator is most useful in a
         communications application for describing the capabilities of a
         network intermediary, such as an IP-PBX or conference bridge.

         Examples of typical use: An IP PBX indicating that it is
         capable of accepting and initiating sessions with data as a
         streaming media type.

         Security Considerations: Security considerations for this
         Feature-capability indicator are discussed in RFC 6809 [1] and
         RFC 3840 [2].


5.4.  Control


      Feature-capability indicator name: sip.control

      ASN.1 Identifier: 4






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      Descrition:
      This Feature-capability indicator indicates that the intermediary
      supports control as a streaming media type.

      Feature-capability indicator specification reference: RFC 3840
      [2].

      Additional information:

         Values appropriate for use with this Feature-Capability
         indicator: Boolean.

         This Feature-Capability indicator is most useful in a
         communications application for describing the capabilities of a
         network intermediary, such as an IP-PBX or conference bridge.

         Examples of typical use: A conference bridge indicating that it
         is capable of supporting a floor control application.

         Security Considerations: Security considerations for this
         Feature-capability indicator are discussed in RFC 6809 [1] and
         RFC 3840 [2].


5.5.  Video


      Feature-capability indicator name: sip.video

      ASN.1 Identifier: 5

      Descrition:
      This Feature-capability indicator indicates that the intermediary
      supports video as a streaming media type.

      Feature-capability indicator specification reference: RFC 3840
      [2].

      Additional information:

         Values appropriate for use with this Feature-Capability
         indicator: Boolean.

         This Feature-Capability indicator is most useful in a
         communications application for describing the capabilities of a
         network intermediary, such as an IP-PBX or conference bridge.





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         Examples of typical use: An IP PBX indicating that it is
         capable of accepting and initiating sessions with video as a
         streaming media type.

         Security Considerations: Security considerations for this
         Feature-capability indicator are discussed in RFC 6809 [1] and
         RFC 3840 [2].


5.6.  Text


      Feature-capability indicator name: sip.text

      ASN.1 Identifier: 6

      Descrition:
      This Feature-capability indicator indicates that the intermediary
      supports text as a streaming media type.

      Feature-capability indicator specification reference: RFC 3840
      [2].

      Additional information:

         Values appropriate for use with this Feature-Capability
         indicator: Boolean.

         This Feature-Capability indicator is most useful in a
         communications application for describing the capabilities of a
         network intermediary, such as an IP-PBX or conference bridge.

         Examples of typical use: An IP PBX indicating that it is
         capable of accepting and initiating sessions with text as a
         streaming media type.

         Security Considerations: Security considerations for this
         Feature-capability indicator are discussed in RFC 6809 [1] and
         RFC 3840 [2].


5.7.  Duplex


      Feature-capability indicator name: sip.duplex






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      ASN.1 Identifier: 7

      Descrition:
      The values of the sip.duplex (not the plurality) Feature-
      capability indicator indicate whether a intermediary can support
      sessions that simultaneously send and receive media ("full"),
      alternate between sending and receiving ("half"), can only receive
      ("receive-only") or only send ("send-only").

      Feature-capability indicator specification reference: RFC 3840
      [2].

      Additional information:

         Values appropriate for use with this Feature-Capability
         indicator: Token with an equality relationship.  Typical values
         include:

            full: The device can simultaneously send and receive media.

            half: The device can alternate between sending and receiving
            media.

            receive-only: The device can only receive media.

            send-only: The device can only send media.

            Note that a list of multiple values can be include (e.g.
            "full, half" indicating that both full duplex and half
            duplex communciations are supported).  If "full" or "half"
            is indicated then support for "receive-only" and "send-only"
            sessions can also be assumed.

         This Feature-Capability indicator is most useful in a
         communications application for describing the capabilities of a
         network intermediary, such as an IP-PBX or conference bridge.

         Examples of typical use: A conference bridge indicating that it
         is capable of accepting sessions with half duplex
         communications (e.g.  Push to Talk).

         Security Considerations: Security considerations for this
         Feature-capability indicator are discussed in RFC 6809 [1] and
         RFC 3840 [2].







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5.8.  Description


      Feature-capability indicator name: sip.description

      ASN.1 Identifier: 8

      Descrition:
      This Feature-capability indicator provides a textual description
      of the intermediary.

      Feature-capability indicator specification reference: RFC 3840
      [2].

      Additional information:

         Values appropriate for use with this Feature-Capability
         indicator: String with an equality relationship.

         This Feature-Capability indicator is most useful in a
         communications application for describing the capabilities of a
         network intermediary, such as an IP-PBX or conference bridge.

         Examples of typical use: An IP PBX indicating that it is the IP
         PBX of example.org.

         Security Considerations: Security considerations for this
         Feature-capability indicator are discussed in RFC 6809 [1] and
         RFC 3840 [2].


5.9.  Event Packages


      Feature-capability indicator name: sip.events

      ASN.1 Identifier: 9

      Descrition:
      Each value of the sip.events (note the plurality) Feature-
      capability indicator indicates a SIP event package RFC 6665
      supported by a SIP UA.  The values for this Feature-capability
      indicator equal the event package names that are registered by
      each event package.

      Feature-capability indicator specification reference: RFC 3840
      [2].




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      Additional information:

         Values appropriate for use with this Feature-Capability
         indicator: Token with an equality relationship.  Values are
         taken from the IANA SIP Event types namespace registry.

         This Feature-Capability indicator is most useful in a
         communications application for describing the capabilities of a
         network intermediary, such as an IP-PBX or conference bridge.

         Examples of typical use: An IP PBX indicating that it supports
         and can accept subscriptions to the message waiting event
         package, (i.e it is also the voicemail server).

         Security Considerations: Security considerations for this
         Feature-capability indicator are discussed in RFC 6809 [1] and
         RFC 3840 [2].


5.10.  Priority


      Feature-capability indicator name: sip.priority

      ASN.1 Identifier: 10

      Descrition:
      This Feature-capability indicator indicates the call priorities
      the intermediary is willing to handle.  A value of X means that
      the intermediary is willing to tak requests with priority X and
      higher.

      Feature-capability indicator specification reference: RFC 3840
      [2].

      Additional information:

         Values appropriate for use with this Feature-Capability
         indicator: An integer.  Each integral value corresponds to one
         of the possible values of the Priority header field as
         specified in SIP.  The mapping is defined as:

            non-urgent: Integral value of 10.  The device supports non-
            urgent calls.

            normal: Integral value of 20.  The device supports normal
            calls.




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            urgent: Integral value of 30.  The device supports urgent
            calls.

            emergency: Integral value of 40.  The device supports calls
            in the case of an emergency situation.

         This Feature-Capability indicator is most useful in a
         communications application for describing the capabilities of a
         network intermediary, such as an IP-PBX or conference bridge.

         Examples of typical use: An IP PBX indicating that it accepts
         emergency calls (e.g. it can connect a user directly to campus
         security).

         Security Considerations: Security considerations for this
         Feature-capability indicator are discussed in RFC 6809 [1] and
         RFC 3840 [2].


5.11.  Methods


      Feature-capability indicator name: sip.methods

      ASN.1 Identifier: 11

      Descrition:
      Each value of the sip.methods (note the plurality) Feature-
      capability indicator indicates a SIP method supported by this
      intermediary.  In this case, "supported" means that the
      intermediary will accept requests with this method.  In that
      sense, it has the same connotation as the Allow header field.

      Feature-capability indicator specification reference: RFC 3840
      [2].

      Additional information:

         Values appropriate for use with this Feature-Capability
         indicator: Token with an equality relationship.  Values are
         taken from the Methods table defined in the IANA SIP parameters
         registry.

         This Feature-Capability indicator is most useful in a
         communications application for describing the capabilities of a
         network intermediary, such as an IP-PBX or conference bridge.





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         Examples of typical use: An IP PBX indicating that it accepts a
         REFER request to transfer the session.

         Security Considerations: Security considerations for this
         Feature-capability indicator are discussed in RFC 6809 [1] and
         RFC 3840 [2].


5.12.  Extensions


      Feature-capability indicator name: sip.extensions

      ASN.1 Identifier: 12

      Descrition:
      Each value of the sip.extensions (note the plurality) Feature-
      capability indicator indicates is a SIP extension (each of which
      is defined by an option-tag registered with IANA) that is
      understood by the intermediary.  Understood, in this context,
      means the same as if the option tag had been included in a
      Supported header field.

      Feature-capability indicator specification reference: RFC 3840
      [2].

      Additional information:

         Values appropriate for use with this Feature-Capability
         indicator: Token with an equality relationship.  Values are
         taken from the option tags table in the IANA SIP parameters
         registry.

         This Feature-Capability indicator is most useful in a
         communications application for describing the capabilities of a
         network intermediary, such as an IP-PBX or conference bridge.

         Examples of typical use: An IP PBX indicating that it supports
         the target dialog extension for use with a session transfer.

         Security Considerations: Security considerations for this
         Feature-capability indicator are discussed in RFC 6809 [1] and
         RFC 3840 [2].








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5.13.  Schemes


      Feature-capability indicator name: sip.schemes

      ASN.1 Identifier: 13

      Descrition:
      Each value of the sip.schemes (note the plurality) Feature-
      capability indicator indicates a URI scheme that is supported by
      an intermediary.  Supported implies, for example, that the
      intermediary would know how to handle a URI of that scheme in the
      Contact header field of a redirect response.

      Feature-capability indicator specification reference: RFC 3840
      [2].

      Additional information:

         Values appropriate for use with this Feature-Capability
         indicator: Token with an equality relationship.  Values are
         taken from the IANA URI scheme registry.

         This Feature-Capability indicator is most useful in a
         communications application for describing the capabilities of a
         network intermediary, such as an IP-PBX or conference bridge.

         Examples of typical use: An IP PBX indicating that it will
         accept redirection of the session to a server that supports
         media content (e.g a music server).

         Security Considerations: Security considerations for this
         Feature-capability indicator are discussed in RFC 6809 [1] and
         RFC 3840 [2].


5.14.  Is Focus


      Feature-capability indicator name: sip.isfocus

      ASN.1 Identifier: 14

      Descrition:
      This Feature-capability indicator indicates that the intermediary
      is a conference server, also known as a focus, and is capable of
      mixing together the media for all calls to the same URI.




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      Feature-capability indicator specification reference: RFC 3840
      [2].

      Additional information:

         Values appropriate for use with this Feature-Capability
         indicator: Boolean.

         This Feature-Capability indicator is most useful in a
         communications application for describing the capabilities of a
         network intermediary, such as a conference bridge.

         Examples of typical use: A conference bridge indicating that it
         is a conference bridge and is capable of acting as a conference
         focus for this session.

         Security Considerations: Security considerations for this
         Feature-capability indicator are discussed in RFC 6809 [1] and
         RFC 3840 [2].


5.15.  Message


      Feature-capability indicator name: sip.message

      ASN.1 Identifier: 15

      Descrition:
      This Feature-capability indicator indicates that the intermediary
      supports message as a streaming media type.

      Feature-capability indicator specification reference: RFC 4569
      [3].

      Additional information:

         Values appropriate for use with this Feature-Capability
         indicator: Boolean.

         This Feature-Capability indicator is most useful in a
         communications application for describing the capabilities of a
         network intermediary, such as an IP-PBX or conference bridge.

         Examples of typical use: An IP PBX indicating that it is
         capable of accepting and initiating sessions with message as a
         streaming media type.




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         Security Considerations: Security considerations for this
         Feature-capability indicator are discussed in RFC 6809 [1], RFC
         3840 [2] and RFC 4569 [3].


5.16.  Interactive Connectivity Establishment


      Feature-capability indicator name: sip.ice

      ASN.1 Identifier: 16

      Descrition:
      This Feature-capability indicator indicates that the intermediary
      supports that the device supports Interactive Connectivity
      Establishment (ICE).

      Feature-capability indicator specification reference: RFC 5768
      [4].

      Additional information:

         Values appropriate for use with this Feature-Capability
         indicator: Boolean.

         This Feature-Capability indicator is most useful in a
         communications application for describing the capabilities of a
         network intermediary, such as an IP-PBX or conference bridge.

         Examples of typical use: An IP PBX indicating that it is
         capable of using ICE to establish media connectivity for
         sessions.

         Security Considerations: Security considerations for this
         Feature-capability indicator are discussed in RFC 6809 [1], RFC
         3840 [2] and RFC 5768 [4].


5.17.  Application Subtype


      Feature-capability indicator name: sip.app-subtype

      ASN.1 Identifier: 17

      Descrition:





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      This Feature-capability indicator indicates the MIME application
      subtypes supported by the intermediary for purposes of streaming
      media.

      Feature-capability indicator specification reference: RFC 5688
      [5].

      Additional information:

         Values appropriate for use with this Feature-Capability
         indicator: Token (equality relationship).

         This Feature-Capability indicator is most useful in a
         communications application for describing the capabilities of a
         network intermediary, such as an IP-PBX or conference bridge.

         Examples of typical use: A conference setrver indicating that
         it supports an application specific media burst control
         protocol for Push to Talk sessions.

         Security Considerations: Security considerations for this
         Feature-capability indicator are discussed in RFC 6809 [1], RFC
         3840 [2] and RFC 5688 [5].


5.18.  Fax


      Feature-capability indicator name: sip.fax

      ASN.1 Identifier: 18

      Descrition:
      This Feature-capability indicator indicates whether an
      intermediary accepts sessions using the ITU-T T.38 [11] fax
      protocol ("t38") or the passthrough method of fax transmission
      using the ITU-T G.711 [12] audio codec ("passthrough").

      Feature-capability indicator specification reference: RFC 6913
      [6].

      Additional information:

         Values appropriate for use with this Feature-Capability
         indicator: Token with an equality relationship.  Values are:






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            t38: The device supports the "image/t38" media type (RFC
            3326) [13] and implements ITU-T T.38 [11] for transporting
            the ITU-T T.30 [14] and ITU-T T.4 [15] fax data over IP.

            passthrough: The device supports the "audio/pcmu" and
            "audio/ pcma" media types (RFC4856) [16] for transporting
            ITU-T T.30 [14] and ITU-T T.4 [15] fax data using the ITU-T
            G.711 [12] audio codec.

         This Feature-Capability indicator is most useful in a
         communications application for describing the capabilities of a
         network intermediary, such as an IP-PBX or conference bridge.

         Examples of typical use: A conference bridge indicating that it
         is capable of distributing T.38 fax media to the participants
         in a conference.

         Security Considerations: Security considerations for this
         Feature-capability indicator are discussed in RFC 6809 [1], RFC
         3840 [2] and RFC 6913 [6].



6.  Acknowledgements

   This document draws heavily on text from the earlier work on RFC 6809
   [1], RFC 3840 [2], RFC 4569 [3], RFC 5768 [4], RFC 5688 [5] and RFC
   6913 [6].  The author would like to thank the authors of these RFCs:
   Christer Holmber, Ivo Sedlacek, Hadriel Kaplan, Jonathan Rosenberg
   Henning Schulzrinne, Paul Kyzivat, Gonzalo Camarillo, D Hanes, G
   Salgueiro and K Fleming for their earlier work which has made this a
   relatively simple IANA registration exercise.


7.  References

7.1.  Normative References

   [1]   Holmberg, C., Sedlacek, I., and H. Kaplan, "Mechanism to
         Indicate Support of Features and Capabilities in the Session
         Initiation Protocol (SIP)", RFC 6809, November 2012.

   [2]   Rosenberg, J., Schulzrinne, H., and P. Kyzivat, "Indicating
         User Agent Capabilities in the Session Initiation Protocol
         (SIP)", RFC 3840, August 2004.

   [3]   Camarillo, G., "Internet Assigned Number Authority (IANA)
         Registration of the Message Media Feature Tag", RFC 4569,



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         July 2006.

   [4]   Rosenberg, J., "Indicating Support for Interactive Connectivity
         Establishment (ICE) in the Session Initiation Protocol (SIP)",
         RFC 5768, April 2010.

   [5]   Rosenberg, J., "A Session Initiation Protocol (SIP) Media
         Feature Tag for MIME Application Subtypes", RFC 5688,
         January 2010.

   [6]   Hanes, D., Salgueiro, G., and K. Fleming, "Indicating Fax over
         IP Capability in the Session Initiation Protocol (SIP)",
         RFC 6913, March 2013.

   [7]   Roach, A., "SIP-Specific Event Notification", RFC 6665,
         July 2012.

7.2.  Informative References

   [8]   Rosenberg, J., "Request Authorization through Dialog
         Identification in the Session Initiation Protocol (SIP)",
         RFC 4538, June 2006.

   [9]   Rosenberg, J., Schulzrinne, H., and R. Mahy, "An INVITE-
         Initiated Dialog Event Package for the Session Initiation
         Protocol (SIP)", RFC 4235, November 2005.

   [10]  Jennings, C., Mahy, R., and F. Audet, "Managing Client-
         Initiated Connections in the Session Initiation Protocol
         (SIP)", RFC 5626, October 2009.

   [11]  International Telecommunication Union, "Procedures for real-
         time Group 3 facsimile communication over IP Networks", ITU-
         T Recommendation T.38, October 2010.

   [12]  International Telephone and Telegraph Consultative Committee,
         "Pulse Code Modulation (PCM) of Voice Frequencies",
         CCITT Recommendation G.711, 1972.

   [13]  Schulzrinne, H., Oran, D., and G. Camarillo, "The Reason Header
         Field for the Session Initiation Protocol (SIP)", RFC 3326,
         December 2002.

   [14]  International Telecommunication Union, "Procedures for document
         facsimile transmission in the general switched telephone
         network", ITU-T Recommendation T.30, September 2005.

   [15]  International Telecommunication Union, "Standardization of



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         Group 3 facsimile terminals for document transmission", ITU-
         T Recommendation T.4, July 2003.

   [16]  Casner, S., "Media Type Registration of Payload Formats in the
         RTP Profile for Audio and Video Conferences", RFC 4856,
         February 2007.


Author's Address

   Andrew Allen (editor)
   Blackberry
   1200 Sawgrass Corporate Parkway
   Sunrise, Florida  33323
   USA

   Email: aallen@blackberry.com


































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