mmusic                                                   B. Greevenbosch
Internet-Draft                                       Huawei Technologies
Intended status: Informational                              July 5, 2012
Expires: January 6, 2013


      Hitchhiker's guide to the Session Description Protocol (SDP)
           draft-greevenbosch-mmusic-hitchhikersguide-sdp-01

Abstract

   The Session Initiation Protocol (SDP) is the subject of numerous
   specifications that have been produced by the IETF.  It can be
   difficult to locate the right document, or even to determine the set
   of Request for Comments (RFC) about SDP.  This specification serves
   as a guide to the SDP RFC series.  It lists a current snapshot of the
   specifications under the SDP umbrella, briefly summarises each, and
   groups them into categories.

































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Note

   Discussion and suggestions for improvement are requested, and should
   be sent to mmusic@ietf.org.

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 6, 2013.

Copyright Notice

   Copyright (c) 2012 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
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   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.  Requirements notation  . . . . . . . . . . . . . . . . . . . .  4
   2.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  5
   3.  SDP  . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  7
     3.1.  Core SDP specifications  . . . . . . . . . . . . . . . . .  7
     3.2.  General purpose infrastructure extensions  . . . . . . . .  7
     3.3.  NAT Traversal  . . . . . . . . . . . . . . . . . . . . . .  8
     3.4.  Minor extensions . . . . . . . . . . . . . . . . . . . . .  8
     3.5.  Security mechanisms  . . . . . . . . . . . . . . . . . . .  8
     3.6.  Conferencing . . . . . . . . . . . . . . . . . . . . . . .  9
   4.  SIP  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
     4.1.  Security mechanisms  . . . . . . . . . . . . . . . . . . . 10
   5.  Documents left to handle . . . . . . . . . . . . . . . . . . . 11
     5.1.  SDP  . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
       5.1.1.  RFCs . . . . . . . . . . . . . . . . . . . . . . . . . 11
       5.1.2.  Working group drafts . . . . . . . . . . . . . . . . . 11
       5.1.3.  Individual drafts  . . . . . . . . . . . . . . . . . . 11
     5.2.  SIP  . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
       5.2.1.  RFCs . . . . . . . . . . . . . . . . . . . . . . . . . 11
       5.2.2.  Working group drafts . . . . . . . . . . . . . . . . . 11
       5.2.3.  Individual drafts  . . . . . . . . . . . . . . . . . . 12
     5.3.  H.248/Megaco . . . . . . . . . . . . . . . . . . . . . . . 12
       5.3.1.  RFCs . . . . . . . . . . . . . . . . . . . . . . . . . 12
       5.3.2.  Working group drafts . . . . . . . . . . . . . . . . . 12
       5.3.3.  Individual drafts  . . . . . . . . . . . . . . . . . . 12
     5.4.  RTCP . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
       5.4.1.  RFCs . . . . . . . . . . . . . . . . . . . . . . . . . 12
       5.4.2.  Working group drafts . . . . . . . . . . . . . . . . . 12
       5.4.3.  Individual drafts  . . . . . . . . . . . . . . . . . . 12
     5.5.  Yet unclassified . . . . . . . . . . . . . . . . . . . . . 12
       5.5.1.  RFCs . . . . . . . . . . . . . . . . . . . . . . . . . 12
       5.5.2.  Working group drafts . . . . . . . . . . . . . . . . . 13
       5.5.3.  Individual drafts  . . . . . . . . . . . . . . . . . . 13
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 14
   7.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 15
   8.  Normative References . . . . . . . . . . . . . . . . . . . . . 16
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 19













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1.  Requirements notation

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].














































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2.  Introduction

   The Session Description Protocol (SDP) [RFC4566] is the subject of
   numerous specifications that have been produced by the IETF.  It can
   be difficult to locate the right document, or even to determine the
   set of Request for Comments (RFC) about SDP.

   This specification serves as a guide to the SDP RFC series.  It is a
   current snapshot of the specifications under the SDP umbrella at the
   time of publication.  It is anticipated that this document itself
   will be regularly updated as SDP specifications mature.  Furthermore,
   it references many specifications, which, at the time of publication
   of this document, were not yet finalised, and may eventually be
   completed or abandoned.  Therefore, the enumeration of specifications
   here is a work-in-progress and subject to change.

   For each specification, a paragraph or so description is included
   that summarises the purpose of the specification.  Each specification
   also includes a letter that designates its category in the Standards
   Track [RFC2026].  These values are:

      S: Standards Track (Proposed Standard, Draft Standard, or
      Standard)

      E: Experimental

      B: Best Current Practice

      I: Informational

   The specifications are grouped together by topic.  The topics are:

   Core:  The SDP specifications that are expected to be utilised for
      each session or registration an endpoint participates in.

   General Purpose Infrastructure:  General purpose extensions to SDP,
      but the ones that are not expected to always be used.

   NAT Traversal:  Specifications to deal with firewall and NAT
      traversal.

   Quality of Service:  Specifications related to multimedia quality of
      service (QoS).

   Operations and Management:  Specifications related to configuration
      and monitoring of SDP deployments.





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   Minor Extensions:  Specifications that solve a narrow problem space
      or provide an optimisation.

   Security Mechanisms:  Specifications providing security functionality
      for SDP.

   Conferencing:  Specifications for multimedia conferencing.

   Typically, SDP extensions fit naturally into topic areas, and
   implementors interested in a particular topic often implement many or
   all of the specifications in that area.  There are some
   specifications that fall into multiple topic areas, but generally
   they will be listed only once.

   This document itself is not an update to [RFC4566] or an extension to
   SDP.  It is an informational document, meant to guide newcomers,
   implementers, and deployers to the many specifications associated
   with SDP.

































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3.  SDP

3.1.  Core SDP specifications

   RFC 2327,  Session Description Protocol (S): [RFC2327] defines the
      original SDP protocol.  The RFC has been obsoleted by its
      successor [RFC4566].

   RFC 3264,  An Offer/Answer Model with the Session Description
      Protocol (S): [RFC3264] defines how SDP is used with SIP [RFC3261]
      to negotiate the parameters of a media session.  It is in
      widespread usage and an integral part of the behaviour of SIP.

   RFC 4566,  Session Description Protocol (S): [RFC4566] defines a
      format for representing multimedia sessions.  SDP objects are
      carried in the body of SIP messages and, based on the offer/answer
      model, are used to negotiate the media characteristics of a
      session between users.

3.2.  General purpose infrastructure extensions

   RFC 3266,  Support for IPv6 in Session Description Protocol (SDP)
      (S): [RFC3266] describes the use of Internet Protocol Version 6
      (IPv6) addresses in conjunction with the Session Description
      Protocol (SDP).  The document clarifies existing text in SDP in
      regard to the syntax of IPv6 addresses.

   RFC 3388,  Grouping of Media Lines in the Session Description
      Protocol (S): [RFC3388] defines a framework for grouping together
      media streams in an SDP message.  Such a grouping allows
      relationships between these streams, such as which stream is the
      audio for a particular video feed, to be expressed.

   RFC 4091,  The Alternative Network Address Types (ANAT) Semantics for
      the Session Description Protocol (SDP) Grouping Framework (S):
      [RFC4091] defines a mechanism for including both IPv4 and IPv6
      addresses to establish a media stream.  This mechanism has been
      deprecated in favor of ICE [ICE].

   RFC 4145,  TCP-Based Media Transport in the Session Description
      Protocol (SDP) (S): [RFC4145] defines an extension to SDP for
      setting up TCP-based sessions between user agents.  It defines who
      sets up the connection and how its lifecycle is managed.  It has
      seen relatively little usage due to the small number of media
      types to date that use TCP.






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   RFC 5583,  Signaling Media Decoding Dependency in the Session
      Description Protocol (SDP) (S): [RFC5583] defines an extension to
      the grouping framework from [RFC3388].  A "DDP" grouping semantics
      identifier and a "depend" attribute are defined to express
      decoding dependencies between different media streams.  The "mid"
      labeling mechanism from [RFC3388] is reused.

3.3.  NAT Traversal

   RFC3605,  Real Time Control Protocol (RTCP) Attribute in the Session
      Description Protocol (SDP) (S): [RFC3605] defines a way to
      explicitly signal, within an SDP message, the IP address and port
      for RTCP, rather than using the port+1 rule in the Real Time
      Transport Protocol (RTP) [RFC3550].  It is needed for devices
      behind NAT, and the specification is required by ICE.

3.4.  Minor extensions

   RFC3890,  A Transport Independent Bandwidth Modifier for the Session
      Description Protocol (SDP) (S): [RFC3890] specifies an SDP
      extension that allows for the description of the bandwidth for a
      media session that is independent of the underlying transport
      mechanism.

   RFC 4796,  The SDP (Session Description Protocol) Content Attribute
      (S): [RFC4796] defines an SDP attribute for describing the purpose
      of a media stream.  Examples include a slide view, the speaker, a
      sign language feed, and so on.

3.5.  Security mechanisms

   RFC4567,  Key Management Extensions for Session Description Protocol
      (SDP) and Real Time Streaming Protocol (RTSP) (S): [RFC4567]
      defines extensions to SDP that allow tunneling of a key management
      protocol, namely MIKEY [RFC3830], through offer/answer exchanges.
      This mechanism is one of three Secure Realtime Transport Protocol
      (SRTP) keying techniques specified for SIP, with Datagram
      Transport Layer Security (DTLS)-SRTP [RFC5683] having been
      selected as the final solution.

   RFC4568,  Session Description Protocol (SDP) Security Descriptions
      for Media Streams (S): [RFC4568] defines extensions to SDP that
      allow for the negotiation of keying material directly through
      offer/answer, without a separate key management protocol.  This
      mechanism, sometimes called sdescriptions, has the drawback that
      the media keys are available to any entity that has visibility to
      the SDP.  It is one of three SRTP keying techniques specified for
      SIP, with DTLS-SRTP [RFC5683] having been selected as the final



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      solution.

   RFC4572,  Connection-Oriented Media Transport over the Transport
      Layer Security (TLS) Protocol in the Session Description Protocol
      (SDP) (S): [RFC4572] specifies a mechanism for signaling TLS-
      based media streams between endpoints.  It expands the TCP-based
      media signaling parameters defined in [RFC4145] to include
      fingerprint information for TLS streams so that TLS can operate
      between end hosts using self-signed certificates.

   RFC5027,  Security Preconditions for Session Description Protocol
      Media Streams (S): [RFC5027] defines a precondition for use with
      the preconditions framework [RFC3312].  The security precondition
      prevents a session from being established until a security media
      stream is set up.

3.6.  Conferencing

   RFC4574,  The SDP (Session Description Protocol) Label Attribute (S):
      [RFC4574] defines an SDP attribute for providing an opaque label
      for media streams.  These labels can be referred to by external
      documents, and in particular, by conference policy documents.
      This allows a UA to tie together documents it may obtain through
      conferencing mechanisms to media streams to which they refer.

   RFC4583,  Session Description Protocol (SDP) Format for Binary Floor
      Control Protocol (BFCP) Streams (S): [RFC4583] defines a mechanism
      in SDP to signal floor control streams that use BFCP.  It is used
      for push-to-talk and conference floor control.






















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4.  SIP

4.1.  Security mechanisms

   RFC3893,  Session Initiation Protocol (SIP) Authenticated Identity
      Body (AIB) Format (S): [RFC3893] defines a SIP message fragment
      that can be signed in order to provide an authenticated identity
      over a request.  It was an early predecessor to [RFC4474], and
      consequently AIB has seen no deployment.

   RFC4474,  Enhancements for Authenticated Identity Management in SIP
      (S): [RFC4474] defines a mechanism for providing a
      cryptographically verifiable identity of the calling party in a
      SIP request.  Known as "SIP Identity", this mechanism provides an
      alternative to [RFC3325].  It has seen little deployment so far,
      but its importance as a key construct for anti-spam techniques and
      new security mechanisms makes it a core part of the SIP
      specifications.

   RFC 4916,  Connected Identity in the Session Initiation Protocol
      (SIP) (S): [RFC4916] formally updates [RFC3261].  It defines an
      extension to SIP that allows a calling user to determine the
      identity of the final called user (connected party).  Due to
      forwarding and retargeting services, this may not be the same as
      the user that the caller was originally trying to reach.  The
      mechanism works in tandem with the SIP identity specification
      [RFC4474] to provide signatures over the connected party identity.
      It can also be used if a party identity changes mid call due to
      third party call control actions or PSTN behavior.






















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5.  Documents left to handle

5.1.  SDP

5.1.1.  RFCs

   3108, 3890, 4317, 4570, 4583, 4585, 5104, 5245, 5432, 5547, 5576,
   5669, 5763, 5888, 5898, 5939, 6188, 6236.

5.1.2.  Working group drafts

   draft-ietf-mmusic-media-loopback-16,
   draft-ietf-mmusic-parallax-attribute-00,
   draft-ietf-mmusic-rfc4566bis-04, draft-ietf-mmusic-sdp-cs-09,
   draft-ietf-mmusic-sdp-media-capabilities-12,
   draft-ietf-mmusic-traffic-class-for-sdp-00,
   draft-ietf-mmusic-signal-3d-format-00, draft-ietf-payload-rtp-mvc.

5.1.3.  Individual drafts

   draft-boucadair-mmusic-altc-04,
   draft-boucadair-mmusic-ipv6-use-cases-00,
   draft-boulton-mmusic-sdp-control-package-attribute-07,
   draft-holmberg-mmusic-sdp-bundle-negotiation-00,
   draft-lennox-mmusic-sdp-source-selection-03,
   draft-petithuguenin-mmusic-ice-attributes-level-02,
   draft-westerlund-mmusic-sdp-bw-attribute-00.

5.2.  SIP

5.2.1.  RFCs

   2976, 3087, 3204, 3261, 3263, 3265, 3311, 3312, 3313, 3323, 3325,
   3326, 3329, 3372, 3398, 3420, 3427, 3428, 3486, 3524, 3578, 3581,
   3608, 3665, 3666, 3680, 3840, 3841, 3842, 3856, 3857, 3891, 3892,
   3903, 3910, 3911, 3959, 3960, 3969, 4411, 4412, 4117, 4235, 4240,
   4320, 4458, 4483, 4488, 4497, 4508, 4538, 4575, 4579, 4662, 4730,
   5049, 5079, 5360, 5361, 5362, 5363, 5365, 5366, 5367, 5368, 5373,
   5393, 5621, 5626, 5627, 5628, 5630, 5658, 5727, 5767, 5839, 5922,
   5923, 6011, 6035, 6050, 6072, 6086, 6157, 6442.

5.2.2.  Working group drafts

   draft-ietf-sip-saml-08, draft-ietf-sip-session-policy-framework-10.







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5.2.3.  Individual drafts

5.3.  H.248/Megaco

5.3.1.  RFCs

   5125, 5615

5.3.2.  Working group drafts

5.3.3.  Individual drafts

5.4.  RTCP

5.4.1.  RFCs

   3611, 6725, 6332

5.4.2.  Working group drafts

5.4.3.  Individual drafts

5.5.  Yet unclassified

5.5.1.  RFCs

   2848;
   3262;
   3310;
   3327;
   3407: att-field definition for sqn, cdsc, cpar, cparmin, cparmax;
   3515;
   3556: bwtype definition for RS, RR;
   3711: proto definition for RTP/AVPF;
   3725;
   3853;
   3926: proto definition for FLUTE/UDP, att-field definition for flute-
   tsi, flute-ch, FEC-declaration, FEC-OTI-extension, content-desc,
   group attribute definition for CS;
   4028;
   4168;
   4169;
   4244;
   4571: proto definition for TCP/RTP/AVP;
   4975: proto definition for TCP/MSRP; att-field definition for accept-
   types, accept-wrapped-types, max-size, path;
   5124: proto definition for RTP/SAVPF;
   5159: att-field definition for bcastversion, stkmstream,



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   SRTPAuthentication, SRTPROCTxRate;
   5245: att-field definition for candidate, remote-candidates;
   5285: att-field definition for extmap;
   5432: att-field definition for qos-mech-send, qos-mech-recv;
   5506: att-field definition for rtcp-rsize;
   5760: att-field definition for rtcp-unicast;
   5761: att-field definition for rtcp-mux;
   5762: proto definition for DCCP, DCCP/RTP/AVP, DCCP/RTP/SAVP, DCCP/
   RTP/AVPF, DCCP/RTP/SAVPF, att-field definition for dccp-service code;
   5764: proto definition for DCCP/TLS/RTP/SAVP, UDP/TLS/RTP/SAVP, UDP/
   TLS/RTP/SAVPF, DCCP/TLS/RTP/SAVPF;
   5956: group attribute definition for FEC, FEC-FR; ssrc-group SDP
   attribute definition for FEC-FR;
   6064: proto definition for UDP/MBMS-FEC/RTP/AVP, UDP/MBMS-FEC/RTP/
   SAVP, UDP/MBMS-REPAIR, att-field definition for 3GPP-Integrity-Key,
   3GPP-SDP-Auth, alt-group, att-field definition for 3GPP-QoE-Metrics,
   3GP-Asset-Information, mbms-mode, mbms-repair, X-predecbufsize,
   X-initpredecbufperiod, X-initpostdecbufperiod, X-decbyterate, 3gpp-
   videopostdecbufsize, framesize, 3GPP-SRTP-Config, alt,
   alt-default-id, 3GPP-Adaptation-Support, mbms-flowid;
   6128: att-field definition for multicast-rtcp;
   6189: att-field definition for zrtp-hash;
   6193: att-field definition for ike-setup, psk-fingerprint;
   6230: att-field definition for cfw-id;
   6284: att-field definition for portmapping-req;
   6285: att-field definition for rams-updates; "ack" and "nack"
   attribute definition for rai;
   6364: proto definition for FEC/UDP, UDP/FEC, att-field definition for
   fec-source-flow, fec-repair-flow, repair-window.

5.5.2.  Working group drafts

   draft-ietf-mmusic-rfc2326bis-28

5.5.3.  Individual drafts
















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6.  Security Considerations

   This specification is an overview of existing specifications and does
   not introduce any security considerations on its own.















































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7.  Acknowledgements

   The author would like to thank Jonathan Rosenberg, the author of "A
   Hitchhiker's guide to the Session Initiation Protocol (SIP)"
   [RFC5411], which served as basis for this document, and from which
   much text was copied.

   The title of this document was inspired by the "The Hitchhiker's
   Guide to the Galaxy" [HGTTG].

   Thanks to Gonzalo Salguiero and Yue Peiyu for their help identifying
   related RFCs and providing feedback.







































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8.  Normative References

   [RFC2026]  Bradner, S., "The Internet Standards Process -- Revision
              3", BCP 9, RFC 2026, October 1996.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2327]  Handley, M. and V. Jacobson, "SDP: Session Description
              Protocol", RFC 2327, April 1998.

   [RFC3261]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
              A., Peterson, J., Sparks, R., Handley, M., and E.
              Schooler, "SIP: Session Initiation Protocol", RFC 3261,
              June 2002.

   [RFC3264]  Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
              with Session Description Protocol (SDP)", RFC 3264,
              June 2002.

   [RFC3266]  Olson, S., Camarillo, G., and A. Roach, "Support for IPv6
              in Session Description Protocol (SDP)", RFC 3266,
              June 2002.

   [RFC3312]  Camarillo, G., Marshall, W., and J. Rosenberg,
              "Integration of Resource Management and Session Initiation
              Protocol (SIP)", RFC 3312, October 2002.

   [RFC3325]  Jennings, C., Peterson, J., and M. Watson, "Private
              Extensions to the Session Initiation Protocol (SIP) for
              Asserted Identity within Trusted Networks", RFC 3325,
              November 2002.

   [RFC3388]  Camarillo, G., Eriksson, G., Holler, J., and H.
              Schulzrinne, "Grouping of Media Lines in the Session
              Description Protocol (SDP)", RFC 3388, December 2002.

   [RFC3550]  Schulzrinne, H., Casner, S., Frederick, R., and V.
              Jacobson, "RTP: A Transport Protocol for Real-Time
              Applications", STD 64, RFC 3550, July 2003.

   [RFC3605]  Huitema, C., "Real Time Control Protocol (RTCP) attribute
              in Session Description Protocol (SDP)", RFC 3605,
              October 2003.

   [RFC3830]  Arkko, J., Carrara, E., Lindholm, F., Naslund, M., and K.
              Norrman, "MIKEY: Multimedia Internet KEYing", RFC 3830,
              August 2004.



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   [RFC3890]  Westerlund, M., "A Transport Independent Bandwidth
              Modifier for the Session Description Protocol (SDP)",
              RFC 3890, September 2004.

   [RFC3893]  Peterson, J., "Session Initiation Protocol (SIP)
              Authenticated Identity Body (AIB) Format", RFC 3893,
              September 2004.

   [RFC4091]  Camarillo, G. and J. Rosenberg, "The Alternative Network
              Address Types (ANAT) Semantics for the Session Description
              Protocol (SDP) Grouping Framework", RFC 4091, June 2005.

   [RFC4145]  Yon, D. and G. Camarillo, "TCP-Based Media Transport in
              the Session Description Protocol (SDP)", RFC 4145,
              September 2005.

   [RFC4474]  Peterson, J. and C. Jennings, "Enhancements for
              Authenticated Identity Management in the Session
              Initiation Protocol (SIP)", RFC 4474, August 2006.

   [RFC4566]  Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
              Description Protocol", RFC 4566, July 2006.

   [RFC4567]  Arkko, J., Lindholm, F., Naslund, M., Norrman, K., and E.
              Carrara, "Key Management Extensions for Session
              Description Protocol (SDP) and Real Time Streaming
              Protocol (RTSP)", RFC 4567, July 2006.

   [RFC4568]  Andreasen, F., Baugher, M., and D. Wing, "Session
              Description Protocol (SDP) Security Descriptions for Media
              Streams", RFC 4568, July 2006.

   [RFC4572]  Lennox, J., "Connection-Oriented Media Transport over the
              Transport Layer Security (TLS) Protocol in the Session
              Description Protocol (SDP)", RFC 4572, July 2006.

   [RFC4574]  Levin, O. and G. Camarillo, "The Session Description
              Protocol (SDP) Label Attribute", RFC 4574, August 2006.

   [RFC4583]  Camarillo, G., "Session Description Protocol (SDP) Format
              for Binary Floor Control Protocol (BFCP) Streams",
              RFC 4583, November 2006.

   [RFC4796]  Hautakorpi, J. and G. Camarillo, "The Session Description
              Protocol (SDP) Content Attribute", RFC 4796,
              February 2007.

   [RFC4916]  Elwell, J., "Connected Identity in the Session Initiation



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              Protocol (SIP)", RFC 4916, June 2007.

   [RFC5027]  Andreasen, F. and D. Wing, "Security Preconditions for
              Session Description Protocol (SDP) Media Streams",
              RFC 5027, October 2007.

   [RFC5411]  Rosenberg, J., "A Hitchhiker's Guide to the Session
              Initiation Protocol (SIP)", RFC 5411, February 2009.

   [RFC5583]  Schierl, T. and S. Wenger, "Signaling Media Decoding
              Dependency in the Session Description Protocol (SDP)",
              RFC 5583, July 2009.

   [RFC5683]  Brusilovsky, A., Faynberg, I., Zeltsan, Z., and S. Patel,
              "Password-Authenticated Key (PAK) Diffie-Hellman
              Exchange", RFC 5683, February 2010.

   [HGTTG]    Adams, D., "The Hitchhiker's Guide to the Galaxy",
              TS 26.234 v5.3.0, September 1979.
































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Author's Address

   Bert Greevenbosch
   Huawei Technologies Co., Ltd.
   Huawei Industrial Base
   Bantian, Longgang District
   Shenzhen  518129
   P.R. China

   Phone: +86-755-28978088
   Email: bert.greevenbosch@huawei.com








































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