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SIMPLE Working Group                                           S. Loreto
Internet-Draft                                              G. Camarillo
Intended status: Standards Track                                Ericsson
Expires: August 20, 2008                                    Feb 17, 2008


    SCTP-Based Media Transport in the Session Description Protocol.
                    draft-loreto-mmusic-sctp-sdp-00

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Copyright Notice

   Copyright (C) The IETF Trust (2008).

Abstract

   Stream Control Transmission Protocol (SCTP) provides a realiable
   communication channel between two end-hosts in may way similar to
   TCP.  This document describes how to express media transport over
   SCTP using the Session Description Protocol (SDP).  It defines the
   SDP 'SCTP' protocol identifier.






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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
   3.  Protocol Identifier . . . . . . . . . . . . . . . . . . . . . . 3
   4.  Multihoming Association Management  . . . . . . . . . . . . . . 4
   5.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
     5.1.  Passive/Active  . . . . . . . . . . . . . . . . . . . . . . 4
     5.2.  Existing Connection Reuse . . . . . . . . . . . . . . . . . 5
   6.  Security Considerations . . . . . . . . . . . . . . . . . . . . 5
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
   8.  Normative References  . . . . . . . . . . . . . . . . . . . . . 6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 6
   Intellectual Property and Copyright Statements  . . . . . . . . . . 7





































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1.  Introduction

   The Session Description Protocol (SDP) [RFC4566] provides a general-
   purpose format for describing multimedia sessions in announcements or
   invitations.  RFC4145, Connection-Oriented Media Transport in the
   Session Description Protocol (SDP) [RFC4145], specifies a general
   mechanism for describing and establishing such connection-oriented
   stream using TCP as transport protocol.  RFC 4572, Connection-
   Oriented Media Transport over the Transport Layer Security (TLS)
   Protocol in the Session Description Protocol[RFC4572], extends
   RFC4145 to allow session descriptions to describe media session that
   use the TRansport Layer Security (TLS) protocol [RFC4346].

   While these transports are appropriate choices for the majority of
   the applications, there are applications for which SCTP[RFC4960] is
   more appropriate.  This document defines a new protocol identifier,
   'SCTP', to describe SCTP associations in SDP.

   SCTP uses to describe an association the same attributes, with the
   same meaning, defined in RFC415 to describe an TCP connection setup:
   'setup' and 'connection'.


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 [RFC2119] and indicate requirement
   levels for compliant implementations.


3.  Protocol Identifier

   The following is the ABNF for an 'm' line, as specified by RFC 2327
   [RFC2327].

       media-field =         "m=" media space port ["/" integer]
                             space proto 1*(space fmt) CRLF

                                 Figure 1

   This document defines a new value for the proto field: 'SCTP'.

   The 'SCTP' protocol identifier is similar to both the 'UDP' and 'TCP'
   protocol identifiers in that it only describes the transport
   protocol, and not the upper-layer protocol.  An 'm' line that
   specifies 'SCTP' MUST further qualify the application-layer protocol



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   using an fmt identifier.  Media described using an 'm' line
   containing the 'SCTP' protocol identifier are carried using SCTP
   [RFC4960].


4.  Multihoming Association Management

   The Association Management is completely equal to the Connection
   Management described in RFC 4145 Section 6.  However, a SCTP
   endpoint, unlike a TCP endpoint, can be multihoming.

   An SCTP endpoint is considered multi-homed if there are more than one
   transport address that can be used as a destination address to reach
   that endpoint.  Moreover if a client is multi-homed, it informs the
   server about all its IP addresses with the INIT chunk's address
   parameters.  Thereby, the client is only required to know one IP
   address of the server because the server provides all its IP
   addresses to the client in the INIT-ACK chunk.

   So for a multi-homed SCTP endpoint it is enough to insert, in the
   connection-address field of the 'c' line, one of the IP addresses of
   the server.


5.  Examples

   The usage of the 'setup' and 'connection' attributes conbined with
   SCTP-based media description is completely equal to the usage
   described in RFC4145.

   The following examples show this equivalent usage.  For the purpose
   of brevity, the main portion of the session description is omitted in
   the examples, which only show 'm' lines and their attributes
   (including 'c' lines).

5.1.  Passive/Active

   An offerer at 192.0.2.2 signals its availability for an application
   session at port 54111:

              m=application 54111 SCTP
              c=IN IP4 192.0.2.2
              a=setup:passive
              a=connection:new

                                 Figure 2

   An answerer at 192.0.2.1 receiving this offer responds with the



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   following answer:

              m=application 9 SCTP
              c=IN IP4 192.0.2.1
              a=setup:active
              a=connection:new

                                 Figure 3

   The endpoint at 192.0.2.1 then initiates the SCTP association to port
   54111 at 192.0.2.2.

5.2.  Existing Connection Reuse

   Subsequent to the exchange in Section Section 5.1, another offer/
   answer exchange is initiated in the opposite direction.  The endpoint
   at 192.0.2.1 wishes to continue using the existing association:

              m=application 54321 SCTP
              c=IN IP4 192.0.2.1
              a=setup:passive
              a=connection:new

                                 Figure 4

   The endpoint at 192.0.2.2 also wishes to use the existing connection
   and responds with the following description:

              m=application 9 SCTP
              c=IN IP4 192.0.2.2
              a=setup:active
              a=connection:new

                                 Figure 5

   The existing connection from 192.0.2.2 to 192.0.2.1 will be reused.


6.  Security Considerations

   See RFC 4566 [RFC4566] for security and other considerations specific
   to the Session Description Protocol in general.


7.  IANA Considerations

   This document defines a proto value: SCTP.  Its format is defined in
   Section 3.  This proto value should be registered by the IANA under



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   "Session Description Protocol (SDP) Parameters" under "proto".


8.  Normative References

   [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.

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

   [RFC4346]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.1", RFC 4346, April 2006.

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

   [RFC4960]  Stewart, R., "Stream Control Transmission Protocol",
              RFC 4960, September 2007.


Authors' Addresses

   Salvatore Loreto
   Ericsson
   Hirsalantie 11
   Jorvas  02420
   Finland

   Email: Salvatore.Loreto@ericsson.com


   Gonzalo Camarillo
   Ericsson
   Hirsalantie 11
   Jorvas  02420
   Finland

   Email: Gonzalo.Camarillo@ericsson.com




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Acknowledgment

   Funding for the RFC Editor function is provided by the IETF
   Administrative Support Activity (IASA).





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