SIMPLE Working Group                                           S. Loreto
Internet-Draft                                              G. Camarillo
Intended status: Standards Track                                Ericsson
Expires: January 15, 2009                                   Jul 14, 2008


    SCTP-Based Media Transport in the Session Description Protocol.
                    draft-loreto-mmusic-sctp-sdp-01

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
   have been or will be disclosed, and any of which he or she becomes
   aware will be disclosed, in accordance with Section 6 of BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   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."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on January 15, 2009.

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.










Loreto & Camarillo      Expires January 15, 2009                [Page 1]

 
Internet-Draft       SCTP protocol identifier in SDP            Jul 2008


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 . . . . . . . . . . . . . . . . . . . . 6
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
   8.  Normative References  . . . . . . . . . . . . . . . . . . . . . 6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 7
   Intellectual Property and Copyright Statements  . . . . . . . . . . 8





































Loreto & Camarillo      Expires January 15, 2009                [Page 2]

 
Internet-Draft       SCTP protocol identifier in SDP            Jul 2008


.  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'.


.  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.


.  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



Loreto & Camarillo      Expires January 15, 2009                [Page 3]

 
Internet-Draft       SCTP protocol identifier in SDP            Jul 2008


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


.  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.


.  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



Loreto & Camarillo      Expires January 15, 2009                [Page 4]

 
Internet-Draft       SCTP protocol identifier in SDP            Jul 2008


   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.

   Considering the SCTP multi-homing capabilities, it is worth to
   underline that is not possible to reuse a media description putting a
   different address in the c= field; in fact according to [RFC3265] (in
   section 8.3.1) to modify an Address, Port or Transport, the offerer
   have to create a new media description.  So if an SCTP association
   changes its active address and then needs to modify the address
   updating the c= line, the offere have to create a new media
   description.






Loreto & Camarillo      Expires January 15, 2009                [Page 5]

 
Internet-Draft       SCTP protocol identifier in SDP            Jul 2008


.  Security Considerations

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


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

   The SDP specification, [RFC4566], states that specifications defining
   new proto values, like the SCTP proto value defined in this RFC, must
   define the rules by which their media format (fmt) namespace is
   managed.  For the SCTP protocol, new formats SHOULD have an
   associated MIME registration.  Use of an existing MIME subtype for
   the format is encouraged.  If no MIME subtype exists, it is
   RECOMMENDED that a suitable one is registered through the IETF
   process [RFC2048] by production of, or reference to, a standards-
   track RFC that defines the transport protocol for the format.


.  Normative References

   [RFC2048]  Freed, N., Klensin, J., and J. Postel, "Multipurpose
              Internet Mail Extensions (MIME) Part Four: Registration
              Procedures", BCP 13, RFC 2048, November 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.

   [RFC3265]  Roach, A., "Session Initiation Protocol (SIP)-Specific
              Event Notification", RFC 3265, June 2002.

   [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.




Loreto & Camarillo      Expires January 15, 2009                [Page 6]

 
Internet-Draft       SCTP protocol identifier in SDP            Jul 2008


   [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

























Loreto & Camarillo      Expires January 15, 2009                [Page 7]

 
Internet-Draft       SCTP protocol identifier in SDP            Jul 2008


Full Copyright Statement

   Copyright (C) The IETF Trust (2008).

   This document is subject to the rights, licenses and restrictions
   contained in BCP 78, and except as set forth therein, the authors
   retain all their rights.

   This document and the information contained herein are provided on an
   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
   THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
   OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
   THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.


Intellectual Property

   The IETF takes no position regarding the validity or scope of any
   Intellectual Property Rights or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
   might or might not be available; nor does it represent that it has
   made any independent effort to identify any such rights.  Information
   on the procedures with respect to rights in RFC documents can be
   found in BCP 78 and BCP 79.

   Copies of IPR disclosures made to the IETF Secretariat and any
   assurances of licenses to be made available, or the result of an
   attempt made to obtain a general license or permission for the use of
   such proprietary rights by implementers or users of this
   specification can be obtained from the IETF on-line IPR repository at
   http://www.ietf.org/ipr.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights that may cover technology that may be required to implement
   this standard.  Please address the information to the IETF at
   ietf-ipr@ietf.org.











Loreto & Camarillo      Expires January 15, 2009                [Page 8]