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