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 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 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]. 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 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 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. 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). 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