TCP-Based Media Transport in the Session Description Protocol (SDP)
RFC 4145

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Network Working Group                                             D. Yon
Request for Comments: 4145                        Tactical Software, LLC
Category: Standards Track                                   G. Camarillo
                                                                Ericsson
                                                          September 2005

  TCP-Based Media Transport in the Session Description Protocol (SDP)

Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2005).

Abstract

   This document describes how to express media transport over TCP using
   the Session Description Protocol (SDP).  It defines the SDP 'TCP'
   protocol identifier, the SDP 'setup' attribute, which describes the
   connection setup procedure, and the SDP 'connection' attribute, which
   handles connection reestablishment.

Yon & Camarillo             Standards Track                     [Page 1]
RFC 4145               Connection-Oriented Media          September 2005

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Protocol Identifier  . . . . . . . . . . . . . . . . . . . . .  3
   4.  Setup Attribute  . . . . . . . . . . . . . . . . . . . . . . .  4
       4.1.  The Setup Attribute in the Offer/Answer Model. . . . . .  4
   5.  The Connection Attribute . . . . . . . . . . . . . . . . . . .  5
       5.1.  Offerer Behaviour. . . . . . . . . . . . . . . . . . . .  6
       5.2.  Answerer Behaviour . . . . . . . . . . . . . . . . . . .  7
   6.  Connection Management  . . . . . . . . . . . . . . . . . . . .  8
       6.1.  Connection Establishment . . . . . . . . . . . . . . . .  8
       6.2.  Connection Reestablishment . . . . . . . . . . . . . . .  8
       6.3.  Connection Termination . . . . . . . . . . . . . . . . .  8
   7.  Examples . . . . . . . . . . . . . . . . . . . . . . . . . . .  9
       7.1.  Passive/Active . . . . . . . . . . . . . . . . . . . . .  9
       7.2.  Actpass/Passive. . . . . . . . . . . . . . . . . . . . .  9
       7.3.  Existing Connection Reuse. . . . . . . . . . . . . . . . 10
       7.4.  Existing Connection Refusal. . . . . . . . . . . . . . . 10
   8.  Other Connection-Oriented Transport Protocols. . . . . . . . . 11
   9.  Security Considerations  . . . . . . . . . . . . . . . . . . . 12
   10. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 12
   11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12
   12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
       12.1. Normative References . . . . . . . . . . . . . . . . . . 13
       12.2. Informative References . . . . . . . . . . . . . . . . . 13

Yon & Camarillo             Standards Track                     [Page 2]
RFC 4145               Connection-Oriented Media          September 2005

1.  Introduction

   The Session Description Protocol [4] provides a general-purpose
   format for describing multimedia sessions in announcements or
   invitations.  SDP uses an entirely textual data format (the US-ASCII
   subset of UTF-8 [11]) to maximize portability among transports.  SDP
   does not define a protocol; it defines the syntax to describe a
   multimedia session with sufficient information to participate in that
   session.  Session descriptions may be sent using arbitrary existing
   application protocols for transport (e.g., SAP [9], SIP [10], RTSP
   [6], email, HTTP [8], etc.).

   SDP [4] defines two protocol identifiers: RTP/AVP and UDP, both of
   which represent unreliable, connectionless protocols.  While these
   transports are appropriate choices for multimedia streams, there are
   applications for which TCP is more appropriate.  This document
   defines a new protocol identifier, 'TCP', to describe TCP connections
   in SDP.

   TCP introduces two new factors when describing a session: how and
   when should endpoints perform the TCP connection setup procedure.
   This document defines two new attributes to describe TCP connection
   setups: '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 [3], and they indicate requirement
   levels for compliant implementations.

3.  Protocol Identifier

   The following is the ABNF for an 'm' line, as specified by RFC 2327
   [4].

    media-field =         "m=" media space port ["/" integer]