The Stream Control Transmission Protocol (SCTP) as a Transport for the Session Initiation Protocol (SIP)
RFC 4168

Document Type RFC - Proposed Standard (October 2005; No errata)
Last updated 2013-03-02
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IESG IESG state RFC 4168 (Proposed Standard)
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Responsible AD Allison Mankin
Send notices to <dean.willis@softarmor.com>, <rohan@cisco.com>, gonzalo.camarillo@ericsson.com
Network Working Group                                       J. Rosenberg
Request for Comments: 4168                                 Cisco Systems
Category: Standards Track                                 H. Schulzrinne
                                                     Columbia University
                                                            G. Camarillo
                                                                Ericsson
                                                            October 2005

            The Stream Control Transmission Protocol (SCTP)
        as a Transport for the Session Initiation Protocol (SIP)

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 specifies a mechanism for usage of SCTP (the Stream
   Control Transmission Protocol) as the transport mechanism between SIP
   (Session Initiation Protocol) entities.  SCTP is a new protocol that
   provides several features that may prove beneficial for transport
   between SIP entities that exchange a large amount of messages,
   including gateways and proxies.  As SIP is transport-independent,
   support of SCTP is a relatively straightforward process, nearly
   identical to support for TCP.

Rosenberg, et al.           Standards Track                     [Page 1]
RFC 4168              SCTP as a Transport for SIP           October 2005

Table of Contents

   1. Introduction ....................................................2
   2. Terminology .....................................................2
   3. Potential Benefits ..............................................2
      3.1. Advantages over UDP ........................................3
      3.2. Advantages over TCP ........................................3
   4. Transport Parameter .............................................5
   5. SCTP Usage ......................................................5
      5.1. Mapping of SIP Transactions into SCTP Streams ..............5
   6. Locating a SIP Server ...........................................6
   7. Security Considerations .........................................7
   8. IANA Considerations .............................................7
   9. References ......................................................7
      9.1. Normative References .......................................7
      9.2. Informative References .....................................8

1.  Introduction

   The Stream Control Transmission Protocol (SCTP) [4] has been designed
   as a new transport protocol for the Internet (or intranets) at the
   same layer as TCP and UDP.  SCTP has been designed with the transport
   of legacy SS7 signaling messages in mind.  We have observed that many
   of the features designed to support transport of such signaling are
   also useful for the transport of SIP (the Session Initiation
   Protocol) [5], which is used to initiate and manage interactive
   sessions on the Internet.

   SIP itself is transport-independent, and can run over any reliable or
   unreliable message or stream transport.  However, procedures are only
   defined for transport over UDP and TCP.  This document defines
   transport of SIP over SCTP.

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [1].

3.  Potential Benefits

   RFC 3257 presents some of the key benefits of SCTP [10].  We
   summarize some of these benefits here and analyze how they relate to
   SIP (a more detailed analysis can be found in [12]).

Rosenberg, et al.           Standards Track                     [Page 2]
RFC 4168              SCTP as a Transport for SIP           October 2005

3.1.  Advantages over UDP

   All the advantages that SCTP has over UDP regarding SIP transport are
   also shared by TCP.  Below, there is a list of the general advantages
   that a connection-oriented transport protocol such as TCP or SCTP has
   over a connection-less transport protocol such as UDP.

   Fast Retransmit: SCTP can quickly determine the loss of a packet,
      because of its usage of SACK and a mechanism that sends SACK
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