draft-ietf-sip-sctp-01.txt   draft-ietf-sip-sctp-02.txt 
Internet Engineering Task Force SIP WG Internet Engineering Task Force SIP WG
Internet Draft Rosenberg/Schulzrinne/Camarillo Internet Draft J. Rosenberg
draft-ietf-sip-sctp-01.txt dynamicsoft,Columbia U.,Ericsson dynamicsoft
November 20, 2001 H. Schulzrinne
Expires: May, 2002 Columbia U.
G. Camarillo
Ericsson
draft-ietf-sip-sctp-02.txt
May 28, 2002
Expires: November, 2002
SCTP as a Transport for SIP SCTP as a Transport for SIP
STATUS OF THIS MEMO STATUS OF THIS MEMO
This document is an Internet-Draft and is in full conformance with This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026. all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that Task Force (IETF), its areas, and its working groups. Note that
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Abstract Abstract
This document specifies a mechanism for usage of SCTP (the Stream This document specifies a mechanism for usage of SCTP (the Stream
Control Transmission Protocol) as the transport between SIP entities. Control Transmission Protocol) as the transport between SIP entities.
SCTP is a new protocol which provides several features that may prove SCTP is a new protocol which provides several features that may prove
beneficial for transport between SIP entities which exchange a large beneficial for transport between SIP entities which exchange a large
amount of messages, including gateways and proxies. As SIP is amount of messages, including gateways and proxies. As SIP is
transport independent, support of SCTP is a relatively transport independent, support of SCTP is a relatively
straightforward process, nearly identical to support for TCP. straightforward process, nearly identical to support for TCP.
Table of Contents
1 Introduction ........................................ 3
2 Terminology ......................................... 3
3 Potential Benefits .................................. 3
3.1 Advantages over UDP ................................. 3
3.2 Advantages over TCP ................................. 4
4 Usage of SCTP ....................................... 5
4.1 Mapping of SIP Transactions into Streams ............ 6
4.1.1 Client Side ......................................... 7
4.1.2 Server Side ......................................... 8
4.1.3 Size of the stream ID space ......................... 9
5 Locating a SIP server ............................... 10
6 Conclusion .......................................... 10
7 Author's Addresses .................................. 10
8 Normative References ................................ 11
9 Informative References .............................. 11
1 Introduction 1 Introduction
The Stream Control Transmission Protocol (SCTP) [1] has been designed The Stream Control Transmission Protocol (SCTP) [1] has been designed
as a new transport protocol for the Internet (or intranets), at the 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 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 legacy SS7 signaling messages in mind. We have observed that many
of the features designed to support transport of such signaling are of the features designed to support transport of such signaling are
also useful for the transport of SIP (the Session Initiation also useful for the transport of SIP (the Session Initiation
Protocol) [2], which is used to initiate and manage interactive Protocol) [2], which is used to initiate and manage interactive
sessions on the Internet. sessions on the Internet.
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enabling it in SIP. enabling it in SIP.
2 Terminology 2 Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119. document are to be interpreted as described in RFC 2119.
3 Potential Benefits 3 Potential Benefits
Coene et. al. present some of the key benefits of SCTP [3]. We Coene et. al. present some of the key benefits of SCTP [4]. We
summarize some of these benefits here and analyze how they relate to summarize some of these benefits here and analyze how they relate to
SIP: SIP:
3.1 Advantages over UDP 3.1 Advantages over UDP
All the advantages that SCTP has over UDP regarding SIP transport are 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 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 that a connection-oriented transport protocol such as TCP or SCTP has
over a connection-less transport protocol such as UDP. over a connection-less transport protocol such as UDP.
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This calculations show that the stream ID space is large enough even This calculations show that the stream ID space is large enough even
for proxies handling heavy traffic loads. And even if a proxy did for proxies handling heavy traffic loads. And even if a proxy did
eventually run out of stream IDs, stream zero is always available for eventually run out of stream IDs, stream zero is always available for
the excess of traffic. the excess of traffic.
5 Locating a SIP server 5 Locating a SIP server
The primary issue when sending a request is determining whether the The primary issue when sending a request is determining whether the
next hop server supports SCTP, so that an association can be opened. next hop server supports SCTP, so that an association can be opened.
This draft assumes that SRV records are the primary vehicle for such This draft assumes that SRV records are the primary vehicle for such
determinations. RFC2543bis [4] describes the process that an entity determinations. RFC3261 [2] describes the process that an entity (UAC
(UAC or proxy) that wishes to send a request to a particular URI MUST or proxy) that wishes to send a request to a particular URI MUST
follow. follow.
The format of the SRV RR as described in [5] is shown below: The format of the SRV RR as described in [3] is shown below:
_Service._Proto.Name TTL Class Priority weight Port Target _Service._Proto.Name TTL Class Priority weight Port Target
When SRV records are to be used, the service to use when querying for When SRV records are to be used, the service to use when querying for
the SRV record is "sip" and the transport protocol is "sctp". So, a the SRV record is "sip" and the transport protocol is "sctp". So, a
SIP client that wants to discover a SIP server that supports SCTP for SIP client that wants to discover a SIP server that supports SCTP for
the domain example.com does a lookup of the domain example.com does a lookup of
_sip._sctp.example.com _sip._sctp.example.com
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Henning Schulzrinne Henning Schulzrinne
Columbia University Columbia University
M/S 0401 M/S 0401
1214 Amsterdam Ave. 1214 Amsterdam Ave.
New York, NY 10027-7003 New York, NY 10027-7003
email: schulzrinne@cs.columbia.edu email: schulzrinne@cs.columbia.edu
Gonzalo Camarillo Gonzalo Camarillo
Ericsson Ericsson
Advanced Signalling Research Lab. Advanced Signalling Research Lab.
FIN-02420 Jorvas FIN-02420 Jorvas
Finland Finland
Phone: +358 9 299 3371 Phone: +358 9 299 3371
Fax: +358 9 299 3052 Fax: +358 9 299 3052
Email: Gonzalo.Camarillo@ericsson.com Email: Gonzalo.Camarillo@ericsson.com
8 Bibliography 8 Normative References
[1] R. Stewart, Q. Xie, K. Morneault, C. Sharp, H. Schwarzbauer, T. [1] R. Stewart, Q. Xie, K. Morneault, C. Sharp, H. Schwarzbauer, T.
Taylor, I. Rytina, M. Kalla, L. Zhang, and V. Paxson, "Stream control Taylor, I. Rytina, M. Kalla, L. Zhang, and V. Paxson, "Stream control
transmission protocol," Request for Comments 2960, Internet transmission protocol," RFC 2960, Internet Engineering Task Force,
Engineering Task Force, Oct. 2000. Oct. 2000.
[2] M. Handley, H. Schulzrinne, E. Schooler, and J. Rosenberg, "SIP:
session initiation protocol," Request for Comments 2543, Internet
Engineering Task Force, Mar. 1999.
[3] L. Coene et al. , "Stream control transmission protocol
applicability statement," Internet Draft, Internet Engineering Task
Force, Apr. 2001. Work in progress.
[4] J. Rosenberg, H. Schulzrinne, et al. , "SIP: Session initiation [2] J. Rosenberg, H. Schulzrinne, et al. , "SIP: Session initiation
protocol," Internet Draft, Internet Engineering Task Force, Oct. protocol," Internet Draft, Internet Engineering Task Force, Feb.
2001. Work in progress. 2002. Work in progress.
[5] A. Gulbrandsen, P. Vixie, and L. Esibov, "A DNS RR for specifying [3] A. Gulbrandsen, P. Vixie, and L. Esibov, "A DNS RR for specifying
the location of services (DNS SRV)," Request for Comments 2782, the location of services (DNS SRV)," RFC 2782, Internet Engineering
Internet Engineering Task Force, Feb. 2000. Task Force, Feb. 2000.
Table of Contents 9 Informative References
1 Introduction ........................................ 1 [4] L. Coene, "Stream control transmission protocol applicability
2 Terminology ......................................... 2 statement," RFC 3257, Internet Engineering Task Force, Apr. 2002.
3 Potential Benefits .................................. 2
3.1 Advantages over UDP ................................. 2
3.2 Advantages over TCP ................................. 3
4 Usage of SCTP ....................................... 4
4.1 Mapping of SIP Transactions into Streams ............ 5
4.1.1 Client Side ......................................... 6
4.1.2 Server Side ......................................... 7
4.1.3 Size of the stream ID space ......................... 8
5 Locating a SIP server ............................... 8
6 Conclusion .......................................... 9
7 Author's Addresses .................................. 9
8 Bibliography ........................................ 10
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