draft-ietf-sip-sctp-03.txt   draft-ietf-sip-sctp-04.txt 
Internet Engineering Task Force SIP WG Internet Engineering Task Force SIP WG
Internet Draft J. Rosenberg Internet Draft J. Rosenberg
dynamicsoft dynamicsoft
H. Schulzrinne H. Schulzrinne
Columbia U. Columbia U.
G. Camarillo G. Camarillo
Ericsson Ericsson
draft-ietf-sip-sctp-03.txt draft-ietf-sip-sctp-04.txt
June 28, 2002 November 19, 2003
Expires: December, 2002 Expires: May, 2004
The Stream Control Transmission Protocol as a The Stream Control Transmission Protocol as a
Transport for the Session Initiation Protocol Transport for the Session Initiation Protocol
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
skipping to change at page 3, line 38 skipping to change at page 3, line 38
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 [3]. document are to be interpreted as described in RFC 2119 [3].
3 Potential Benefits 3 Potential Benefits
Coene et. al. present some of the key benefits of SCTP [4]. 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 (a more detailed analysis can be found in [5].)
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.
Fast Retransmit: SCTP can quickly determine the loss of a Fast Retransmit: SCTP can quickly determine the loss of a
packet, as a result of its usage of SACK and a mechanism packet, as a result of its usage of SACK and a mechanism
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chosen the simplest one; a SIP entity SHOULD send every SIP message chosen the simplest one; a SIP entity SHOULD send every SIP message
(request or response) over stream zero with the unordered flag set. (request or response) over stream zero with the unordered flag set.
On the receiving side, a SIP entity MUST be ready to receive SIP On the receiving side, a SIP entity MUST be ready to receive SIP
messages over any stream. messages over any stream.
Note that previous versions of this document proposed to Note that previous versions of this document proposed to
use SCTP stream IDs as lightweight SIP transaction use SCTP stream IDs as lightweight SIP transaction
identifiers. That proposal has been withdrawn because SIP identifiers. That proposal has been withdrawn because SIP
now provides a transaction identifier in the branch now provides a transaction identifier in the branch
parameter of the Via entries. This transaction identifier, parameter of the Via entries. This transaction identifier,
missing in the previous SIP spec [5], makes it unnecessary missing in the previous SIP spec [6], makes it unnecessary
to use the SCTP stream IDs to demultiplex SIP traffic. to use the SCTP stream IDs to demultiplex SIP traffic.
Some applications introduce an extra layer between the transport Some applications introduce an extra layer between the transport
layer and SIP (e.g., compression and/or encryption). This extra layer layer and SIP (e.g., compression and/or encryption). This extra layer
sometimes requires ordered delivery of messages from the transport sometimes requires ordered delivery of messages from the transport
layer (e.g., TLS [6]). In this case, it is RECOMMENDED that SIP layer (e.g., TLS [7]). In this case, it is RECOMMENDED that SIP
messages belonging to the same transaction are sent over the same messages belonging to the same transaction are sent over the same
stream and messages belonging to different transactions are sent over stream and messages belonging to different transactions are sent over
different streams. Note that if both sides of the association follow different streams. Note that if both sides of the association follow
this recommendation, if a request arrives over a particular stream, this recommendation, if a request arrives over a particular stream,
the server is free to return responses over a different stream. This the server is free to return responses over a different stream. This
way, both sides manage the available streams in the sending way, both sides manage the available streams in the sending
direction, independently of the streams chosen by the other side to direction, independently of the streams chosen by the other side to
send a particular SIP message. This avoids undesirable collisions send a particular SIP message. This avoids undesirable collisions
when seizing a particular stream. when seizing a particular stream.
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.
SIP entities follow normal SIP procedures to discover [7] a server SIP entities follow normal SIP procedures to discover [8] a server
that supports SCTP. that supports SCTP.
6 Security Considerations 6 Security Considerations
No extra security risk outside these specified by [2] are foreseen. No extra security risk outside these specified by [2] are foreseen.
7 Conclusion 7 Conclusion
This draft has presented a discussion on the applicability of SCTP to This draft has presented a discussion on the applicability of SCTP to
SIP transport, and provided a mechanism for allowing two SCTP-capable SIP transport, and provided a mechanism for allowing two SCTP-capable
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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
9 Normative References 9 Normative References
[1] R. Stewart, Q. Xie, K. Morneault, C. Sharp, H. Schwarzbauer, T. [1] R. J. Stewart, Q. Xie, K. Morneault, C. Sharp, H. Schwarzbauer,
Taylor, I. Rytina, M. Kalla, L. Zhang, and V. Paxson, "Stream control T. Taylor, I. Rytina, and M. Kalla, "Stream control transmission
transmission protocol," RFC 2960, Internet Engineering Task Force, protocol," RFC 2960, Internet Engineering Task Force, Oct. 2000.
Oct. 2000.
[2] J. Rosenberg, H. Schulzrinne, et al. , "SIP: Session initiation [2] J. Rosenberg, H. Schulzrinne, G. Camarillo, A. R. Johnston, J.
protocol," Internet Draft, Internet Engineering Task Force, Feb. Peterson, R. Sparks, M. Handley, and E. Schooler, "SIP: session
2002. Work in progress. initiation protocol," RFC 3261, Internet Engineering Task Force, June
2002.
[3] S. Bradner, "Key words for use in RFCs to indicate requirement [3] S. Bradner, "Key words for use in RFCs to indicate requirement
levels," RFC 2119, Internet Engineering Task Force, Mar. 1997. levels," RFC 2119, Internet Engineering Task Force, Mar. 1997.
10 Informative References 10 Informative References
[4] L. Coene, "Stream control transmission protocol applicability [4] L. Coene, "Stream control transmission protocol applicability
statement," RFC 3257, Internet Engineering Task Force, Apr. 2002. statement," RFC 3257, Internet Engineering Task Force, Apr. 2002.
[5] M. Handley, H. Schulzrinne, E. Schooler, and J. Rosenberg, "SIP: [5] G. Camarillo, H. Schulzrinne, and R. Kantola, "Evaluation of
transport protocols for the session initiation protocol," IEEE
Network , vol. 17, no. 5, 2003.
[6] M. Handley, H. Schulzrinne, E. Schooler, and J. Rosenberg, "SIP:
session initiation protocol," RFC 2543, Internet Engineering Task session initiation protocol," RFC 2543, Internet Engineering Task
Force, Mar. 1999. Force, Mar. 1999.
[6] T. Dierks and C. Allen, "The TLS protocol version 1.0," RFC 2246, [7] T. Dierks and C. Allen, "The TLS protocol version 1.0," RFC 2246,
Internet Engineering Task Force, Jan. 1999. Internet Engineering Task Force, Jan. 1999.
[7] H. Schulzrinne and J. Rosenberg, "SIP: Locating SIP servers," [8] J. Rosenberg and H. Schulzrinne, "Session initiation protocol
Internet Draft, Internet Engineering Task Force, Feb. 2002. Work in (SIP): locating SIP servers," RFC 3263, Internet Engineering Task
progress. Force, June 2002.
 End of changes. 

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