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Stream Control Transmission Protocol(SCTP)

SCTP is a TCP for datagrams with a flexible order-of-delivery and the support of multi-homed nodes realising enhanced TCP concepts including better protection against blind attacks.

SCTP is standardized in the IETF first in the Signalling Transport Work Group (SIGTRAN WG) and since 2001 it has found a new home in the transport Area Work Group (TSV WG):

The protocol itself is described in RFC2960. The SCTP checksum algorithm has been changed. A SCTP implementation guide with updates, error corrections and clarifications to the protocol is now nearing completion. A more in depth introduction to SCTP is given in the RFC3286: a Introduction to SCTP and in SCTP for beginners. The possible applicability of the protocol is described in the RFC 3257 SCTP applicability statement.. The original idea was to develop SCTP for the transport of signalling information (see Architectural Framework for Signaling Transport (RFC 2719) ), but then things got out of hand...

A standard compliant implementation(= a implementation that survives a SCTP interoperability test) must take into account the following Mandatory RFC's (or RFC's to be ):

• RFC2960: Stream Control Transmission protocol
• RFC3309: SCTP checksum change
• the SCTP implementation guide: corrections, updates, clarifications to RFC2960

Optional SCTP features can also be included in a implementation. A few optional SCTP features are in the works:

• RFC3758: SCTP Partial Reliability extension
• Add and delete IP addresses to a association
• Authenticated Chunks for SCTP
• Padding chunk and parameter for SCTP Can be used for detecting the MTU of a path(See PMTUD WG)

A secure SCTP association can be obtained by using :

• RFC3554: on the use of SCTP with IPSEC(=Internet Protocol security Protocol) : How to use IPSEC with SCTP
• RFC3436: TLS over SCTP :Transport Layer Security over Stream Control Transmission Protocol
• Datagram Transport Layer Security for SCTP
• Secure SCTP

The MIB of SCTP can be found in :

• RFC3873: SCTP Management Information Base (MIB)

Information concerning SCTP multihoming and NAT traversals can be found in :

• Multihoming issues in SCTP
• SCTP Network Address Translation

Some drafts can be viewed while in construction(exciting, isn't it).

Applications using SCTP:

• ISDN User Adaptation Layer(IUA : RFC3057): transporting Q921 signalling information from a Voice-over-IP(VOIP) Gateway(MG) to a Media Gateway Controller(MGC) or Softswitch.
• MTP level 2 User adaptation Layer(M2UA : RFC3331 )
• MTP level 2 Peer user adaptation Layer( M2PA : RFCxxxxx)
• MTP level 3 User adaptation Layer(M3UA : RFC3332)
• SCCP User Adaptation Layer(SUA : RFC3868) This site contains a GPL'ed SUA implementation.

And the security protocols to be used with the above protocols are described in :

• RFC3788: Security Considerations for SIGTRAN Protocols

All of the above are adaptation protocols  mostly based on protocols already existing in the Signalling System nr7 networks(and no, this has nothing to do with James Bond, 007). More detailed info about what SS7 is can be found on this website. Specific issues regarding SCTP for transporting signalling information can be found in the Telephony signalling applicability Statement.
Other signalling protocols (like SIP) might use SCTP in adition to TCP and UDP. See SIP WG.
The basic work on SCTP is done in the Transport Area(TSV)WG
The following additions/enchancements to SCTP are currently being considered::

• ECN Nonces for Stream Control Transmission Protocol (SCTP): draft-ladha-sctp-nonce-04.txt
• Based on Add/delete IP addresses draft and the authentication draft, a mobile SCTP solution draft-riegel-tuexen-mobile-sctp-06.txt
• SCTP Stream Reset: draft-stewart-sctpstrrst-02.txt
• UDP Encapsulation of SCTP Packets: draft-tuexen-sctp-udp-encaps-00.txt
• SCTP Packet Drop Reporting: draft-stewart-sctp-pktdrprep-04.txt
• Preventing SCTP Congestion Window Overgrowth During Changeover: draft-iyengar-sctp-cacc-03.txt

SCTP has also other non-signalling applications such as:

• Transport of Authentication, Authorization and Accounting(AAA) information. See AAA WG
• Transport of Block Storage traffic(examples SCSI, Fibre Channel...) See IPS WG
• Transport of Remote Direct Data Placement traffic. See RDDP WG
• Transport of Reliable Server poolling traffic. See RSERPOOL WG
• Transport of IP Flow information export traffic. See IPFIX WG

Adittional SCTP development is in the wings concerning:

• Header compression: used in Wireless networks because of the finite bandwith of the air interface: See ROHC WG.
• How to specify SCTP based mediatransport in SDP: see MMUSIC WG
• IPSEC and SCTP: how to make a multihomed SCTP association more manageable in IPSEC. See IPSEC WG

It is recommended to browse the IETF meeting proceedings of each of the WG's as they are sometimes more up to date than the WG charters pages.

The history of SCTP

• visual history of SCTP
• what's in a name
• .....

SCTP all over the world:

• Randy Stewarts SCTP site: Home of the SCTP reference implementation. A xxx BSD implementation is in the works.
• Michel Tuexen SCTP site : Home of the Siemens/University of Essen(Germany) SCTP implementation
• the Linux SCTP site: Home of the SCTP implementation coming to a Linux kernel near you....
• The Solaris SCTP page (is back...): SCTP is included from vs10 onwards..
• SCTP on xxx BSD SCTP is a part of the KAME stack. SCTP will gradually show up in FreeBSD, NETBSD... whatever BSD ... as long as they base on the Kame stack....
• SCTP @ University of Delaware: The homepage of Protocol Engineering laboratory at the University of Delaware. They are working on SCTP support for the network simulator NS-2 and tcpdump.
• Andreas Jungmaier's "The SCTP homepage for Beginners" Contains links to other presentations of Andreas also.
• Ethereal: A graphical packet analyzer with SCTP support running under Linux, FreeBSD, Solaris, ... and Windows. Adaptation layers are also supported.
• Faster than a speeding bullet. More powerful than a locomotive. Able to leap tall buildings in a single bound ....Look! Up in the sky"??? NO...It's not a bird or a plane or Superman ---Look out on the Net-- it's SCTP!
• The SCTP Group of Internet Engineering Lab Nara University, Japan
• SCTP DataTAG : site for performance measurements results of SCTP
• to be continued...for more SCTP stuff, click on SCTP research and simultation page...

SCTPlib implementation running on Microsoft Windows XP :SCTP Windows download page

What is going on in the SCTP world :SCTP research and simulation page

What software does utilise SCTP :SCTP Software page

How to write application software on top of SCTP :SCTP application Software production page

Books about SCTP:

• "Stream Control Transmission Protocol (SCTP), a reference guide" , R. R. Stewart & Q. Xie, Addison-Wesley, ISBN 0-201-72186-4 Can be bought on amazon.com, barnesandnoble.com or at your nearest bookstore. A CD containing the source code of the reference implementation is contained in the book.
• A couple of extra chapters on the use of SCTP is included in the Third edition of the "UNIX Network Programming, Volume 1" Bible, by Stevens-Fenner-Rudoff, Addison-Wesley, ISBN 0-13-141155-1

 
 

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