SIGTRAN

SIGTRAN is the name given to an Internet Engineering Task Force (IETF) working group that produced specifications for a family of protocols that provide reliable datagram service and user layer adaptations for SS7 and ISDN communications protocols. SIGTRAN is logically an extension of the SS7 protocol family. It supports the same application and call management paradigms as SS7 but uses an IP transport called Stream Control Transmission Protocol (SCTP) as its underlying transport vehicle.^[1] Indeed, the most significant protocol defined by the SIGTRAN group was SCTP, which is used to carry PSTN signaling over IP.

The SIGTRAN group was significantly influenced by telecommunications engineers intent on using the new protocols for adapting VoIP networks to the PSTN with special regard to signaling applications.^[2] Recently, SCTP is finding applications beyond its original purpose wherever reliable datagram service is desired.

For more information on SIGTRAN, refer to RFC 2719: Architectural Framework for Signaling Transport.

RFC 2719 also defines the concept of a Signaling Gateway (SG), which converts CCS messages from SS7 to SIGTRAN. Implemented in a variety of network elements including softswitches, the SG function can provide significant value to existing common channel signaling networks, leveraging investments associated with SS7 and delivering the cost/performance values associated with IP transport.

SIGTRAN Protocols

The SIGTRAN family of protocols includes:

• Stream Control Transmission Protocol (SCTP), RFC 3873, RFC 4166, RFC 4960.
• ISDN User Adaptation (IUA), RFC 4233, RFC 5133.
• MTP2 User Peer-to-Peer Adaptation Layer (M2PA), RFC 4165.
• MTP2 User Adaptation Layer (M2UA), RFC 3331.
• MTP3 User Adaptation Layer (M3UA), RFC 4666.
• SCCP User Adaptation (SUA), RFC 3868.
• V5 User Adaptation (V5UA), RFC 3807.

SCTP provides the transport protocol which provides transport of SIGTRAN user adaptation layer messages across an IP network. It is described in RFC 3873, RFC 4166 and RFC 4960.

IUA provides an SCTP adaptation layer for the seamless backhaul of Q.921 user messages and service interface across an IP network. Some users that it supports are Q.931 and QSIG.^[3] It is specified in RFC 4233.

V5UA provides a SCTP adaptation layer for the seamless backhaul of V5.2 user messages and service interface across an IP network. It is a variation of IUA and is specified in RFC 3807.

M2PA provides a SCTP adaptation layer for providing an SS7 MTP signalling link over an IP network. It is specified in RFC 4165.

M2UA provides a SCTP adaptation layer for the seamless backhaul of MTP Level 2 user message and service interface across an IP network. It is specified in RFC 3331.

SUA provides a SCTP adaptation layer for the seamless backhaul of SCCP user messages and service interface across an IP network. It is specified in RFC 3868.

Notes

References

• Dryburgh, Lee; Jeff Hewitt (2004). Signalling System No. 7 (SS7/C7): Protocol, Architecture, and Services. Indianapolis: Cisco Press. ISBN 1-587-05040-4.  Link to online version of text below.
• Russell, Travis (2002). Signaling System #7 (4th Edition ed.). New York: McGraw-Hill. ISBN 978-0071387729. 

External links

• Signaling System No. 7 (SS7/C7): Protocol, Architecture, and Services. Full HTML version of the 2004 edition of the Dryburgh/Hewitt book (above).
• IETF SIGTRAN WG - IETF SIGTRAN working group status pages.
• sigtran.org - A reference of SIGTRAN information, tools, and products.
• openss7.org - open source implementations of SIGTRAN protocols.
• IEC Tutorial - IEC SS7 over IP (SIGTRAN) protocols

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