SIGTRAN
Encyclopedia
SIGTRAN is the name, derived from signaling transport, of the former 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 Signaling System 7 (SS7) and ISDN communications protocols. The SIGTRAN protocols are an extension of the SS7 protocol family. It supports the same application and call management paradigms as SS7 but uses an Internet Protocol
(IP) transport called Stream Control Transmission Protocol
(SCTP). Indeed, the most significant protocol defined by the SIGTRAN group is 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. Recently, SCTP is finding applications beyond its original purpose wherever reliable datagram service is desired.
SIGTRAN has been published in RFC 2719, under the title Framework Architecture for Signaling Transport. RFC 2719 also defines the concept of a signaling gateway
(SG), which converts Common Channel Signaling (CCS) messages from SS7 to SIGTRAN. Implemented in a variety of network elements including softswitch
es, 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.
The Stream Control Transmission Protocol
provides the transport protocol for 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
. It is specified in RFC 4233.
V5UA provides an 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 an SCTP adaptation layer for providing an SS7 MTP signaling link over an IP network. It is specified in RFC 4165.
M2UA provides an SCTP adaptation layer for the seamless backhaul of MTP Level 2 user messages and service interface across an IP network. It is specified in RFC 3331.
M3UA provides an SCTP adaptation layer for the seamless backhaul or peering of MTP Level 3 user messages and service interface across an IP network. It is specified in RFC 4666.
SUA provides an SCTP adaptation layer for the seamless backhaul or peering of Signalling Connection Control Part user messages and service interface across an IP network. It is specified in RFC 3868.
Internet Engineering Task Force
The Internet Engineering Task Force develops and promotes Internet standards, cooperating closely with the W3C and ISO/IEC standards bodies and dealing in particular with standards of the TCP/IP and Internet protocol suite...
(IETF) working group that produced specifications for a family of protocols that provide reliable datagram
Datagram
A datagram is a basic transfer unit associated with a packet-switched network in which the delivery, arrival time, and order are not guaranteed....
service and user layer adaptations for Signaling System 7 (SS7) and ISDN communications protocols. The SIGTRAN protocols are an extension of the SS7 protocol family. It supports the same application and call management paradigms as SS7 but uses an Internet Protocol
Internet Protocol
The Internet Protocol is the principal communications protocol used for relaying datagrams across an internetwork using the Internet Protocol Suite...
(IP) transport called Stream Control Transmission Protocol
Stream Control Transmission Protocol
In computer networking, the Stream Control Transmission Protocol is a Transport Layer protocol, serving in a similar role to the popular protocols Transmission Control Protocol and User Datagram Protocol...
(SCTP). Indeed, the most significant protocol defined by the SIGTRAN group is SCTP, which is used to carry PSTN
Public switched telephone network
The public switched telephone network is the network of the world's public circuit-switched telephone networks. It consists of telephone lines, fiber optic cables, microwave transmission links, cellular networks, communications satellites, and undersea telephone cables, all inter-connected by...
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
Public switched telephone network
The public switched telephone network is the network of the world's public circuit-switched telephone networks. It consists of telephone lines, fiber optic cables, microwave transmission links, cellular networks, communications satellites, and undersea telephone cables, all inter-connected by...
with special regard to signaling applications. Recently, SCTP is finding applications beyond its original purpose wherever reliable datagram service is desired.
SIGTRAN has been published in RFC 2719, under the title Framework Architecture for Signaling Transport. RFC 2719 also defines the concept of a signaling gateway
Signaling gateway
A Signaling Gateway is a network component responsible for transferring signaling messages between Common Channel Signaling nodes that communicate using different protocols and transports...
(SG), which converts Common Channel Signaling (CCS) messages from SS7 to SIGTRAN. Implemented in a variety of network elements including softswitch
Softswitch
A softswitch is a central device in a telecommunications network which connects telephone calls from one phone line to another, typically via the internet, entirely by means of software running on a general-purpose computer system...
es, 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 ProtocolStream Control Transmission ProtocolIn computer networking, the Stream Control Transmission Protocol is a Transport Layer protocol, serving in a similar role to the popular protocols Transmission Control Protocol and User Datagram Protocol...
(SCTP), RFC 2960, RFC 3873, RFC 4166, RFC 4960. - ISDN User Adaptation (IUA), RFC 4233, RFC 5133.
- Message Transfer PartMessage Transfer PartThe Message Transfer Part is part of the Signaling System 7 used for communication in Public Switched Telephone Networks. MTP is responsible for reliable, unduplicated and in-sequence transport of SS7 messages between communication partners....
2 (MTP) User Peer-to-Peer Adaptation Layer (M2PA), RFC 4165. - Message Transfer PartMessage Transfer PartThe Message Transfer Part is part of the Signaling System 7 used for communication in Public Switched Telephone Networks. MTP is responsible for reliable, unduplicated and in-sequence transport of SS7 messages between communication partners....
2 User Adaptation Layer (M2UA), RFC 3331. - Message Transfer PartMessage Transfer PartThe Message Transfer Part is part of the Signaling System 7 used for communication in Public Switched Telephone Networks. MTP is responsible for reliable, unduplicated and in-sequence transport of SS7 messages between communication partners....
3 User Adaptation Layer (M3UAM3UAM3UA stands for MTP Level 3 User Adaptation Layer as defined by the IETF SIGTRAN working group in RFC 4666 . M3UA enables the SS7 protocol's User Parts to run over IP instead of telephony equipment like ISDN and PSTN...
), RFC 4666. - Signalling Connection Control Part (SCCP) User Adaptation (SUA), RFC 3868.
- V5V5 interfaceV5 is a family of telephone network protocols defined by ETSI which allow communications between the telephone exchange, also known in the specifications as the local exchange , and the local loop...
User Adaptation (V5UA), RFC 3807. - DPNSS/DASS2DASS2Digital Access Signaling System 2 is an obsolescent protocol defined by British Telecom for digital links to PSTN based on ISDN...
User Adaption (DUA), RFC 4129
The Stream Control Transmission Protocol
Stream Control Transmission Protocol
In computer networking, the Stream Control Transmission Protocol is a Transport Layer protocol, serving in a similar role to the popular protocols Transmission Control Protocol and User Datagram Protocol...
provides the transport protocol for 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
Backhaul (telecommunications)
In a hierarchical telecommunications network the backhaul portion of the network comprises the intermediate links between the core network, or backbone, of the network and the small subnetworks at the "edge" of the entire hierarchical network...
of Q.921 user messages and service interface across an IP network. Some users that it supports are Q.931
Q.931
ITU-T Recommendation Q.931 is ISDN's connection control protocol, roughly comparable to TCP in the Internet Protocol stack. Q.931 doesn't provide flow control or perform retransmission, since the underlying layers are assumed to be reliable and the circuit-oriented nature of ISDN allocates...
and QSIG
QSIG
QSIG is an ISDN based signaling protocol for signaling between private branch exchanges in a Private Integrated Services Network . It makes use of the connection-level Q.931 protocol and the application-level ROSE protocol...
. It is specified in RFC 4233.
V5UA provides an 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 an SCTP adaptation layer for providing an SS7 MTP signaling link over an IP network. It is specified in RFC 4165.
M2UA provides an SCTP adaptation layer for the seamless backhaul of MTP Level 2 user messages and service interface across an IP network. It is specified in RFC 3331.
M3UA provides an SCTP adaptation layer for the seamless backhaul or peering of MTP Level 3 user messages and service interface across an IP network. It is specified in RFC 4666.
SUA provides an SCTP adaptation layer for the seamless backhaul or peering of Signalling Connection Control Part user messages and service interface across an IP network. It is specified in RFC 3868.
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