SS7 Implementation

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In Yate the following SS7 components are implemented:


MTP Layer 1

For MTP1 (physical level) we support PRI TDM computer cards that have wanpipe or DAHDI (former Zaptel) drivers.

The corresponding modules in Yate are wpcard and zapcard. Note that the same modules provide ISDN D-Channel support and TDM voice channels on the timeslots not used by signaling.

These cards perform HDLC and FCS (checksum) in hardware or firmware so MTP2 doesn't need to deal with it.

MTP Layer 2

For MTP2 (Data Link Layer) we support several technologies:

  • MTP1 for local TDM cards - as described above.
  • M2PA (SIGTRAN) to connect over SCTP/IP to another SS7 node.
  • M2UA (SIGTRAN) to connect over SCTP/IP to a Signaling Gateway that implements MTP2.
  • Cisco SLT to connect over RUDP/IP to a Cisco Signaling Gateway that implements MTP2.

M2PA and M2UA are supported by the ysigchan module while the actual SIGTRAN transport is provided by sigtransport.

In a standard configuration the lksctp module need also be loaded to provide SCTP communication to the kernel. Yate also supports non-standard SIGTRAN over TCP/IP or UDP/IP.

Cisco RUDP, Session Manager and Signaling Link Transport are implemented by the ciscosm module.

MTP Layer 3

MTP Layer 3 is currently implemented only as the standard ITU Q.704 describes. Support is provided by the ysigchan module.

One MTP3 instance needs to be configured for each linkset and it describes the type, local and adjacent Point Codes and routes to any other node in case the adjacent node is a STP. One or more MTP Layer 2 links must be attached to each MTP3 and MTP Testing and Maintenance (ITU Q.707) if performed on the attached links.

MTP Router

A shared SS7 message router typically connects all MTP3 instances and the Applications using them. This component performs MSU routing and distribution and also deals with the MTP Restart procedures.

Optionally, the router can be configured to allow transfer of messages between linksets turning Yate into a STP. Additional route maintenance and advertising is performed in this configuration.

MTP Management

This built-in component is created automatically by the MTP router to perform part of the Management procedures for links and linksets. It does also handle route management messages by delivering them to the router.

Application Layer

  • ISUP provides local telephony signaling using the ysigchan module, needs also voice circuits - either local TDM (wpcard or zapcard) or on a remote Media Gateway (mgcpca).
  • Parameters of non-local ISUP calls passing through the STP can be modified by the isupmangler module (this is not a standard SS7 behavior).

Overview of Yate's SS7 layers

This schema focuses on how yate's SS7 configuration objects are created. You can use this to understand which objects are created and in which order, but you can also use it to understand the objects you have to configure to make a specific setup.

Ss7 layers.png

See also

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