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SS7What is SS7?

SS7 or C7 signalling is the core signalling/control protocol used within fixed and mobile networks. The SS7 network is both a high speed and high availability network providing the backbone of all telephony networks worldwide.

A-Link Interconnect, Non Associated, Quasi Associated Signalling

A-Link - Typical Softswitch Deployment diagram

An A-link interconnect provides connections directly into the SS7 telecommunications network generally via redundant STP Signal Transfer Point pairs. STPs or Signalling Transfer Points provide a secure and fully redundant signalling only network, in diagram opposite showing a typical softswitch deployment.

The SS7 gateways connect directly to the two STP's (or adjacent points) and terminates directly the signalling links.

In general no voice circuits are present on the TDM interfaces that are carrying the signalling links. The STP's direct the signalling information generated at the originating point [1] through the redundant network to the appropriate SSP. The SSP terminates the voice circuits associated with the call and presents them to the media gateways via the voice only TDM interface [2]. The SSP interconnects can be many miles from the STP SS7 interconnect allowing for centralised routing of traffic over many different territories.

F-Link Interconnect or Associated Signalling

SSP interconnect - F-Link diagram

An F link interconnect provides an SS7 connection where the signalling and all TDM traffic is terminated on the same equipment.

TDM interfaces will usually carry both voice and signalling links.