Signaling System 7 (SS7)

Signaling System #7 (SS7) is a set of telephony signaling protocols which are used to set up the vast majority of the world's PSTN telephone calls.

It is usually abbreviated to SS7 though in North America it is often referred to as CCS7, an acronym for "Common Channel Signaling System 7". In some European countries, specifically the United Kingdom, it is sometimes called C7 (CCITT number 7) and is also known as number 7 and CCIS7. (ITU-T was formerly known as CCITT.)

In the past, in-band signalling techniques were used on interoffice trunks. This method of signalling used the same physical path for both the call-control signalling and the actual connected call. This method of signalling is inefficient and is rapidly being replaced by out-of-band or common-channel signalling techniques.

The primary function of SS7 is to provide call control, remote network management, and maintenance capabilities for the inter- office telephone network. SS7 performs these functions by exchanging control messages between SS7 telephone exchanges (signalling points or SPs) and SS7 signalling transfer points (STPs).

The switching offices (SPs) handle the SS7 control network as well as the user circuit-switched network. Basically, the SS7 control network tells the switching office which paths to establish over the circuit-switched network. The STPs route SS7 control packets across the signalling network. A switching office may or may not be an STP.

Vector Communications offers SS7 solutions as part of its extensive range of telecom protocols – allowing operators to connect media processing and signalling platforms directly to a carrier’s network.

Sangoma SMG is an SS7 Solution designed for Open Source PBXes such as Asterisk or FreeSwitch. The Sangoma SMG solution has been designed to be scalable and cost affective.

The combination of the Signaling System 7 (SS7) software and the Sangoma SS7 adapters provides application developers with access to SS7 networks over serial V.35/X.21 as well as direct T1/E1/J1 links.

Available Architectures

•   SINGLE Server Architecture - Total voice capacity is maxed out at 16 spans depending on PC hardware.
•   MULTI Server Architecture: SIGNALING Server + MEDIA Server - allowing full redundancy


•   SIGNALING Server - Supports multiple redundant/crosslinked F-links over multiple signaling systems. The signaling servers only handle SS7 F-links.
•   MEDIA Server - Supports MEDIA only channels and is connected to the SIGNALING server via fast ethernet. Total voice capacity is maxed to 16 spans per MEDIA Server.

SS7 MPT2 features

•   Designed in accordance with ITU-T Q.703, ANSI T1.111.3 and NTT ( Japan ) recommendations.
•   Implements full interaction with the application level (Level 3) as defined in the listed recommendations. This includes functions such as "Retrieval request and FSNC" and "Retrieve BSNT".
•   Includes all "unspecified implementation dependent functions" such as congestion control.
•   Handles both the Basic Error Correction Method and the Preventive Cyclic Retransmission Error Correction Method (used largely in satellite communications).
•   Optional automatic internal congestion control mechanisms for both inbound and outbound traffic have been included. Outbound congestion control adheres to ITU-T Q.704 and implements congestion thresholds for both international and national signaling networks.
•   Sangoma cards all support internal or Master clocking for local connections to third party DTE equipment.