What is SS7 or C7?

All major networks around the world use SS7 to provide their major services including POTS (Plain Old Telephony Service), Intelligent Networking, LNP (Local Number Portability), 0800, GSM, SMS and a whole host of other services. The following is a brief overview of the different SS7 architectures.

SS7 is a Common Channel Signalling (CCS) protocol that separates the control or signalling information from the voice for circuit based services (ISUP, TUP, NUP, etc). The circuit-based operation is in comparison similar to ISDN, however circuit based SS7 signalling information for a given circuit is carried on a different E1 to the voice circuit. This allows for a high available signalling interconnect that is unaffected by the less redundant voice circuits.

Intelligent networks allow for the control of services through the PSTN network at remote intelligent nodes. These nodes are interconnected by SS7 allowing for centralised development and deployment of telephony services using man machine interfaces (MMIs) or GUIs allowing for new services to be rapidly deployed. The following diagram shows a minimal overview of the Intelligent Network.

The SSP (Service Switching Point) provides local PSTN access, the SCP (Service Control Point) provides the intelligence of how a call located on a given SSP is to be handled and the IP (Intelligent Peripheral) provides media resources such as DTMF plants, voice resources, speech recognition, etc.

SS7 signalling is used in GSM networks to provide voice and texting services through the SS7, ISUP and MAP protocols.

With SS7 interconnect the service provider can benefit from integrating directly into the mobile network and providing SMS, EMS and MMS services as well as having access to other mobile network nodes such as HLR which contain subscriber information allowing for location based services.