Signalling System 7
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Signalling System 7
Definition
Signalling System 7 (SS7) is architecture for performing out-of-band signalling in support of the call-establishment, billing, routing, and information-exchange functions of the public switched telephone network (PSTN). It identifies functions to be performed by a signalling-system network and a protocol to enable their performance.
Overview
Signalling refers to the exchange of information between call components required to provide and maintain service.
SS7 is a means by which elements of the telephone network exchange information. Information is conveyed in the form of messages.
The SS7 network and protocol are used for: -
Basic call setup, management, and tear down
Wireless services such as personal communications service (PCS), wireless roaming, and mobile subscriber authentication
Local number portability (LNP)
Toll-free (800/888) and toll (900) wireline services
Enhanced call features such as call forwarding, calling party name/number display, and three-way calling
Efficient and secure worldwide telecommunications
Out-of-band Signalling
Out-of-band signalling is signalling that does not take place over the same path as the conversation.
We are used to thinking of signalling as being in-band. We hear dial tone, dial digits, and hear ringing over the same channel on the same pair of wires. When the call completes, we talk over the same path that was used for the signalling. Traditional telephony used to work in this way as well...