SS7 (Signaling System 7)

The SS7 network allows call control and transaction messages from the integrated voice and data network to be transferred on communications paths that are separate from the voice and data connections. It delivers out-of-band signaling that provides fast call setup by means of high-speed, circuit-switched connections and transaction capabilities which deal with remote database interactions. SS7 makes such enhanced telephony features as caller ID, call forwarding, and call waiting widely available. SS7 also plays an integral role in the deployment of ISDN.

The SS7 protocol consists of four basic sub-protocols:

• MTP (Message Transfer Part), which provides functions for basic routing of signaling messages between signaling points;
• SCCP (Signaling Connection Control Part), which provides additional routing and management functions for transfer of messages other than call setup between signaling points;
• ISUP (Integrated Services Digital Network User Part), which provides for transfer of call setup signaling information between signaling points;
• TCAP (Transaction Capabilities Application Part), which provides for transfer of non-circuit related information between signaling points.