Overview

Signaling System #7 (SS7) is a specialized network protocol used for the connection/disconnection of all telephone calls. Without this powerful network and its associated protocols, telephone companies could not deliver the many services they do today, such as 800 services, calling name display, and custom routing features.

When a telephone call is placed, the local telephone switch generates a data message identifying the various aspects of the call and routes this message through the network to an adjacent telephone switch. The intent of this message is to establish a connection between the two switches to route the telephone call. The adjacent telephone switch confirms that the circuit identified is available and reserves this circuit until the connection is actually ready to be made (when the called party answers the phone).

The adjacent telephone switch must then generate a similar data message and send it to the next switch in the connection path. This process repeats itself until an end-to-end connection has been made. The terminating switch then rings the called party s telephone and when it is answered, sends a data message in the backward direction, completing the connection phase. This is an oversimplified explanation of what SS7 is used for; it is much more complex than this.

SS7 is also used for connecting to databases used in telephone networks for routing instructions, user profile data (calling card information, billing information, custom feature definitions, and so on), and specialized applications used by the telephone companies. It may sound like this...