There are two key parts to the signaling process: an identification scheme and a linking or connection process. Signaling can be initiated by the user or by the network. Signaling can also take place between two or more users using the network. Routing and switching depend on signaling within the framework of voice, data, and Internet.

All of the switching and transmission in the world wouldn t be worth much without signaling capability. Signaling has many forms and capabilities, but only one function, which is to enable the user and the network to communicate with each other. The user tells the network what to do. The network tells the user that it has done it or failed to do it. The simple model has been around since dial telephones replaced human operators. Successful signaling and network operation requires a unique terminal or telephone numbering and identification plan whereby each unit or telephone is the only unit on the network with that number (Table 4-4). The equivalent in a local area network (LAN) is the media access control (MAC) address. In the Internet, it s the IP address.

In North America, the telephone numbering scheme relies on a fixed, 10-digit numbering plan. Outside North America, the number of digits in the plan will vary...