Overview

All telecommunications networks, regardless of the services that they provide, share the following common characteristics:

1. Communications networks transport information (such as voice, data, and video) between the source and destination. Broadcast television and radio are examples of information from one source being distributed to many different destinations.
2. Networks concentrate information. In other words, networks contain entities that concentrate information from multiple information sources prior to transmission.
3. Networks contain entities that distribute information among multiple destinations.
4. Networks contain entities that simply carry information from one point in the network to another. These elements are called transmission facilities (or simply facilities).
5. Networks can modify the information to improve transmission quality. Simple examples are analog-to-digital conversion, line coding, and modulation.
6. Networks exchange information with other networks. For example, when a caller initiates a long-distance telephone call, the information flows through at least two local exchange networks and one long-distance network. Another example is when a wireless caller calls a wireline subscriber and the information flows through a wireless network and through a wireline network.

Local-Area Networks (LANs), Wide-Area Networks (WANs), Virtual Private Networks (VPNs), the Internet, and broadcast television are just some examples of networks.

The terms call and information are used interchangeably. Whether information takes the form of voice, video, or an electronic text/graphic file, all of these objects are classified as information. Networks carry information from one place to another.

The following diagram (Figure 1-1) provides a high-level view of a common telecommunications signaling network.