Networking Bible

Chapter 13. Wide Area Networks and Backbones

IN THIS CHAPTER

• Wide Area Networks

• Circuit switching networks and the phone system

• ISDN and DSL phone connections

• Connect WANS with high-speed carrier links and SONET

• Packet switching networks

• Packet protocols — X.25, ATM, and Frame Relays

• Internet and Internet2 infrastructure

A Wide Area Network, or WAN, is a collection of networks connected through a public service or covering a large geographical area. To enable a WAN requires a routing or switching technology and a set of protocols that create paths from one point to another. There are four kinds of WANs: circuit switching, packet switching, cell relay, and leased lines.

The Public Switched Telephone Network (PSTN) is used as an example of a circuit switching network. The PSTN is built hierarchically. Different methods for connecting to the PSTN for data services are described. In particular, two of the most popular connection types, ISDN and DSL, are described in detail. The backbone technologies for connecting networks are through T- and E-carrier networks. Different standards and grades exist, and the higher-speed grades require optical fiber cables. SONET/SDH is the most popular protocol for data transfer on these backbones. Data that flows over SONET can be in the form of Asynchronous Transfer Mode (ATM) or Packet over SONET (PoS).

Packet switching networks define endpoints but not the routes. IP networks are built from packet switching, with the Internet being the prime example. Protocols ...