ration, and survivability from the start because the likelihood of damage is great. Vulnerability to damage caused by wildlife-A number of flora and fauna cause damage to fiber. Some birds really like the Kevlar reinforcing material Fiber Optics and think it makes lovely nests for their babies, so they peck away at fiber- optic cables to get at that Kevlar material. Rodents such as beavers like to sharpen their teeth on exposed cable. Several different types of ants seem to enjoy the plastic shielding in their diet, SO they nibble at the underground fibers. Sharks have been known to chomp on cable near the repeating points. A plant called the Christmas tree plant thinks that fiber-optic cable is a tree root and wraps itself around it very tightly and chokes it off. This page intentionally left blank Chapter Establishing Communications Channels This chapter discusses the key definitions and characteristics associated with establishing communications channels. It covers networking modes and switching modes, including the differences between routing and switching. It also covers the details of circuit switching and its particular applications, where it shines, and where it has fallen short in the past. This chapter also looks at packet switching- why it has become such a darling in recent years, what its potential prospects are, and what challenges it faces in the future. The chapter ends with a quick compari- son between the public switched telephone network (PSTN) and the Internet. Establishing Connections: Networking Modes and Switching Modes For messages to travel across a network, a transmission path must be established to either switch or route the messages to their final destinations. Therefore, network providers need a mechanism that allows them to deliver the proper connections when and where a customer requests them. When, as you can imagine, is ideally now, or bandwidth on demand. Where has two components: path calculation, which entails establishing the proper physical or logical connection to the ultima