ch intermediate node. Time-sensitive applications suffer on a connectionless network because the path is not guaranteed, and therefore it is impossible to know where in the range of best to worst the network will perform. As a result, it is difficult to anticipate the actual latency, and the delay may change from packet to packet. Connectionless networks imply the use of packet switches, SO only packet- switched networks are connectionless. An example of a connectionless packet- switched network is the public Internet-that wild and woolly place over which absolutely no one has any control. It's a virtual network that consists of more than 183,052 separate autonomous systems and more than 10,000 ISPs, SO being able to guarantee performance is nearly impossible at this time. One solution is to use private internets (i.e., Internet Protocol [IP] backbones), which achieve cost-efficiencies but, because they are private, provide the ability to control their performance and thereby serve business-class services. For example, a large carrier might own its own Internet infrastructure, over a very wide geographic area. Because it owns and controls those networks end to end, the company can provision and engineer the networks SO that business customers can get the proper service-level agreements and can guarantee the performance of their virtual private networks and streaming media networks. The downside in this situation is reliance on one vendor for the entire network. Chapter 3 Establishing Communications Channels Switching Modes Let's start our discussion of switching modes by talking about switching and rout- ing. Switching is the process of physically moving bits through a network node, from an input port to an output port. (A network node is any point on the network where communications lines interface. So a network node might be a PBX, a local exchange, a multiplexer, a modem, a host computer, or one of a number of other devices.) Switching elements are specialized computers used to connect two or more transmission