 switch user. Switching is an extremely active research area. As a result, the scope of this book is not intended to exhaustively cover the technology that has been invented in the field. However, we will discuss some basic notions of some of the most acceptable and widespread techniques along with several interesting and exotic methods in order to stimulate the imagination of readers who are new in this field. Several references are provided at the end of the chapter for a deeper study of the subject. For our discussion, a switch is a network module with many inputs and outputs. A switch can provide a physical connection at any time between inputs and outputs and can transfer data that are available at any of its inputs to any of its outputs. Network switches can be divided into two categories: circuit switches and packet switches. If we want to be extremely purist in our pronouncements, the packet switch category can be further divided into two subcategories: packet switches (also known as routers in everyday lingo, which connect the various Internet segments together), which can handle variable-size packets, and ATM switches, which are optimized for small, fixed-size packets (cells). A important variety of these switches is a hybrid of these two siblings known as the multiservice router (MSR). The MSR can service multiple ports with multiple protocols and technologies. In this study, we will mostly discuss packet switches and multiservice switches. Circuit switches are part of the traditional telephony or ATM network. These networks do not seem to be dominating the future networking landscape, although both will continue influencing it and playing a role. Originally, it was thought that the traditional telephony and ATM networks were quickly becom- ing obsolete as we moved rapidly into the packet-switched networks. This has turned out not to be the case since the bad economy of recent years has dramatically forced carriers to massively scale back their investments for the introduction of new packet-switched te