Traditionally, three methods of switching have been discussed: circuit switching,
packet switching, and message switching. The first two are commonly used today.
The third has been phased out in general communications but still has networking
applications. Packet switching can further be divided into two subcategories—virtualcircuit
approach and datagram approach—as shown in Figure 8.2. In this chapter, we
discuss only circuit switching and packet switching; message switching is more conceptual
than practical