alling in the Circuit-Switched Network The dedicated transmission path between terminals provided by circuit- switching networks is well suited for the analog transmission of voice. After a circuit has been established, the transmission delay is small and is kept constant through the duration of the connection. Its suitability for analog transmissions is of course the key reason why circuit-switching technology spread SO far and wide in pre-digital days. We will see that when new traf- fic patterns were introduced, including the transmission of data between computers, circuit-switching began showing its limitations. Weaknesses of Circuit-Switching Before an information exchange between terminals can take place, a path through the network must be established. Setting up a path takes time, and the actual transmission is delayed until the path establishment phase is finished (see Figure 1-4). Note that path establishment delay is distinct from switch delay. By its nature, establishment delay occurs before any transmission takes place. The delay introduced by the switches during the transmission of user data occurs after the path has been established. Once a dedicated path is established between two terminals, the resources associated with it cannot be used for another connection until the path is torn down. Therefore, even if at some point both terminals stop transmitting, the path stays open and resources allocated to the connection through all the switches along the path remain in use. That's a non-efficient use of available resources, to say the least. This limitation, while not a big problem in analog voice transmission, becomes very important in digital transmissions and particularly in data transmissions between computers. Terminal Terminal FIGURE 1-4 Establishment delay in a circuit-switched Path establishment request network. Establishment delay Path established Transmission of user data Chapter 1 Two terminals in the act of exchanging data are actually idle most of the time, and so are the resources allocat