 which kind of traffic is transported, the user equipment is called a "terminal" and the set of switches is called the "network." Usually terminals are manipulated by the end user while the network is managed by the service provider. The network establishes the communica- tion path between terminals, whose role is to receive information from the user and transmit it to the network in the proper format. Terminals also perform the opposite task: receiving information from the network and transmitting it to the user. In both cases, it's the terminal alone that exam- ines the content of the information being transmitted and performs the nec- essary operations on it. Conversely, switches establish a dedicated path between two or more terminals and are not concerned with what they transmit between them. We've seen that this dedicated path can be as rudimentary as a set of cables strung between terminals and switches. In more advanced systems, paths consist of, for instance, a frequency inside a cable, a time slot, or a wavelength inside an optical fiber. No matter how sophisticated the path, however, the key to circuit-switching remains the same: switches are obliv- ious to the contents of the messages they are transporting. They maneuver connections based solely on the position of the cables (that is, cable #1 has to be connected to cable #4), the frequency (that is, output from cable #1 at 400 Hz has to be transmitted on cable #4 at 600 Hz), and the time slots inside a frame. We will see in Chapter 2, "Packet Switching, IP, and the IETF," that this is the main difference between circuit-switching and packet-switching. Strengths of Circuit-Switching Circuit-switching provides some good features. These systems are very fast. Since switches do not examine the contents of the transmission, the deci- sion on where to send the information received at a certain interface is made just once, at the beginning of connection, and remains the same for the duration. Thus, the delay introduced by a switch is almost negligible. Sign