s 2. 2.3 Communication Channels So far in our discussion, communication signals have been sent on wires. However, there are a number of different ways in which a communication signal can be sent from one point to another. Using a wire is just one way-POTS likes and embraces this way. In this section, I'll outline the different ways you can send a signal from one point to another-that is, I'll outline different communication channels. 2.3.1 Transmission Lines (Wires) There are two types of transmission lines (wires) over which communication signals are commonly sent. These are twisted-pair cable and coaxial cable. Telecommunication Networks Class 4 Switching Center Class 5 S.C. DS-1 Class 5 S.C. DS-1 extra to class 3 Class 5 S.C. DS-1 added Class 5 S.C. DS-1 Class 3 Switching Center Class 4 S.C. Class 4 S.C. extra to class 2 Class 4 S.C. added Class 4 S.C. Class 2 Switching Center Class 3 S.C. Class 3 S.C. Class 3 S.C. extra to class 1 Class 3 S.C. added Class 3 S.C. Figure 2.13 (a) Creation of DS-2 signal, (b) Creation of DS-3 signal, (c) Creation of DS-4 signal Chapter Two In twisted-pair cable, a signal is sent from one point to another as a current along a wire. Signals that are sent in the frequency range of 0 to 1 MHz can be supported. The most common use for twisted-pair cables is in POTS. It forms most of the local loop connections. Specifically, in POTS, an insulated twisted-pair cable leaves from a home and is combined with many other twisted-pair cables from neighboring homes. You end up with one, big fat set of twisted-pair cables sent to the end office (Class 5). Coaxial cables are the second type of "wire" used to send communication signals. In coaxial cables, the communication information is sent as a current along a wire. Coaxial cables can support signals in the 100 kHz to 400 MHz range (a much larger range of frequencies than the twisted-pair cable can support). Perhaps the most common use of coaxial cable is in connections from TV cable providers to your home. Other uses include long-distance li