r, E-carrier, and J-carrier standards Chapter 4 The PSTN Termination Termination Equipment Equipment Digital Transmission (channel banks, (channel banks, CSU/DSU Media (twisted copper multiplexers, CSU/DSU multiplexers, pair, coaxial cable, digital cross- digital loop microwave radio fiber) connect PBXs) carriers, digital cross-connects) Customer Premises Local Exchange Figure 4.5 PDH components Transmission Media PDH can include a wide variety of transmission media, and the type you use is contingent on the bandwidth you want to support. You could use copper pairs to provision T-1, E-1, or J-1 services, but if you wanted to get into the higher-bandwidth capacities afforded under T-3, E-3, or J-3, you would deploy a higher-bandwidth medium, such as coax, microwave, or fiber. PDH oper- ates on four-wire circuits, which means it operates in full-duplex and you can com- municate in both directions simultaneously. CSUs A CSU terminates each end of a T-, E-, or J-carrier facility. It equalizes the received signal, filters the transmitted and received waveforms, and interacts with customers' and carriers' test facilities. You use a CSU to perform diagnostic tests on span lines and to set up a T-1, E-1, or J-1 line with a PBX, a channel bank, a multi- plexer, or any other compliant data terminal equipment. Multiplexers A series of time division multiplexers enables us to move up the hierarchy of the PDH infrastructure. The first in the series of multiplexers is gener- ally referred to as channel banks. A channel bank has several purposes. First, it con- solidates the individual voice and data channels SO that they can travel over the higher-speed transmission line. In the case of a T-1 line, a channel bank consoli- dates 24 channels; in the case of an E-1 line, a channel bank consolidates 32 chan- nels. Channel banks can accept analog inputs, which means they can digitize analog voice. If you're using an analog switch-either a local exchange or a PBX- the channel bank should be equipped with the codecs that run an analo