upported by a fiber-optic multiplexer, several additional features warrant considera- tion. Those additional features include support for asynchronous or synchronous data on each channel, the electrical interface and electrical connector on each channel, and the maximum data transmission rate supported. Because a fiber-optic multiplexer includes a built-in fiber- Fiber in the Building optic modem, you also need to consider the type of fiber supported, the type of fiber connectors on the fiber-optic modem portion of the multiplexer, and the loss budget. Representative Multiplexers To obtain an appreciation for some of the potential functionality of a fiber-optic multiplexer, we will consider two TC Communications prod- ucts, which represent two variants of the vendor's TC8300 fiber-optic multiplexer. THE TC8300p The first version of the TC8300 represents a four-chan- nel T1/E1 fiber-optic multiplexer: the TC8300p. Figure 8.6 illustrates the rack-mounted version of the TC8300p. The TC8300p represents a special- ized type of fiber-optic multiplexer that can be used to interconnect digital PBXs, channel banks, and similar devices that operate at 1.544 or 2.048 Mbits/s within a building. In addition, the TC8300p can be used to extend the termination point where T1 or E1 channel banks are installed within a building. The TC8300 supports several types of line coding associated with T1 and E1 copper circuits, such as alternate mark inversion (AMI), under which positive pulses are alternated by polarity and the energy of each pulse is concentrated within the middle portion of the pulse area. Two other line coding techniques supported by the TC8300p are the Binary 8 Zero Suppression (B8ZS) and High Density Binary Three (HDB3) cod- ing. Both B8ZS and HDB3 are techniques that look for a group of eight or four consecutive zeros, respectively, and use bipolar violations to Figure 8.6 The TC8300 is a four-channel T1/E1 fiber-optic multiplexer. (Photograph courtesy of TC Communications.) Chapter Eight substitute for a predefined