CHAPTER 7 - Communication Concentration

Abstract

The main factor in the cost of networks with terminals spread over wide geographical areas is the communication channels and not the data communication equipment. Accordingly, a major design consideration in adopting a network is the minimizing of the cost of the communication channels. If the volume of data originating from any point is relatively small, no design planning can reduce the cost of each bit transmitted along the transmission channel beyond a certain figure. The only way for further reducing the cost per bit transmitted is to find means of concentration of the data volume transmitted in the channel, that is, sharing the same transmission channel with other data sources. Multiplexors and concentrators are the means of concentrating the data volume transmitted. Multiplexors and concentrators have an identical function: providing means by which a single common communication channel can be shared between two or more terminals. This chapter discusses the types channel sharing. There are two different fundamental types of channel sharing. One, known as frequency division multiplexing, assigns fixed portions of the frequency bandwidth to each terminal for all the time. The other assigns the whole available channel bandwidth to each terminal for a given period of time and is therefore referred to as time division multiplexing.