CONCENTRATORS AND MULTIPLE ACCESS
When a fixed number of facilities are available for use they can be assigned to users in a fixed or variable manner. In today's telephone systems, the local loops are normally assigned on a fixed basis, and the trunks are assigned on a variable basis. The trunks are therefore used much more efficiently than the local loops.
Suppose that there are 100 subscribers in a locality who use their telephones occasionally. There is, in theory, no need for 100 channels to connect them to their local switching office. Twenty channels, for example, could be used with some means of allocating a channel to a subscriber when he needs it. This technique is called concentration. There are various ways in which it can be done; ...
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