"How a telephone is connected" Tour 4/6
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About Telephone Networks

As the number of telephones increases, so does the number of transmission lines used for calls between them, at a surprisingly large expense. Switching equipment is used to share these expensive transmission lines. A network consisting of at least one switching system (exchange) and accommodated transmission lines (optical fiber microwave) is referred to as a telephone network.

Connections between few telephones Direct interconnections of many telephones require many transmission lines, leading to higher costs. An exchange that accommodates and switches telephones requires only as many transmission lines as the number of telephones.