Q. What are concentrators? Elucidate how it helps in connecting number of subscribers.

Ans:

In rural areas, subscribers are usually dispersed. It is both expensive and unnecessary to provide a dedicated pair for each subscriber. 3 techniques are used to gain on the number pairs:

1. Parity lines

2. Concentrators

3. Carrier Systems.

In first technique, two or more subscribers are connected to one line that is called parity line. This scheme isn't used commonly since it has a number of drawbacks. Only one subscriber at a time can use this line. Selective ringing is difficult in addition privacy also isn't maintained. Dialing between two subscribers on same line isn't possible.