Impedance and return loss performance of telephone plant in metropolitan areas

The fundamental design and successful operation of the nation-wide switching plan assumes a specified return loss performance of the metropolitan area plant. Metropolitan area plant includes the terminating trunks and subscriber loops which are involved at each end of an intercity telephone connection. The return losses not only must be adequate over the voice band as a whole in order to limit echo currents, but also must meet certain minimums at individual frequencies to avoid singing conditions.