Abstract: A channel redundancy system for use with a central office connected to a remote location. A central office terminal at the central office has a plurality of channel units including at least one spare channel unit. A remote terminal at the remote location also has a plurality of channel units including at least one spare channel unit. The channel units in the remote terminal are correspondingly associated with the channel units in the central office termimal. From a repair service bureau located remote from both the central office and the remote location in a defective channel unit can be identified and replaced by the spare channel unit.

Abstract: A testing system is disclosed for telephone subscriber loops which are in part derived by multiplex facilities in what have come to be known as pair gain systems. In this testing arrangement, the local drop wires from the remote terminal of the pair gain system to the subscriber are separated from the carrier system itself and tested by connecting them to a separate metallic pair extending from the central office to the remote terminal location. Simultaneously, the carrier-derived portion of the subscriber loop is connected to automatic testing apparatus which sequences through a plurality of automatic tests for not only transmission characteristics of the carrier-derived channel but also tests for the ability of the derived channel to transmit supervisory information such as ringing, coin control and party identification information. The remote terminal of the pair gain channel is selectively terminated by a reflective or absorptive termination to assist in these testing procedures.