Digital Transmission Over Existing Subscriber Cable

The paper first describes strategies to permit the smooth transition to all-digital operation in the subscribers' area. This emphasizes the essential employment of the existing network to support alldigital working. Two particular aspects of the many factors relevant to such realization are then highlighted-signaling and transmission. It is claimed that the former must provide a rich signaling repertoire, but that such a system may demand international agreement. An outline of a possible solution is given. The transmission capabilities of the existing subscribers' area network are discussed, with particular reference to limitation by near-end crosstalk, and the results of swept-frequency measurements of typical cable crosstalk characteristics are analyzed. An outline of the statistical simulation method of interference summation used to combine these results with differing digital system parameters is described. It is concluded that, with suitable line codes and stackable systems, the existing network will normally support all-digital working.