It is common to test telephone lines of the two, four, and six wire types by connecting a test board to the lines and transmitting or measuring signals thereover. As a rule it is inconvenient to perform these tests right at the communication lines themselves and therefore a test position is usually established at a remote test center. Past practice has been to route test loops from the distribution frames to jackfields at the test center, but as the telephone lines have grown in number this has become impractical. Accordingly, the prior art recognizes systems to selectively tap the communication lines at a suitable access point and route them through suitable test loops to the testing position. To do this it is necessary to be able to remotely select the desired communication line and make a connection to it at the access point. Such a system is disclosed in the G. A. Barbary et al. U.S. Pat. No. 3,525,822.
This prior art system utilizes an electromechanical cross bar switching system which is expensive, slow and limited in the number of access functions that can be performed. The present invention contemplates a digital solid state electronic system for selecting and accessing communication circuits remotely which is more efficient and can be expanded to accomodate thousands of communication lines as described hereinafter.