The present invention relates to digital telephone switching systems and more particularly to an improved integrated telephone transmission and switching system.
Digital telephone switching systems have been utilized in automatic message accounting systems such as described in the cross-referenced application entitled "Integrated Message Accounting System." That system, which may be termed a base switch, utilizes pulse code modulated (PCM) techniques for switching telephone signals in PCM format from one time slot on a multitime slot digital data bus commonly known as a T-1 line to any other time slot on any T-1 line in the system. A T-1 line generally has 24 time slots each having eight bits together with a framing bit for a total of 193 bits per frame operating in a multiframe format of 12 frames. The base switch handles in one embodiment up to 64 T-1 lines or 1536 time slots and additionally provides for detecting, sending and receiving of dial pulses, detecting on-hook and off-hook conditions indicated in the signaling frames of a multiframe format, generating and sending necessary service tones in PCM format and sending and receiving multifrequency tones.
It would be desirable to utilize the existing digital switching capabilities of the above described system at a local subscriber line level so that a plurality of local subscribers can be connected to the base switch thereby enabling connections to any other subscriber line in the telephone system.
In view of the above background, it is an objective of the present invention to provide an improved integrated transmission and switching system.