1. Field of the Invention
This invention relates to communication system switches through which digitally coded call signals are coupled to effect call switching.
2. Prior Art
Various types of signal switches are known in the art and some examples include space division switching matrices, resonant transfer systems, and systems in which pairs of time gated subscriber lines are interconnected through a time-shared bus. Most of the existing switching systems have been primarily designed for handling continuous analog signals or discrete samples of such analog signals. However, the space division matrices have been utilized, often in conjunction with time slot interchangers, for switching digitally coded signal samples. In addition, techniques are known for effecting limited call signal switching by writing digitally coded signal samples into a buffer memory and then reading them out in appropriate time slots to effect their transfer to a second party on a call connection. However, none of the foregoing systems has convenient arrangements for processing call signals for, e.g., custom insertion of loss or gain to compensate in part for factors such as different line lengths between the switch and the subscriber's terminal equipment.
In prior art switching systems the conference capability has often been satisfied by employing an add-on type of conference bridge in which call signals of all conference participants are combined and the combined result is returned to each individual participant's line circuit where that particpant's input signal is substantially subtracted out. The need to balance these conference circuits against signal regeneration is a problem that is usually present, and it becomes particularly acute as the number of conference participants increases. Here again the conference bridge usually serves no other useful purpose in the system in the absence of a current need for the conferencing function. Electronic switching systems, to the extent that they have been applied to the switching of digitally coded signals, can provide many services to subscribers by utilization of the common control processor capabilities, but those services usually are limited to call administration services as distinguished from call signal modification services. In addition, such systems still generally depend upon the employment of separate, controlled, space division switching matrix for call path switching; and they generally are not deemed to be practical for processing call signals for providing, e.g., customized loss or gain in individual call connections.
It is, therefore, one object of the present invention to improve communication system switches.
It is another object to facilitate the provision of special services in addition to the primary call signal switching service performed by a system switch.