ISDN tools: common channel signalling and interoperation; open systems
John Ronayne · 2023
Digital transmission and switching allied to spc provided a very powerful tool with which to realize integrated networks. It is a tool, however, that is largely ineffective unless the switching machines, the exchanges, can communicate freely. The tremendous increase in long-distance and international telephony caused by the advent of direct dialling and undersea cables using repeaters and, later, satellite communications, led to the concept of providing signalling more effectively for large numbers of conversational circuits over a common channel. The appearance, at roughly the same time, of spc made such common channel signalling (CCS) a practical proposition. The first part of this chapter will be devoted to digital ccs. It might have been supposed that this would involve the consideration of one system, #7, but for various reasons, not all of them necessarily sensible, this is not the case.