Telephone exchange

Claim 1

An automatic telecommunication switching system in which connections are set up in time division multiplex (TDM) manner using pulse code modulation (PCM), in which; the system includes group switching units (GSU's) each of which serves a group of system terminals such as subscribers' lines, tie lines and trunks to the remote exchange, and control means associated with each said GSU; the system also includes a central control processor (CCP) coupled separately to control means of each said GSU and arranged to control the establishment of all calls through the system, and digital co-ordinate switching means associated with and under the control of the CCP; the system further includes digital links interconnecting the GSU's and said digital switching means in a star-like manner, said digital links also providing the physical media for the couplings between the CCP and the respective control means of said GSU's; all connections through the system are set up under the control of the CCP and of the control means associated with the GSU or GSU's to which the terminals involved in the said connections are connected; each said connection is set up via a said digital link from the GSU serving one of the terminals involved in that connection to the digital switching means and therefrom via one of said digital links to the GSU serving another one of the terminals involved in that connection, each one of said connections being set up via the digital switching means whether the said connection is an inter-GSU connection or an intra-GSU connection; the digital links provide sufficient TDM slots to ensure that all of the subscribers served by the same GSU can be talking at once, so that the system is fully non-blocking; and all signalling between different ones of the terminals of the system is controlled by the CCP and is conveyed over the same physical transmission path as is used for the conveyance of speech.