Patent GB-1326747-A (GB)
Title: Telephone switching systems
IPC: H04Q11/04
Filed: 1971-04-30
Abstract: 1326747 Automatic exchange systems PLESSEY CO Ltd 30 April 1971 [8 May 1970] 22328/70 Heading H4K In a PCM, TDM transit exchange of the type disclosed in Specification 1,229,684 wherein superhighways have access via input and output switching matrices to cord circuits that provide time slot interchange utilizing only one storage location per call, some of the junctions connected to the superhighways may be used as both way junctions i.e. seizable from either end, instead of strictly only as originating or terminating junctions. In order to accommodate this facility it is necessary to halve the number of junctions connected to a superhighway i.e. to use 4 rather than 8, and to permit a channel on a junction access to either an originating channel or to the adjacent terminating channel on the superhighway in accordance with the current operational mode of the junction while at the same time busying the adjacent unused terminating or originating channel respectively to prevent double connections. Brief system description.-Each junction is of the four wire type and carries 24 channels of 8 serial bit pcm. Alternate channels are normally reserved for originating and terminating traffic. At the exchange eight such junctions are grouped and their incoming channels are redistributed so that all the originating channels on two junctions are fed along one highway RHIA (Fig. 1a) while all the terminating channels of the same two junctions are fed along highway RHIB. The eight (A-H) highways making up a group are connected to a serial/parallel converter i.e. S/P SR1 which consists of a shift register per highway. The register associated with the first highway of a group has 8 stages while that pertaining to the last highway has 16 stages. The eight most significant bit positions of the registers are read out in parallel on a cyclical basis to a superhighway RSH/W1 during the course of a single highway-time-slot whereby in a single highway-frame the superhighway carries the data pertaining to each of 192 (8 highways x 24 channels) channels. The superhighway-time-slots alternately carry originating and terminating traffic, the former being gated (matrix RS) into a storage location e.g. magnetic plated wire, in a cord circuit which is next in the cyclic addressing of the locations while the latter is gated into the location pertaining to the call under the control of an address obtained from the just preceding cyclically addressed location. (The effect of this cyclic and random or acyclic addressing is that a speech sample from the caller is inserted in a store location whose address bears some relation to the identities of the channel and junction of the caller and that during the called party's time slot Tc this sample is read out and a returning speech sample is inserted in the same location utilizing an address that central control has inserted in the storage location which is cyclically addressed at Tc-1). Read-out data from a storage location is appropriately gated (matrix TS) via a parallel/serial converter to the relevant outgoing highway TH (Fig. 1b). Both way junctions are grouped in fours BWJA-D Fig. 2, and their incoming speech pairs are connected to respective shift registers SRA-D without any intermediate channel redistribution process. The registers contain respectively 8, 11, 13 and 15 stages. Depending on whether a junction is being used as an originating or a terminating junction, its 8 most significant or its 8 next most significant stages are gated by OAG or TAG to an originating or a terminating time slot on the eight wire superhighway RHG. The system operation is otherwise the same as that previously described. Central control may effect network supervision by monitoring a ninth free/busy wire associated with each superhighway and switched therewith or it may contain a memory map in which case the 9th wire is not necessary. Data may be transmitted over the system possibly using more than eight bits per channel.