Patent GB-1496041-A (GB)
Title: Pcm tdm switching networks
IPC: H04Q3/52
Filed: 1975-03-07
Abstract: 1496041 Automatic exchange systems SIEMENS AG 7 March 1975 [29 March 1974] 9492/75 Heading H4K In a TDM, PCM switching network, each incoming/outgoing highway pair has an associated store whose capacity is equal to the maximum number of bits on a highway and the store is divided into zones, such that each channel of the highway may utilize any zone. The zones each have an inlet and an outlet additional to those used for connecting them to highway channels and these inlets and outlets of correspondingly numbered zones in each store are multipled together. A space switching network interconnects the multipled inlets and outlets so as to provide full availabitity between channels on the various highways. In practice each of the eight zones in a store contains four areas (which are also randomly allocated to channels) and, during any time frame, the area is successively filled with the incoming and outgoing words pertaining to the temporarily associated channel. In Fig. 1, each storage zone S1-S8 pertaining to a single highway pair, e.g 1PCM1e, 1PCM1s is shown with two inlet/outlet pairs. The left hand pair of each zone is connectible by a gating assembly Re/Ra to the highway. The assembly Re/Ra portrays the random access nature of the connection of the highway channels to the storage zones, further random access to the areas within each zone being provided by not shown gates in the blocks S1-S8. The right-hand pair is multipled to those right-hand pairs emanating from correspondingly numbered zones in all the stores making up a highway group. (The prefixes 1-n indicate the different groups). The multiples, e.g. S8 of one group are then connectible to the corresponding multiples S8 of the other groups via a respective crosspoint switch RM8. As described each storage area is an 8 stage shift register (for the 8 bits of a PCM word) so that readout and write-in can take place simultaneously. Each area has its own command circuit which is filled with command data from a central control in order to perform the various read/write operations required during each time frame (Fig. 4, not shown). In order to connect channel 10 of highway 1PCM1e to channel 20 of highway nPCM8s, a gate in Re/Ra is opened during slot 10 to give access to, say, storage zone S8. In the latter another gate opens to access the area allotted to the call. Any word already in this area is simultaneously readout to the outgoing highway 1PCM1s. During a swtiching time slot, e.g. 17, the area is read-out via switch RM8 to an allotted area in that zone S8 currently pertaining to the highway nPCM8s. Simultaneously of course any word in the latter area will be transmitted into the former area via the Return path through switch RM8. Finally during slot 20, the word in S8 is read-out to nPCM8s while any word on nPCM8e will be simultaneously written-in to the area. Fig. 3 (not shown) illustrates schematically how a very large number of groups and crosspoint switches may be physically arranged. The arrangement organizes the Fig. 1 groups into sets of three so-called supergroups with full availability between channels in different supergroups. The command circuits for the crosspoints that permit intergroup working are illustrated in Fig. 5 (not shown). These circuits operate autonomously throughout a call once they have been loaded with command data by a central control.