Patent GB-1470701-A (GB)
Title: Digital switching system
IPC: H04L12/52
Filed: 1974-03-29
Abstract: 1470701 Automatic exchange systems STROMBERG-CARLSON CORP 29 March 1974 [27 Sept 1973] 14112/74 Heading H4K A switching system for digital signals includes two switching stages interconnected by intermediate T.D.M. highway, each switching stage including at least one random access memory (RAM) and being arranged to effect time slot switching between at least two said intermediate highways and a T.D.M. input or output highway, said system further comprising means to select a switching time slot and an intermediate highway to be used between a given input and a given output the time slot repetition rate on the intermediate highways being higher than the time slot repetition rate on the input and output high ways. As described incoming digital data or P.C.M. speech samples are multiplexed on to group incoming highways 28 by group and MVX units 40, intermediately stored in a corresponding RAM 50, read out during an intermediate time slot, space switched at 56 to an intermediate highway 58 leading in the embodiment of Fig. 3, not shown, each to the group of the wanted output or in the embodiment shown to a selectively controlled concentrator 61 in each group and thus in either embodiment to a receive RAM 68 which effects further intermediate storage of the samples, the latter being read out in receive time slots on receive highways 32 and distributed to receive lines by cyclically operating receive MVX units 42. The stores 50, 68 and the switches 56, 61 are controlled via decoders by synchronously operating recirculating stores 54, 70 and 59, 73 each having 512 time positions one for each time slot on an intermediate highway. The recirculating stores each comprise synchronized recirculating shift registers in which addresses are stored in parallel one bit in each register, twoadditional registers in the send line number store 54 and one in the receive line number store 70 storing busy/free bits for each incoming line, switching time slot and send line respectively. The common control unit 26 receives the numbers of the send and receive lines to be interconnected from a data processor and effects a search through the send and receive line number stores of the appropriate groups to find a common free time slot. When such is found the corresponding time slot busy bit is set in store 54 and a signal passed to the processor that the connection can be effected. A search is then effected through these send and receive line stores for the numbers of the two subscribers to be interconnected. If both are free the numbers are written in the respective stores at the selected time slot and the corresponding busy bits set. For a bidirectional connection the subscriber numbers are interchanged and a second path set up. If for any reason the connection cannot be effected the fact is signalled to the data processor. The processor can enter a test mode in which the processor identifies the highway and time slot to be used and the system returns a specific response for the identified path. The processor can also initiate tracing the connection from any given subscriber or all active subscribers. Connections are broken down in a manner similar to that in which they are set up a check that both subscribers specified are busy on the same call being effected before disconnection takes place. The network may comprise sufficient paths to be non-blocking or may comprise two parallel sections each capable of interconnecting any two subscribers and which together constitute a non-blocking network, the two sections being interconnected to prevent double connections.