Patent GB-1270472-A (GB)
Title: High-capacity time division multiplex switching network having blocking characteristics
IPC: H04Q11/06
Filed: 1969-07-01
Abstract: 1,270,472. Automatic exchange systems. C.I.T. COMPAGNIE INDUSTRIELLE DES TELECOMMUNICATIONS. 1 July, 1969 [5 July, 1968], No. 33268/69. Heading H4K. A TDM blocking switching network comprises a plurality of incoming highways each of which is provided with a buffer memory for storing channel data e.g. speech, occurring during a time frame, a plurality of groups of outgoing, highways to any channel on any of which an incoming channel is connectible, and, for each outgoing group, a common line to which stored data in a buffer may be read out during a portion of the time slot allotted to the outgoing channel under the control of a memory uniquely associated with the line. The latter is terminated by a distributor which ensures that the data is delivered to the correct outgoing highway of the group. The system provides access between N incoming highways LREI ... LREN and a total of N1 Î N2 outgoing highways. The latter are arranged in N1 groups, each of which has an individual distributor CR1 giving cyclic access to the N2 highways associated therewith. Each outgoing highway carries 32 t.d.m. channels. The incoming highways on the other hand each carry only 16 t.d.m. channels so that two such highways are associated with every normal 32 channel incoming multiplex (not shown). The incoming highways each have an associated buffer store MTI ... MTN which is selectively read-out under the control of a memory MCI ... MCNI pertaining to a junction line LJI ... LJNI associated with a particular outgoing highway LRS1 ... LRSN1N2. The system clock (not shown) provides a frame time of 125 Ásecs which is divided into 32 primary time slots of 3À9 Ásecs each of which is further subdivided into 32 secondary time slots. PCM utilizing 7 bit parallel coding is used on all the highways of the system. In operation, incoming data on the 16 channels of a highway LRE is written into a respective compartment of associated buffer memory MT. In order to convey a data item to a particular channel of an outgoing highway say LRS1, the relevant control memory MC1 of the junction LJ1 giving access via its distributor CR1 to this highway provides two addresses on lines LAP1 and LAM1 during one secondary time slot of the primary time slot corresponding to the required channel. The addresses on lines LAP1 and LAM1 cause, via gate E 1  ; the particular data item corresponding to the relevant incoming channel to be read out from MT (and applied to line LJ11. The address on LAM1 causes, via gate E a1 <SP>1</SP>, this data to be applied to line LJ1 and thence to the relevant channel of outgoing highway LRS1. During any one primary line slot the distributors connect their associated junction lines LJ to each outgoing highway in turn during secondary time slots ts1 ... ts32 (N2=32). This means that if a primary time slot say tp19 is in use on one of the highways say LRS(N1-1))N2+1) i.e. the first highway of the last group, then no other first highway of any other group may be connected to that buffer memory say MT1 to which LRS(N1-1)(N2+1) is effectively connected at the time tp19/ts1. In other words a blocking situation arises. This is overcome to a certain extent, by means of an entraide facility, shown dotted at ENT, wherein some outlets are reconnected as inlets to the network. By this means of course, the required data in MT1 is transferred to another buffer via the network at a convenient time whereby during a subsequent time tp19/ts1 the data may be conveyed to the first highway of a group without any interference from the connection between MT1 and LRS(N1-1)(N2+1) that exists simultaneously. Space division equivalents of the TDM network, with and without entraide, are depicted in Figs. 5 and 6 (not shown).