Patent GB-1349370-A (GB)
Title: Time division multiplex telecommunication system
IPC: H04J3/00
Filed: 1971-06-21
Abstract: 1349370 Automatic exchange systems PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 21 June 1971 [24 June 1970] 28945/71 Heading H4K In a TDM exchange the incoming and outgoing lines are formed into subgroups each having associated therewith a receive or send intermediate TDM highway and the subgroups are arranged in main groups each having associated therewith a receive or send main TDM highway on which the bit rate is considerably higher than it is on an intermediate highway and the main highways are interconnectable by a switching network. An additional multiplexing of main highways on to superhighways may be effected in which case it is the superhighways that are connectible by the switching network. 2 wire, 4 wire, PAM, PCM and delta modulation systems are described. Timing.-The exchange clock provides a basic pulse rate that is applied to counters (dividers) which provide an output in parallel binary code form. Combinations of outputs from the counters permit an exchange time frame to consist of k=16 main time intervals t 0  ... t 15 , these being used as time slots on the intermediate highways, k + m = 16 x 8 sub-time intervals, these being used as time slots on the main highways and k+mÎn=16Î8Î8 elementary time intervals, these being used at time slots on the superhighways. System description (Fig. 1).-Incoming lines 100 are arranged in 8 main groups 100-0 to 100-7. Within a main group, e.g. 100-0 the lines are further sub-divided into eight groups 100-0-0 to 100-0-7 each of which consists of p +1=256 lines, e.g. 100-0-0-0 to 100-0- 0-P. A line group terminates on an A stage multiplexer, e.g. 103-0 which permits selective connection of the lines to a 16 channel intermediate highway 105-0 via crosspoints 104 under the control of a circulating memory 106 and decoder 107. The intermediate highways 105 pertaining to a main group terminate on a B stage multiplexer which permits selective connection of the channels on these highways to a 16Î8=128 channel main highway 109-0 via crosspoints 108 under the control of a circulating store 110 and a decoder 111. The main highways 109 pertaining to the lines of the main groups 100-0 to 100-7 terminate on a C stage multiplexer which permits selective connection of the channels on the main highways to a 16Î8Î8=1024 channel superhighway 113 via crosspoints 112 under the control of a circulating memory 114 and a decoder 115. The superhighway terminates in a D stage demultiplexer which permits the channels of the superhighway to have access on a strictly one-to-one basis to the channels of the main highways 117 extending via the E and F stage demultiplexers (these providing selective access between channels, as indicated by rewritable circulating stores 122, 126) towards the outgoing lines 101. The trunking in the E and F stages and the grouping of the outgoing lines follows the pattern laid down for the incoming lines. System operation.-In order to set up a connection between incoming line 100-0-0-0 and outgoing line 101-0-0-P it is necessary to quantify two integers x and y which together with the identity z of the main outgoing group concerned are sufficient to fully determine the route. The reasoning behind this choice of integers lies in the fact that no delay is provided by the just described network i.e. all crosspoints must operate simultaneously. In other words if we select main time slot t=x for use on the intermediate highway 105-0 the same slot must be used on intermediate highway 121-0 which terminates on the F demultiplexer. Similarly on main highway 109-0 a sub-slot s=y must be chosen out of the eight sub-slot s covered by the main slot t=x and whichever is chosen this must also be allocated on main highway 117-0 which terminates on the E stage demultiplexer. Finally, in view of the one-to-one relationship between the channels on the superhighway and those on the main highways 117 it must be ensured that the elementary time slot e chosen within the range t=x, s=y is the one which permits access to the main intermediate highway 117-0 pertaining to the main outgoing group concerned. In the case under consideration the slot chosen will be e=z=0. In summary then, the incoming and outgoing line addresser (or at least the crosspoints to which they are connected) are written in position x of circulating stores 106 and 126 respectively; the addresses of intermediate highways 105-0 and 121-0 are written in position x, y of circulating stores 110 and 122 respectively; and the address of main highway 109-0 is written in position x, y, z of circulating store 114. The logic for performing the above write-in operation (but not that for allocating values to x and y i.e. the path finder) is described with reference to Fig. 2 (not shown). Time slot interchange.-This can be effected by inserting a delay line in the superhighway in which case the values of x and y inserted in stores 126 and 122 have to be incremented by the values u and w which correspond to the number of main and sub-time slots which are introduced by the delay line. It is implied that the value of z may also be incremented by a number w of elementary time slots but it is not described how the system copes with this situation. 4-Wire operation (Fig. 3, not shown).-Here a strict relationship exists between the incoming and outgoing lines since each pair of these now constitute Go and Return lines of a particular subscriber. It is necessary to use two exchange frames in order to write-in control instructions for a connection. It is arranged that the Go time slot x for one path leads that for the other path by half an exchange frame i.e. x+8. The CD super-highway contains a ¢ frame delay line. The values of y will be the same for both but of course the values for z will again depend on the outgoing line groups concerned. (Time slot interchange may be effected as before by increasing the delay time of the delay line by the values u, v, w). Economics on the circulating stores used in the E and F stages may be effected by connecting the decoders of these stages to the circulating stores of the A and B stages via delay lines having a delay one half frame greater than that of the delay line in the superhighway. PCM and delta modulation operation, Fig. 4, not shown.-It is postulated that only one bit of a PCM or delta word is transmissible per frame. Each stage contains at least one one-bit shift register which serves to regenerate the bit and ensures that it occupies a defined portion of the ever-shortening time slots (at least as the centre of the network is approached). The superhighway comprises one one-bit shift register and the crosspoints in the D, E, and F stages are each replaced by three such registers which perform selecting, regenerating, and synchronizing functions. Synchronization is necessary in respect of the channels of the different highways leaving a stage as well as in respect of the channels of the highways or lines of the stage to which they extend. The passage of a single bit through the system in terms of its delay at each stage and the relative positions of the time slots on successive highways is described in detail, the cumulative delay is equal to two time frames. Time slot interchange and 4-wire working for PCM or delta signals follows the general pattern outlined heretofore. Trunking.-It is demonstrated (Fig. 5, not shown) that the system is equivalent to a full availability 5 stage network consisting of eight groups each of eight, P x 16, A switches and sixteen 8 x 8, B switches which are fully linked to 128, 8Î8, CD switches (it will be appreciated that the time division C and D switches are only equivalent to a single space division stage in view of the non-selectivity associated with the outlets of the D stage). The latter are linked to eight groups each of sixteen, 8 x 8, E switches and eight, 16 x P, F switches.