Patent GB-1370319-A (GB)
Title: Time switch for time-division multiplex systems
IPC: H04Q11/08
Filed: 1971-12-22
Abstract: 1370319 Automatic exchange systems SOC LANNIONNAISE D'ELECTRONIQUE and COMPAGNIE INDUSTRIELLE DES TELECOMMUNICATIONS CIT-ALCATEL 22 Dec 1971 [22 Dec 1970] 59717/71 Heading H4K In a TDM system, time slot interchange between channels of an incoming highway and those of an outgoing highway is effected with the aid of delay lines. The amount of delay required for each connection is recalculated every frame. Sufficient lines are provided to permit delays varying in length from zero to a full frame period. The lines are connected in parallel or series. They may consist of cables, optical fibres, wave guides or shift registers. Speech samples may be in analogue or coded digital form and in the latter case bit transmissions may be in series or parallel mode. The input and output highways may each be a supermultiplex and although time slots of equal length and synchronized phase are used thereon, the phase of the frames and the number of time slots in a frame period may differ in the two cases. The subsequently described circuits may be provided in integrated circuit format. In the arrangement of Fig. 1 an incoming highway carrying e channels is connectible to an outgoing highway of s channels via the delay lines L1 to LD having delays of respectively zero to (D - 1)d where d is the length of a single time slot. In order to set up a connection between incoming channel Ei and outgoing channel Sj a control circuit (not shown) writes the address Sj at the location Ei of a connection memory 11. An address generator 9 synchronized with the channels on the incoming highway periodically produces the address Ei so that the address Sj is read out of memory 11 into logic 7. The latter determines the lag or lead R that slot Sj has with respect to the current time slot S being produced by an address generator 16 which is synchronized with the channels on the outgoing highway. The time R is used to switch the incoming sample in channel Ei on to that delay line L which will provide the just calculated required delay and in addition it is entered into output memory 19 together with the address Sj which is still present at the output of connection memory 11. Subsequently when generator 16 produces the address Sj, the value R is read out of memory 19 so as to switch the sample from the delay line identified by this value on to the output highway. In view of the calculation for R in respect of every channel it is clear that precise frame synchronization for the incoming and outgoing highways is unecessary. At the end of the call the address Sj is rewritten as zero in memory 11 thereby clearing- down this connection. In an alternative arrangement the delay lines are connected directly to the outgoing highway (Fig. 2, not shown) so that the output memory and its read/write circuitry MCS is dispensed with. In another arrangement, the input highway is connected directly to the delay lines and switching of the samples thereon is effected at the output thereof (Fig. 3, not shown), the operation being analogous to the Fig. 2 arrangement except that now it is the identity of the incoming channel Ei that is stored in memory 11 at a location Sj corresponding to the required outgoing channel. In the embodiment of Fig. 4 (not shown) the delay lines are connected in series and the control circuit taps off the required sample at the time slot of the outgoing channel in the same manner as for the Fig. 3 embodiment.