Patent GB-1485876-A (GB)
Title: Time division multiplex transmission system
IPC: H04Q11/04
Filed: 1974-10-04
Abstract: 1485876 Multiplex pulse code transmission SIEMENS-ALBIS AG 4 Oct 1974 [10 Oct 1973] 43048/74 Heading H4M A TDM concentrator includes synchronizing arrangements for compensating changes in the phase difference between TDM pulse frames on a transmission line between the concentrator and a main switching centre, on which TDM words are transmitted serially, and the pulse frames of the switching arrangements in the concentrator, which handle the TDM words to be transmitted or received in parallel form. The concentrator incorporates, in order to receive incoming serial TDM words on the transmission line KML each occupying a time slot in the TDM frame which is 8 bits long, a serial-parallel converter S/P, operating at the line bit rate as determined by a flywheel circuit S. The output from this converter is passed to a first one word intermediate store under the control of an external word pulse train wee which is derived from the line bit rate. The words are transferred from this store to a second one word store ZJ under the control of one or other of two "intermediate" word pulse trains displaced from one another but having periods corresponding to the internal word pulse train which corresponds to the TDM frame in accordance with which the switching system operates. The output of words from the second store is controlled by the internal word pulse train. In the transmitting side of the switching system there is a complementary arrangement of one word stores ZJ, ZE and parallel-serial converter S/P, the first store receiving PCM words to be transmitted under the control of the internal word pulse train, passing them to ZE under the control of the one or other intermediate word pulse train, from whence they pass to the parallel-serial converter under the control of the external word pulse train. When the phase difference between the pulse frames of the external word pulse train and the one or other intermediate train exceeds a particular limit or falls below another lower limit, this condition is detected and used to switch over control of the intermediate stores to the other of the two intermediate trains. The timing of this change is arranged such that it occurs when the synchronizing time slot, as distinct from transmission word time slots, of the external TDM frame occurs and has the effect of either halving or doubling the length of this time slot. The internal bit rate is produced by a generator BiG which feeds an 8 stage counter which will deliver word pulses at various times and thus enable the required internal word wi and intermediate words Za, Zb to be produced. The external bit rate is derived from a flywheel circuit S which feeds a counter Ze8 delivering pulses representing the external words we. Pulses are derived from this counter via LK and compared with that output from EZ, which is controlled by an intermediate word, occurring at the synchronizing time slot (established by the equivalence gate Sy) by AND gate Usy. An output from this causes the bi-stable trigger AB to switch and select the other intermediate word train. The effect of one of these changes taken over the pair of stores, is either to eliminate the sync. time slot in the external TDM frame, or to repeat it. If the external line bit frequency exceeds the internal bit frequency, the phase difference between the two TDM frames will increase. The upper limit to which this is allowable is set by the point where the seventh bit of the 0 time slot of the external frame falls into the range between the 8th bit of the 31st time slot and the 1st bit of the 0 time slot of the intermediate internal bit frequency. Received signals, after being operated on by the above procedure, are passed to a PCM/PAM decoder, thence via a directional hybrid G to coupling switches kkm, mkg. These enable a number of different TDM lines to be coupled at individual phase positions within the time slots, to a concentrator multiplex bus-bar ZMS. Connections from this bus-bar to individual subscribers Tin are made via cyclically operated time channel switches XS and subscriber circuits TS. Outgoing signals to be transmitted are handled similarly, along the complementary path including the stores JZ, ZE. Between the store ZE and the parallel serial converter of the transmitting path, logic circuitry is included which enables sync. information to be inserted in an appropriate time slot.