GB1257124A - - Google Patents

Abstract

1,257,124. Automatic exchange systems. SIEMENS A.G. 1 Oct., 1969 [2 Oct., 1968], No. 48140/69. Heading H4K. In a TDM systemhaving 4-wire highways between exchanges, the time frames on all the incoming pairs to any one exchange are synchronized to each other as also are the frames on all the outgoing pairs, the latter frames being delayed by a period tv relative to the incoming ones. Time slot interchange is effected by delaying a channel in one direction through an exchange by a time tx and by delaying the corresponding channel in the other direction by a time ty such that tx + ty = 2tv. In Fig. 1 mutual synchronization of the incoming pairs Aan1, Aan2 to exchange A is effected by delay devices Vab and Vac, the other incoming highways and the outgoing highways being similarly synchronized by devices not shown. In Fig. 2a it can be seen that a time frame T on incoming pairs Aan1, Aan2 leads the corresponding frame on outgoing pairs Aab2, Aab1 by a time tv. An incoming PCM channel, depicted by a single pulse on Aan1 is delayed by a time tx before it is relayed along an outgoing pair Aab2 in the required direction. In the opposite direction, the corresponding channel is delayed by a time ty between incoming pair Aan2 and outgoing pair Aab1. As already mentioned tx+ty=2tv. The dotted pulses indicate the case when tx=2tv and ty=0. The delay may be effected by devices Vab etc. or by separate store pairs (one for each direction) having a total delay of 2tv. Since there are inevitably some channels which cannot conform to the above rule these are handled by stores having a delay of T+2tv (Fig. 2b, not shown). Overall the number of long-delay stores required is very small. Since the short-delay stores may be utilized more than once in a frame, the total number of stores required is much reduced compared with previous time slot interchange systems.