GB1397760A - Pcm tdm telecommunication network systems - Google Patents

Abstract

1397760 Multiplex pulse code signalling SIEMENS-ALBIS AG 17 Nov 1972 53152/72 Heading H4L A p.c.m.-t.d.m. exchange (V si O, Fig. 1, not shown) which clocks received data into a buffer store PS, Fig. 3, at the received data bit-rate and clocks it out at its own bit rate, uses socalled blind bits and inhibition of the local clock TG to correct undesired pulse-frame shifts arising from extraneous causes. The start-bits I, II, III, Fig. 2a, of respective data frames from other exchanges V st 1-3, when formed to arrive during the time # preceding the start-bit # of the receiving exchangedata-frame, are appropriately delayed by the buffer PS and read out by the local clock TG. If however they arrive in the interval γ and require a delay of less than this minimum value γ, then the exchange inserts blind bits to delay #. Correction for undesired frame shifts may be effected by similar use of these blind bits. If however the frame shift exceeds the maximum buffer storage time # (which in practice also equals T) then inhibition of the clock is effected, preferably for a period of ¢ #. Each blind bit is generated by a control circuit BB in response to coincidence at UBB of a received start bit ae from a synchronizing word detector SE connected to the incoming line, and a signal from bi-stable CA or AP which generate outputs respectively corresponding to the γ and r periods. Counters Zp and Zpc and dividers B, K control these bi-stables in response to the clock TG. The clock is inhibited by a circuit SS for a period such as ¢#, determined by a delay therein, when the circuit SS senses no received start-bits ae from SE during the # period as represented by the output of another bi-stable PA.