GB1217696A - Electrical signal transmission systems - Google Patents

Abstract

1,217,696. Multiplex pulse code signalling. NIPPON ELECTRIC CO. Ltd. 12 Feb., 1968 [12 Feb., 1967], No. 6733/68. Heading H4L. In a system of the type in which a plurality of relatively low speed P.C.M. signals are combined in time division multiplex on a high speed system and wherein redundant pulses are included in the high speed pulse train to correct for timing errors (pulse stuffing) a plurality of different code signals are used in a predetermined sequence to indicate when pulse stuffing has occured. Fig. 6 (1) shows a main frame of the high speed multiplexed signal having a fivedigit framing code 11 and comprising subframes separated by stuff information codes S1, S2 &c. Each subframe consists of 320 information bits and the codes S1, S2 &c. each consist of five bits. The subframes are divided into 64 five bit time slots each of the five bits being a corresponding information digit of the respective five slow speed systems Fig. 6 (2) shows the composition of a subframe and Fig. 6 (3) shows the digit time positions occupied by the second low speed system. Stuffing is carried out for each low speed system by using one of its available digit time slots, the stuff information codes 12 to 16 indicating whether or not stuffing has taken place for the slow speed systems one to five respectively. For example in Fig. 6 (2) and (3) stuffing takes place at 21 for the second low speed system as indicated by code 52 and is a space when stuffing occurs. Four stuff information codes 11111, 11000,00100 and 00011, 41 to 44, Fig. 6 (4) are provided and are used in rotation and in each case one digit error is allowed so that for code 41 any code in the group 45 is acceptable. Similarly for codes 42, 43, 44 a code in the group 46, 47 or 48 respectively would be acceptable. The transmitter, Fig. 3 (not shown), includes a counter for each low speed system for transmitting the stuff information codes. When no stuffing occurs the previous stuff information code is repeated and when stuffing becomes necessary the next code in the sequence is transmitted. This is detected at the receiver to apply any necessary correction to the de-multiplexed output signals.