GB1206714A - Improvements in or relating to telegraph signalling systems - Google Patents

Abstract

1,206,714. Digital transmission systems; multiplex pulse code signalling. PLESSEY TELECOMMUNICATIONS RESEARCH Ltd. 14 Jan., 1969 [22 Jan., 1968], No. 3299/68. Headings H4L and H4P. In a digital transmission system in which signals are transmitted at a rate greater than the rate of the data at the transmitter input, groups of "fill" digits are added to the data prior to transmission. The signals are sent in blocks comprising a number of data and fill groups. The number of fill digits in the last group of a block varies, and this number is indicated by the code combination of a preceding fill group. At the transmitter, input binary data at a speed which may vary is transmitted over a higher speed sub-channel of a multiplex channel. The serial input data passes via a buffer and regenerator to a unit comprising a store from which it passes to a data register. A counter is incremented whenever a bit is placed in and is decremented whenever a bit is read from, the data register, so that the counter shows the number of bits in the data register which have yet to be transmitted. The cell in the data register from which the data is read out is selected in dependence upon the content of the counter. Under the control of a unit fed by clock pulses at the transmitted bit rate, readout from the data register is stopped periodically for the transmission of a fill group. Each block of signals starts with a synchronizing fill group. The last fill group in a block has a nominal length which is increased or decreased by one bit in dependence upon whether the counter content lies below a certain value or exceeds another value at the end of the preceding data block. An intermediate fill group in the current block shows by its element combination the number of bits in the last fill group of this block. At the receiver the fill groups are removed from the received block, the data groups passing to a register associated with a counter similar to that at the transmitter and which feeds a unit which selects from which cell read-out shall take place. If the counter content exceeds or falls below certain values the rate of read-out from the register is increased or decreased, readout being at a lower rate than write-in to the register.