GB940463A - Telegraph system with correction by repetition of disturbed signals - Google Patents

Abstract

940,463. Telegraphy. DE STAAT DER NEDERLANDEN, TEN DEZE VERTEGENWOORDIGD DOOR DE DIRECTEURGENERAAL DER POSTERIJEN, TELEGRAFIE EN TELEFONIE. June 16, 1961 [June 28, 1960], No. 21819/61. Heading H4P. In a two-way telegraph system in which errors are corrected by repetition and in which a number of transmission channels is allocated to a larger number of terminal stations on a time allocation basis, means is provided for extending the allocation period by the period of the repetition cycle if such a cycle is in progress at the normal end of the allocation period. In the embodiment described, a 32-character allocation period and a 4-character repetition cycle are used, and there are 32 stations and 16 channels. The transmitter Z and remote receiver O, Fig. 1, contain similar equipment comprising a ring counter T32, which determines the normal allocation period, and T4, which determines the repetition period. Under normal conditions, at the end of the allocation period T32 and T4 are both at full count. T4 therefore feeds a positive voltage to diode 2 and T32 sets trigger Az to feed a positive voltage to diode 1. The repetition distributer, being inoperative, provides a like voltage to diode 3 so that when the transmitter distributer provides a positive pulse to diode 4 trigger Sz is set, which action resets Az. When set, Sz permits the station to be allotted a new channel. However, if a repetition cycle is in progress due to faulty reception, diode 3 is fed with a negative voltage and so Sz can not be set until T4 has regained a count of 4 and the repetition cycle has been completed, i.e. the allocation period is extended by 4 or a multiple of 4 characters. Re-allotment of the channels is performed by the arrangement of Fig. 4. A matrix of triggers corresponds in rows to each channel, and in columns to each station. When a station has data to transmit its corresponding contact ct is closed. Assume that contacts ct2, ct4 . . . ctn are closed (n=32). At the end of the present allocation period of any one channel, 16-stage counter K1-K16 receives a pulse so that K1 supplies an output to the first row of triggers. 32-stage counter T1-T32 is now brought into operation and pulses each column of triggers in turn until it reaches a column having a requesting station on it, in this instance column 2. The result of the three inputs to trigger T2.1 is to allocate channel 1 to station 2 and for counter K1-K16 to be stepped by one. Counter T1-T32 starts again, and this time allocates channel 2 to station 4. The process continues until all the channels have been allocated or until there are no more requesting stations. A channel can not be re-allocated if Sz is not set, i.e. if a repetition cycle is proceeding on that channel.