Patent GB-960855-A (GB)
Title: Improvements in or relating to telecommunication transmission systems
IPC: H04L1/18
Filed: 1961-10-31
Abstract: 960,855. Telegraphy. PHILIPS ELECTRICAL INDUSTRIES Ltd. Oct. 31, 1961 [Nov. 3, 1960], No. 38909/61. Heading H4P. In a communication system, a block of information comprising a constant number of code groups is transmitted from an information carrier and the receiver checks the incoming block and requests transmission of the next block if no errors arc detected, or repetition of the block just received if an error is detected. In the embodiment described, a complete block comprises a number identifying the block, forty-eight information code groups and a control symbol. The identifying number takes one of two values alternately for successive blocks, each code group comprises 7 digits and has an odd number of " 1's," and the control symbol is such as to make the total number of "1's" transmitted in each digit position throughout the block an odd number. Special control signals may be transmitted between blocks. System operation.-The equipment shown in Fig. 1 is provided at each end A, B of the system. Initially, the same identifying number is set into number store NGh and number generator NGn at A and B. At the start of transmission NGn transmits the first identifying number via transmitter ZS and steps on to the second number. Next, tape reader L transmits 48 code groups, and finally generator CtSGn. transmits the parity control symbol. The entire block of fifty code groups transmitted is stored at ZGh, and the 48 data code groups received are stored at OGh. The received block of information is examined for errors at CtS and detector Dt supplies its identifying number to comparator Cp. If no errors are detected and the number in store NGh is the same as that supplied by Dt, OBS causes the number stored in NGh to assume its other value, the contents of OGh are read out to tape punch S, and a confirmation " good " signal is transmitted via ZBS and CfSGn as soon as the transmitter is free. When a confirmation " good " signal is received it is detected by Dt and ZBS erases the contents of ZGh and initiates transmission and storage of the next block. If Cp detects inequality of the identifying numbers the incoming block is not stored in OGh and if CtS detects an error the block is erased from OGh. In each case a confirmation " wrong " signal is transmitted, reception of this signal at the other end causing retransmission of the contents of ZGh. A counter may be included in OBS to actuate an alarm AlS when a predetermined number of repetitions have occurred. ZBS may include a timing circuit which produces a signal having the same effect as a confirmation " wrong " signal if a confirmation " good " or " wrong " signal is not received or is not recognized by Dt within a given period after the transmission of a block. A special " stop " signal may be transmitted between blocks when the tape at L or S is nearly exhausted, transmission then being interrupted until a " start " signal is transmitted after a fresh supply of tape has been inserted. The order of transmission priority is as follows : (1) complete transmission of block being handled; (2) " stop " or " start " signal; (3) confirmation " good " or " wrong " signal (4) block of information.