Patent GB-1465909-A (GB)
Title: Supervisory systems for telecommunication line transmission system
IPC: H04B3/46
Filed: 1973-12-18
Abstract: 1465909 Data transmission; methods of testing PLESSEY CO Ltd 8 Nov 1974 [18 Dec 1973] 58463/73 Heading H4P A system having one or more repeaters, e.g. employing a disparity code binary 4 digit to ternary triplet, each repeater including a digital regenerator and error detector, has a supervisory control incorporated which is rendered operative by an interrogating signal over one access path also used as a data path, which control returns a response signal comprising a different number of pulses for each of two output states of the error detector. Each repeater may be one of a similar pair incorporated in different paths, each pair being interconnected so that account is taken of both error detector conditions. Response signals may have 1 pulse = no error, 2 pulses=1 fault and 3 pulses=2 faults detected, the particular error detector being identified by a unique spatial relationship. The transmission system may have two separately repeated transmission paths and at each repeater a response signal is returned, with a delayed interrogate signal passed to the next repeater. Repeaters may be of the dependent or independent power feed type. A dependent type, i.e. having power fed over data transmission path, e.g. coaxial cable, which is one of an oppositely facing pair in a bi-direction system (see Fig. 1, not shown) has incoming data in self checking form applied through high pass filter HF1 and regenerator DR1 to error detector RED1 preferably of the type as disclosed in Specification 1,388,553, and which comprises an output failure circuit OFD disparity counter DC and further counter SC. If output of DR1 ceases this is detected by OFD which through G1 sets bi-stable toggle T; also if upper or lower disparity limit has been reached, DC sends a pulse to SC which resets every 5 seconds, i.e. at the interrogate pulse rate. Toggle T is twinned with (T) of a paired repeater to OR gate G2.  In Fig. 2 data direction is from RRL to RXL but interrogate pulses are applied in opposite direction to data transmission, i.e. from the receiving end of the path, but in other arrangements (not shown) data and interrogate pulse direction may be the same. A received interrogate burst (25 kHz) of 1 m.sec. duration is passed through 1.p. filter LF 1 and tuned transformer TR1 (also connected to a power supply PC not shown) to a "tone detector" D1 from which the leading edge of output activates monostable circuit M1 for 4À75 m.sec. and the trailing edge activates monostable M6 for 8 m.sec. this disabling linear gates LG1, LG3. When M1 resets, monostable M2 is set which opens linear gate LG4 (a linear gate passes A.C.) enabling a relayed interrogate burst to be passed through another tuned transformer TR2 and low pass filter to a repeater next ahead. When M2 resets, gates G4 and LG2 are disabled and monostables M3, M4 are succes. sively set for 1 m.sec. periods, the latter applying to 1 to AND G3 which is primed if a regenerator fault exists hence through G4, linear gate LG2 is reactivated causing a second response burst to be sent to the interrogating terminal station at the receive end, this being the second response burst in fault conditions, but with no fault, gate G3 is blocked hence only one burst is sent. When monostable circuit M4 is reset, M5 is set for 1 m.sec. which resets toggle T and storage counter SC. Lead RS extends to a corresponding lead of the twinned repeater. The circuit is now prepared for the next interrogation burst from the receive end at 5 second intervals. Fig. 3 (not shown) shows an arrangement for an independently powered repeater utilizing a shift register (SR) as a distributer to sequentially control the various operations. To adapt circuits of Fig. 2 (and 3) to codirectional flow, connections J, K (L, M) need only be interchanged. Alternative arrangements to Figs. 2 and 3 are described with reference to Figs. 4 and 5 (not shown) respectively. The arrangement is equally applicable to a system having two paths operating in the same direction, i.e. a parallel system used for example in television signal transmission, one path acting as standby to the other. One path may be interrogated from the transmitting end and the other from the receiving end if desired and it is stated that interrogation may be carried out from both ends of a both way system by removal of interconnections at each repeater.