Patent GB-776946-A (GB)
Title: Improvements in or relating to telegraph switching systems
IPC: H04L12/54
Filed: 1954-11-18
Abstract: 776,946. Telegraph exchange systems. WESTERN ELECTRIC CO., Inc. Nov. 18, 1954 [Nov. 18, 1953], No. 33432/54. Class 40 (3). In a telegraph system comprising a principal station and a plurality of outlying stations including transmitters each connectable over a common channel to the principal station which has a signal transmission means adapted to invite message transmission from each of the transmitters individually and in sequence over the channel, means is provided to generate an acknowledgment signal if a transmitter has no message for transmission and the said signal is suppressed if a transmitter commences message transmission in response to the signal inviting transmission. The principal station transmits a roll call comprising two sequences of code signals, each sequence including a code designation for each outlying message-signal transmitter, and the codes for any transmitter are different. The roll-call transmitting means is arranged to transmit one sequence followed subsequently by the other, and any transmitter is normally conditioned for operation in response to one or other of the codes. The transmission of the second sequence of codes is precluded unless there is no response of a transmitter to its code in the first sequence. Also, after the response of a transmitter to a code in the first sequence and its message has been transmitted, stations subsequent to the one which has responded are nvited to transmit in response to the firsti calling sequence, and this process is repeated until there is no further response to the first sequence of code signals, and in consequence the second portion of the roll call is transmitted to control transmission in sequence from stations which have been conditioned according to their code designation in the second sequence of code signals. The circuit arrangement shown in Figs. 2 to 5 is generally similar to that described in respect of Figs. 9 to 12 of Specification 696,552, and this generally diagrammatic arrangement, in conjunction with Fig. 1, includes a multistation line 1-01 with station control circuits 1-13, 1-14, 1-15 associated with outlying stations 1-06, 1-07, ... 1-10 and a duplex line 1-20 having a single station 1-19 comprising distributer 1-22 and transmitter receiver 1-21 connected to a switching centre which is connected by channels 1-27 ... 1-32 with a switching centre 1-26 and by a channel 1-36 with a centre 1-37 serving prescribed stations and connected by a channel 1-38 to the centre 1-26. A switching centre 1-39 is connected to the centre 1-26 and a further switching centre 1-34 is connected by duplex channel 1-33 to the switching centre shown in Figs. 2 to 5. The circuit shown in Fig. 4, which is similar to Fig. 10 of Specification 696,552 and is related mainly to the interconnection of switching centres, is not described in the present Specification which is concerned with the selection and control of a number of stations on a party line. During the period when traffic is not being received at the incoming line circuit 2-01 the transmitter start circuit operates to interrupt outgoing traffic over the line 1-01 and transmits the first of a series of signals inviting transmission from a transmitter of one of the stations 1-06, 1-07.... The transmitter 2-17 initiates a roll-call comprising a first series of signals U, F, C ... controlling priority or urgent transmission and subsequently a series A, S, I ... inviting regular transmission. The selecting signal is prefixed by a sequence comprising a blank, followed by a pause of ¢ second, and the code combination for space which operates the station control circuits 1-13, 1-14 and 1-15 and the character signal selects the transmitter from which transmission is invited, a key being operated according to priority or regular designation respectively of the message. If a transmitter has no priority message the associated control circuit sends a signal for the character H to which the circuit 2-01 responds to operate the circuit 2-17 to send the signal corresponding to the next transmitter in the sequence. After the sequence of signals for priority transmission has been sent, the start circuit operates to send the sequence for regular or non-priority transmission. If at the end of the two sequences, no transmitter is brought into operation, the traffic on the outgoing channel is resumed, if it had been interrupted, and at the end of a prescribed period, e.g. 1¢ to 2 minutes, the dual roll call of the transmitters is again initiated. At the switching centre a multibank stepping switch controls the sending out of the priority and regular codes for the various stations and two further switches assume positions corresponding to the station which has transmitted so that the subsequent roll call begins at the station next in sequential order. In all cases, whatever the nature of the previous response to the roll-call, the priority signals are transmitted prior to the sequence inviting non-priority transmissions. Switches are provided at the centre to skip stations for priority and/or non-priority transmission. If a message has been inserted in one of the transmitters, e.g. that at station 1-07, and is assumed to be urgent, the transmission of the letter F from the start circuit 2-17 will connect the transmitter 1-51 and the initial signals received by the incoming circuit 2-01 suspend the operation of the circuit 2-17 which permits the resumption of traffic over the outgoing line 1-03. At the end of the transmission of the messageend signal the circuit 2-01 reoperates the circuit 2-17 which allows telegraph traffic from the centre to be resumed and after a predetermined period resumes the transmission of the priority starts codes at the station next in the sequence after the station which transmitted a message during the previous roll call. The tape prepared for transmission has the signals Letters, Figures, H, Letters preceding the address code letters, which as described in Specification 696,552, operate to effect the cross-office connection by means of the cross-bar switch, Figs. 3, 5, and to control the transmission of the message to the desired station. Assuming that the message is for the station 1-09, the address signals followed by the message is received by reperforator 2-02 and passed by transmitter 2-04 to the director circuit 2-07 operating select magnet 3-01 of the cross-bar switch, and if one of the reperforators 2-08 or 2-09 is idle, the circuit 2-07 operates hold magnet 5-16 or 5-01 to establish a connection to the transmitter-perforator 2-08 or 2-09 where it is recorded. In response to the disconnect signal, the circuit 2-07 restores to normal and magnet 5-16 or 5-01 is released. The free transmitter 2-08 or 2-09 under control of relays 2-13 or 2-14 and relays 2-16 is connected to the line 1-03 when free and all the control circuits 1-13-1-15 respond to the code CD, but solely the teleprinter 1-52 of station 1-09 is connected. The carriage return and line-feed signals following the address code CD render non-operative the control circuits 1-13, 1-14, 1-15 so that they cannot respond to code signals which may occur in the message and form call-directing codes of the various stations on the line 1-03. One of the station control circuits, preferably 1-13, includes a circuit arrangement which allows any sequence of two character code signals transmitted over channel 1-03 and not allocated to any of the stations on party line 1-01 to bring in printer 1-11 or 1-56, when the station control circuits are operative. This prevents a message being lost when the address code has been garbled after the appropriate reperforator 2-08 or 2-09 has been correctly selected, or the address code mutilated in transmission over the line 1-03. The central station includes means for indicating that a station called has not replied or sent the acknowledgement signal and the skip key can be operated to eliminate the station from the roll call. Further arrangements are included for suspending incoming transmission from a transmitter and also for feeding out a prescribed length of tape from a reperforator receiver after the message has ended. Specifications 540,612, 564,893, [both in Group XL], 674,245, 696,554, and U.S.A. Specifications 1,965,572, 1,965,602, 1,969,891 and 2,042,788 also are referred to.