Patent GB-696552-A (GB)
Title: Improvements in or relating to telegraph switching systems
IPC: H04L12/54
Filed: 1950-09-29
Abstract: 696,552. Telegraph exchange systems. WESTERN ELECTRIC CO., Inc. Sept. 29, 1950 [Oct. 1, 1949], No. 23883/50. Class 40 (iii). In a telegraph network including a number of switching centres each of which may have party-lines, stations throughout the network are characterized by a combination of 2 (or more) code characters, each such combination being effective to establish automatically communication between any two stations in the network. Other two-character combinations are used to make multiple calls to any desired combination of stations (the multiple code being followed by the individual codes of all the desired stations), to call predetermined groups of stations (only the multiple and group codes being required in this case), or to call all stations for a broadcast message (multiple code followed by broadcast code). The selective connection of each station on a party-line to receive or transmit a message is controlled by apparatus of the kind described in Specification 696,541 and 674,245, in which contacts are operated in response to two- (or more) character combinations. Transmission from stations on a party-line takes place in succession under control of apparatus at the switching-centre end of the line and for this purpose the transmitters are selected by a particular sequence of signals including a one-character code which is only distinctive of the different stations on any one line. Figs. 8-12 show a lay-out diagram for one switching centre with junctions extending to other similar switching centres and Figs. 13- 185 (not shown) give the complete circuits corresponding to Figs. 8-12. The nature and function of the circuit elements shown in Figs. 8-12 with an outline of their method of operation will be described in the following paragraphs which mainly deal with the establishment of various kinds of connection. The main claims relate to means for seizing a plurality of outlets (local or to another switching centre) in all the required directions in the case of a multiple-address call or a group-code call. Starting transmission from a station on a party-line. Party-line 8-01 has separate trans. mitting and receiving channels 8-02, 8-03 and has connected to it nine stations 8-06 to 8-09, 8-11 to 8-14, and 8-16. Each station has a tape-transmitter 8-17 on which messages for transmission are recorded, and a receiving teleprinter 8-04. The apparatus responsive to the selective codes is located in a station-control circuit 8-21 &c., certain adjacent stations being grouped for this purpose, e.g. stations 8-06 to 8-08 have a common control circuit 8-21. Transmission is started by operating a key, corresponding to the first station 8-06, in the key group 9-18. In response to operation of this key, two stepping-switches in the transmitter start circuit 9-17 move to a position corresponding to the particular key, and a third stepping-switch, acting as a sequence switch, controls the transmission of the following sequence of signals: blank, 0.7 seconds pause (marking condition), space code, 0.25 seconds pause, station-selecting code (A for station 8-06), 0.25 seconds pause, letters, 1.9 seconds pause. The distributer of one of two transmitter-reperforators 9-08, 9-09 associated with the receiving channel 8-03 is used to control the transmission of the four codes, the stationselecting code being composed by wiring between the banks of the three stepping-switches. The pauses are produced by controlling the stepping magnet of the third switch by a thermionic-valve circuit having a condenser time-constant circuit varied over a wiper of the switch to provide the different pauses mentioned. If the first station 8-06 has no tape ready for transmission, the third switch returns to normal and the start key of the next station is operated. If this has tape ready, a signal will be sent back during the 1.9 seconds pause and starting codes will then be sent automatically to all the stations in succession. If at the end of a cycle, no station is found to have tape prepared, the pause before recommencing the cycle is lengthened. Skip keys are provided for excluding any station from the transmitterstart cycle. At the station control circuit, 8-21, the blank code followed by the 0.7 second pause opens contacts to prevent the receiving teleprinter from responding to the start code, and unblocks the selecting lever responsive to the space code. The space code lever similarly unblocks the lever or levers responsive to the selective code, this sequence of operations ensuring that the transmitter will not be started by any of these codes occurring during an incoming message. The station selective code completes the transmitter start circuit if tape is present and this circuit is locked so that the selective-code lever may be unlocked by the letters code. Transmission continues as long as tape is present and a valve delay circuit may be provided to permit a new tape to be inserted (within 20 seconds) and the transmitter to be restarted without the re-sending of the start code. The transmitter start circuit 9-17 is controlled so that a start signal cannot be sent between the two characters of a selecting code, the carriage-return and line-feed signals at the end of a code or codes, and the figures and H code at the end of a message; it can break in upon a transmission at any other time without mutilating any character. Call from station 8-07 to station 8-12 (CD) on the same party-line. The characters recorded in the tape are: several " letters " (to provide tape for insertion in the transmitter), figures and H (to restore any off-normal condition), letters, code CD, letters, carriage-return and line-feed (to indicate end of code), letters, message text, figures and H (to indicate end of message), letters. Further messages for other stations, with the appropriate codes, may be recorded on the same tape, the last one being followed by the sequence: figures, H, letters, H, letters, to indicate no more messages ready for transmission. The received signals are recorded on a reperforator-transmitter 9-02, 9-04 and a controlling circuit 9-07 termed a " director " is taken into use. The letters, figures, and H codes ensure the normal condition of the director and are discarded, i.e. not retransmitted. The two code letters CD are transmitted to and recorded on two groups of relays in the director and complete a marking test circuit to the outgoing circuit of the party-line. This outgoing circuit includes two transmitterreperforators 9-08, 9-09 with corresponding control relay sets 9-11, 9-13 and 9-12, 9-14 (referred to as "upper level" and " lower level "), these being used in turn without any preference. If one is idle, the marking circuit is completed through one of the relay sets 9-11, 9-12 to the corresponding " hold " magnet 12-16, 12-01 (which does not yet operate) of a cross-bar switch, Figs. 11, 12. The " select " magnet 11-01 corresponding to the incoming circuit 8-02 is then operated through a sequence circuit 10-01 (which prevents more than one " select " magnet being operated at a time) and the " hold " magnet operates to complete the connection between the director 9-07 and the upper or lower level outgoing line circuit. The two code digits CD are retransmitted to and recoded on the reperforator-transmitter 9-08 or 9-09, the first in accordance with the setting of the first relay group in the director and the second in accordance with the setting of transmitter 9-04 which has not moved in the meantime, and the transmitter 9-04 is then reoperated to transmit the rest of its record including the message, and the director is released and restored to normal and the " hold " magnet released. The signals recorded at 9-08 or 9-09 are transmitted over circuit 8-03 to the station control circuits 8-21 ... 8-24. At all of these, permutation bars corresponding to the letter C will be operated in response to the first code digit preparing other bars to be operated in response to the second code digit in accordance with the codes allocated to the stations controlled by the circuits 8-21 to 8-24 but only in circuit 8-23 will the prepared bar be operated by the second code digit D and this bar will close contacts for connecting the receiving apparatus at station 8-12 to line 8-03. The carriage-return and line-feed signals following the code characters " de-activate " the permutation bars to prevent response to the same code occurring during the message and the apparatus is re-" activated " by the end of message signal. Call from station 8-07 to receiving-only teleprinter 9-03 at switching centre. The incomming line circuit 9-01 in response to the code GZ associates the teleprinter 9-03 with line 8-02 and disconnects reperforator-transmitter 9-04. The end-of-message signal restores the normal connections. Call from station 8-07 to receiving-only teleprinter 9-03 and also to station 8-34 (BG). Code GH causes the incoming line circuit 9-01 to associate teleprinter 9-03 with line 8-02 without disconnecting reperforator-transmitter 9-04 which then responds to code BG to extend the connection over the cross-bar switch to line 8-32. Multiple-address call from station 8-34 to station 8-14 (BB) on party-line 8-01 and to a station (GB) at another switching centre. The characters recorded in the tape at station 8-34 are letters, BC (indicating a multiple call), letters, BB, letters, GB, letters, carriage return, line feed, letters, message, figures, H, letters. The call goes as before to a director 9-24 which, in response to the multiple-address code BC, extends the circuit over the cross-bar switch to one or other " level " of a multiple-address circuit 10-51 for recording one a reperforatortransmitter 10-52 or 10-53. (If another multiple-address call comes in at the same time, e.g. that referred to in the next paragraph, this will go to the other reperforator-transmitter and whichever has tape available