Patent GB-759343-A (GB)
Title: Automatic telegraph switching system with multiple call processing
IPC: H04L12/54
Filed: 1954-10-18
Abstract: 759,343. Telegraph exchange systems. AUTOMATIC ELECTRIC LABORATORIES, Inc. Oct. 18, 1954 [Oct. 21, 1953], No. 29915/54. Class 40 (3). An automatic telegraph switching system includes a switching centre, and a number of stations, each identified by address codes, and means in the switching centre can record a number of address codes followed by a message, and store the message in connection with the outgoing line indicated by each address code, further means then transmitting the message independently over each outgoing line accompanied by the appropriate address codes. The apparatus is broadly similar to that in Specification 722,777 and if a message has a single destination the operation is the same. In the case of a multiple address message, the apparatus of the original application directed the message to a manual operator position for dealing with multiple calls. In the present apparatus, automatic means are substituted for the manual operator. As shown in Fig. 2A, an incoming line circuit X400 of a switching centre UAC (shown on the diagram of Fig. 1) contains a director assignor X800, directors X200A, and cross office selectors X3300 all operating as described in the prior Specification. In addition each unit X3300 can select one of a number of multiple call storage units 1400 when a multiple address call is received and the latter is recorded by reperforator 1410 in the unit. A multiple call message consists of the following items :- (1) The start of message indicator. (2) A three-letter code identifying the incoming line, together with a number indicating the number of messages so far received over this line. (3) A precedence indicator as described in Specification 722,777. (4) The routing indicator identifying the relay switching centre that is responsible for retransmitting the message to a number of destinations (VAC in this example). (5) A multiple call indicator (ZVA). (6) Letters which identify the precedence and letters which identify the various destinations. (7) The body of the message. (8) The date and time. (10) The end of message indicator. When such a message is received, the first two items when detected cause a director (e.g. X200A) to be associated with incoming circuit X400. The precedence and muting indicator are then detected and registered, and, as a result, routing translator X2900 applies a potential to a jack in patch panel X3200 resulting in the operation finally of a multiple call relay XR2450 in cross office selector group X2600 (Fig. 7A). An indication is also registered in the multiple call register in the precedence detector X2300. Multiple call relay XR2450 is operated and this causes the director X200A to pick up a multiple call storage unit 1400 from the pool or one that already contains a multiple call message of the same precedence, the unit 1400 containing a register which receives signals from the precedence indicator switch. The main parts of unit 1400 are shown in Fig. 14. When one of the latter has been picked up, a signal is returned to incoming line circuit X400 to permit it to start retransmission of the entire message, and the motors of unit 1400 are started to drive its reperforator 1410, tape reader 1420, and transmitter 1430. When the tape reader X340 (Fig. 7B) senses the end of message indicator, it controls the feed of tape X333 to ensure the passage of this indicator through retransmitter X360, and the incoming line circuit X400 disconnects and restores to normal, while unit 1400 is left marked busy. As a precaution the start relay of the latter cannot operate until a slack tape operated switch indicates that the reperforator 1410 has processed enough tape. Also means are provided to insert a definite amount of blank tape between messages, in order to ensure the release of common equipment to be described later. The latter is called for when storage unit 1400 has detected and registered a start of message indicator. The calling means (control unit 1000, Fig. 2A) includes relays connected with the precedence detector so arranged that a particular message can always interrupt the calling process of a message of lower precedence. Operation in the storage unit 1400 is as follows. At first the unit is connected to the precedence sensing unit 6700, the prosign detector 2900, and the address detector 3300 in the common equipment, and the tape reader 1420 transmits information from the recorded message to them, though the prosign detector 2900 does not use the information if the message contains no prosigns. A counter in unit 1000 also counts the characters in the message, after the start of message indicator. The use of this will appear later. As the routing indicator follows the precedence indicator it is arranged that any possible letter formation of the former will not be acceptable to the interlocked relays of the precedence detector and no false indication can be produced in the latter. The routing indicator when read by detector 3300 is then stored in the routing register 3700. If this indicator has a " good " first character followed by a second character which is a " good " first character but not usable as a second character both are registered and if the third character received is a " good " second character the first " good " first character is abandoned. When the multiple call indicator is registered, the address detector 3300, and the routing register 3700 restore and all indications in the latter are abandoned. After this the indicator identifying the destinations is read and the following processes are set into operation. The multiple-call translator 2100 (Fig. 2B) is associated with the routing register 3700 (Fig. 2A) so that each indicator may be processed and also recorded on tape and stored. When a routing indicator is processed through translator X2900 (Fig. 2A), the identity of the outgoing line is registered in channel converter unit 4500 (Fig. 2B). The latter then seizes a channel relay unit such as 7900 corresponding to the desired outgoing line and the routing indicator is stored in unit 7900, unless it relates to an outgoing line directly connected to a tributary station of the present switching centre. The second routing indicator appearing on the message stored in the multiple call storage unit is now sensed and a channel relay unit corresponding to a suitable outgoing line for this indicator is seized. Sensing continues until all the routing indicators are processed and a character indicating the end of these appears on the message stored in unit 1400. The latter terminates the sensing operations of tape reader 1420. If the message is being transmitted to several destinations all reached by one line from the present station, the one channel relay unit registers the indicators for these destinations in preparation for sending. out one message with several routing indicators. If there is a cross office unit X3400 connected to the desired outgoing line and containing messages of a similar precedence to the message being considered, this unit is seized. If there is no cross office unit marked with the desired precedence, hunting switches search for an empty cross office unit. With messages of high precedence the first step is omitted, and an empty unit is searched for at once. The channel relay unit 7900 is then connected through its cross office selector 8300 to the cross office unit X3400 which has been chosen. After the various routing indicators for the message have all been processed and the various channel relay units have been connected to their appropriate cross office units, the precedence indicators for all the messages to be sent out are transmitted to all the engaged cross office units. A channel multiplying unit 8700 is provided, with groups of connected contacts for providing the desired number of identical signals. A monitor page printer 8750 is also provided which records some of the code signals of all multiple call messages, and also records the pilot message headings of all messages sent out in response to receipt of a multiple call message. After the above units have operated the channel selector switch control unit 4600 (Fig. 2B) is operated and the channel selector switch 4601 selects channel relay units one at a time so that certain relay switching centre routing indicators and certain prosigns may be transmitted. Also the unit 4600 may be used a second time to control the transmission of tributary station routing indicators. As the result of processing in the apparatus the original multiple call message is now stored in a number of cross office units X3400 but the multiple call equipment has modified some of the pilot headings in these messages so that they only now have the information required for the particular outgoing line they are on. The entire original message as it appears on the tape on the multiple storage unit is then simultaneously transmitted to all of the marked cross office units. Each of the latter has now produced a perforated tape which is used, as soon as its outgoing line is available to transmit independently the original message, preceded by the new pilot heading information, over this line. The pilot heading information will contain prosigns, which indicate to subsequent switching centres which of the routing indicators to process. For example, the prosign ZWL indicates that all the tributary station indicators, except those following the prosign, are to be processed in the relay station. Another class of prosign is defined as a network prosign and consists of three identical characters. These prosigns indicate that only tributary station indicators beginning with the same letter as that of the prosign should be processed. As a result of the above processes a single message from switching centre UEP (Fig. 1) reaches centre UAC where, for example, a message is sent to tributary centre UACZZ and the message passes on also