Patent GB-922156-A (GB)
Title: Improvements in or relating to automatic telephone systems
IPC: H04Q3/00
Filed: 1959-10-13
Abstract: 922,156. Automatic exchange systems. TELEFONAKTIEBOLAGET L. M. ERICSSON. Oct. 13, 1959 [Nov. 24, 1958], No. 34683/59. Class 40 (4). The wanted exchange in an inter-exchange call in a network of exchanges is searched for by simultaneously seizing all idle alternative interexchange routes from the calling exchange and from each exchange en route. The system is described for a network catering for ordinary subscribers and is also described for subscribers who are mobile, as with car subscribers, where the wanted exchange is the one within the transmitting area of which the mobile subscriber happens to be. System catering for ordinary subscribers.- An exchange suitable for such a system is shown in Fig. 2 where adjacent exchanges A, B, C and D are connected over the groups of twoway trunks TA, TB, TC and TD, with relay sets RA, RB, RC and RD. Outgoing calls are made over lines LNE with a relay set RE and a register SREG. Incoming calls are routed over lines LNT via a selector GV and register LREG. Each relay set is associated with a set of selectors GA, GB, GC, GD and GE controlled by a marker M such that an outgoing line LNE may be connected to all trunks TA to TD simultaneously, and any trunk TA to TD may be connected to the incoming line LNE or to any other or all other trunks TA to TD. If a calling signal indicates the wanted exchange only then the network can handle only one call at a time. If the calling exchange identity is also indicated a call between two exchanges does not prevent a call between other exchanges being set up at the same time. For more than one call between two exchanges to be handled concurrently the calling signal may indicate the number each such call occupies in a cyclic sequence determined by a relay chain or the register involved in setting up the call. The sets of cyclic sequence numbers for such concurrent calls may differ for each exchange and consequently carry the calling exchange identity. The calling signal preferably comprises a combination of audio frequencies, two out of five upper frequencies with two out of five lower frequencies indicating the called exchange and being sent alternately with three out of the five upper and three out of the five lower frequencies to indicate the calling exchange. A further combination of four out of five frequencies may indicate the call sequence number. The indications are distinguished by the number of frequencies present. Spaces are left between signals to permit reception of answering signals. An initial pulse of 50 cycles may be used to prepare the relay sets. The relay sets RA to RD respond to a calling signal incoming to an exchange and seize the marker M in which registers P1 to P5 store the wanted and calling exchange identities together with the call sequence number. The registers mark a multiple MR over which an answering device V responds if the call is to this exchange and an answering signal is reverted over the incoming trunk, say trunk TA. A control circuit K then sets selector E of the group GA to connect trunk TA to a local line LNT, a register LREG being taken into use to establish the call in response to further signals. If the call is not for this exchange a finder MS seizes an idle one of the stores Q1 to QP to which the contents of registers P1 to P5 are transferred. The control circuit K then sets selectors B, C and D, of the group GA on idle trunks in the groups TB, TC and TD, to send the calling signal on to next adjacent exchanges. The marker is released except for the seized store in Q1 to QP which is held for about 3 seconds in case the call reappears over an alternative route. If an answering signal is received back over any of these trunks the associated relay set together with relay set RA remain in use but the other relay sets are released letting the seized trunks go idle. If the call had already been received the registration in one of the stores Q1 to QP finds coincidence over the multiple MR causing forced release of the marker M and setting relay set RA in suspense until the calling exchange signals its release as an unwanted alternative route. If the exchange shown in Fig. 2 is a calling exchange a line LNE seizes a register SREG which records the routing information and takes marker M into use to set outgoing selectors A, B, C and D of the group GE on to idle trunks. Marker M is then released and SREG transmits a calling signal over relay set RE to all seized outlets. When an answer is received a release signal is sent out over all unwanted trunks. System catering for mobile subscribers.-A system suitable for car subscribers, and also having access to an ordinary exchange network, is shown in Fig. 3 which represents a car subscriber's exchange connected to similar exchanges A, B, C and D, over groups of trunks TA, TB, TC and TD, and having access to an ordinary exchange over incoming and outgoing lines LNT and LNF. The exchange serves cars within the broadcast area of a radio station F and it is assumed that there is no overlap between the areas of different exchanges. The radio station transmits a number of carriers marked idle by a continuous audio frequency and car substations, such as AB, automatically set themselves on an idle carrier to listen out. Car subscribers are identified by three digit numbers which when broadcast elicit an answering signal if the car is within range; if not within range the trunks TA to TD are used to broadcast over all neighbouring stations and so on until an answer is found. When a car subscriber initiates a call an audio signal is sent to station F which removes the busying modulation, seizes a register REG over finder RS, and sends dialling tone. In register REG register P1 differentiates between car-to-car and car-to-ordinary subscriber calls. If the call is to an ordinary subscriber the marker M is seized to set selector GV on to a line LNF to the ordinary exchange network. If the call is carto-car registers P2, P3, P4 register the called car number and marker M is connected to initiate transmission of this member from station F over all idle channel carriers. If the called car is within range an answering signal is given on an idle channel carrier and is detected by circuit V which conditions M to set selector GV on to the responding channel and connect a loop to station F between calling and called cars. If the called car is out of range the marker M, after a time delay, sets selector GV to a line TE and controls selectors A, B, C, D of the group GE to connect with idle trunks to the neighbouring exchanges. The marker M retires and register REG sends out the wanted car number. An answer over one of the trunks releases unwanted trunks with REG. A call reaching the exchange over a trunk, such as one of the group TA, causes relay set RA to seize a register REG in registers P2, P3, P4, of which the called car number is stored. Marker M is taken into use to control broadcasting of the wanted number over station F, an answer causes circuit V to respond, and an answering signal is sent back over the TA trunk. If no answer is received a control circuit Q and multiple MR in common to all registers REG determine whether the called subscriber is already the subject of a call and if this is so the transmitter F and the calling line TA are held in suspense until a release signal is received. If the call is not already in progress and the time limit for an answer expires, marker M connects the line of group TA with the incoming call over selectors B, C, D of group GA to trunks to all other neighbouring exchanges to widen the search for the wanted car. Register REG remains held in service until an answering or release signal is received. If a call to a car subscriber is incoming from the ordinary exchange network over a line LNT a register REG is connected over finder SS and registers the wanted car number to initiate search for the wanted car over the exchange network. A variety of calling signals is suggested comprising consecutive two or three out of five or six and is frequency codes depending on the number of car subscribers catered for by the network. The network sets up one call at a time.