Patent GB-908700-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q1/26
Filed: 1958-12-19
Abstract: 908,700. Automatic - exchange systems. WESTERN ELECTRIC CO. Inc. Dec. 19, 1958 [Dec. 31, 1957], No. 41006/58. Class 40 (4). A plurality of subscribers' lines are connectable through a satellite switching centre, known as a line concentrator, to a smaller number of trunks extending from an exchange which includes a memory device for maintaining a record of the connections established through the concentrator. The system described comprises ten concentrators 200-209, each of which serves fifty substations 2S00-2S94 on lines 2L00-2L94 and is connected to the exchange by ten trunks 4T0-9 and two control pairs 4CP1-2. A pulse generator 900 at the exchange transmits scanning pulses through ten concentrator control circuits 600-609 and the control pairs to the concentrators and also to a register circuit 800. The subscribers' lines are arbitrarily arranged, as in ordinary crossbar systems, in groups designated vertical groups, vertical files, and horizontal groups. All the lines connected to one concentrator are in the same horizontal group which is divided into ten vertical groups each including five vertical files. Thus each vertical group pulse from the generator 900 selects a group of five lines at each concentrator. Individual lines are selected by the vertical file pulses, five of which appear between any two successive vertical group pulses. The complete pulse cycle lasts 240 milliseconds and comprises ten vertical group pulses and fifty vertical file pulses. The first vertical group pulse of each cycle also serves as a reset pulse to keep the concentrators 200-209, the register 800, and the pulse generator 900 in synchronism. The generator 900 also supplies timing pulses at rates of 250 (for scanning) and 500 (for pulsing out information) per second. Outgoing call.-If a line, say 2L00, is in calling condition, its associated concentrator 200 transforms its vertical file pulse into a service request pulse which is sent over control pair 4CP1 to the corresponding concentrator control circuit 600. This halts register 800 at the identity of the calling line 2L00, stops vertical group pulsing to the concentrator 200, and supplies an inhibiting potential to the other control circuits 601-609 which block vertical group pulsing to their concentrators 201-209. Control circuit 600 also supplies the identity of the calling concentrator 200, i.e. the horizontal group, to a frame control circuit 2100, which also receives the calling line identity (vertical group and vertical file) from register 800 and thereupon seizes a line link marker connector 2009 followed by a marker 2008 and a line link connector 2010. Marker 2008 seizes an outgoing or " originating register 2004 through a connector 2005 and controls line link connector 2010 to supply the identity of the calling line 2L00 to frame control circuit 2100, which is also given an indication that the call is outgoing. (The calling line information is fed back to frame control circuit 2100 in this way so that the procedure shall be the same for both outgoing and incoming calls.) Check for abandoned calls.-When control circuit 600 stops vertical group pulsing, vertical file pulses continued to scan the five lines 2L00-2L04 in the vertical group " O," and each scan of the calling line 2L00 sends a service request pulse via control pair 4CP1 and control circuit 600 to register 800. If one of these pulses failed to arrive, the call would be considered abandoned and register 800 would initiate release. When frame control circuit 2100 receives the calling line information from marker 2008, it causes control circuit 600 to block vertical file pulsing and indicates to register 800 that the abandoned call check is ended. Connection of calling line to an idle trunk.- Frame control circuit 2100 sends the calling line information to outpulsing control circuit 1400 and to memory circuit 1100 which keeps a running record of all connections set up. When the calling line information reaches memory circuit 1100, an idle test is made of the calling line 2L00. (This is not necessary in the present case, but is done in order to maintain uniformity of procedure.). An idle line indication is sent to outpulsing control circuit 1400. Frame control circuit 2100 also supplies start potential to trunk selector circuit 1700, which uses a timing pulse from generator 900 and trunk availability information from memory circuit 1100., Six of the trunks 4T0-9 are available for connection to any one of lines 2L00-2L94, with an order of preference in which the two trunks 4T8-9 are always last. The six available trunks, known as a " trunk multiple," are the same for all five lines of a vertical group and there are ten trunk multiples, one of each vertical group. When memory circuit 1100 and trunk switch 1000 both give an idle indication for a trunk, earth is extended over the corresponding lead from memory circuit 1100 to trunk selector circuit 1700, the trunks being tested in their order of preference. The first idle trunk found is selected by trunk selector circuit 1700 which sends its identity to trunk switch 1000 and memory circuit 1100. Trunk switch 1000 (after a memory cheek described below) connects the selected trunk through trunk link frame 2000 to originating register 2004, while memory circuit 1100 registers the line and trunk identities. Trunk selector circuit 1700 sends an indication that a trunk has been selected through frame control circuit 2100 and line link connector 2010 to marker 2008, which completes the seizure of originating register 2004. (If all trunks in the multiple are busy, trunk selector circuit 1700 sends an overflow indication to frame control circuit 2100 which starts a reset operation, and the call is abandoned.) When concentrator control circuit 600 stopped the abandoned call check, it readied paths from outpulsing control circuit 1400 to control pairs 4CP1-2 and applied starting potential to outpulsing control circuit 1400, which supplies a reset pulse to concentrators 200-209. Outpulsing control circuit 1400, having received an idle line indication from memory circuit 1100, passes timing pulses from generator 900 to trunk selector circuit 1700 which uses them to send an indication of the selected trunk through outpulsing control circuit 1400, concentrator control circuit 600, and control pair 4CP2 to concentrator 200. At the same time, circuit 1400 pulses out the vertical group identity of the calling line 2L00, followed by the vertical file. The first vertical file pulse prepares concentrator 200 to receive mark pulses (of the same polarity as the trunk identifying pulses) over control pair 4CP2. Memory circuit 1100 registers the outpulsed line and trunk identities and sends a memory check indication to outpulsing control circuit 1400 which sends mark pulses via concentrator control circuit 600 and control pair 4CP2 to close the relevant crosspoint at concentrator 200, thereby connecting the calling line 2L00 to the selected trunk, say 4T0. The scanning circuits are disassociated from line 2L00 to provide a clear tip and ring connection to the exchange, and concentrator 200 sends a crosspoint closure indication to outpulsing control circuit 1400 which stops the mark pulses and sends reset pulses to concentrators 200-209. Connection in trunk switch 1000 to other end of selected trunk 4T0.-When marker 2008 sent the identity of the calling line 2L00 to frame control circuit 2100, the latter passed it on to trunk switch 1000 which sends to line link connector 2010 an indication of which of the channels to trunk link frame 2000 are busy. If all channels are busy, marker 2008 releases and initiates a reset sequence. If channels are available, marker selects one through trunk switch 1000 and provides operating potential via line link connector 2010 to trunk switch 1000 and via trunk link connector 2011 to trunk link frame 2000. Memory circuit 1100 gives a memory check indication to trunk switch 1000, as well as to outpulsing control circuit 1400 as described above. (If the check is not received, trunk switch 1000 does not operate and marker 2008 times out and gives a fault indication.) Trunk switch 1000 operates to connect the selected trunk 4T0 through trunk link frame 2000 to originating register 2004, as mentioned above, and sends a crosspoint closure indication to outpulsing control circuit 1400. This circuit, having received crosspoint closure indications from both concentrator 200 and trunk switch 1000, initiates a reset sequence to release trunk selector 1700, memory 1100, and register 800. When the connection is established through trunk switch 1000 to originating register 2004, marker 2008 is released and in turn releases connectors 2010 and 2009 and frame control circuit 2100. Scanning is now resumed. Under the control of register 800, service requests at concentrator control circuits 600-609 are not recognized for a random interval, in order to prevent a faulty line from presenting a continuous demand and denying service to lines later in the scanning cycle. Calling subscriber dials.-A connection has now been set up from the calling line 2L00 to originating register 2004, and the calling subscriber dials the wanted number. Originating register 2004 seizes marker 2008 which in turn seizes frame control circuit 2100 via line link connector 2010. Marker 2008 sends the line and concentrator identities to frame control circuit 2100 which passes them to memory circuit 1100. The memory determines which of the trunks was used for the connection (4T0 in the present case) and gives the information to trunk selector circuit 1700 which passes it to trunk switch 1000. This operates to extend the connection from the selected trunk 4T0 through trunk link frame 2000 to outgoing trunk 2003. Marker 2008 releases, followed by frame control circuit 2100, trunk selector 1700, and the read-out circuitry (not shown) of memory 1100. Incoming call.-The pr