Patent GB-1228892-A (GB)
IPC: H04Q11/04
Filed: 1968-09-06
Abstract: 1,228,892. Automatic exchange systems. TELEFONBAU UND NORMALZEIT G.m.b.H. 6 Sept., 1968, No. 42627/68. Heading H4K. Each connection in a time division multiplex PABX is allotted a row in a magnetic core matrix comprising a call store- JSP each row of the store having compartments for a calling terminal identity, a called terminal identity, and a program word which determines the processing applied to a call in response to changed loop conditions, or the presence of a key signal requesting an enquiry path facility, as detected by a scanner ZA, or in response to one-digit registers RG passing digits one-by-one to a corresponding call store. The scanner ZA supervises extension circuits B1 to TSn, exchange line circuits AUel to AUem, and operator's positions PS1 to PSk. Open loop is seen as a positive potential, closed loop is seen as half that potential, while an extension key requesting an enquiry path facility while connected to an exchange line is seen as zero potential. The circuits TS, AUe, and PS, are connectable over modems to a highway SA. Also accessible from the highway is a group of one-digit registers RG1 to RGu seizable from an allotter RGZu in accordance with loop conditions determined by scanner ZA and the loop conditions from the preceding scan recorded in a store FBSP. If a loop transition from open to closed is detected a register RG is seized. If a loop transition from closed to open is detected a release register AS1-RG is seized. Pulse positions and the multiplex frame are determined by a clock circuit TG and a number converter RNU produces the identities of calling circuits in accordance with their pulse position. The call store JSP as well as storing in each row calling party identity, called terminal data, and a program word also stores a class of service code and the identity of the register seized for a call. The magnetic core matrix of JSP has 100 rows and 34 to 48 columns according to exchange requirements. The cycle time of JSP is 100 Ásec. Data concerning a task for processing is stored in input register JEG and control of the highway gates consequent on processing is effected from an output register JAG. Whenever a task is presented for processing the scanner is inhibited until the store JSP has gone through the necessary number of cycles to complete the task. A logic circuit PST has a timing circuit PSG for counting off program cycles and a store PSP which records the program word indicating the point to which a call sequence has progressed. Call origination.-The open to closed loop transition detected by ZA seizes a register RG and JEG is given the calling line and register identities along with class-of-service code. Call store JSP is run through row by row to see if either the calling line or register identity is present and since neither will be present for an origination a free row of JSP is seized and given the data in JEG. A check is made to see if the data read into JSP is the same as that in JEG before scanning is resumed and dial tone is connected in accordance with instructions relayed over JAG.  Dialling.-Registers RG are connected to calling lines over the highway SA and on receipt of each digit demand the service of the processor to transfer the digit to the associated call store. When JEG is free it selects the first register demanding service and locates the associated call store by matching the register identity with that recorded in the call store. The digit is written into the call store, the program word is advanced, the data in JEG being checked with what has been written in JSP before scanning is resumed and, if necessary, dial tone is disconnected. When the last digit is received, as indicated by the advance of the program word in the call store, transfer of the digit is effected and checked and the called number is transferred from the call store to a location SoSp in the logic circuit PST. From its position in SoSp the called identity is used for a free/busy test in which a search is made for that identity in JSP where, if busy, it will be recorded as a calling or a called identity. At the end of these processing cycles either busy tone is connected or the connection is set up over the highway to connect ringing tone. Reply.-The called party identity having been returned to JSP, the off-hook condition of the called party causes his identity to be put in JEG and a match will be found with his identity in the call store in association with the appropriate program word. The program word is advanced to the conversation mode and remains so for as long as the call persists. Release.-The transistion from closed to open of the first extension to release causes release register AS1-RG to be seized, the extension identity to be placed in JEG and a search for its position in a call store as either calling or called extension is undertaken. On locating the associated call store the identity of the released extension is deleted and the program word is advanced to indicate that the second extension is still to release and to connect busy tone to that extension. When the second extension releases the call store is cleared by a similar searching operation. Exchange line call.-Internal calls are prefixed with digit 2 or 7, outgoing exchange calls are obtained by dialling 0 in response to which the processor tests for class-of-service before connecting a free exchange line circuit over which the extension receives exchange dial tone. Further digits dialled over the exchange line can be monitored by the call store in association with class-of-service to bar calls dialled outside the local area. Enquiry call and transfer.-When engaged in a call over an outside-line an extension may hold the line and dial another extension by pressing an earth key. The processor examines class-ofservice to see if the facility is permitted and, if so, marks the class-of-service code in the call store to indicate that the exchange line is being held pending enquiry. A free call store is allotted the extension and this is used as for an internal call to set up the enquiry path. To restore the connection to the exchange line the extension earth key is pressed again. To transfer the exchange line to the second extension the first extension hangs up. The class-of-service of the second extension is examined, in case it is barred access to outside lines, and if there is no bar the call particulars in the call store used for the enquiry path are transferred to the call store used for the original exchange line call. Incoming calls.-A call origination detected in an exchange line circuit is treated in the same fashion as internal call or is routed to an operator according to a code written into the classof-service portion of the call store. This provides for direct dialling into the palex or direct connection to an operator who sets up a connection to a wanted extension in the manner of an enquiry call.