Patent GB-1279330-A (GB)
Title: Switching system controlled by a stored program
Inventor: KANEYASU HIROSHI
IPC: H04Q3/545
Filed: 1970-07-07
Abstract: 1279330 Automatic exchange systems NIPPON ELECTRIC CO Ltd 7 July 1970 [16 July 1969] 32838/70 Heading H4K [Also in Division G4] In a telephone exchange of the stored program type the peripheral devices to be interconnected transmit signals indicative of their states to call state registers which normally store these states and which can be set when idle to indicate busy condition by an electronic common control equipment to reserve that peripheral for use by that common control. The system described employs two stored program processors which share the function of common control. During normal working one processor operates in a service mode monitoring lines and trunks for switching signals, updating registers and senders, effecting translations and provisionally selecting speech path elements for use, and in the following mode performs a further test on the busy/free states of these elements and (if all prove free) effects establishment of the connection. The second processor normally works simultaneously but in the other mode, the two modes take about the same time to perform. If one processor finishes first it awaits completion of operations of the other processor. Each processor includes a number of timers which time out if particular operations cannot be completed in predetermined times. Some faults cause trouble signals to be produced alerting maintenance staff and causing that processor to withdraw from operation. As shown the two processors 150 and 150<SP>1</SP> are identical and share a common magnetic drum store 140 and other common equipment shown in Fig. 1A. The magnetic drum includes a number of read only program tracks 143 each of which contain a plurality of program commands. Some commands are micro-commands and others macrocommands. The macro-commands are multiple instruction commands controlling such functions as line circuit request detection, trunk selection, link matching, office code translation, directory number translation and busy test, register track scanning and register timing. A macrocommand to be processed is entered in a command track 144. This command track has read and write heads positioned # of a drum revolution apart so that the individual instructions of the macro-command are as they are read out during processing re-written # of a drum revolution ahead such that the complete macrocommand is available each # of a drum revolution. With the exception of the register track 149 which is similarly arranged and clock track 141, 142 all other tracks store equipment state data in locations having addresses corresponding to equipment numbers. A macro-command includes the address of the next macrocommand to be processed and during the processing of a macro-command the next macro-command is selected and entered in a second command track so as to be available when required, the command tracks being selected alternately as successive track change instructions are encountered. The processing of the individual instructions within a macrocommand is controlled by a wired logic 170 individual to the macro-command and selected by a control 171. The wired logics and controls Figs. 36 to 52 (not shown), vary in complexity from simple arrangements of bi-stables and gates to complex networks such as the directory number translator and busy test logic which includes receives to receive digits in either dial pulse or multi-frequency form and to convert them to common logic signals and a code converter which receives the first digit and depending on this digit produces a binary coded indication of the number of digits yet to be received. A bank of registers 161 to 167 is used as a quick access store for the wired logics during the processing of each macro-command. Data is transferred from the drum as it is scanned to the registers for subsequent use when required. Each processor during the service mode selects and reserves the path to be used including trunks &c. in accordance with stored data as to the states of the path elements. This data is derived from the indications given by the call state registers. During the other (path establishing) mode a test circuit 199 in the processor tests the busy/idle states of the selected path elements by sampling the speech path through these elements. If due to an error or a change in state of an element since its states was last stored a selected element proves busy, the reservation signals in the call state elements are cancelled and a fresh selection is effected during the next service mode. The call state registers (Figs. 19 to 27, not shown) are wired logics. All include a bi-stable which is reset when the associated speech path element is free and not reserved. At least in the case of those call state registers associated with speech path elements which can be taken into use by both a processor and signals arriving over the speech path the bistable is set when reserved and is reset when in use. Each call state register includes one or more converters (Figs. 18A to 18C, not shown) which are each connected to a speech or supervision wire. The converters used are of three different types giving a "0" or "1" output under different input signals classified as negative, ground, positive, and earth. One converter responds when the wire is taken into use setting the busy/idle bi-stable to busy if this indicates idle or resetting it idle if set to reserved (busy) state and in the latter case taking over the function of sending a busy signal to the common control. Additional converters and bi-stables are provided in some-call state circuits and detect and store additional conditions such as "dial tone returned". In one call state circuit associated a subscriber line the outputs of two converters are also combined to detect dial pulse, the detected pulses increment a first counter and reset a second counter incremented by clock pulses, during an interdigit pause the second counter reaches a preset count and requests the common control to transfer the digit accumulated in the first counter in coded form to the drum register track. Another call state circuit (associated with an outgoing trunk) receives coded digit signals from the drum, converts them to 16's complement form, enters them in a counter and causes them to be counted out over the trunk. Other call state circuits (Figs. 24 and 27, not shown) couple trunks to and from which multi-frequency signals are received to the drum register track. Switching network, path selection.-The switching network or main link 108 comprises four stages of switching matrices. In the preferred form the switch matrices are ferreed matrices. Three conductor paths (four in the case of certain trunks) are employed and supervision of established path is effected in known manner using the third (or third and fourth) conductor by peripheral devices. Each matrix is an 8 x 8 crosspoint array except for those of the first stage which are 32 x 8 arrays (built up from four 8 x 8 arrays) to provide a 4 to 1 concentration ratio. The b links between the second and third stages are shown diagrammatically at 121 in the figure and are regarded as links capable of connecting any one of a group of inlets (subscribers 101) to any one of a group of outlets trunks 111 to 119). The magnetic drum stores in the link track 147 at addresses corresponding to the equipment numbers of the "b" links the group addresses of the groups of inlets and outlets. During a route search parts of the addresses of the line and trunk to be connected are compared with the stored link data and for each suitable link found the state of the call state register of that link is determined, if free it is reserved and the states of the call state registers of the "a" and "C" links are investigated and these are reserved if free. This process is repeated with cancellation of any reserved equipment until a complete through path is found or all links have been investigated in which case the calling line is connected to a tone trunk, or an alternative trunk is selected and a further attempt is made. In the ease of a local call a local connection trunk 111 having two appearances on the network 108 must be used. Such a trunk has two equipment numbers one for each end and two paths are selected through the network, firstly between the calling line and one end of the trunk and subsequently between the called line and the other end. For certain types of call, such as incoming trunk calls, two different types of trunks must be connected together e.g. a multifrequency incoming trunk call arriving on an incoming trunk MFICT must be connected through a register trunk MFIRT. This is effected by an auxiliary switching network 120 comprising two stages of formed switching matrices and controlled by a network common circuit 126. Cross-bar switches could be used instead of ferreed matrices.