Patent GB-1346205-A (GB)
Title: Communication switching system
IPC: H04L12/50
Filed: 1971-08-13
Abstract: 1346205 Automatic exchange systems NIPPON TELEGRAPH & TELEPHONE PUBLIC CORP NIPPON ELECTRIC CO Ltd HITACHI Ltd OKI ELECTRIC INDUSTRY CO Ltd and FUJITSU Ltd 13 Aug 1971 [15 Aug 1970] 38106/71 Heading H4K [Also in Division G4] A stored programme controlled exchange utilizes duplicated magnetic drums for storing basic programme data that does not require frequent use and high speed, e.g. core storage, for storing data that is required frequently and also programme for retrieving data from the drums. The cost saving outweighs any marginal disadvantage in terms of processing time but even this is minimized by ensuring that data required from a drum is extracted from that drum which is currently exhibiting the shortest access time (this reduces the average access time from 10 ms to 6À7 ms). The exchange switching network (Fig. 1) comprises two wire or four wire latching, crossbar switches arranged in line link and trunk link frames having subscriber lines and trunks terminated thereon respectively although some trunks also have appearances on the line-link frame. The trunk terminating circuits incorporate latching relays for supervision and like purposes. All the peripheral circuits are controlled by interface unit SPCF which in effect translates control orders and data emanating from the central control CPF into signals that are readily utilizable by the peripherals i.e. they consist of a register device and a relay driver device, and vice versa. Within SPCF most of the signal distributers are duplicated so that either may carry the full load in the event of fault conditions. One interesting point is that the distributer SC1 for conveying trunk link frame switching orders may be replaced by the distributer SC0 which normally conveys line link frame commands or by a standby distributer ST-SC. Direct intervention in exchange control may be effected by duplicated typewriter units TYP. Binary addressing of SPCF units is utilized. Central control comprises two processors CC, one of which operates on line while the other is in standby mode although each processes the same data simultaneously, in step working being  achieved by match circuits. Each processor can be controlled manually by circuits CNS. The usual logic functions associated with processors active on real time operations are provided by the processors. As already indicated memory comprises two slow speed (10 msec access time) drum units MDU each of which can be addressed by either processor via either interface unit MDCH. Each drum has 1023 data tracks carrying 2048 words of 16 bits each and two tracks carrying synch and clock pulses respectively. High speed memory in the form of core stores TM is provided in a quantity appropriate to the exchange size. Each store TM is connected by independent buses to the processors. In the event of a fault, a standby store ST-TM or a drum unit is substituted for the faulty store, duplication of data in stores TM not otherwise being provided for. Beyond stating that programme originally stored on the drum may be transferred to a core store during exchange growth (the new address of the programme replacing the first word of the programme on the drum) and a reference to clock level programme (see below) no specific details of the type of programme deemed suitable for storage in a store as opposed to on a drum are given. Emergency action arises in the event that a fault detecting timer in CC overflows, if there is a power loss or clock failure in CC, if there is mismatch between the two processors, or, if a timer in the emergency action sequencer itself times out following the start of an emergency procedure. The action consists in establishing a fault free assembly of the various processing subsystems. A so-called clock level programme viz line or trunk scanning, digit reception, which is normally accommodated in the spare store ST-TM, is transferred to a drum during an emergency from where it can be transferred to another store TM having an area specifically reserved for accommodating data arising during a fault correcting sequence. The details of the programme transfers arising when a CC, a TM, an MDCH or an MDU goes faulty as opposed to faults in a peripheral or buffer SPCF) are outlined. Exchange operation.-A calling line brings up line relay L (Fig. 9) thereby marking a particular crosspoint in the 16 x 16 diode matrix DM. A column relay X therefore comes up so as to pull an XK relay whence it is confirmed that only one X relay is operative. XK holds the operative X relay and permits a row relay Y to come up. YK then confirms that only one Y relay has operated and signals the central control over (200 msec) scanner lead SR of the existence of a calling line whose identity is provided as 3/6 markings on leads X, Y emanating from an X, Y relay contact tree code converter CNV. When central control has absorbed the information and set up a register connection it releases the relays in the call detector by bringing up DIS which is itself released once it is confirmed that X, Y, XK, YK have fallen back. Although not particularly apparent from the drawings, the purpose of the XK, YK relays is to ensure that only one calling line at a time is processed. Central control determines class of service viz exclusive line, party line, public box, dial pulse, multi-frequency push-button, or calls barred, from the drum store and causes a connection to a suitable register attached to the trunk link frame to be set up utilizing its memory map for determining a free path and the interface SPCF for conveying its commands. Dial tone is reverted. The register is scanned every 10 msecs until the call details are fully known whereupon CC causes busy or ringing tone to be reverted as appropriate. The network paths during the establishment are best appreciated from Fig. 11. Note that the final path is reserved but not implemented during the ringing phase. The feed bridge or supervisory junctor IOT is monitored at 100 msec intervals to detect hang up by either party. If one party remains off hook his connection to the junctor is forcibly released. Interrupt request masking and address translation (for addressing purposes using logical program addresses) are referred to.