Patent GB-1027317-A (GB)
Title: Improvements in or relating to time-division multiplex communication systems
IPC: H04Q11/04
Filed: 1963-04-18
Abstract: 1,027,317. Automatic exchange systems. SIEMENS & HALSKE A.G. April 18, 1963 [April 19, 1962], No. 16257/63. Heading H4K. In a PBX system in which connections are set up under control of pulses in a recurring series of such pulses, one pulse position being allocated to each connection, arrangements are provided to keep a reserve of pulse positions in order that priority connections, e.g. connections to the main exchange may have a greater probability of being set up. Thus in the case where there are forty exchange lines, five pulse positions are kept free, unless there are less free exchange lines in which case a number of pulse positions equal to the number of free exchange lines is reserved. The invention is described in relation to a system of the type described in Specification 1,027,315 in which a connection is set up over a T.O.M. highway in one of a hundred pulse positions allocated at the initiation of the call, the lines being scanned by a scanner which steps once per 100 pulse positions unless, as a result of indications received an operation has to be performed in which case the scanning is arrested. The scanner consists of a counter which not only emits time equipment numbers but also operates a translator which emits inter alia the class (e.g. exchange line) of the line concerned. The gates connecting the line circuits to the multiplex highways are controlled by two circulating stores, one for the calling lines and the other for the called lines, in which the identities of the lines are stored in the pulse positions allotted to the respective calls. The calling line store is arranged to provide to a control circuit pulses in all free time positions. First method. Fig. 3 (not shown). A special store is provided in which the identity of a calling incoming exchange line is stored in the pulse position allocated to the call. In the control circuit, during any scanning interval of 100 Ás. free pulses are received and inserted in a 100 Ás. delay line. During the same 100 Ásec. period a counter Za 2  (not shown), is stepped by pulse received from the special store to a position indicative of the number of engaged exchange lines. This counter is fed during the next 100Ás. with the stored free pulses which thereupon step the counter to forty after which it opens a gate to permit the emission of subsequent stored free pulses the first of which is then taken to set up the connection. Thus, if 38 exchange lines are engaged the counter is set to 38. The first two free pulses step the counter to 40 (thus reserving two free pulse positions) and the remainder are then emitted for selection. A second counter Za 1  is also provided which is stepped by the stored free pulses and operates after it has received five free pulses to open the above-mentioned gate to emit free pulses for selection. Thus no more than five pulses can be reserved. When the incoming line is an exchange line a class of service signal recovered from the translator opens the gate immediately to allow all the stored free pulses to be available for selection. Second method, Fig. 4 (not shown). In this case pulse reservation conditions remain stationary for a complete scanning cycle (100 x 100 Ás.). During a scanning cycle when each line is scanned, if the line is busy and the translator class of service indicates an exchange line a pulse is inserted in a temporary store. Then during the next cycle the stored pulses are connected into a counter Za 4  and if the count exceeds 35 any remaining pulses are fed into a further counter Za 3 . When a connection is to be set up stored free pulses are then fed to Za 3  which when the count reaches five opens a gate to pass free pulses for selection. Thus as before, a number of free pulses equal to the number of exchange lines is reserved subject to a limit of five. Third method, Fig. 5 (not shown). In this case operation is similar to the second method except that a counter Za 6  receives a count of the number of free exchange lines. If this is less than five it transfers the count to a second counter Za 5 . If the count is more than five the counter Za 5  is set to five. Counter Za 5  is then stepped backwards by free stored pulses and when the count equals zero it opens a gate to pass free stored pulses for selection.