Patent GB-1333775-A (GB)
Title: Telecommunication call diversion equipment
IPC: H04Q3/00
Filed: 1970-12-31
Abstract: 1333775 Automatic exchange systems PLESSEY CO Ltd 27 Oct 1971 [31 Dec 1970] 61977/70 Heading H4K In an exchange call diversion facilities are provided with the aid of both-way translators of the type described in Specification 1,311,489. One of the latter is provided for every subscriber having the facility and these are consulted for every call incoming to the exchange so as to discover if the facility is in operation in respect of the special subscribers. Preparing a translator for call diversion.-The privileged subscriber on lifting his handset is identified as described in the aforementioned Specification by means of translator SCA which reverts his identity over bus HO to a calling line identifying register R1 in central control C. He dials a three-digit diversion code followed by a single digit indicative of the line to which calls are to be diverted into e register R2. During a defined time frame the contents of R2 are read out on to bus HI so that, in this case, translator CT responds to the diversion code and the single digit in order to prime one of the row leads (e.g the two leads immediately below rx, ry) pertaining to the designated diversion line say Y. In addition OR gate G8 opens to trigger monostable M which applies a react signal to lead 3. Central control construes the diversion code in R2 and thereby disconnects it from bus HI and connects register R1 in its place. The identity of the caller is thus presented in n out of m code to translators SC1 to SC3. One of the latter, say X, responds and marks its output lead O1 thereby further marking column lead CX of a set of bi-stables B3, B5 reserved for use by the translator SC1. Consequently gates g31, g51  open to reset these bi-stables thereby removing any pre-existing diversion marking. When monostable M relapses gate g32 becomes effective (cx marking and the Y diversion party marking on the lead just below rx) to set bistable B3. Central control times out and applies a restore signal to lead 4 thereby clearing unwanted signals from the system. Cancelling a call diversion.-This follows the above procedure except that the single digit dialled corresponds to a party other than Y. Suppose that this be Z. Then following the end of the reset signal on lead 3, B5 rather than B3 is set. Suppose that the digit be X-corresponding to the caller's own line. In this case, the lead marked by CT (i.e. the lead immediately above rx) is not provided with a bi-stable in the column associated with cx so that when M restores so bi-stables are set and the diversion facility is terminated. Call diversion in operation.-A called subscriber's number stored in register R2 is readout on to bus HI during a first time frame and is entered into a store T. If it is not a diversion number it will be read-out into translator SCA one or more time slots later. However if it is a number subject to diversion and diversion is in operation, read-out is inhibited by gates G3 and the diversion number is inserted in its place. This occurs as follows. In addition to entry into T, the called number is applied to translators SC1-SC3 so that in the case of the number X SC1 responds by marking lead o1 and hence cx. If no bi-stable B3, B5 is set, nothing further happens and the contents of T are readout to SCA. If however B3 say is set, gate g33 opens to mark lead ry. Gate G7 opens to set bistable B7 in central control thus inhibiting (gates G1) further input to store T and also inhibits output from the store by closing gates G3 as well as clearing the store via gate G9. At the same time the mark on ry is conveyed to translator Y which therefore supplies a directory number to bus ho. The number is written into store via gates G2 and is subsequently read-out into translator SCA which thereupon supplies the equipment number of the line to which the call is to be diverted. Armed with this information central control restores the system. Access to the diversion bi-stables may be restricted by means of a device L which serves to prime gates G4-G6 only when a particular digit or digits in a particular position of a number are applied to bus HI. Details of such a device are provided in Fig. 4 (not shown). The array of diversion recording bi-stables may be implemented in integrated circuit MOST technology, Fig. 3 (not shown).