Patent GB-981175-A (GB)
Title: Multiplex switching stage and its associated control circuits
IPC: H04J3/00
Filed: 1962-11-02
Abstract: 981,175. Automatic exchange systems. STANDARD TELEPHONES & CABLES Ltd. Nov. 2, 1962 [Nov. 3, 1961], No. 41612/62. Addition to 972,237. Heading H4K. The time division multiplex exchange system of the parent Specification, in which a plurality of multiplex highways are connectible via a coordinate switch to a further plurality of highways and in which the time slot occupied by a call when passing through the switch is different from either of the time slots used by the call on the highways, is modified so that if no common free time slot between two highways to be connected is available in the switch (i.e. internal blocking) although each of these highways has access to a free time slot in the switch, then the other connections (between other highways) occurring during these last mentioned time slots are rearranged in order to provide a common free time slot for said two highways. Thus a row highway JAE2 (Fig. 2) (abbreviated to Ro, where o = 1 . . . n 1 ) may have access to a free time slot tr in the switch but cannot be connected to a particular column highway JAS3 (Co, where o = 1 . . . n 2 ) at this time because some other row highway (Rn) is already connected to highway Co during this time slot. Similarly the column highway Co (JAS3) has access to another free time slot ty. Consequently it is necessary to transfer the connection between Rn and Co from time slot tx to time slot ty so that time tx becomes free for the connection of Ro and Co. However Rn may already be connected to a column highway Cp during time ty so that it is necessary to arrange for connection Rn Cp to be set up at time tx and this may involve rearranging another connection between a row highway Rv and the highway Cp already in existence at this time. The number of rearrangements is limited by the number of row or column highways (whichever number, n 1  or n 2 , is the smaller) but the mere fact that a row and a column highway each have access to a free time slot means that all the existing connections and the new connection (Ro Co) will be set up after at most n - 1 rearrangements. Setting-up a call.-A calling channel Vs on highway JAS3 brings in a common control and marker circuit (Figs. 8-13, not shown) so that a free channel Ve on a highway JAE2 in the wanted direction can be found, in the same way as is described in the parent Specification. Free time slots through the switch are found by scanning stores 108 and 129 and observing in the marker whether during any time slot there is no channel code stored in these stores, these time slots tx and ty respectively then being marked. The stores 109 of the row highways are successively selected using decoder 497 and each store is then scanned whereby the column highway code stored therein during the time slot tx (free for row highway JAE2) may be compared with the code Co (i.e. JAS3). This continues until the row highway Rn connected to JAS3 at time tx is found. Store 109 of highway Rn is then scanned again in order to discover which (if any) of the column highways, Rn is connected to at time ty, assume this to be Cp. The channels in use on highways Rn and Co during time slots tx and ty are then found and stored in the marker by scanning the corresponding stores 108 and 129. During the next scanning period and at time tx, the code Co in store 109 of Rn is cancelled (decoder 490) and the code Co is written into store 109 of Ro (decoder 497) and the channel codes on highways Rn and Co which were originally stored at time ty are now stored at tx. At time ty the code Co is written into store 109 of Rn and the channel codes on highways Rn and Co which were stored originally at time tx are now stored at ty. During the next scanning period the connection Rn . Cp is maintained via a by-pass circuit (Fig. 12, not shown) connected to conductors 41R and 41C, the codes Rn and Cp which open the relevant gates 488 and 489 being delivered by decoders 498 and 497. In the by-pass circuit there are further stores to which the stores 101 and 102 of highway Rn are connected at time tx and the stores 121 and 122 of Cp are connected at time ty. Connections on a highway Rv which is connected to dp during time slot tx are then similarly rearranged so as to allow connection Rn Cp to be set up through the switch at time tx. When all the connections are set up through the switch i.e. the by-pass circuit is no longer in use, the marker is released. The breaking down of a connection is performed in exactly the same way as in the parent Specification. Specification 960,511 also is referred to. Reference has been directed by the Comptroller to Specification 922,798.