Patent GB-957194-A (GB)
Title: Improvements in or relating to communication switching networks
IPC: H04Q3/00
Filed: 1960-11-15
Abstract: 957,194. Electric selectors. WESTERN ELECTRIC CO. Inc. Nov. 15, 1960 [Dec. 4, 1959], No. 39192/60. Heading H1L. [Also in Divisions H3 and H4] A switching matrix uses relays which are operated or released depending on the remanent state of a magnetic member, the operated state of a relay being detected by reversing the state of the magnetic member and restoring the state before the relay contacts release and without releasing them. Relays suited to such operation are described in Specifications 870,906, 941,653 and 941,654. One such relay is shown in Fig. 1 and comprises soft magnetic reed contacts controlled by flux drawn from the soft polepieces 4 across the ends of the legs 12 and 13 of remanent magnetic material. When the legs are magnetized as shown in Fig. 2A, the reeds draw flux and the contacts close. When leg 13 is reversed as shown in Fig. 2B, there is no potential across the ends of the reeds and the contacts release. Whereas the leg 13 may be switched within a few microseconds the mechanical response of the reeds occupies a few milliseconds which allows leg 13 to be reversed and restored without releasing the contacts. By this means busy connections may be detected by reading out the legs 13. To operate the relay half-strength pulses are applied to windings 16 and 17 on leg 13, the pulse in winding 17 being applied to a winding 19 on leg 12 to prevent partial reversing of the permanently held remanent state of leg 12. To release the relay a full-strength pulse is applied to winding 16 on leg 13. To interrogate the relay it is released over winding 16 and the read-out pulse generated in winding 18 on leg 12, if the relay is operated, causes re-operation over windings 16 and 17. Since winding 17 is idle during interrogation it may be used as the read-out winding in place of winding 18. The symbolism used to represent the relays is shown in Fig. 4. where they are employed in an nXn matrix where the reeds 15 are connected in columns 41a to 41n and the reeds 14 are connected in rows 42a to 42n. The windings 16 are connected as row windings while the windings 17 and 19 are connected as column windings 44a to 44n and the windings 18 are connected as second column windings 58a to 58n. Control circuiting is shown whereby a connection can be established from a given one of the column wires 41a to 41n to the first free one of the row wires 42a to 42n. Access to the matrix is made over the row control circuits 45, from which the rows are connected sequentially by stepping circuit 56 controlling gates 59a to 59n pulses being generated in source 51, and also by means of column control circuits 46 in which the columns are selectively connected over gates 61a to 61n under the management of a common control circuit 71 or from the column read-out windings 58a to 58n pulses being generated in source 52. Release of an operated path is governed by the circuit 88. Apprised of a given inlet to the matrix, say column wire 41a, the common control circuit sets the row control circuits in search of an idle row of relays by triggering a full-strength negative reset pulse from source 51 which reads out the first row marked by stepping circuit 56 made active by the start pulse over diode 72. If a relay in the first row is operated its leg 13 is reversed and the read-out pulse in winding 18 over an OR gate 50 and normally open inhibition gate 70 triggers the pulse sources 51 and 52 to produce half-strength pulses (set pulses) on the row wire 41a and the column wire marked amongst gates 61a to 61n by its associated active read-out wire. Leg 13 of the operated relay is thereby restored and its contacts stay operated. As well as triggering the set pulses the read-out pulse, over a normally open inhibition gate 73 and delay circuit 60, advances the stepping circuit 56 to connect the second row for interrogation and triggers a reset pulse from source 51. Interrogation continues until a row is connected from which no read-out pulse is generated. In the absence of a read-out pulse an inhibition gate 76 in the row control circuits 46 is enabled and gives passage to the reset pulse, delayed and inverted over circuits 74, 75, which signals the common control 71 to indicate connection and effects connection over diode 77 to trigger set pulses. The appropriate column is marked over gate 61a by the common control 71 corresponding to the given inlet 41a. By inhibiting gate 73 the reset pulse prevents a further advance of the stepping circuit 56. Common control 71 stores the row and column co-ordinates of the connection so that when release is initiated the identity of the row is set up in a translator 81 from a storage matrix 78, a pulse source 79 advances the stepping circuit 56 over the rows until its output matches that of the translator when the matching circuit 82 produces a pulse to disconnect the stepping pulses from 79 and to trigger a reset pulse from source 51 while inhibiting gate 70 in detector 47 to prevent restoration of the relay as with interrogation. An exchange employing the matrix of Fig. 4 as switches is shown in Fig. 5. The relays employed do not, however, have the read-out windings 18, the windings 17 being used for this purpose. The switch contacts are represented by crosses. The inlets, such as 41a to 41n, of a first stage of matrices 40a to 40m are connected to subscribers. The outlets of each first stage matrix are distributed over corresponding inlets in each one of the second stage matrices 40n to 40z the outlets of which are connected to a junctor 90. The exchange is shown with two identical halves to left and right of the junctor, one half being used to connect the calling line to the junctor and the other half being used to connect the called line. Corresponding columns of the matrices in the same stage are controlled in common from a circuit 46 while the rows of each matrix are controlled individually from a circuit 45. When possessed of the calling and called party identities the common control sets off a search in the subscribers' matrices for idle rows corresponding to idle links to the second stages, the search employing detectors 47, as in Fig. 4. When an idle link is found the cross-point relay is operated and the corresponding matrix in the second stage is subjected to a search for a free outlet to the junctor. Should this matrix be fully employed the operated relay connecting the link in the first stage matrix is released by means of a circuit 88 and a search for a further idle row is made to connect with another second stage matrix, interrogation of the matrices continuing in this way until an idle path to the junctor from both the calling and called subscribers is made and a match in the junctor is found. If the subscribers can be offered no match in the junctor, the caller is connected to busy tone. Release of a connection is initiated by the common control 71 in response to an on-hook condition, the control 71 identifying the relays in the path for restoration using the circuits 88.