1,003,404. Automatic exchange systems AUTOMATIC TELEPHONE & ELECTRIC CO. Ltd. April 23, 1964 [May 9, 1963], No. 18464/63. Heading H4K. A register controlled automatic exchange, Fig. 1, in which a router gives access to outgoing junction relay sets AOGRS, BOGRS, or BWRS, for transit calls appearing at relay circuits IRS or BWRS, the routes of access being over one set of paths if a marker LMX is employed and a second set of paths if a marker LMY is employed, the markers dealing with calls one at a time and marking a selected group of outgoing relay sets according to the required direction, and the marked relay sets responding by indicating at least one idle set over which a route may be established. An arrangement is provided whereby test calls may be set up from a maintenance control board MCB, the outgoing relay set over which the test call is to be made being conditioned from the test board to mark itself idle only to the test call. The exchange comprises four first-stage cross-bar routers 1SR(1) to 1SR(4) each of which serves 50 bothway interexchange relay sets BWRS and 50 incoming inter-exchange relay sets IRS. The relay sets command register senders AREG, BREG, with route controllers RCX and RCY having access to common coding devices ICX and ICY. In each first stage router such as 1SR(1) the relay sets are connected individually to the bridge inlets of 10 cross-bar switches each switch having 10 inlets and two groups of 10 outlets giving access to the 10 switches RSBX or the 10 switches RSBY, respectively. The outlets of the switches RSBX, RSBY, are similarly divided into X and Y groups with access over either group to the outgoing relay sets AOGRS, BOGRS, by way of the connecting field, TCF, and with full access over either group to the bothway relay sets BWRS by way of connecting field TCF, two second stage cross-bar routers 2SR(1) and 2SR(2), and back by way of field TCF. The provision of direct access to the outgoing relay sets AOGRS, BOGRS for the first stage routers 1SR(1) to 1SR(2) is possible because the marker LMX or LMY, depending on whether an X route or Y route is sought, extends a marking to all relay sets in the wanted direction and all such free relay sets are conditioned thereby to return marks into the routes whereby a route is set up according to the selfsteering principle. With the bothway relay sets BWRS the return of marks from all free sets is deemed impracticable and only one free set is conditioned to return a mark and a second stage router, such as 2SR(1), is needed to establish a route to the calling path. Whereas full access is given to the bothway relay sets from the first stage routers, full access to the relay sets AOGRS, BOGRS can only be provided for groups of ten or less. The markers LMX, LMY are included in the second stage routers and are seized by the route controllers RCX, RCY, and on instruction cause the operation of a relay in the connecting field TCF to provide a path between the outgoing relay sets and the relevant X or Y path of the calling first stage router. The maintenance control board MCB has access to the originating side of any relay set BWRS or IRS. The board also has keys for each of the relay sets BWRS, AOGRS and BOGRS, by means of which and over paths TC a relay can be operated in any of these sets to busy it out to normal traffic but allow its seizure to a call from the board MCB. As an alternative to selection by individual keys the relay sets may have two position plugs or test links to condition them for seizure by the control board. However conditioned the relay set is connected to the board by way of a free relay set BWRS or IRS and the normal routing code preceded by eleven consecutive loop disconnections or its equivalent in 2-out-of-6 code. In response to this prefix the marker LMX or LMY seized for the connection establishes a special test for the relay set precondition from the control board. Should the wanted relay set be busy it is not disturbed until it falls free. Detailed circuits.-In Figs. 2, 3 and 4, the bottom portions of the drawings show the marker LMX and the upper portion of Fig. 2 shows the connecting relays in the connecting field TCF. In the marker a relay CA is normally operated in a chain provided by relays IDA to 4DA. Relay CA holds relay KA operated to connect control leads MD1 to MD4 from the router control of each first stage router. Supposing a call originates with first stage router 1SR(1) then control RCX marks lead MD1 to operate 1DA which locks out the other relays in the chain and continues to support relay CA and consequently KA. A contact of 1DA also connects up relay 11RX in the connecting field so that the outlets of RSBX in the first stage router 1SR(1) are connected by way of 100 contacts to the second stage router 2SR(1) and to the outgoing relay sets AOGRS, BOGRS. Routing relays 11BX to 41RX control the X routes from the first stage routers in the connection field, routing relays 11RY to 41RY control the Y routes. A further eight such relays is necessary to provide X and Y routes to the second stage router 2RS(2). The marker has 14 group relays GA to GP selectively operated from the controller RCX to mark any required group of outgoing relay sets. The upper portion of Fig. 3 shows a fraction of a bothway relay set BWRSF arranged to be last choice in a chain with another such relay set BWRSL, Figs. 3 and 4, as first choice. Contacts tx1 of test relays TX in earth relay set are connected in chain to an earth provided by relay ECM which, with an alarm circuit relay MP, operates on seizure of the marker. If a relay set BWRS is busy contacts on1 are open so that marks extended to the group over individual leads MX from its group relay GA do not find a path to test relay TX. The idle relay set closest to the earth supplied by relay ECM, as shown BWRSF, Fig. 3, energizes its test relay TX which holds up over contacts tx1 and in doing so prevents the remaining idle rest relays in the chain from locking up. A relay MG energizes in the holding circuit of TX and together they extend earth over the lead M(X) to mark the circuit for connection by way of switch 2RSAX in the second stage router. Contacts of TX also isolate the test relay TY in the relay set to prevent seizure for a Y-route from marker LMY. Should both markers compete for the same idle relay set the test relay TX is given priority. Test relays TY are connected in a chain circuit in the same way as relays TX but in order to equalize use of the sets the order of priority in the chain is reversed relative to relays TX. Should a relay TY be energized during establishment of a Y-route, the relay TX is isolated. When a route is finally connected a relay K responds and relay ON, not shown, operates contacts on1 on2, to busy the relay set to both X and Y-routes. The group marking is withdrawn with the release of relay GA and TX falls back consequent on the release of the marker from RCX. Release of relay 1DA also releases MP and ECM so that guard relay MRG releases after a delay. A contact of MRG in the chain 1DA to 4DA holds back to deny access to the marker for a guard period after which the normal near earth potential is extended to the leads MD1 to MD4. If all relay sets of a group are busy a relay ALB, normally held back from operation by a contact of an energized test relay TX, energizes and after the slow release of MP a signal is returned to the controller RCX to indicate that no junction is available. Meter leads ABM to PBM are also connected up by group relay contacts to accumulate statistics for all trunks busy conditions. If the control board wants to test a particular relay set, such as BWRSF, it operates a key KTCF to energize relay TTC in the set. Contacts of TTC switch the test relays TX, TY from their normal group marking paths to paths marked from relay TPA in the marker. Relay TPA is operated from the controller, such as RCX, in response to the special prefix dialled from the control board and only that relay set conditioned by its relay TTC can respond. The relay set can be similarly conditioned, independently of relay TTC and for access from the control board over an X or a Y-route, by switching links XA-XB, or YA-YB, to YBYC or XB-XC. If a relay set is busy contacts on1 on2, deny access to the board until the set is free. The upper right hand side of Fig. 4 shows a fragment of an outgoing relay set AOGRS which is one of a group marked by group relay GP. Test relays OTX, OTY, of all free relay sets operate in response to the group markings, busy sets being isolated by relays such as KR of which only contacts are shown. Markings are returned to the first stage routers directly from all free relay sets of the group by contacts of the test relays. The relay sets AOGRS otherwise behave in the same way as relay sets BWRS.