408,261. Automatic exchange systems. TELEPHONAKTIEBOLAGET L. M. ERICSSON, 33, Kungsgatan, Stockholm. Sept. 29, 1932, No. 27110. Convention date, Sept. 29, 1931. [Class 40 (iv).] In a system comprising a number of small automatic exchanges A, B, C, arranged in a chain, auxiliary apparatus TM<1> (termed a " transit set ") at each intermediate exchange in the chain sends back a signal (two impulses) on being taken into use to cause a register M at the originating exchange (A, say) to send out the exchange-designating digits. If these indicate that the wanted exchange has been reached, the transit set causes the call to be extended to a local register M<1> which then sends back a different signal (one impulse) to cause the register M to send out the numerical portion of the wanted number. If the wanted exchange has not been reached, the transit set extends the connection to the next exchange in the chain and the transit set thereat acts in a similar manner, the exchange-designating digits being thus repeatedly sent out as many times as required. The system described includes a manual exchange D at one end of the chain, the operator at which may extend preferred calls, the arrangement being such that ordinary and preferred calls are extended in part over common connecting circuits (FL) and in part over separate connecting circuits (SL2, SL6), particular to the type of call, the selection of the appropriate separate circuit being effected by an additional numerical switching operation under the control of the register M. Local calls within an exchange are made over a non-numerical link SL1, a feed link FL, and a further link SL2 controlled by the register M which for this purpose acts as a marker. Calls from D to A are made over a junction DL, a feed link FL, and a special link SL6 selected and controlled by the register M. Outgoing calls from A to B or C are made over an outgoing link-circuit SL4 and a two-way junction BL which becomes associated non- numerically at its incoming end with the transit set TM<1> if idle. Outgoing calls from D to B or C are similarly extended, but in this case the first digit sent out by the register M consists of two impulses instead of one to indicate to the receiving register-marker that the call is a preferred one. Figs. 2 and 5 show in detail the apparatus for dealing with external calls at the exchanges A and B, respectively, whilst Figs. 3 and 4, which should be arranged below both Fig. 2 and Fig. 5, show the local connecting- apparatus and the register marker at either exchange. Local call within exchange A. Relay RI, Fig. 4, characteristic of a call to be completed locally is energized over banks of registers RE1, RE2, relay RG1 is energized when all the digits have been received, and the establishment of the connection proceeds in a manner substantially identical with that described in Specification 391,445. Call from manual exchange D to exchange A. Relay DLR operating over junction DL connects up magnet IVM to advance switch IV in search of an idle feed-link FL and when relay IVT2 operates, relay IR3 in the register-marker energizes to open the delayed-busy-signal stepping circuit for sequence switch SO1 and to prepare a starting circuit 205 for the start relay UIS of the links SL6. This starting circuit is independent of contacts of relay RL so that the connection is extended to the wanted line independently of its busy or idle condition. Relay IR3 also operates relay IR1, Fig. 3, which in turn operates STR to cut out the automatic ringing. Switches ILV, ISS hunt in succession and when the connection is completed relays UIT2, SBR, SHA, operate, releasing the registermarker, and operating relay DSR to transmit a current-reversal signal over the junction DL. Ringing is effected by the operator operating her dial causing the energization of relays SHB, IR2, the latter applying ringing current. Relay UIB also operates and in turn energizes UIT3 which short-circuits condensers 226, 227, these being provided to permit the operator to communicate with a busy party. When the called subscriber replies, relay SB operates releasing DSR which transmits a second reversal back over the junction. Call from exchange A to exchange B. When the second digit (3 or 4) has been dialled, relay RG2 operates completing circuit 54 for relay UFR1, Fig. 2, which closes a starting circuit 55 through relay UFA. Switch UFS hunts for feed link FL marked over circuit 58 by relay RG2, and switch UFV then hunts for an idle junction BL, the group of junctions being marked by relay UFR1 over circuit 60. (In exchange A there is only one outgoing group of junctions, but in exchange B relays UFR1<1>, UFR2<1>, Fig. 5, similarly controlled by the marker in accordance with the hundreds digit dialled, determine whether a junction BL to exchange A or a junction CL to exchange C is to be seized.) Relay UFA is now energized in series with relay MP, Fig. 4, which releases relay RG2. Relay FLR<1>, Fig. 5, energizes over the selected junction, operating relays TA<1>, TH<1>, of idle links SL5<1>. When the calling junction is found, relay TT1<1> operates driving sequence switch SO3<1> to its second position, from which it is driven by interrupter 73 to position 5. In positions 2 and 4 two impulses are transmitted to relay BSR<1> which repeats them back over the junction as current-reversals to operate polarized relay UFP which further repeats them over lead 75 to magnet SOM2, Fig. 4, to drive sequence switch S02 into position 3. Relay MS now operates connecting magnet REM5 in series with relay MR1 which energizes MR2 to transmit an impulse forward over the junction to magnet TRM1<1> of register TR1<1>. Relay MR2 also short-circuits relay MR1 to enable magnet REM5 to operate. In position 2 of register RE5 relay MT operates in circuit 80 over a bank of thousands register RE1 to prevent further impulsing, to advance SO2 to position 4, and to operate MV which causes REM5 to restore to normal. The hundreds digit (3) is then repeated in a similar way to register TR2<1>, Fig. 5, and in position 7 of SO3<1> a circuit 86 is completed for relay BI<1> which causes the junction BL to be extended over the incoming link SL3<1> to a local feed-link FL<1> and a register-marker M<1> in exchange B. When this connection is completed, relay RSR in the register-marker M<1> energizes over lead 98 in series with relay BSR<1> which transmits a further reversal back to exchange A causing switch S02 to move to its sixth position and thence by the operation of relay MB to its normal position. Relay MA now operates to complete a circuit for magnet REM5 and relay MR1 as before and the four recorded digits are successively transferred to marker M<1> by which the connection is completed in the manner already described. Switch S02 then moves to position 5 in which a circuit 108 is completed for relay SHA, Fig. 3, which releases the marker M<1> and switches through to the junction. Call from exchange D to exchange B. The operation is in general similar to that in the preceding paragraph, but since relay IR3 is energized in register-marker M the first digit sent to the marker M<1> consists of two impulses instead of one, and a special link SL6<1> is selected instead of an ordinary link SL2<1> as in the case of a call from D to A. Call to exchange C. The registers TR1<1>, TR2<1>, Fig. 5, complete a circuit for the stepping magnet TVM<1> of switch TV<1> and also mark in the fourth bank of TV<1> a group of contacts CG corresponding to the junctions which lead to exchange C. When an idle junction CL is found, relay TT2<1> operates and completes a loop from polarized relay TP<1> over the junction. Relay TP<1> responds to reversals of current sent from the distant transit set operating relay BSR<1> to transmit similar reversals to the register M. The remaining operations are similar to those already described. The Specification as open to inspection under Sect. 91 states also that the arrangement for extending calls of different kinds partly over common circuits and partly over separate circuits may be applied to systems in which some connections require amplifiers. This subject-matter does not appear in the Specification as accepted.