Patent GB-946076-A (GB)
Title: Improvements in or relating to automatic telephone systems
IPC: H04Q3/00
Filed: 1960-05-13
Abstract: 946,076. Automatic exchange switches. TELEFONAKTIEBOLAGET L. M. ERICSSON. May 13, 1960 [May 15, 1959], No. 17005/60. Heading H4K. A call to a wanted subscriber is made over one or other of two kinds of relay sets depending on whether a marker finds the wanted line idle or busy. One group of relatively simple relay sets is used for connecting to idle lines while another much smaller group of relay sets is used for connections with busy lines and can supply busy tone, enable calls to a busy line to camp until the line becomes free, and gives an operator facilities for breaking in for trunk offering or testing. Should all the simple relay sets be in use, it is arranged that the busy line relay sets are made available for calls to idle lines. Should a call be attempted to a subscriber already subject to camping or trunk offering, the attempt is forcibly released. Switches.-The exchange to which the invention is applied uses code-bar relay selectors of the kind described in Specification 832,865. These selectors each have ten bridges served by six code bars coincidence of slots in two of which gives access to any one of four row wires and coincidence of slots in the remaining four giving access to any one of thirteen columns. Although four rows and thirteen columns gives a capacity of 52 outlets from the inlet to each bridge only 50, and in one stage 40, of the outlets are used. Having selected an outlet by setting the code bars the bridge magnet appropriate to the inlet is pulsed to mechanically latch the inlet to the wanted row wire and all the contacts of the selected column to all the row wires. The outlets are multipled over the ten bridges of each selector to be accessible to each of 10 inlets. General arrangement of exchange.-As shown in Fig. 1, the exchange has 1000 subscribers such as A and B connected in groups of 50 to the outlets of 20 selectors SLA. The 200 inlets to the SLA selectors are linked with 5 SLB selectors each having 40 outlets such that each SLB selector has two links to each SLA selector. The 50 inlets of the SLB selectors have access to connecting relay sets SNR and are accessible from 5 selectors SLC by way of 5 busy condition relay sets LKR and 45 idle condition relay sets LLR. A call from a subscriber is identified at IDS and with the cooperation of marker SLM connects a free relay set SNR over stages SLA, SLB. An idle register REG is seized over selector RS and marker RSM and in response to dialled digits seizes an identifier IDG, code receiver KMG, and marker GVM to set up a connection over stages GVA, GVB, to stage SLC. From this point an identifier IDC is seized and connects register translator KMS which in response to 2 out of 5 audio frequency codes seizes marker SLM and identifier IDS to test the wanted subscriber's line. If the line is idle, a path is set up over a relay set LLR, if it is busy a path is set up over a relay set LKR. An operator's position is provided with a relay set ULR and a register REG-T. Subscriber's numbering scheme.-The first and last selectors in the SLA stage are shown in Fig. 3 where each contact represents a set of contacts connecting a three-wire line. The selectors are grouped in pairs to embrace 100 subscribers such that columns 1 to 10 take subscribers with units and tens digits 00 to 39 and 50 to 89 and columns 11, 12 and 13 take subscribers with digits 40 to 49 and 90 to 99 in the odd and even numbered selectors of a pair respectively. Thus, a hundreds digit indicates the pair of SLA selectors having the wanted outlet while the tens and units digits differentiate between the pair by selecting one out of 8 relays associated with the rows and one out of 13 relays associated with each column. Register translator KMS.-In Figs. 4, 5, 6 and 7 the exchange is illustrated in detail with the exception of the group selector stages GVA, GVB, and it is assumed that a call has been set up as far as stage SLC from which point it is immaterial whether the call is local or incoming to the exchange. Shown to the right of Fig. 7 a register REG has been seized by operation of relay S3 in either a relay set SNR or an operator's position ULR, and the inlet of stage SLC taken into use is identified in IDC, Fig. 7, where an A relay marks the SLC selector and a B relay marks the bridge. A relay such as A101 operates to connect code-bar magnets CG1, CG2, C1, C2, C4, C8, and bridge magnets such as VO, as well as connecting the line over contacts of the operated B relay and an operated relay BA to an audio-frequency receiver TM controlling hundreds, tens, and units relays NS, ND and NU, in the register translator KMS of Fig. 6. Audio frequencies received by TM operate two of the five units relays NU followed by the corresponding pair of hundreds relays NS which lock-up to relay BB in IDC and operate relay BP which operates BG and holds up for so long as audio-frequency is received by TM. In this condition frequencies #2 and #3 are returned to register REG which transmits the second digit. Before receipt of a second digit relays BP and NU release bringing up T1 to release BG and connect up the tens relays ND which lock-up in train with NU relays in response to the second digit, BP and BG reoperating and releasing to operate T2 and call for the third digit which is registered on the relays NU. When the relays NU lock-up, relay AKM responds to extend positive potential over the code relay contacts to identifier IDS of stage SLA, Fig. 4, where one of the relays 50 to 59 responds to the hundreds marking and selects the eight A relays associated with rows of the wanted pair of SLA selectors, and one of the eight A relays and one of thirteen B relays being energized in response to tens and units markings to select the wanted row, column and selector. Testing the subscriber's line.-Operation of an A relay in IDS, Fig. 4, connects the code and bridge magnets by operating a relay such as VMA1 and operates an associated relay such as A101 connecting the subscriber's line to a busy test. With a B relay operated the normally energized relay BA falls back and relay BB responds slowly. Relay TK1 responds before BB and releases with BB momentarily offering the line to relay LL. If the line is idle the c-wire is negative and LL responds. If the line is busy it is positive and LL stays back, TK2 following TK1 so that the line is offered to relay LU which responds to signal the busy condition. Before TK1 and TK2 fall back to connect LU a relay TB is connected to the line but only responds if the line is already subject to camping or trunk offering when it is marked positive over two parallel paths and has low resistance. Establishment of connection: subscriber's line idle.-In the marker SLM, Fig. 5, a relay such as VMA1 of identifier IDS connects test wires from the bridge magnets to relays 1T0 to 1T9 which responds if a bridge is idle and prepare paths to connecting relays VMB1 to VMB5 of selector SLB. If the called subscriber is idle relay LL responds in IDS and connects negative polarity over all free relay sets LLR to operate the earliest relay in the chain F1 to F5. The operated F relay extends the markings from a set of ten relay sets LLR to a relay chain G0 to G9. In register-translator KMS, Fig. 6, relay BP is energized and reverts frequencies f2, f3 to register REG. With an F relay operated normally energized relay FA falls back and relay FB responds connecting operating poten. tial to the G chain in which the earliest marked relay operates to seize a relay set LLR. With one F and one G relay operated a particular connecting relay such as VMB1 is energized to seize the selector SLB to which the chosen relay set LLR has access. As each SLB selector has two links to each SLA selector it is necessary to discriminate between them and for this purpose the test relays 1T0 to 1T9 are paired and associated with paired subsidiary test relays 2T0 to 2T9 which for a given F relay choose the first idle one of the two bridges in the wanted selector SLA. Depending on which subsidiary test relay operates a relay TU or TJ operates to vary the code-marking extending from the A relay of IDS to the code-magnets of SLB. The code-magnets of stage SLC are marked over contacts of the relays F and G in marker SLM. When relay GA operates in response to any G relay current is supplied to operate the code magnets of all three stages SLA, SLB, SLC. In marker SLM, relay US follows GA and interacts once with relay K2 to pulse the selected bridge magnets in stages SLA, SLB, causing the contacts to make and lock-up mechanically and releasing the code-magnets. In the identifier IDC of Fig. 7 relay VK1 follows relay US and interacts with VK1 to pulse the chosen bridge magnet in stage SLC and to operate busy relay F0 which connects the established path to relay set SNR or operator's position ULR. With F0 operated the identifiers and markers IDC, KMS, SLM, IDS release and the c-wire over stage SLC is marked positive operating relay L1 in relay set LLR and energizing cut-off relay BR to busy the subscriber. Ringing is now fed over relay L2 which trips when subscriber replies so that feed relay L4 is connected up. Called subscriber busy.-In this event, as described above, relay LU responds in identifier IDS and extends negative marking overall free LKR relay sets, one of which is seized and a connection is set up substantially as with an LLR relay set. In the register translator KMS, Fig. 6, relay BRK is energized and reverts frequencies #1, f2 to register REG. In relay set LKR relay L3 operates when busy relay F0 energizes and the calling line is terminated on L5 from which busy tone is sent. Relay L1 in LKR only operates if the called subscriber hangs up when L2 is connected to effect ringing whereafter L2 and L4 respond on reply. Relay L1 does not energize sooner, since although it is connected in parallel with a similar relay, the current, while sufficient to hold the already energized