Patent GB-947767-A (GB)
Title: Improvements in or relating to automatic telephone systems
IPC: H04Q11/04
Filed: 1960-05-02
Abstract: 947,767. Automatic exchange systems. TELEFONAKTIEBOLAGET L. M. ERICSSON. May 2, 1960 [April 30, 1959; Sept. 10, 1959], No. 15382/60. Heading H4K. An automatic exchange receives communication signals from a subscriber in " analogue " form, but sends such signals in " deltamodulated " form, i.e. during a time interval it sends a number of pulses indicative of the change of value of two successive samples of the signal which the subscriber is to receive, the substation equipment containing an integrating circuit for reconstructing the analogue signal from these pulses. A system having main exchanges and concentrators is described. Connections within and between main exchanges are effected on a P.C.M. basis, outgoing circuits from exchanges to subscribers being provided with means for converting to delta code. In connections made via concentrators, the concentrator converts the analogue speech from the subscriber to P.C.M. for onward transmission to the main exchange, and the main exchange transmits delta code to the concentrator for onward transmission to the subscriber. Connections are set up on a " T.A.S.I." basis, i.e. a speech path is only established whilst a subscriber is speaking, each talk spurt over a concentrator-main exchange link being preceded by the identity of the relevant subscriber connected to the concentrator. Subscriber's apparatus.-Incoming deltamodulated signals received over Ab are amplified by the flip-flop B0 and demodulated by the resistance-capacity circuit R 1 , C 4 , and after filtering at F are fed to loud-speaker HT in the case of calling signals, or via an attenuator to receiver TE in the case of speech signals. During reception of incoming signals transistor TB is blocked to prevent the passage of outgoing signals. The latter may be signals from the microphone M, or from the V.F. key-sender KN and pass via filter F, transistor TB, and transformer TR in unmodulated form. Operation of concentrator. Speech signals from main exchange to subscriber.-These are fed in over incoming lines li1 . . . li10 in the form of pulses in phase 1 (each pulse position being divided into three equal phases), and are recorded on a corresponding row of a matrix of cores lim. The rows are read out successively in phase 3 positions 3/1 . . . 3/10. The information received from the junction lines is phase staggered in such a way that the whole number is readable at once. Thus, for row 1, the information is received in the following order of pulse positions 1/2 ... 1/10, 1/1. The first signal of the speech burst is the identity of the subscriber the tens and units digits each being represented in 2-out-of-5 code. Row 1 of the incoming subscriber's identity store Aim for the line li1 being empty at this time, readout of this store at time 2/1 produces no output, whereupon the flip-flop Ail produces a pulse to enable the gates G1 . . . G10 for the next twophase positions. At time 3/1 the subscriber's identity is read out of row 1 of store lim into store 01, Fig. 5, and at time 1/2 this identity is read out of 01 into row 1 of Aim via gate G10. During the cycle just commenced, i.e. 1/2 . . . 1/10, 1/1 speech information is recorded in row 1 of lim. During the next cycle at time 2/1 the subscriber's identity is non-destructively read out of row 1 of Aim to the decoder array 02, from which the subscriber's identity is read out decimally at 3/1 on two groups of 10 leads AbmV to switch one of the 100 cores AbmV indicative of the subscriber's identity. Also at this time subscriber's speech information is read out of store lim into store 01. At time 1/2, AbmV is read out to enable a row of store Abm associated with the subscriber to receive the speech information which is read out of store 01 at this time. During the succeeding cycle 2/2 ... 2/10, 2/1 the speech information is fed out to the subscriber over Ab1 via monostable amplifier AF 1. During subsequent cycles speech information is similarly transmitted. When the speech burst ceases the integrating circuit i1 discharges to open gate ri1 to pass a phase 2 pulse to destroy the subscriber's identity in row 1 of Aim. Speech from subscriber to main exchange.-All subscriber's lines are tested once every 5 cycles defined by pulses p 1 ... p5 to discover any new speech bursts. Two subscribers are tested for each coincidence of one of the p1 . . . p5 pulses and one of the 1 . . . 10 pulses in a cycle, one of the subscribers being tested at phase 1 and the other at phase 3. At each testing instant a transformer such as A049 emits a pulse to condenser C A  in the subscriber's line circuit, which if charged due to subscriber's speech causes transformer TC to emit a pulse whose magnitude depends on that of the speech signal. This pulse is applied to a threshold device Vj, Fig. 3, and if large enough energizes an input to gate GS. Seizure of a fresh junction is arranged through the emission of a pulse on KL of phase 1 or 3. This must not occur if the subscriber has already been allocated a junction. In this case, as will be seen later, pulses of phase 2 are emitted from transformer A049 and these charge condenser Cu which inhibits the transformer Tu from emitting phase 1 or 3 pulses. It is also arranged that if speech is going towards the subscriber the condenser is charged via amplifier AF so that seizure is again inhibited. If, however, KL emits a pulse, GS conducts and writes the subscriber's identity into cores N1 . . . N20 in terms of p1 . . . p5 and cycle pulses 1 . . . 10. Meantime the subscriber's identity store Aum which contains a row for each junction is being scanned by pulses 1 . . . 10 in phase 1 and when an empty row, say the first corresponding to outgoing junction lu1 is found flip-flop Aul emits a pulse which enables gates G11-G20; and at the same time causes G21 to emit a phase 3 pulse which reads out store N1 . . . N20 to a coder 04 whose output consisting of a 2-out-of-5 code for each digit is inserted via amplifiers F11 . . . F20 into the row of Aum which has just been indicated as free. This number is also written into the corresponding row of store lum at this time. During the succeeding cycle the row is read out to line lu1 the reading out pulses being so applied that the left-hand core is always read first, i.e. for row 1, the left-hand core is read out at instant 1/2. At the next instant 1/1 row 1 of Aum is read out and recorded in decoder 03. At instant 2/1 the decoded number is read out in decimal form on two of twenty leads AvsT, AvsE, to pulse A049, Fig. 4. As a result, the subscriber's speech is sampled and transmitted via transformer TC to the PCM coder, Fig. 3. The coder output is read out at 3/1 and written into row 1 of store lum whence it is transmitted over line lu1 during the next cycle at phase 1 to the main exchange. When no pulses are received on lu1, ru1 is pulsed to clear row 1 of Aum. Clearance when the subscriber hangs up, this results in an impulse larger in amplitude than speech, which when received in the P.C.M. coder, provides a pulse in a position not used for speech. This clears Aum (by means not shown) and the corresponding signal is also transmitted to the main exchange for processing therein. Main exchange.-A pulse cycle of 50 positions P1 . . . P50 is used, five of these positions corresponding to one of the positions at the concentrator. Each main exchange pulse position is divided into two portions T 1 , T 2 . Operations are under the control of a common control circuit CC (not shown) which stores details of all calls in progress. Incoming signals from a local subscriber.- Local subscribers are divided into 10 groups of 1000 subscribers. Subscriber's line circuits are of the type shown in Fig. 4 and a group of 1000 is arranged in a 32 Î 32 matrix S4 for scanning purposes. Newly-active subscribers are tested in phase T 1 , in rows, in pulse positions P 1  . . . P 32  respectively. If a row contains such a subscriber an output over one of leads Kl 1  . . . Kl 32  sets one of the bi-stable devices B1 . . . B32 and enables, via M, a set of gates controlled by pulses P 1  . . . P 32  via a binary coding arrangement 5/32 to indicate the row identity to CC. The column identity is obtained by scanning the outputs of B1 . . . B32 with pulses P1 . . . P32 and converting the result in codes 32/5 into binary form for transmission to CC. The control circuit now knowing the line's identity inserts that identity and the identity of the wanted subscriber into a row of Am which has a free pulse position which is also free in Abm (in the case of a local subscriber) or in lum (in the case of a subscriber reached over a concentrator). During the T 2  phase of the pulse position corresponding to this row, the identity of the " calling " subscriber is read out of Am to code converters OC 1 , OC 2  to cause the signal on that line to be sampled and this is fed to the P.C.M. coder. Store Am at the same time provides, over leads 11-14, to the 4/16 converter, the identity of the 1000 group containing the wanted line or of the group of lines to a concentrator. Am also provides over leads 15-24 the identity of the subscriber or the concentrator line within its thousands group. In either case the output of the P.C.M. coder is applied to a differencing circuit Add1 which is also fed with the output from store Ampm which stores the value of the signal transmitted as a result of the previous scanning of this line. The difference signal can take one of 16 values, but this signal is limited to the lower ten values and fed to a decoder MK which emits the limited difference signal as a marking on a plurality of 10 leads, the number of leads marked indicating the value of the difference signal. The limited difference signals is added in Add 2 to the existing signal received from Ampm and substituted in Ampm. The output from the 4/16 converter enables gates AbmVG to direct the outputs from leads 15-24 to p