Patent GB-843175-A (GB)
Title: Improvements in or relating to telecommunication systems
Inventor: BAKER GEORGE THOMAS
IPC: H04Q3/42
Filed: 1955-11-03
Abstract: 843,175. Automatic exchange systems. BRITISH TELECOMMUNICATIONS RESEARCH Ltd. Oct. 31, 1956 [Nov. 3, 1955; March 13, 1956], Nos. 31489/55 and 7871/56. Class 40 (4). Information regarding a connection to be set up is sent from a magnetic drum at the originating exchange to a magnetic drum at the terminating exchange over a common channel, the information being recorded on the second-mentioned drum in a space individual to the source. General information regarding pulses and equipment. The system is concerned with a line of transit exchanges between which signalling is effected on a carrier frequency of 1200 c/s. modulated with a Gaussian waveform of frequency 600 c/s. Each track on a magnetic drum holds ten registers, each register containing 14 TB blocks, and each block has 6 TA positions. Additionally, TX and TY pulses are used for controlling transmission and reception of digital information. The TX and TY pulses are of the same nominal frequency but the TY pulses are controlled by the TX clock at the sending exchange. One TZ pulse is equal to 6 TY pulses and corresponds to each complete digit. Nomenclature. The writing leads are indicated in the usual manner, a final A indicating that 0 is to be entered, a final B that 1 is to be entered. When 1 is detected by a reading head lead SL is marked, when 0 is detected lead SL is marked. The addition of letter A refers to the incoming register, B the outgoing register, C the transmitter track, D the receiver track, E the transfer track, F the incoming register address track, G the outgoing register address track. Detailed description. Dialled digits are set up on a magnetic drum register at the originating exchange in the manner described in Specification 717,689. This information is transmitted over the common channel associated with a junction incoming to a transit exchange and is recorded in the receiver track VT, the identity of the incoming junction being recorded in block TB5 and the wanted subscriber's number in blocks TB6-TB12. When an " information in receiver track " mark at TA6, TB14 is detected electronic toggle MAA (Fig. 2, not shown), is set up to initiate hunting for the required incoming register by comparing the digit in TB5 with the several digits in the incoming register address track AT, MAA being repeatedly reset until correspondence occurs when the information in the receiver track VT is transferred to the chosen incoming register track IT and the receiver track is cleared. Translation then takes place in the manner described in Specification 717,690 to select a single digit to indicate the junction outgoing to the next exchange on the required route. This digit is entered in block TB4 of the incoming register track IT and a mark is entered at TA1, TB3. Electronic relay MBA (Fig. 3, not shown), is then set up to seize the transfer track FT and the mark at TA1, TB3 is removed. The translation digit operates a track switching device TS (not shown) to render effective the track OT containing the appropriate outgoing registers. The address of the incoming register is then entered on the transfer track FT followed by the wanted number and a " hunt for free outgoing register " mark at TA1, TB13. MBA is restored by this mark which also sets up MBB (Fig. 3, not shown) repeatedly until it seizes the first free outgoing register in the desired group. The address of the incoming register and the wanted number are then transferred from the transfer track to the chosen outgoing register in track OT after which MBB and TS restore. All outgoing junctions busy. If all the required outgoing junctions are busy so that the hunt for a free outgoing register continues until it reaches the starting point MBD (Fig. 3, not shown), operates to enter a busy mark at TA4, TB13 on the transfer track FT. It also enters a mark at TA6, TB13 to initiate hunting for the incoming register. A signal is then extended back to the calling subscriber as described later. Assuming, however, that a free outgoing junction is available the information in the chosen outgoing register is transferred to the transmitter track MT under the control of the busy mark TA1, TB12 in the last block of the called party's number and an " information transmitted " mark is made in the outgoing register. A start signal at TA1+TA5+TA6, TB3, two further marks at TA1, TB4 and TA1, TB13, and an " information in track " mark at TA6, TB14 are also entered in the transmitter track. These entries are sent to the next exchange in a manner described later. Signalling back by final exchange. In the final exchange the incoming register IT carries at TA3 or TA4 of TB13 an indication as to whether the wanted number is idle or busy. Entry of the mark TA6, TB14 into this register indicates that information must be sent back to the earlier exchange. When the transmitter track is free this mark sets up MDA (Fig. 5, not shown), which enables each digit of the wanted number to be set up on four toggles MDB-MDE (not shown) and so transferred to the transmitter track. The idle or busy condition of the wanted line is also entered together with a start signal and MDA is then restored. Transmission to the earlier exchange then takes place in a manner described later. At the earlier exchange the information is received on the receiver track and referred to the outgoing register which handled the call in the forward direction by electronic relays MEA, MEB (Fig. 6, not shown). The necessary information is then transferred over electronic relays MFA-MFE (Fig. 7, not shown), to the register associated with the incoming line from which this outgoing register was seized. The information stored in blocks TB4 and TB5 of this incoming register is then used, if the signal received indicates that the called subscriber is free, to set switches such as S1, S2 (Fig. 1), in the speaking route. On the other hand if the called subscriber is busy, electronic relays MDF, MDG, MFD, MFE (not shown) to clear the registers as the signal is extended backwards. At the end of a successful call clearance is effected under the control of scanners PTA, PTB (not shown) which produce outputs from the calling and called lines respectively, only when they are in use. As incoming or outgoing junctions are released as MDF or MFD operate to initiate clearance. Signalling; sending equipment. Waveforms of the type shown in the third line of Fig. 9 are controlled by waveforms of type SF or SF, the latter being shown in the fourth line of Fig. 9 to produce an output on the line with the waveform shown at the bottom of the Figure when the transmission gate is open. Receiving equipment. The incoming signals are amplified at AG, Fig. 13, and rectified at FR. They are sent to low pass filter LPF2 and signal output circuit SO to produce an output D<SP>1</SP> shown in the fourth line of Fig. 14. The pulses are also inverted to produce an output D<SP>1</SP>. Automatic gain control is provided by AGCR. The low-pass filter LPF2 also feeds a ringing circuit RC and phaseshifter PS2 to produce the waveforms shown in the fifth and sixth lines of Fig. 14. PS2 feeds pulses to a squarer SQ2 which feeds a toggle MW to produce square waveforms MW, MW. These waveforms drive SG2, SG3 to produce strobe pulses ts2, ts3 of frequency 600 c/s. Transmission code. Transmission of decimal digits uses a 4-digit binary code with the addition in fifth place of a pulse whenever the binary code of a digit comprises two pulses. A single pulse in fifth place is used as a synchronizing pulse. Pulses in third-fifth places are used as a starting signal and pulses in all five places are used as an erase signal. Strobe pulses ts1 of frequency 600 c/s. are generated in the sending apparatus and applied to a circuit comprising toggles L, M, N, Fig. 18, to produce pulses TX1-TX5, two of which are shown. The TY pulses which govern reception are controlled by toggles A, B, C (Fig. 19, not shown), in the same manner, these toggles being controlled by further toggles G, H, I, J, Fig. 22, which are controlled by pulses received on lead D<SP>1</SP> in transmission from the preceding exchange. Operation of TZ clock. The TZ clock at the receiving exchange runs only during the transmission of information. Reception of a start signal 00111 sets up I, J, K, Fig. 22, to operate K<SP>1</SP> (Fig. 23, not shown). At the coincidence of an output from K<SP>1</SP>, a strobe pulse ts3 and a TY5 pulse gate 112, Fig. 20, opens to start the TZ clock. This clock comprises four toggles D, E, F, P, Fig. 21, which co-operate to produce 11 TZ pulses, three of which are illustrated in the lower part of the Figure. At the end of the cycle pulse TZ11 restores K<SP>1</SP> (Fig. 23, not shown), to stop the clock. Detection of error in transmission. The bits of each digit or signal are received by toggles G, H, I, J, K, Fig. 22, reception being dependent on gates receiving timing pulses TY1- TY5. None of the combinations of bits comprising a signal are even in number, any binary code having an even number of pulse places being supplemented by a pulse in fifth place. If, at any time, the number of pulses received is even then a toggle Q, Fig. 24, which is operated at each signal, restores to set up R. Toggle R then energizes lead SAD to erase all the information entered on the receiver track. R is reset at the end of transmission. Recording received signals. If the start signal has been correctly received so that the TZ clock is operative and if R is normal, then the signals incoming on lead D<SP>1</SP> or D<SP>1</SP> operate S or S controlled by strobe ts2, then T or T, controlled by strobe ts3. T produces square pulses to signal the recording circuit for each binary 1 received. The pulse positions in each digit are directed by clock pulses TY2-TY5 and TA3-TA6 to cathode followers C/F. They are further directed by TZ and TB pulses over lead SBD to appropriate blocks on the receiving regi