Patent GB-430753-A (GB)
Title: Improvements in or relating to automatic or semi-automatic longdistance telephone or other electric signalling systems
IPC: H04M3/50
Filed: 1933-12-20
Abstract: 430,753. Automatic exchange systems. STANDARD TELEPHONES & CABLES, Ltd., 63, Aldwych, London.-(Hertog, M. den, and Kruithof, J.; 4, Rue Boudewyns, Antwerp, Belgium) Dec. 20, 1933, No. 35898. [Class 40 (iv)] In a long distance connection involving repeaters with gain control equipment at tandem exchanges, the gain at each tandem exchange except one (the last) is adjusted automatically in accordance with the attenuation of the incoming junction whereas the gain at the remaining tandem exchange is adjusted in accordance with the attenuations of both incoming and outgoing junctions. The invention is described in connection with a system using switching stages at each exchange comprising one or more stages of backwardly hunting switches controlled by markers which also serve to indicate to the gain control equipment whether the exchange is an intermediate or last tandem exchange, the attenuations being signalled in code from the ends of the junctions adjacent the repeaters. Overflow arrangements are provided as between groups of junctions of different quality or giving different service or using different signalling arrangements. Further, alternative routing is used, and when an exchange which would be the last tandem on a preferred route, becomes an intermediate one, it is arranged that this is indicated to the gain control equipment. The Provisional Specification describes a gain control system in which the attenuation of the outgoing line is signalled over the wipers of an auxiliary switch controlled by the marker. Toll switching arrangements. In the single digit toll-switching stage shown in Fig. 1, incoming local lines LL and toll lines IL have access over marker controlled finders with outgoing junctions in two directions A, B. One group may be subdivided into sub-groups of different quality lines, e.g. according to transmission velocity, attenuation, &c. of two and four-wire circuits ; of junctions giving access to local or long distance lines at their incoming ends ; or, as shown, of junctions FAL using 50-cycle signalling and junctions VAL using voice frequency signalling. The digit received by the marker DIM from a register-controller determines the group or sub-group of finders to be started up, but calls over 50-cycle junctions FAL may overflow into the voice-frequency group and if this is busy, an alternative-route finder ARF extends the call to finder BF of the B group, and a circuit associated with ARF sends a digit to exchange B to effect selection of a junction to A, the normal signal to the registercontroller to send the next digit being held up until this has been done. Repeaters are connected up by switch RF. If no outlets are available, a delayed call circuit is connected up over DLF and busy tone is sent back or an operator called in. The operator may be called only if the incoming line is local. In the modification shown in Fig. 2, the outgoing lines are made fully available to a larger number of incoming lines by the use of groups of intermediate finders IAF, IBF for the two outgoing groups. The intermediate finder IAF makes a test of the setting of the marker and extends marking and starting circuits to the requisite subgroup of finders FAF, VAF. In the further modification shown in Fig. 3, the two stages of finders are controlled by separate markers D1M1, 2. The junction groups accessible over imtermediate finders IF1, IF2, lead in different directions. In the further modification shown in Fig. 8, the marker-controlled finder groups at exchange A give access to junctions NTL giving local service at exchange B, and to junctions TL giving toll and local service at B. If a call for B overflows from group NTL to group TL, the local finder at B must be started up. For this purpose, the register-controller is adapted to send digit 1 for a call local to B while a starting impulse is sent from A to B only when a junction TL is seized. Thus, when a junction NTL is taken, the digit 1 functions as a start impulse at B whereas when TL is seized, digit 1 sets marker D1M2 to indicate a local call. Gain control. Repeaters are automatically inserted at tandems, and their gain adjusted so that the total loss is always 9db. Repeaters at all tandems except the last are automatically adjusted to compensate the loss of the incoming line whereas the repeater at the last tandem is adjusted to a gain of 9db less than the sum of the losses of the incoming and outgoing lines. The gain of a repeater is adjusted, as fully described below, by attenuation pads under the control of relays which receive code signals from the incoming and outgoing lines according to their measured attenuation, the indication as to whether an exchange is the last tandem or not being given by the marker controlling the tollswitching at the exchange. Single digit switching stage, Figs. 9 to 12; call to 50-cycle junction group. An incoming start impulse over IL received in IRU prepares the circuits for the reception of the digit which is repeated to marker D1M in a manner not shown. It will be assumed that this digit (2) indicates that the call is to proceed over a 50-cycle trunk, D1M therefore completes a marking circuit over dima for finders FAF, and a starting circuit over dimb in which Fs1, Fc1 pull up to energize FAFM. When line IL is found, test relay Tt pulls and Th cuts in a low resistance winding of Tt to check for double testing and to shottcircuit Fs1 over dima, b. The digit also indicates whether the exchange, Figs. 9 to 12, is the last tandem point, not the last, or that no repeater is required, and for this purpose contacts of dimc are jumpered to terminals A-C respectively as the case may be. In the first two cases (repeater probably required) Ag marks the k bank of repeater finders RF and operates start relays Fs, St and when the calling circuit is found, T and S pull up to check for double test, and D operates in series with Tr in the line circuit which stops the finders and opens the circuit between the connections incoming to and outgoing from the repeater. D operates E and continues to be held. Tr also completes a holding circuit between Co, Fig. 9, and Ho, Fig. 11, so that Co releases Tt, Th, while Ho energizes switching relay Ch, and relays Ao, Bg. Relay Ft sends start impulse (terminated by slow-operating relay Ba) to the distant end of the outgoing line, while Bs, Fig. 9, signalled by Bg sends a backward impulse (terminated by the release of Bg by Ba) to the register-controller which sends the next digit. Gain control. It will first be assumed that the exchange is the last tandem in the connection so that the repeater inserts a gain according to the formula a + b - 9, where a and b are the incoming and outgoing attenuations. Bracketed terminals 1-4 of contacts of relay Ag are grounded according to a code representing the attenuation of the incoming line so that relays G1-G4 representing losses of 1, 2, 4 and 8 dbs. respectively, are operated according to the code and lock up. Similarly, contacts 1-4 of Bg, Fig. 11, are grounded according to the attenuation of the outgoing line, these grounds being connected over the speaking and two other wires of finder FAF, and contacts of Ic, C, E, to relays H1-H4 of which H1-H3 lock up in series with K while H4 locks in series with J. For a reason which will be apparent later, the H1-H3 code for the outgoing line is such that the signalled loss is 1db less than the real loss if this loss is less than 9db, while H4 and therefore J operate if the real loss is 9db or less. Relay I operates if the combined losses indicated by G1-G3, H1-H3 is 8db. The repeater is adjusted for a maximum gain of 15db which is normally counteracted by the attenuation pads, at the bottom of Fig. 10, connected between the hybrid coils and the two paths of the repeater, the hybrid coils being connected to the incoming and outgoing lines and to the balancing networks over terminals 1 to 4 and 5 to 8 connected up by relays B and C, Fig. 10, which pull up when J or K operate, that is, in response to any code from the outgoing line. When this occurs L operates to remove anti-singing shunts on the paths of the repeater. The pads are rendered ineffective by relays P1-P4 which are operated and locked over relay F, according to the total losses indicated by G1-G4, H1-H3 and I. If the total loss is 9db or less, the repeater is not required and is released. With such a loss, J is operated in any case ; G4 and I may both be unoperated; G4 or I may be operated provided F is back (8db relay P4 operated alone). Under any of these conditions relay D connecting up the repeater is short-circuited over a front contact of K which is operated since the actual loss of the outgoing line must be 8db or less. When the total loss exceeds 9db, if the loss in the outgoing line is 9db or less, K and J will both be operated and although I is operated (total of G1-G3, H1-H3 equals 8) it is without effect and P4 cannot pull up so that the gain of the repeater depends only on the state of G1-G3, H1-H3, and is less by 9db than the combined losses (1db artificially deducted by the code from the outgoing line and 8db because P4 is prevented from operating). When the loss of the outgoing line exceeds 9db, the code from the outgoing line indicates the real loss less 9db so that the repeater is again adjusted to 9db less than the total. Considering now the case in which the exchange is not the last tandem, the repeater is adjusted to compensate the loss in the incoming line only, and for this purpose an artificial signal of 9db is used for the outgoing line by the operation of relay Ic, Fig. 9, over terminal B and marker DIM, so that all the code lines from the outgoing line are connected to operate relay H4 alone, The effect of this is to put relays P1-P4 under the control of G1-G4 alone. The previously described repeater releasing arrangement for total losses 9db or less is not effective in this case s