Patent GB-1244269-A (GB)
Title: Switching network control for telecommunication exchanges
IPC: H04Q3/00
Filed: 1969-12-11
Abstract: 1,244,269. Automatic exchange systems. INTERNATIONAL STANDARD ELECTRIC CORP. 11 Dec., 1969 [18 Dec., 1968], No. 60483/69. Heading H4K. The invention relates to a telecommunication exchange of the type in which a route through cascaded stages of relay crosspoint matrices is selected by applying offering and access potentials successively to opposite ends of the " C " wires through the network. The Figure shows four crosspoint relay KP11, KPm1, KP1n and KPmn of a matrix BKV1 1 in one stage of a regular network. Relays C1 to Cm close contacts C1 to Cm respectively to earth corresponding auxiliary wires C1 to Cm of the interstage links linking to different matrices in the preceding stage to the left of the Figure, when those links are taken into use. During a search for a free path the marker M closes a contact an in each stage applying + 24 volts via resistors such as R1 to Rn to all "C" wires at the output of the associated stage via isolating diodes G1<SP>1</SP> to Gn<SP>1</SP> and to the input E of an amplifier AV for each matrix of that stage via diodes G1 to Gn. The output of each amplifier is connected via diodes to the "C" wires C1 to Cm on the preceding stage side. Each amplifier which is idle and marked at sp by the marker and each amplifier which during route searching does not receive an offering signal AZ from a subsequent stage earths its output. Each amplifier which receives an offering signal removes the earth output and propagates the offering signal to a plurality of "C" wires of the preceding stage. The inputs of offering amplifiers act as voltage stabilizers and maintain the potential on the "C" wires of offered links as about 10 volts. When offering signals reach the inlets of the first stage the marker selects one matrix in each stage commencing with the first stage and marks an input Zu of the corresponding offering amplifier causing the input resistance of that amplifier to change to infinity and its output to be connected to a corresponding line i to the marker. The change in input resistance causes the potential on free "C" wires of interstage links leading to the next subsequent stage to rise to + 24 volts causing, if a path using the selected amplifier exists, a line i to the marker from an offering amplifier in the subsequent stage to receive the + 24 volt potential. The matrices to be used in the path can thus be selected stage by stage. After selection the matrices are operated by selectively closing contacts SK and ZK in each stage enabling relays K and R for each selected matrix. Operation of relay K closes contacts K so that one of a set of testers P1 to Pm, after checking that access potential is present at that matrix, closes a corresponding contact P1 to Pm and a corresponding contact P<SP>1</SP>l to P<SP>1</SP>m causing a crosspoint relay to operate and hold over its series contact, e.g. KP 11 could be operated by closing contact P<SP>1</SP>l in that stage and contact P1 in the subsequent stage. A non-regular network is also described. In each stage the testing means P1 to Pm having a lock-out circuit to prevent double selection and the relay K has an additional set of break contacts one in each of the wires Kh1 to Khm. The Specification also describes how terminal equipment such as junctors can be regarded as additional stages and selected by the same technique.