Patent IL-22243-A (IL)
Title: Communication switching system
IPC: G06F17/00
Filed: 1964-10-12
Abstract: 1,081,817. Automatic exchange systems. WESTERN ELECTRIC CO. Inc. Oct. 13. 1964 [Dec. 31, 1963], No. 41688/64. Heading H4K. In the Bell System No. 1 Electronic Switching System the central processor program store contains subroutines for the direction through appropriate sequences as required of multi-state communication path circuits. As shown in Fig. 1 the switching network comprises a fourstage line link network having access over a junctor group frame to junctor circuits for local connections, and having access over a four-stage trunk link network and a trunk distribution frame to universal and miscellaneous trunk frames for connection to incoming and outgoing trunk circuits, dial pulse and/or touch tone receivers and dial tone supply, ringing circuits, tone or recorded announcement circuits, operator trunks, and dial pulse and multi-frequency code transmitters. Incoming calls are also connectable to the service circuits of the universal and miscellaneous trunk frames by way of the junctor grouping frame. The circuits made available on the universal trunk frame are plug-in units each having no more than six outlets to the signal distributer of the frame (by means of which commands from the processor are executed) and having no more than four scan points (by means of which the frame scanner provides the processor with data). The miscellaneous trunk frame accommodates wiredin circuits which are generally more complex than the plug-in circuits and to some extent govern their own sequence of operations as with the inclusion of ring-trip relays and impulse repeating and tip-party test relays. The operative state of a communication path circuit is set up by an associated set of magnetically latching relays which can be switched on or off one at a time by the signal distributer of a frame under command of the processor. Selection of free paths in the network, and the seizure of first free circuits of a group, is effected in the processor according to its record of idle and busy conditions in the call store. The class of trunk groups is recorded in the call store by means of a nine-bit word giving access on translation to three words setting out the options and features of a trunk group and a fourth word pointing to the program for sequencing the trunk circuit appropriated from the group. Subscribers' dial pulse receivers; party line identification. Fig. 19.-To serve a calling line one of these circuits is seized in the miscellaneous trunk frame. Standing in the idle state the magnetic latching relays A, B, C, D are all released. With relay A operated a test of tip and ring conductors for foreign potentials is made by connecting the conductors in parallel to a link F0 of a ferrod in the local scanner. The scanner is protected by a varistor RV1. A link F3 of a local scanner ferrod tests for operation of the relay A and confirms continuity of a fuse F01 controlling contacts F1 in the dial tone supply leads. Given satisfaction of the test results relayed by the scanner, and if a party line is indicated by the program store data, the processor sets up a party line test by operating relay C which connects both ring and tip conductors to a test relay TP. Tip parties are connected to earth at a centre-tap of the sidetone coil of their sets and in the calling condition causes TP to respond and its state is forwarded to the processor over the ferrod link F1. To connect dial tone the relay B is operated and on receipt of the first dial pulse, repeated by relay L, a signal transmitted over ferrod link F2 direct to the master scanner causes the processor to release A and disconnect the tone. If touch-tone signals are received a tone receiver associated with the circuit signals the master scanner direct to direct the scanner to a prompt examination of the digit output leads of the tone receiver. On completion of digit signals a second test of party type is made over relay TP by releasing B and given consistent results C is released to disconnect the circuit and leave it in the idle state. With individual parties no party test is involved and the relays operate in the sequence A, AB, and B. The sequence is modified in the case of a PBX caller attempting to dial outside a prescribed area. In face of this the processor directs the operation of relay D to accompany B, thereby reversing battery to the PBX to divert the call to an operator or connect up a tone or recorded announcement. Should the PBX caller be a privileged party and entitled to the call the PBX will ignore the battery reversal and the call will proceed without interference. The D relay operated on its own effects a loop across the line for a continuity test not otherwise described. Tone circuit and recorded announcement circuits, Fig. 22, not shown.-The circuit has two latching relays A and B which define the idle state, a state in which continuity of the connection is tested by coupling to a scanner ferrod, a state in which tone &c. is connected to a local subscriber and a further state for connection to a trunk circuit. A fuse in the tone &c. supply circuit is also tested by the scanner. Busy tone and no such number tone are specifically mentioned. Ringing circuit, Fig. 24.-From its idle state with magnetically latching relays A, B and C released the ringing circuit is commissioned by locking up A which connects a ferrod scanner link F0 to test for foreign potential on the lines. Given a clear path and according to class-ofservice data, ringing is applied over the ring or tip conductor. For ring wire ringing a test for short circuit is conducted by operating relay B and ringing current is applied by releasing A, relays RT1, RT2 coming up during these actions and being restored with the circuit when ring trip relay RT responds to dc in the answering loop. For tip wire ringing a test for ground is conducted by operating C, and not B, ringing being effected as before by release of A. The state sequences are therefore A, AB, B for individual and ring party customers and A, AC, C for tip parties. Outgoing trunk circuit, Fig. 20, not shown.- When idle this circuit terminates the trunk and with three latching relays has a by-pass state for pulse or multifrequency signalling, a hold state in which the trunk loop is closed, a tandem working state in which a transformer coupling is employed between the trunk and the network, and a further tandem working state in which the transformer is disconnected as may be necessary when connected with an operator trunk which provides transformer coupling, and a local termination state in which the transformer is connected and the trunk loop is closed. For a local termination the sequence states are C, BC, B, AB, B; for a first tandem connection the sequence is C, BC, B, AB, ABC, AB, B; and for a second tandem connection the sequence is C, BC, B, AB, A. Incoming trunk, Fig. 21, not shown.-This circuit has an idle state terminating the trunk and has a by-pass state, a state for local termination with no metering charge and a corresponding state with metering charge produced by reversal of battery to the trunk, a state in which continuity of the trunk is tested, a state for tandem connection with no metering charge and a corresponding state with charge by battery reversal. Operators' trunk circuits, Fig. 23, not shown.- Apart from its idle state this circuit can have a by-pass state provided for purposes of testing, four states for talking connections for local and tandem connections in both on-hook and offhook conditions, a seize and hold state, and a state in which a routine continuity test is made on the network.