Patent GB-998007-A (GB)
IPC: H04Q11/04
Abstract: 998,007. Automatic exchange systems POSTMASTER GENERAL. Oct. 26, 1961 [Oct. 27, 19601, No. 37004/60. Drawings to Specification. Heading H4K. A telecommunication switching system comprises a plurality of first time division highways, each serving a number of subscribers, each of which is connected by gates to a number of second time division highways (hereinafter referred to as " cords ") each of said second highways having a storage system for controlling the gates whereby communication can be selectively established between subscribers over one of said second highways. A 3000 line exchange is described in which the lines are divided into 1000 line blocks, each block being divided into two 500-line groups, each group comprising five 100-line subgroups, each subgroup having ten decades. Connections from the line to the cord are established by opening gates in accordance with the units, tens, hundreds and group identities in suitable pulse positions defining the channel used in the cored. The tens and units gates are used in common by all cords, and are opened by pulses derived by coincidence with the hundreds pulses of the tens and units pulses respectively. Group gates are individual to cords. Adjacent pulse positions are used for each call (each separated by 1 Ásec.), ), connection from a calling line to a called line being effected using a position P from calling line to cord, where it is delayed to position P + 2 and transmitted to the called line; and position Q ( = P + 1) both for called line to cord and cord to calling line. This involves the insertion of pulse P in the stores indicative of the calling line and Q in the stores indicative of the called line. Each store has a direct output available, and another delayed by 1 Ásec., so that all the necessary pulses are available for completing the connection. Line scanning. A test pulse is inserted in each cord's CDU (hundreds, tens and units) stores in which the count is stepped cyclicly through all the combinations, simultaneous scanning being effected in all blocks, one cord being allocated to a block for this purpose. When a looped line is found a pulse amplitude detector responds and if the condition persists emits the pulse in a PP time indicative of the cord (and hence of the block). Eleven such PP times of 100 Ás. occur cyclically, the early PP times being used to indicate the respective cords. This pulse is used to set identify toggles in common equipment indicative of the calling line. Initial selection (of register). A register is associated with a pulse position. A free pulse position is then selected and a cord with this free position is selected and the pulse inserted in the CDU stores of the selected cord, and also in the thousand store of the cord (known from the identity of the cord which detected the call). The pulse (in P and Q positions) is inserted in the cords register store. The Q pulse is also written into the thousands store of the 2 block (used for dial tone) and this causes the Q pulse modulated with dial tone to be reverted over the highways, and hence to the subscriber. Common equipment is then released. Blocks 2, 3, 4 are given an order of priority in case simultaneous detection of a calling in more than one block occurs. Receipt of dial pulses. The pulse amplitude detector of the selected cord feeds a timing device which times the duration of the impulses and intertrain pauses and counts the first digit provision being made for sending N.U. tone if the first digit is not one in use by deleting the P pulse from the register store and inserting the Q pulse in the cords thousands store 4, which causes N.U. to be sent in the same manner as dial tone. The first dial break also deletes the Q pulse from the register store to interrupt the dial tone. If the first digit is genuine a Q pulse is inserted into the thousands store of the cord. The remainder of the digits are inserted directly into the cords CDU stores in the Q position, each dial break causing this pulse to be emitted to the stores which are connected up to act as counters. When all the digits are received the CDU pulses are caused to operate the identify toggles in accordance with the identity of the called line. Final channel selection.-Toggles indicative of the calling and called lines groups are also operated, and all Q pulse trains are fed to a gate inhibited by those in use in the called and calling groups, the first pulse emitted being selected as the final channel. Final cord selection.-The final selected channel is offered to all cords and a cord selected in which this channel is free. Testing called line.-When a line is busy a test pulse is stored in a busy line store, so dimensioned that it will not emit its stored pulse until the line is again scanned. This occurs immediately on detection of a calling line or connection to a called line. When the wanted line is scanned the identitify toggles cause the test pulse to be emitted and coincidence with that in the busy store operates a busy toggle. If this coincidence is absent a " write final called " toggle is operated and the test pulse is inserted in the busy line store. Setting up final connection.-The final selected pulse Q is inserted into the identified called line stores of the selected cord and into the thousands store under control of the called group toggle. The final selected pulse Q is inserted into the cord supervisory store. The identify toggles are now reset. The presence of the initial select P in the calling lines stores is now used to set the identify toggles in accordance with the calling lines identity and final selected P is inserted into corresponding CDU stores in the final selected cord, and using the group calling line detected toggle the pulse is written into the cord's thousands store. The common equipment is then released. Busy conditions.-The busy toggle causes inter alia the insertion of the initial selected Q pulse into the register store of the cord and the thousand store corresponding to digit 3. This causes busy tone to be reverted in a similar manner to N.U. tone. The busy toggle may also be operated if no free channel is found. Ringing.-Final selected Q pulse is derived from the pulse in the supervisory store and used to derive ringing tone and calling tone in the appropriate phases for sending to the calling and called lines. Called party answers.-The output from the cord pulse amplitude detector appearing at time Q is timed and if persistent Q is deleted from the cord supervisory and P is inserted. This opens gates for completion of the connections between the highways. Clearing.-This is detected by a timer, controlled by the pulse amplitude detector, whose output causes the identity toggles to be operated, so causing the test pulse to be produced during the scan time of the line. This is used to delete the pulse from the busy line store. The cord line stores are also cleared. N.U. tone for individual lines or sets of lines. A separate highway is provided, appropriate strappings to additional gates fed by the Q pulses from the CDU stores causing the Q pulses to be provided to the cord circuit for modulation with NU tone and reversion to the calling subscriber.