Patent GB-1411056-A (GB)
Title: Message transmission system for a multi-branched network
IPC: H04J3/16
Filed: 1973-02-21
Abstract: 1411056 Automatic exchange systems LICENTIA PATENT-VERWALTUNGS GmbH 21 Feb 1973 [22 Feb 1972 23 Feb 1972] 8535/73 Headings H4K and H4P A communication system comprises a multibranch two wire line to which subscriber stations are connected, a unit adapted to apply a synchronizing code to one wire of the line and means at the end of each branch to transfer the code to the other wire of that branch, each station being adapted to divide the period between synchronizing codes into time slots usable for message transmission. In one embodiment shown the stations which include telephone substations 2, data devices 6, picture devices 7, telex units 8 and display devices 71, data bank 4 and computer 9 are connected as shown to the line having a main branch extending between the synchronizing unit 3 and a terminating device 32, and side branches terminated at 10. All terminating devices couple the synchronizing codes on the send line SL to the receive line EL. The terminating devices 10 absorb without reflection any message code while the terminating device 32 couples these codes received on line SL to the receive line EL. Each time slot is divided into two portions. To initiate a call a calling station must first select an idle time slot. This can be effected by monitoring the time slots on the receive channel until a free slot is found and using the known loop delay associated with that station's branch of the line, (which may be the same throughout the system if the devices 10 have appropriate delays, Fig. 10, not shown) the transmit time slot to be used may be calculated, or determined by transmitting test codes round the system, measuring the delay incurred and retiming the transmission in accordance with the delay, each branch point of the system being adapted to intermediately store these codes until an outgoing time slot in each outgoing branch is available. To call the wanted station B the calling station A transmits the wanted station identity B followed by its one identity A in a selected time slot. If the wanted station is free it selects a free time slot for the return transmission and transmits the two identities in the reverse order i.e. (B, A). The calling station responds transmitting (B, B) which causes ringing to be effected at the station B. When station B answers both stations transmit the other station identity followed by a message code. The wanted station identity need not be sent once the connection is established. In another embodiment (Fig. 1, not shown) the terminating device 32 is identical with the devices 10 and every station transmits and receives on both lines of the pair. In both embodiments the branching devices 5 absorb synchronizing codes after reflection at the terminating devices 10 and 32 and are equipped if necessary to effect intermediate storage of the codes for time slot synchronization and/or storage until a free slot can be found. The branching devices may include slave synchronizing devices which take over if the main device fails and may be adapted to transmit codes only to appropriate branches discriminating using the addresses transmitted.