COMMUNICATION SYSTEM

1490260 TDM loop systems; conferences HASLER AG 3 June 1975 [17 June 1974] 23907/75 Heading H4K A loop highway system is provided with means for setting up conference connections, the system being of a type in which no central exchange is provided. Each telephone station is provided with a receive store 5, a transmit store 8, a decoder 9, control logic 7 and three registers 22-24, comprising a transmit address register 22, a receive address register 23 and an auxiliary address register 24. During a normal two party connection the transmit and receive address registers 22, 23 both contain the identity of the station with which communication has been established. A station B of two stations A and B in communication, can add a further station C to the connection by first depressing a hold key to cause the address of A to be stored in auxiliary address register 24 and registers 22, 23 to be cleared. A signal is also sent to station A to cause the address B to be erased from the receive address register thereat. Station B now sets up a connection with station C, on the establishment of which the registers 22, 23 in station C contain the address B and the registers 22, 23 at station B contain the address C. To complete the conference connection station B now depresses a conference button causing a signal to be sent to station C which includes the address A from register 24 at station B. In station B the address A replaces address C in the receive address register 23 and register 24 is cleared. Receipt of the signal from station B at station C causes the address A to replace the address B in the transmit address register 22 and a signal is sent from station C to station A to cause the address C to be set up in the receive address register of station A. A conference loop is thereby set up, which further stations may be added. The stations are further provided with means for ensuring that the speech from only one station circulates at a time round the loop, the means including an arrangement for comparing the signal level received at the station with that being produced by the microphone of the station. A speech switch at the station is operated should the speech level thereat exceed the level being received and a signal is sent on round the loop to the other stations of the conference to cause similar switches thereat to operate to cause signals received by them to be transmitted on to the next station in the conference loop, in addition to being supplied to the s