Signalling method and device for bidirectional digital transmission link

摘要

A method of transmitting signalling along a bidirectional digital transmission link consists in transmitting from an intermediate equipment of the link a signalling message in two parts. One is a characterizing part the form of which depends on the signalling type and which is substituted for data of one of the digital bit streams carried by the link in the direction from one of the terminals referred to as the processing terminal. The other is a localizing part whose form is independent of the signalling type and which is substituted for data of the digital bit stream carried by the link in the direction towards the other, so-called relay terminal. The relay terminal responds by sending an acknowledgement message to the processing terminal, the time-delay of this relative to the characterizing part being used to identify the sending equipment. A signalling message transmission circuit controls switching circuits inserted into the paths of the digital bit streams carried by the link. The equipment for transmitting signalling along a bidirectional digital transmission link comprises a clock circuit defining in terms of the period of its output signal the duration of a signalling message characterizing part. Its half-period defines the duration of a localizing part. There is also a circuit for selecting the first complete period of the clock circuit output signal after a signalling transmission request, as well as circuits for composing the two parts of the message.