GB1388039A - Telecommunication systems - Google Patents

Abstract

1388039 Automatic exchange system TELEFONAKTIEBOLAGET L M ERICSSON 17 May 1972 [18 May 1971] 23273/72 Heading H4K In a telecommunication system two subscribers who are already engaged in an audio connection can both send a special service request to a connection centre which on reception of both requests causes the establishment of a special connection path between the subscribers. Two systems in which some subscribers have video or data equipment are described. In one embodiment (Fig. 1, not shown) the connection centre is a registering and signalling only centre, each substation with wide band equipment being coupled to a common wide band transmission line via a channel selecting circuit (Fig. 2, not shown) arranged to respond to tones from the centre. In a second embodiment (Figs. 3 and 4, not shown) the connection centre is a wide band switching arrangement capable of interconnecting wide band subscriber lines and trunks. During a call in either embodiment either subscriber can initiate a video connection request by depressing either a transmit or a receive button at his substation. Depression of a button loops a wide band line pair to the associated connection centre which identifies the subscriber and test to see if there is a first tone on the line pair. As there is not metering is initiated and the time pair is coupled to a generator for the tone which is transmitted over the line pair to the substation, then over the audio connection to the other subscriber. If that subscriber responds by depressing his receive or transmit button as appropriate looping the line pair to the associated connection centre, the latter makes a second response identifying that subscriber and testing the line for the presence of the tone. As the tone is present the centre responds and scans the appropriate video links for a free channel. When a free channel is found a tone characteristic of the channel is transmitted to aud registered in (in the case of the first embodiment) the two subscriber channel selecting circuits or (in the case of the second embodiment) the connection centre equipment which responded to the first subscriber to initiate a video connection request. The required connection is established and retained until one or other subscriber depresses a release key. The direction of video transmission can be reversed during the call by both subscribers depressing the appropriate buttons.