Patent GB-1284241-A (GB)
Title: Improvements in or relating to communication arrangements
Inventor: ANDERSON HAROLD PETER
IPC: H04N7/14
Filed: 1970-06-10
Abstract: 1284241 Automatic exchange systems WESTERN ELECTRIC CO Inc 10 June 1970 [11 June 1969] 28084/70 Heading H4K In a telephone system a substation has appearances on two different exchanges which both respond to a call one being released in response to substation originated signals. As described a conventional exchange serving ordinary substations is supplemented by video/ audio exchange serving subscribers having video equipment. When a video substation goes offhook the video/audio exchange responds and calls in the audio-only exchange. Both exchanges receive subscriber dialled digits and the video/audio exchange releases one or other exchange in accordance with those digits. The arrangement allows subscribers with video equipment to choose between an audio only connection and a video/audio connection and to select the appropriate equipment by dialling. The exchange still connected receives further dial signals designating the wanted subscriber. As shown, if for example a video station A goes off-hook the video/audio system 10 responds selecting an idle register and connects the video line circuit V1 to this register. A marking signal is returned to the video line circuit V1 which in turn marks an associated audio line circuit A1 in the conventional audio-only system 40. The conventional system responds connecting an idle register circuit 45 to the audio line circuit and this register returns dial tone to the caller. When the first digit is dialled it is registered by both registers. The first digit is either a fixed preselector digit indicating that a video/audio connection is required, or the first digit of a wanted subscriber designation if an audio-only connection is required. A gate circuit in the video system responds if the preselector digit is dialled signalling to the video line circuit which in turn releases the audio line circuit A1 releasing the conventional exchange. If however at the end of the first digit the gate circuit has not responded the call in an audioonly call and the video/audio system releases. The video system establishes separate paths for the audio and video parts of a video/audio call, four wire switching being employed. After the establishment of a video path it is tested by a video continuity test circuit 23, prior to release of the central control and if the video path is not or prescribed quality a video connection is established to an operator. Video trunk calls.-If a video station dials a nine following the preselector digit a gate circuit connected to the appropriate outputs of the thousands digit register responds and initiates a test of the class of service of the calling line followed by selection of an idle outgoing trunk and the marking of the inlets and outlets of the switching network necessary to make a connection thereto. Incoming trunk calls are routed to an operator who inserts the preselector digit if a video connection is required. If the called station does not have video equipment the call can be completed as an audioonly call. Dialling wrong numbers, dilatory dialling.-If a video subscriber dials the preselector digit but does not dial the required subscriber number a timer times out after a ten second interval and establishes a video connection between the caller and an operator. A connection is made to a speaking machine if the caller dials a wrong or audio-only equiped number. Register and scanner equipment.-The line register and trunk scanners and the registers, incorporate at least one circuit combination comprising a three state chain counter which for each cycle steps a four state chain counter. This circuit "combination" receives serial pulses (either pulses of a dial digit or clock pulses) and converts them to a 2 out of 7 code (one marking from one stage of each counter). The video line scanner (Figs. 4 and 5, not shown) employs two such "combinations" which receive clock pulses and are connected in cascade. The outputs of the two combinations operate in co-ordinate fashion to enable individual line gates in succession. When a video substation handset is on-hook its video line gate (LA, Fig. 2, not shown) is normally turned on. When the handset is off-hook and the audio line is bridged by a low resistance the gate turns on. When the line scanner next scans this line the gate turns off again enabling a transistor (Q1, Fig. 2, not shown) which connects earth potential to the common control causing the scanner to stop and requesting dial tone. The registers (Figs. 27 and 28, not shown) employ four such "combinations" of counters the "combinations" being arranged to receive the units, tens, hundreds and thousands digits of a video subscriber designation. Some subscribers are equipped with multi-frequency dialling equipment, Each digit received is converted to the 2 our of 7 form used by a "combination" are entered directly into the stages of a further "combination" (Fig. 29, not shown) which is stepped to its original state by a rapid pulse generator which also pulses the register. The register scanner and trunk scanner employ a single "combination" the outputs of the three stage counter being used to scan the three registers and the outputs of the four stage register being used for trunk scanning.