Siemens Aktiengesellschaft

Societa Italiana Telecomunicazioni Siemens S.p.a.

Italtel Societa Italiana Telecomunicazioni S.p.a.

Virgilio Mosca

Robert Lechner

Hans-Werner Rudolf

Nigel P Dyer

Pierre Albouy

Harald Stader

Norbert Wingerath

Robert K Galpin

Antonio Nicastro

Ramatchandirane Nadaradjane

Christopher C Priest

Robert Le Gougnec

Marcello Manca

Ennio Bonaparte

A digital interface between at least two subscriber line interface circuits and a processing unit is described. The interface is configured in the form of a parallel interface. The level of an input/output register and of a control register is allocated, as needed, to the connections of the processing unit. These connections can be operated selectively as inputs or outputs. They can also be operated in two modes, depending upon which type of subscriber line interface circuit (SLIC) is connected. The connections of the last-mentioned units are partially operable as inputs or outputs and partially operable only as inputs but in the input case, selectively for various types of input signals.

Digital interface between at least two subscriber line interface

A digital interface of an integrated subscriber line interface circuit is provided. The interface serves for the connection of a signal processor unit. Individual connections are used as signal inputs in signal entry operation of the interface, and as signal outputs in signal transmission operation. Other connections are used as signal inputs in both operating mode, but receive different signals in each operating mode. One group of connections includes two registers with respective associated decoders to enable switching from one to the other, so that the number of operating instructions that can be represented by means of binary signal value combinations applied to the connections is doubled.

Digital interface of an integrated subscriber line interface circuit

A line loop (a, b) serving two telephone subscribers with sets (U.sub.1, U.sub.2) each normally connected between ground and a respective line conductor, coupled at the exchange via a line transformer (T) to a voice path, includes a pair of line relays (RA, RB) respectively inserted in these conductors in series with two high-ohmic resistors (RR.sub.1 ', RR.sub.1 ') and two low-ohmic resistors (RR.sub.2 ', RR.sub.2 ') forming part of a switching network (CI) which interfaces the loop with call-control circuitry (CCT) at the exchange. Two selection relays (RE.sub.1, RE.sub.2) in the switching network normally connect the two line conductors to negative battery whereby an off-hook condition at one set, grounding the corresponding conductor, causes a current flow insufficient to operate the associated line relay but detectable by a line monitor (RI.sub.1, RI.sub.2) connected across the low-ohmic resistor thereof which generates an engagement signal (i.sub.1, i.sub.2) when that conductor is being addressed by a slow-rate scanning pulse (u.sub.1, u.sub.2). A resulting switchover of the exchange circuitry to fast-rate scanning energizes the respective selection relay and locks it operated to short-circuit the high-ohmic resistor, thereby actuating the corresponding line relay and disconnecting the other subscriber set from the loop. When the exchange detects a persisting off-hook condition in the absence of activity in an assigned time slot, it emits an isolating command (in) concurrently with the scanning pulse to set a flip-flop (FF.sub.1, FF.sub.2) causing the release of the selection relay.

Switching network interfacing telephone-exchange equipment with

The outlying stations of a videotelephone system, adapted to communicate with one another through a central office, include each a video-reception section and a video-transmission section as well as an audio section provided with telephone equipment. A sync-pulse generator in the video-transmission section, comprising a crystal-controlled oscillator working into a pair of frequency dividers, controls the line-scan and frame-scan generators thereof as well as those of a remote station to which it is connected via an outgoing video line. A local sync-pulse extractor connected to an incoming video line controls the line-scan and frame-scan generators of the associated video-reception section. A switch enables replacement of the crystal-controlled oscillator with a variable-frequency oscillator locked in step with the sync-pulse generator of the remote station by the output of the local sync-pulse extractor whereby interference phenomena due to pick-up of incoming sync pulses, in random phase relationship with the locally generated sync pulses, are eliminated. The switchover to the variable-frequency oscillator may be carried out manually or, at a called station, by a detector circuit responsive to incoming audio or video signals, preferably to ringing current; the detector circuit includes a relay which locks for the duration of the established connection under the control of a hook switch.

Videotelephone system with anti-crosstalk means

A central office of a videotelephone system has a cross-bar switch to establish connections between incoming and outgoing video lines terminating at the transmitters and receivers of the videotelephone sets of the several outlying stations. A central sync-pulse generator works into the incoming video lines to control the sweep circuits of the video receivers of stations to which connections have been established, each video receiver being linked with the associated video transmitter through a delay circuit which actuates the line-scan generators of the transmitter and of the receiver with a relative offset compensating for the transit time of the sync pulses between the central office and the station. The sync pulses are supplied to each incoming video line through an amplifier stage preceded by a shunt circuit including a transistor to which quenching pulses for grounding the line are periodically applied by the sync-pulse generator.

Videotelephone system with centralized synchronization control

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Milan, Italy

Virgilio Mosca