Telephonic communications – Telephone line or system combined with diverse electrical... – To produce visual-graphic copy
Patent
1993-07-23
1995-11-14
Chan, Wing F.
Telephonic communications
Telephone line or system combined with diverse electrical...
To produce visual-graphic copy
H04M 1100
Patent
active
054673860
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a method for signalling/communication within an entrance telephone system or similar, and a system which operates according to the method.
BACKGROUND OF THE INVENTION
Within an entrance telephone system, the connection of subscribers/tenants is usually carried out using a 2-wire circuit for verbal communication, and a further 2-wire circuit is used to control the entrance lock in such a way that an opening operation is performed. When additional tenants are connected to a circuit having only 2.times.2 wires as disclosed above, each subscriber requires a substation, which, for example, can be addressed using PCM-signalling techniques (Pule Code Modulation), in order to facilitate the possibility of selectively calling and establishing communication with a certain chosen subscriber. A galvanical make operation for the pair of cables influencing the entrance lock will initiate an opening operation. However, this solution involves major problems, e.g. since a subscriber not replacing the handset will block the circuit, and also since intervention of calls in progress and opening operation can be performed by subscribers other than the party presently called. An alternative solution is to use more conventional connection techniques ("switching") with selection of subscriber by means of delays or the like, involving use of separate cables or successively reduced group of cables. Communication secrecy and opening operation exclusivity can thus be accomplished, but not guaranteed to 100% due to capacitive coupling between included wires. Such systems also involve problems with regard to service, maintenance and repair. In order to prevent a non-replaced handset of any of the subscribers from blocking the loop completely, a relatively complicated surveillance technique is often required within the entrance center. Particularly for large installations, wiring will often be complicated, multiwired and expensive. The cost for the entrance center with associated switching means and the piece cost for each substation should also be added hereto. When a "loop" has been completed, any increase/reduction of the number of substations also involves large problems.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a method and a system which removes the problems discussed above, and which offers simple switching techniques and installation/wiring using a simple 2-wire circuit. Furthermore, complete communication secrecy, opening exclusivity and protection against blocking caused by "off-hook" is achieved.
The method according to the present invention for signalling/communication within an entrance telephone system or the like is intended to facilitate selective communication from an entrance center or central unit to a desired and addressed substation via a loop including at least two conductors, and also facilitate entrance lock opening or similar functions from such a substation. According to the method, the central unit, after an approved addressing operation is performed by a visitor, as a first step, feeds work current to the loop joining the central unit and connected substations. The central unit in connection herewith transmits an address code unique for the addressed substation. The addressed substation, using a signal detecting means, then establishes a galvanical connection between loop and substation. The central unit performs generation of a ring signal, detection of "off-hook" or other statuses or signalling changes. The central unit on detection of an incomplete reply, or terminated entrance telephone communication/function, interrupts the feed of work current to the loop.
The entrance telephone system according to the present invention includes an entrance center or central unit arranged to facilitate selective communication with a desired and addressed substation via a loop including at least two conductors, and also facilitate entrance lock opening or similar functions from such a substation. During operation of the entra
REFERENCES:
patent: 4987589 (1991-01-01), Trell
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