CH623439A5 - Device for limiting call duration in a telephone system - Google Patents

Description

The present invention relates to a device for the selective limitation of the call duration for unauthorized users in a telephone system. The advent of self-dialing for long-distance and international connections and the increase in telephone taxes make it increasingly important that a telephone subscriber can restrict the use or misuse of his telephone while he is away. Many electronic and mechanical devices have been proposed which block the use of the telephone for outgoing local, long-distance and international calls, but which allow its use for local calls and emergency calls.

Many known devices are based on a number lock, i.e. they effect such a block on the basis of recognizing the type of number, either by the type and location of individual digits, e.g. the first digit zero,

or by the number of digits in a dialed number. However, certain numbering systems do not allow local calls to be recognized in such a simple way. In Great Britain, for example, change the recognition criteria from one central area to another, which brings unacceptably high costs. A further limitation of such devices is that, unless there are dial tone detection devices, they can often be circumvented by sending an additional number, e.g. One before the office is ready to receive the dialed number. Such a number is evaluated by a call blocking device as a pre-number for local calls, but is ignored by the control center, which accepts the dialed number as one with a remote code.

It is now the object of the invention to provide a device which keeps the costs arising from unauthorized telephone calls low in a simple manner. m

This object is achieved by the features mentioned in the characterizing part of the first claim. Advantageous further developments can be found in the further claims.

Some embodiments of the invention are subsequently explained in more detail. Since it is not the number that is used as the criteria for limiting the call, but rather the charge counting pulses, the call limiting device contains a detection circuit that responds to charge pulses.

the type of which depends on the type of charge signal. Where the charge pulses are transmitted by reversing the loop current, the charge pulse detector is a polarized device. Charge meter pulses are more common with the aid of short pulses outside the normal telephone bandwidth, e.g. 50 Hz or 16 KHz sent back to the caller. Simple devices for the detection of such impulses are already known and are frequently used for the operation of the private fee counter at the subscriber and at cashier stations.

In its simplest form, such a limiting device can be set in such a way that it forcibly ends a call after receipt of one or a small number of conversation pulses. This would of course end all calls, whether local or not. However, if it is desired that local calls can be made, which is sensible when local calls are charged with a low toll rate, then a timer is added to the call limiting device to cover the period between receipt of the first charge pulse, which is normally immediately after the answer of the call occurs and the next charge pulse occurs after a time that is inversely proportional to the charge meter frequency. A simple logic circuit can then be used to forcibly end a call if this period is shorter than that corresponding to a local call. The duration of this period is, of course, dependent on the particular tariff structure of the corresponding telephone administration and on the degree of local traffic, which is considered acceptable, the gradual structure of such tariff structures normally allowing the choice of its period for which no critical time measurement is necessary.

An unauthorized user could circumvent the facility of repeatedly making a new call until he has finished his call, which places an additional burden on the telephone exchange. To avoid this, the logic circuit controlled by the timer can be designed so that all further outgoing calls are temporarily blocked if an unauthorized call has been determined and ended. Such a lock can be for a predetermined period of time or until a manual reset, e.g. with a key to be effective. It would also be possible to carry out the reset electrically from the control center by transmitting a special signal from there. It should be noted that most telecommunications administrations would only allow such a block if it can be bypassed for an emergency call. This can be done relatively easily if the same emergency code, e.g. B. 999 in the UK, used throughout the country.

Connections made in manual mode are billed separately and can therefore be tracked, so it is doubtful whether the additional costs for enabling call prevention are justified. However, if it is considered important that such calls be prevented as well, they can be determined by the complete lack of charge pulses and the logic can be designed to end such calls as well. In those countries in which emergency calls are not charged, however, it will then again be necessary to take steps to overcome this block.

It should be noted that a limiting device based on the detection of billing meter pulses can be used in connection with a device relating to the recognition of the desired digit code. In fact, when using a call barring service after an interrupted call, certain means for recognizing the number code are necessary so that emergency

3rd

case calls can be made.

Physically, a call block, as described above, is a small unit that can be arranged in a subscriber station, but also as a separate unit for table or wall mounting, or combined with another device at the subscriber, e.g. B. can be arranged with a fee pulse counter at the subscriber. This device can be installed either at the subscriber or at the control center, in which case it is monitored by the operating personnel. The latter solution can be particularly advantageous for private branch exchanges.

If the unit is located in locations of the subscriber, a key operated switch enables the lock for authorized subscribers with corresponding keys to be removed and a choice made regarding the lock, e.g. "Only local calls" or "all outgoing calls blocked". It is also possible to make a choice regarding the permissible duration of the call after receiving the

623439

first charge counter pulse until the lock takes effect. If a duration of 35 seconds is set, e.g. According to today's British tariffs, a user can make local calls at any time of the day. Calls up to 56 kilometers only during normal and discount hours and calls over 56 kilometers only during the discount hours. In this case too, the call limiting device limits the call costs.

Such a limiting device is also a relatively simple and inexpensive device for controlling the traffic load of telephone exchanges. It is effective and independent of the signaling methods used in the control center and no change is necessary if audio frequency signaling is used instead of loop interruption. The limiting device can be provided for each line and is effective whether the calls are set up by dialing a turntable, pushbutton dialing or call repeater. Furthermore, the way they work is not affected by sending out extra digits to receive the dial tone.

Claims (3)

623439 PATENT CLAIMS 1. Device for the selective limitation of the call duration for unauthorized users in a telephone system, characterized by means for the detection of charge impulses, which are given by the central office to a telephone subscriber 5, by a timer, and by the timer controlled means which force a call terminate after a certain time has passed since the first charge pulse, or if the time interval between two charge pulses is less than a predetermined value or if no charge pulse arrives within a predetermined time after the connection has been set up. 2. Device according to claim 1, characterized by means which respond to a forced call termination and block the subscriber station for all subsequent outgoing 15 calls either during a predetermined period of time or until a manual reset or until a reset signal is received from the control center. 3. Device according to claim 1 or 2, characterized by means for recognizing emergency number code to disable the 20 call barring when dialing emergency numbers.