METHOD FOR SIGNALLING THE REASON FOR BREAK-OFF OF A CONNECTION TO A MAIN UNIT

Abstract: This invention relates to a method for signalling the reason for a break-off of a connection between a subscriber unit (1) and a main unit (2) to the main unit (2) in a telecommunication system, the subscriber unit (1) comprising a switching means (S1) which in the ON position forwards operating voltage to the subscriber unit (1), and which in the OFF position breaks off the supply of operating voltage to the subscriber unit (1); and an energy-storing device (T) which is arranged to discharge and supply operating voltage to the subscriber unit (1) when the operating voltage forwarded to the subscriber unit (1) via the switching means (S1) falls below a predetermined limit. In order to signal the reason for the break-off of the connection to the main unit (2) in as much detail as possible, the position of the switching means (S1) and the level of the operating voltage forwarded via the switching means to the subscriber unit (1) are supervised, and when said operating voltage falls below a predetermined level, a first alarm signal is transmitted to the main unit (2) if the switch (S1) is in the OFF position, and a second alarm signal is transmitted to the main unit (2) if the switch (S1) is in the ON position. The invention also relates to a subscriber unit.

Description: Method for signalling the reason for break-off of a connection to a main unit The present invention relates to a method for signalling the reason for a break-off of a connection between a subscriber unit and a main unit to the main unit in a telecommunication system, the subscriber unit comprising a switching means which in the ON position forwards operating voltage to the subscriber unit, and which in the OFF position breaks off the supply of operating voltage to the subscriber unit; and an energy- storing device which is arranged to discharge and supply operating voltage to the subscriber unit when the operating voltage forwarded to the subscriber unit via the switching means falls below a predetermined limit. The invention also relates to a subscriber unit of a telecommunication system having a data transmission connection with a main unit of the telecommunication system, the subscriber unit comprising means for receiving telecommunication signals forwarded by the main unit and for transmitting telecommunication signals to the main unit; a power supply; a switching means which in the ON position forwards operating voltage to the subscriber unit, and which in the OFF position breaks off the supply of operating voltage to the subscriber unit; and an energy-storing device which is arranged to discharge and supply operating voltage to the subscriber unit when the operating voltage forwarded to the subscriber unit by the switching means falls below a predetermined limit. In this connection, the telecommunication system refers to a computer network, a telephone network, a radio network or the like system in which the different components of the system have a data trans- mission connection with each other by means of a trunk circuit or via the radio path. In order to ensure the quality of the data transmission connection, it is most important to detect fault situations of different components as fast as possible. In this case, modems, data circuit-terminating equipments and other subscriber units are in a special position as far as supervision is concerned, since they are often positioned at the end user's location, they get their supply of electricity there and are subject to the operation of the end user. In a previously known telecommunication system subscriber units use a voltage source which can supply current and a signal notifying of a break-off of electricity even a moment after a power failure. Then the subscriber unit transmits a signal to the main unit of the system by which it informs that it is a question of a power failure. The main unit can thus distinguish between a line failure and a power failure. However, a drawback of the above-mentioned known arrangement is that the main unit cannot distinguish between a situation in which a power failure is caused by an actual power failure and a situation in which a power failure is caused by the user having switched off the subscriber unit by pressing an electric switch. At the main unit end these situations appear to be alike, due to which the main unit will unnecessarily send an alarm to the operator in a situation which does not in fact concern a fault at all. The object of the present invention is to solve the above-mentioned problem and provide a method by means of which the reason for a break-off of a connection can be signalled from a subscriber unit to a main unit in a more detailed way than previously, so that the main unit will not unnecessarily alarm the operator. This object is achieved by the method of the invention which is characterized in that the position of the switching means and the level of the operating voltage forwarded via the switching means to the subscriber unit are supervised, and when said operating voltage falls below a predetermined level, a first alarm signal is transmitted to the main unit if the switch is in the OFF position, and a second alarm signal is transmitted to the main unit if the switch is in the ON position. The invention further relates to a subscriber unit with which the method of the invention can be applied. The subscriber unit of the invention is characterized in that the subscriber unit comprises a signal generator responsive to the position of the switching means, which generator is arranged to generate a first alarm signal when the operating voltage forwarded by the switching means to the subscriber unit falls below a predetermined limit if the switching means is in the OFF position, and which generator is arranged to generate a second alarm signal when the operating voltage forwarded by the switching means to the subscriber unit falls below a predetermined limit if the switching means is in the ON position; and means for forwarding the first and second alarm signal to the main unit of the telecommunication system. The invention is based on the idea that when the electric switch of the subscriber unit is supervised electromechanically, the switching off of the subscriber unit by the user can be distinguished from a power failure, whereby the first alarm signal is transmitted to the main unit in a situation in which the electric switch is in the OFF position as the subscriber unit is losing electricity, and the second alarm signal in a situation in which the electric switch is in the ON position as the subscriber unit is losing electricity. Consequently, the main unit can make a distinction between situations in which the connection is broken off: - by the user so that the main unit will receive the first alarm signal before the connection is broken off; - due to a power failure so that the main unit will receive the second alarm signal before the connection is broken off; - due to a line failure, whereby the main unit will not receive either the first or the second alarm signal before the break-off but the connection is "abruptly" broken off. The most significant advantages of the method and the subscriber unit of the invention are thus that the reason for a break-off of a connection between a subscriber unit and a main unit can be signalled in detail to the main unit, and that the main unit will not unnecessarily alarm the operator. One preferred embodiment of the subscriber unit according to the invention utilizes a transformer known per se for storing energy. This transformer comprises means for generating a predetermined signal when the voltage of its primary winding falls below a pre¬ determined level. In this case, the secondary winding of said transformer can supply operating voltage to the subscriber unit a sufficiently long time so that the signal generator can transmit, depending on the position of the switching means, the first or the second alarm signal to the main unit. The most significant advantage of the embodiment of the invention is that it is inexpensive and uncomplicated. The preferred embodiments of the subscriber unit of the invention are disclosed in the appended dependent claims 3 to 5. In the following, the invention will be explained in more detail by means of a few preferred embodiments of the invention with reference to the accompanying figures, of which Figure 1 shows a first preferred embodiment of the subscriber unit according to the invention, and Figure 2 shows a second preferred embodiment of the subscriber unit according to the invention. Figure 1 shows a first preferred embodiment of the subscriber unit according to the invention. In Figure 1 the subscriber unit is switched off, that is, its on-off switch SI is in the OFF position. A subscriber unit 1 shown in Figure 1 is a terminal of a telecommunication system, such as a computer network, telephone network or a radio system and it is positioned at the user's location and has a data transmission connection with other parts of the system. The subscriber unit 1 in Figure 1 has a data transmission connection with a main terminal 2 via a connection cable 6. Figure 1 indicates that the on-off switch SI comprises two separate circuits that shift between the ON and OFF positions at the same time as the user presses the switch SI manually. The operating voltage (220 V, for example) is supplied via the first circuit to a transformer T of the subscriber unit 1. The transformer T transforms and rectifies the operating voltage, whereby it supplies 5 V of direct voltage, for example, from its output to the other parts of the subscriber unit 1. In the case of Figure 1 these other parts, which receive operating voltage from the transformer T, comprise a central processing unit 3, a signal generator 4 (via an interface A) and an I/O unit 5 (Input/Output) through which the subscriber unit is connected to the connecting cable 6. Peripheral devices (such as a visual display terminal, a keyboard, etc.) included in the subscriber unit 1 are connected to the central processing unit 3 by means of a bus 7. The output of the transformer T is connected via the second circuit of the on-off switch SI to an interface B of the signal generator 4. Hence, the signal generator 4 supervises the position of the switch SI electro- mechanically. During normal use of the subscriber unit 1, the switch SI is in the ON position (not shown in Figure 1) , wherein current is flowing through both of its circuits. In that case, the I/O unit 5 is responsive to the cen¬ tral processing unit 3 in a way that it forwards signals between the central processing unit 3 and the main terminal 2. The signal generator 4 is then in a passive state, that is, it does not generate or forward signals. Said passive state continues until the transformer T supplies a predetermined signal to an input C of the signal generator. Said signal notifies the signal generator 4 that the primary winding of the transformer T is losing operating voltage. When a user switches off the terminal 1 by shifting the switch SI to the OFF position, the signal generator 4 detects this in a way that the transformer supplies a predetermined amount of signals to its input C at the same time as the voltage signal is lost at the interface B. The transformer T can, however, supply operating voltage to the interface A of the signal generator and to the I/O unit 5 some time still (at least for a period of a few milliseconds) after losing operating voltage (220 V) . The signal generator 4 is thus able to generate the first alarm signal and transmit it via the I/O unit 5 to the main terminal 2. The I/O unit stops forwarding signals from the central processing unit 3 to the main terminal in response to the first alarm signal. The main terminal 2 continually monitors the signals supplied to it, due to which it immediately detects and identifies the first alarm signal. The main terminal 2 (and the operator) is thus notified that the break-off of the connection to the subscriber unit 1 is caused by the user having switched off the subscriber unit 1 by means of the on-off switch SI. On the other hand, when the current is broken off because of a power failure, the signal generator 4 detects this in a way that the transformer T supplies a predetermined signal to its input C at the same time as a voltage signal of 5 V is still supplied to its input B. Even in this case, the transformer T is able to supply the operating voltage to the interface A of the signal generator and to the I/O unit 5 some time still (at least for a period of a few milliseconds) after losing operating voltage (220 V) . The signal generator 4 is thus able to generate the second alarm signal and transmit it via the I/O unit 5 to the main terminal 2. The I/O unit stops forwarding signals from the central processing unit 3 to the main terminal in response to the second alarm signal . The main terminal 2 continually monitors the signals to be supplied to it, due to which it immediately detects and identifies the second alarm signal. The main terminal 2 (and the operator) is thus notified that the break-off of the connection to the subscriber unit 1 is caused by a power failure. If the main terminal 2 detects that the connection to the subscriber unit 1 is broken off without the main terminal 2 having received the first or the second alarm signal, it means that the connection is broken off due to a line failure or a like disturbance. In this case, the main terminal generates an alarm to the operator's terminal. The first and second alarm signals generated by the signal generator preferably consists of bit sequences with at least 64 bits. When using shorter bit sequences than these, it is possible that the exchange terminal will not have time to identify the first or the second alarm signal . Said bit sequence is in one case preferably scrambled 1 and in the other case scrambled 0. The signal generator 4 (or the I/O unit 5) thus comprises preferably a scrambler in which the polynomial can be 1+X^+X "7 , for example. Hence, the main terminal 2 comprises a corresponding descrambler. Figure 2 shows a second preferred embodiment of the subscriber unit according to the invention. The subscriber unit shown in Figure 2 is both by its structure and its operation to a great degree identical to the subscriber unit shown in Figure 1. In the subscriber unit of Figure 2, the switch SI is arranged after a transformer T' . The output of the transformer T' is thus switched to the first circuit of the switch SI, whereby the voltage to be supplied to the switch is 5 V. The poles of the second circuit of the switch SI are also switched in a different way to the case of Figure 1, that is, to interfaces D and E of a signal generator 4' . In the embodiment of Figure 2, the transformer T" does not supply the predetermined signal explained in connection with Figure 1, as an indication that it is losing operating voltage. On the other hand, a device measuring operating voltage and a device storing energy are integrated to the signal generator 4', the device preferably being a winding, a capacitor, a battery or the like which is charged during the use of the subscriber unit 1. Depending on the necessary amount of energy, an energy-storing device can naturally also be accomplished by means of the signal generator 4' as a separate unit. When operating voltage is after this switched off at the subscriber unit, the signal generator 4' detects that the operating voltage is declining, whereby the energy-storing device discharges in a way that it supplies operating voltage to the signal generator 4' and the I/O unit 5 a sufficiently long time so that the signal generator has time to generate and transmit the first or the second alarm signal to the main terminal . When the user switches off the subscriber unit 1 of Figure 2 with the switch SI by shifting it to the OFF position, the signal generator 4' detects the change in the position of the switch SI in a way that the galvanic contact between the interfaces D and E is broken off when the secondary winding of the switch SI opens at the same time as it loses the operating voltage supplied to its interface A. Then the energy-storing device (capacitor) in the signal generator starts to discharge, whereby it supplies operating current to the signal generator and to the I/O unit a sufficiently long time so that the first alarm signal generated by the signal generator 4' can be transmitted to the main terminal 2. In case of a power failure, the signal generator 4' notices that it is losing the operating voltage supplied to its interface A. In that case, the galvanic contact between the interfaces D and E is retained because the switch SI is still in the ON position. Therefore, the signal generator 4' perceives that it is a question of a power failure. Then the energy-storing device in the signal generator starts to discharge, whereby it supplies operating voltage to the signal generator and to the I/O unit a sufficiently long time so that the second alarm signal generated by the signal generator 4' can be transmitted to the main terminal 2. It is to be understood that the above specification and the figures related to it are only meant to illustrate the present invention. The different variations and modifications of the invention will be evident to those skilled in the art without deviating from the scope and spirit of the invention presented in the appended claims.

Claims: Claims : 1. A method for signalling the reason for a break-off of a connection between a subscriber unit (1) and a main unit (2) to the main unit (2) in a tele¬ communication system, the subscriber unit (1) comprising a switching means (SI) which in the ON position forwards operating voltage to the subscriber unit (1) , and which in the OFF position breaks off the supply of operating voltage to the subscriber unit (1) ; and an energy-storing device (T, 4') which is arranged to discharge and supply operating voltage to the subscriber unit (1) when the operating voltage forwarded to the subscriber unit (1) via the switching means (SI) falls below a predetermined limit, c a r¬ a c t e r i z e d in that the position of the switching means (SI) and the level of the operating voltage forwarded via the switching means to the subscriber unit (1) are supervised, and when said operating voltage falls below a predetermined level, a first alarm signal is transmitted to the main unit (2) if the switch (SI) is in the OFF position, and a second alarm signal is transmitted to the main unit (2) if the switch (SI) is in the ON position. 2. A subscriber unit (1) of a telecommuni¬ cation system having a data transmission connection with a main unit (2) of the telecommunication system, the subscriber unit (1) comprising means (3, 5) for receiving telecommunication signals forwarded by the main unit (2) and for trans¬ mitting telecommunication signals to the main unit (2) ; a power supply (T, T' ) ; a switching means (SI) which in the ON position forwards operating voltage to the subscriber unit (1) , and which in the OFF position breaks off the supply of operating voltage to the subscriber unit (1) ; and an energy-storing device (T, 4') which is arranged to discharge and supply operating voltage to the subscriber unit (1) when the operating voltage forwarded to the subscriber unit (1) by the switching means falls below a predetermined limit, c h a r a c¬ t e r i z e d in that the subscriber unit comprises a signal generator (4, 4') responsive to the position of the switching means (SI) , which generator is arranged to generate a first alarm signal when the operating voltage forwarded by the switching means to the subscriber unit (1) falls below a predetermined limit if the switching means (SI) is in the OFF position, and which generator is arranged to generate a second alarm signal when the operating voltage forwarded by the switching means (SI) to the subscriber unit (1) falls below a predetermined limit if the switching means (SI) is in the ON position; and means (5,6) for forwarding the first and second alarm signal to the main unit (2) of the telecommuni¬ cation system. 3. A subscriber unit according to claim 2, c h a r a c t e r i z e d in that the first and second alarm signals consists of predetermined bit sequences, whereby the subscriber unit (1) comprises means (4, 4') for scrambling said bit sequences before transmitting them to the main unit (2) . 4. A subscriber unit according to claim 2 or 3, c h a r a c t e r i z e d in that said energy- storing device is a winding, a capacitor, a battery or the like arranged in connection with the signal generator (4'), whereby the signal generator (4') is arranged to generate the first or the second alarm signal when the operating voltage forwarded to the subscriber unit (1) by the switching means (SI) falls below a predetermined limit and the energy-storing device starts to discharge. 5. A subscriber unit according to claim 2 or 3 , c h a r a c t e r i z e d in that the power supply (T) is a transformer and said energy-storing device is a secondary winding of the transformer, whereby the transformer comprises means for generating and supplying a predetermined signal to an input (C) of the signal generator (4) when the operating voltage of a primary winding of the transformer falls below a predetermined limit, whereby the signal generator (4) is arranged to generate the first or the second alarm signal in response to said predetermined signal.

Inventors: LAPPALAINEN PEKKA, MANTILO KARI, LAPPALAINEN, PEKKA, MANTILO, KARI
Applicants: LAPPALAINEN PEKKA, MANTILO KARI, NOKIA TELECOMMUNICATIONS OY, LAPPALAINEN, PEKKA, MANTILO, KARI
Application year: 1995
Main classification: H04Q1
IPC codes: H04M1, H04M3