Private branch exchange system

0001This invention relates to a private branch exchange system and, more particularly, to a private branch exchange system which accommodates external line wires and extensions and, on the extension side, communications equipment usable in event of a power failure, wherein communications such as a telephone conversation can be carried out by the communications equipment for power failure when a power failure occurs.

0002JP 60-103896 describes a communication system comprising an extension terminal including communication means for performing communication and an internal network to which an external line is connected and said extension terminal is connected to the internal network through an extension line.

0003JP 61-23496 discloses a further private automatic branch exchange system. This system uses a specific extension telephone set when a power failure occurs.

0004In a private branch exchange, a well-known technique in the prior art is to change over the circuit to a telephone for power failure when a power failure occurs, thereby making it possible to receive calls and make calls during the power failure.

0005Fig. 3 illustrates the construction of the conventional private branch exchange apparatus. As shown in Fig. 3, numeral 400 denotes an external line wire, 401 a line-wire changeover relay, 404 an exchange apparatus, 406 a extension changeover relay, and 408 an extension telephone usable in the event of a power failure. When the exchange 404 is being supplied with power from a commercial power supply or the like in a normal manner, the line wire 400 is connected to the exchange 404 via the make side (indicated by the dashed line) of the line-wire changeover relay 401 and a line 403.

0006A telephone call is placed by way of a path leading to the power-failure backup telephone 408 via a line 405, a line on the make side (indicated by the dashed line) of the extension changeover relay 406, and a line 407. When the supply of power to the exchange 404 ceases owing to a power failure or the like, the line-wire changeover relay 401 and the extension changeover relay 406 are restored automatically so that the line wire 400 is connected directly to the power-failure backup telephone 408.

0007When supply of power to the exchange 404 is restored, the line-wire exchange relay 401 and extension changeover relay 406 are driven automatically so that a telephone call can be placed via the ordinary route, described above.

0008Further, in another example of the prior art, the line-wire exchange relay 401 and extension changeover relay 406 may be replaced by manually operated changeover switches.

0009A problem encountered in the above-described example of the prior art is that when the extension telephone usable in a power failure starts to be used during a power failure and then power is restored during a telephone conversation, the path being used for the conversation is cut unconditionally if the line-wire and extension changeover means are automatic means, such as relays. As a result, the call is cut off while still in progress.

0010If the line-wire and extension changeover means are manual means such as switches, on the other hand, an operating error is possible if the switches are operated erroneously or if the operator forgets to make a changeover. In addition, operating the switches is troublesome and therefore the system is not easy to use.

0011Accordingly, an object of the present invention is to provide a private branch exchange in which back-up and restoration processing of a line at occurrence of a power failure is performed automatically and reliably without requiring a troublesome operation.

0012Another object of the present invention is to provide a private branch exchange which uses communications equipment, usable in during a power failure, having both line-wire and extension interfaces, wherein channel backup and restoration processing can be performed reliably even when a power failure occurs repeatedly.

0013Still another object of the present invention is to provide a private branch exchange system in which restoration from a power failure can be carried out without interrupting communication in progress.

0014These objects are achieved with a system according to Claim 1, a terminal according to Claim 9 and a method according to Claim 16.

0015Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof. <ul id="ul0001" list-style="none" compact="compact"><li>Fig. 1 is a block diagram illustrating a private branch exchange in an embodiment of the present invention; and</li><li>Fig. 2 is a block diagram showing the peripheral circuitry of a call monitoring circuit.</li><li>Fig. 3 is a block diagram illustrating the construction of a private branch exchange apparatus according to the prior art;</li></ul>

0016An embodiment of the present invention will now be described with reference to the drawings.

0017In this embodiment, the changeover is carried out on the side of the telephone usable also in the event of a power failure.

0018Fig. 1 is a block diagram illustrating the construction of a private branch exchange system in the embodiment.

0019In Fig. 1, numeral 1 denotes the main apparatus which mainly comprises a line-wire interface 4, an extension interface 5, a call channel unit 6 for administering the switching of calls by time-division switching, and a CPU 7 for administering control of each of the components of the main apparatus 1, and for executing communication with a telephone, which is connected to an extension, via an extension line 3. A ROM 8 for storing the control program of the CPU and a RAM 9 used as a work area are connected to the CPU 7.

0020In Fig. 1, numeral 2 is line wires. The block indicated by numeral 10 on the right-hand side of Fig. 1 is a telephone usable also in the event of a power failure. (As shown in Fig. 1, a plurality of these telephones are capable of being connected to the main apparatus 1.) The telephone 10 is connected to the main apparatus 1 by the extension lines 3. Also the main apparatus 1 is capable of accommodating a extension telephone which can not communication in the power failure. The structure of the power-failure telephone 10 will now be described.

0021The telephone 10 includes a CPU 11 for administering control of the overall telephone, a ROM 12 storing the control program of the CPU 11, a RAM 13 which stores various control data and various information of the telephone 10, and which provides a working area for various types of processing, an interface circuit 14 for performing an exchange of communication signals and control signals with the main apparatus 1, a key matrix 15 which accepts inputs from numeric keys, function keys and the like, an off-hook detecting circuit 16, and a display unit 17.

0022The power-failure telephone 10 also includes a speech network circuit 18 used at the time of ordinary operation, namely when a power failure is not in effect, a speaker 19, and a handset 20. In the event of a power failure, only the handset 20 is used in a conversation, and the speaker 19 is used only for ringing at the time of a power failure.

0023Further, the telephone 10 includes power-failure relays 21, 22. The power-failure relay 21 is for connecting the channel at the time of a power failure, and the power-failure relay 22 is for connecting the speaker 19 and the handset 20 to either the ordinary speech network circuit 18 or a speech network circuit 26 for use in the event of a power failure and a ringing-signal generating circuit 25. These power-failure relays are changed over, under the control of the CPU 11, depending upon the state of power feed from a feeder circuit 29. The positions of the contacts indicated by the dashed lines are make positions for a case where power feed is being performed normally and a relay drive circuit 23 is ON owing to control performed by the CPU 11. These contact positions are held by passage of a current through the relays. The positions of the contacts indicated by the solid lines are break positions for a case where a power failure has occurred or power is being supplied and the relay drive circuit 23 is OFF owing to control performed by the CPU 11.

0024The relay drive circuit 23 for driving the aforesaid relays holds the power-failure relays 21, 22 in the aforementioned make positions in a case where power feed is being performed normally and drive circuit is ON owing to control by the CPU 11.

0025The power-failure telephone 10 is further provided with a hook switch 24, a ringing-signal generating circuit 25, a power-failure speech network circuit 26, a dialing circuit 27, a call monitoring circuit 28, and a circuit 29 for feeding the telephone with power. The call monitoring circuit 28 detects the status of a call (the status of an on-hook signal) at restoration of power. The detailed construction of this circuit will be described later.

0026The operation of this apparatus under ordinary circumstances, operation when a power failure occurs, operation when a call is in progress during a power failure, operation immediately after power is restored, and operation at the end of a call following the restoration of power will now be described.

<ORDINARY OPERATION>

0027In the ordinary state, namely the state in which current is being fed, the relay drive circuit 23 is placed in the ON state by the CPU 11, so that relays pf1, pf2, pf3 and pf4 are changed over to the make side, indicated by the dashed lines. As a result, the ringing signal generating circuit 25, power-failure speech network circuit 26, dialing circuit 27 and call monitoring circuit 28 are not fed with power, and the call is implemented by the path constituted by the speech network circuit 18, interface circuit 14 and extension lines 3.

<OPERATION AT OCCURRENCE OF POWER FAILURE>

0028When a power failure occurs and feed to the main apparatus 1 ceases, feed from the feeder circuit 29 in the power-failure telephone 10 also ceases, as a result of which the relay drive circuit 23, CPU 11, ROM 12, RAM 13, interface circuit 14, off-hook detecting circuit 16, display unit 17 and speech network circuit 18 get to be not fed. Accordingly, the relays pf1, pf2, pf3 and pf4 of the power-failure relays 21, 22 are changed over to the break side indicated by the solid line, and line wire 2 is directly connected to the hook switch 24 without connecting the channel unit 6.

<CALL OPERATION DURING POWER FAILURE>

0029The details of the construction of the call monitoring circuit and related portions are illustrated in Fig. 2. Portions similar to those shown in Fig. 1 are indicated by like reference characters.

0030The line wires 2 are connected to the power-failure speech network circuit 26 via the hook switch 24 (see Fig. 10). The speech network circuit 26 includes a parallel connected capacitor 34 and rectifier stack 35. The + output of the rectifier stack 35 is inputted to the call monitoring circuit 28 via a resistor 33 and is connected to a resistor 31 within the call monitoring circuit 28.

0031The call monitoring circuit 28 is connected to a line of the power-failure speech network circuit 26 via the resistor 33. The call monitoring circuit 28 comprises a photocoupler 30 for detecting a call on this line, the resistor 31 and a resistor 32.

0032The operation through which an outgoing call is made from the power-failure telephone to the line wires 2 will now be described.

0033When the handset 20 is lifted (taken off the hook), the line wires 2 are connected to the power-failure speech network circuit 26 by the hook switch 24 via the power-failure relay 21, and a loop is closed at the proper impedance by the power-failure speech network circuit 26.

0034As a result, a dial tone is returned from the local exchange of the line wires 2 and dialing is performed using the key matrix 15. In accordance with the input from the key matrix 15, an outgoing call is made to the line wires 2 by DP or PB via the dialing circuit 27. Thereafter, a telephone conversation is carried out when there is a response from the called party on the side of line wires 2.

0035In a case where a power failure is in effect and an incoming call is received from the line wires 2, i.e., an incoming call arrives from the line wires 2 in a state where the handset 20 is on the hook, the incoming signal enters the ringing signal generating circuit 25 via the power-failure relay 21 and hook switch 24, and an incoming tone is outputted to the speaker 19 from the ringing signal generating circuit 25.

0036When the incoming call is responded to by lifting the handset 20 (taking the handset off the hook), the hook switch 24 is changed over to the side of the power-failure speech network circuit 26 and a telephone conversation is carried out.

0037In the above-described outgoing and incoming call operations, lifting the handset 20 connects the line wires 2 to the power-failure speech network circuit 26 via the hook switch 24. When this occurs, the power-failure speech network circuit 26 is fed from the line wires 2 and the output side (the + and - terminals) of the rectifier stack 35 develops a voltage. During a power failure, however, the +5 V power supply shown in the call monitoring circuit 28 of Fig. 2 vanishes and the CPU 11 stops being supplied with power.

<OPERATION AT RESTORATION OF POWER>

0038When a telephone conversation is started during a power failure and power is restored while the conversation, which has been allowed to continue, is in progress, power feed to the main apparatus 1 is resumed and this is accompanied by start up of the feeder circuit 29 in the power-failure telephone 10. Accordingly, power is supplied to the relay drive circuit 23, CPU 11, ROM 12, RAM 13, interface circuit 14, off-hook detecting circuit 16, display unit 17 and speech network circuit 18.

0039When power is thus supplied again, the CPU 11 effects a power-on reset and executes initializing processing by the reset operation. This processing includes placing the relay drive circuit 23 in the OFF state and holding the power-failure relays 21, 22 on the break sides indicated by the solid lines.

0040In a case where a telephone conversation is in effect since prior to the restoration of power, a voltage is produced at the output of the rectifier stack 35 in the power-failure speech network circuit 26 by feed from the line wires 2, as described above. Therefore, when the +5 V is fed to the photocoupler 30 via the resistor 32 owing to the restoration of power, a current flows into a light-emitting diode on the input side of the photocoupler 30 via the resistors 33, 31, and the collector output of the transistor on the output side falls to a low level.

0041In a case where the low-level output of the call monitoring circuit 28 is detected, the CPU 11 maintains the relay drive circuit 23 in the OFF state and holds the power-failure relays 21, 22 on the break sides indicated by the solid lines, thereby holding the call in progress.

<OPERATION AT END OF CALL AFTER RESTORATION OF POWER>

0042When, as described above, a held telephone conversation ends after the restoration of power and the handset 20 is hung up, the hook switch 24 is changed over from the side of the power-failure speech network circuit 26 to the side of the ringing signal generator circuit 25.

0043As a result, the line wires 2 connected to the power-failure speech network circuit 26 via the power-failure relay 21 and hook switch 24 are disconnected, the feed of power to the power-failure speech network circuit 26 ceases, and the voltage at the output side of the rectifier stack 35 vanishes. The current flowing into the light-emitting diode on the input side of the photocoupler 30 via the resistors 33, 31 also vanishes so that the collector output of the transistor on the output side assumes a high level.

0044Upon detecting the high-level output of the call monitoring circuit 28, the CPU 11 turns on the relay drive circuit 23 so that the power-failure relays 21, 22 are changed over to the make sides indicated by the dashed lines. Thereafter, the telephone conversation is carried out through the usual path.

0045In accordance with the embodiment described above, a telephone for a power failure is internally provided with monitoring means for monitoring the call status of this telephone prevailing immediately after restoration from a power failure. Based upon the results of the monitoring operation, means for connecting line wires directly to a telephone for a power failure is controlled automatically. As a result, a telephone conversation continuing from the onset of a power failure can be held in this state immediately after the restoration of power, and the conversation in progress is no longer cut off at restoration of power, as occurs in the prior art.

0046Furthermore, the end of the call continuing since the onset of the power failure is detected and the usual operating state is restored automatically. Thus, the private branch exchange of the present invention does not require troublesome manual changeover means and therefore is easy to use and highly reliable.

0047Though a power-failure telephone is illustrated in the foregoing embodiment, the terminal apparatus is not limited to a telephone, and various communications equipment can be used.

0048In accordance with the embodiment, as described above, there is provided a private branch exchange system which accommodates line wires and an extension, as well power-failure communications equipment on the extension side, wherein communication by the power-failure communications equipment is carried out when a power failure occurs. The power-failure communications equipment is provided with means for switchingly making a connection to a power-failure line which makes it possible to use the power-failure communications equipment in event of power failure, monitoring means for monitoring call status on the power-failure line, and control means for performing control in such a manner that, in a case where communication using the power-supply line is in the process of being continued at restoration from a power failure, a connection to the power-failure line is held until the communication ends, and a changeover is made to a main-line side after the end of the communication. As a result, communication allowed to continue from the onset of the power failure can be maintained immediately after power is restored. When communication ends, the ordinary operating state can be restored automatically. Accordingly, the private branch exchange system of the present invention does not require a troublesome manual operation, and line back-up and restoration processing at occurrence of a power failure are performed automatically and in a reliable manner.

0049As many apparently widely different embodiments of the present invention can be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments thereof except as defined in the appended claims.

0050In a private branch exchange system which includes a private branch exchange accommodating a plurality of line wires and extensions for switching lines between the two, and telephones, which are usable in the event of a power failure, connected to the extensions, the line wires and the power-failure telephones are connected when power feed to the private branch exchange is no longer performed owing to a power failure or the like. When power feed is restored, the call status of the power-failure telephone is monitored and, if it is found that a call is in progress.