GB2366936A

GB2366936A - Key telephone system

Info

Publication number: GB2366936A
Application number: GB0129768A
Authority: GB
Inventors: Tamotsu Wakabayashi; Masashi Ishida; Katsunori Utsumi; Nobuhiro Masaki
Original assignee: Toshiba Corp
Current assignee: Toshiba Corp
Priority date: 1999-08-23
Filing date: 2000-08-22
Publication date: 2002-03-20
Anticipated expiration: 2020-08-22
Also published as: GB2366685B; GB2366685A; GB2366936B; GB0129768D0; GB0129760D0

Abstract

A key telephone system comprising:<BR> ```interface means having a line interface function of transmitting digital data to an ISDN network via a U point or via S and T points of an ISDN line and an extension interface function of transmitting digital data to an ISDN terminal, for selectively setting one of the functions; and<BR> ```control means for setting said interface means to implement one of said line interface function and said extension interface function in accordance with line setting information.

Description

2366936 ELECTRONIC EXCHANGE AND KEY TELEPHONE SYSTEM The present invention

relates to an electronic 5 exchange and a key telephone system.

An electronic exchange has been capable of controlling call reception from and call transmission to other electronic exchanges by employing the QSIG protocol defined by the European Computer Manufacturers 10 Association, which is the international standard for digital lines.

The services can be provided by constructing the networking by use of this kind of electronic exchanges as if one single electronic exchange were operated for 15 the user using the electronic exchanges.

FIG. 1 is a view showing a networking using conventional electronic exchanges. FIG. 2 is a view showing a sequence of a message signal forwarded between the electronic exchanges in the networking of 20 FIG. 1.

in FIG. 1 electronic exchanges 10, 11 and 12 are respectively connected to one another in digital lines 21, 22 and. 23 employing the QSIG protocol.

it is assumed now that telephones I and 2 25 communicate with one another via the electronic exchanges 10 and 11, and the telephone 2 forwards the call with the telephone 1 to a telephone 3 connected to the electronic exchange 12 so that the telephones 1 and 3 communicate with one another.

When the user of the telephone 2 executes hooking operation to the electronic exchange 11, a dial tone 5 signal is transmitted from the electronic exchange 11 to the telephone 2. At the same time, the telephone 1 of the communication partner is made to be in the on-hold state by the electronic exchange 11.

The user of the telephone 2 dials a telephone 10 number of the telephone 3 as the forwarding destination by the telephone 2 after having confirmed the dial tone.

The electronic exchange 11 transmits a forward acknowledgement signal "Facility message" defined by 15 the QSIG protocol to a digital line 22, in response to the dialing. At this time, specific information about the telephone number of the call destination, a person who forwards this message, a person who receives the forwarded message, etc., i.e. facility information 20 elements are added to the Facility message.

Receiving the "Facility message,, from the electronic exchange 11, the electronic exchange 12 checks whether the telephone 3 is idle or not. If the telephone 3 is idle, the electronic exchange 12 25 transmits to the electronic exchange 11 a "Call proceeding message", which indicates that the forwarding is acceptable.

On the other hand, the telephone 2 is in the on-hook state and remains idle after the dialing.

Receiving the "Call proceeding message" from the electronic exchange 12, the electronic exchange 11 5 recognizes that the telephone 3, which is a destination of a call to be forwarded to the electronic exchange 10, is idle and can accept the call. At this time, the electronic exchange 11 inserts the information about the forwarding into the "Facility message,, and 10 transmits the message to the electronic exchange 10 so that the electronic exchange transmits a calling request "Setup message" as a formal call start request to the electronic exchange 12.

The electronic exchange 10 transmits the "Setup 15 message" to the electronic exchange 12 in accordance with the information included in the "Facility message".

Receiving the "Setup message", the electronic exchange 12 checks again whether the telephone 3 20 is idle or not. If the telephone 3 is idle, the electronic exchange 12 transmits the "Call proceeding message", which represents the acknowledgement of acceptance for the call, to the electronic exchange 10.

At the same time, the electronic exchange 12 transmits 25 a calling signal to the telephone 3 and transmits "Alerting", which represents a state of extension calling, to electronic exchange 10.

Incidentally, with the conventional electric exchanges, in a case where a calling operation is executed at the telephone 3 or a call from the other telephones,is received at the telephone 3 after the 5 electronic exchange 12 has received the "Facility message" and transmitted the "Call proceeding message" representing that the forwarding is acceptable, when there is an incoming call from the electronic exchange 10, the telephone 3 is busy and thus the forwarding is 10, not accomplished, as shown in a flow chart of FIG. 3.

in this case, there is also a drawback that the data traffic unnecessarily increases since an invalid signal is transmitted within the network.

Calling restriction as to whether a call from 15 extension telephones should be accepted is often executed in accordance with international, long distance and local destinations of calling. In this case, with the conventional electronic exchanges, the information unique to the manufacturer, common to only electronic exchanges of the same manufacturer is inserted into the manufacturer information element of the QSIG protocol, and is provided to electronic exchanges connected to the public telephone network by those connected to extension telephones.

25 Transmission of the manufacturer information element needs to be executed under the dedicated coding rules, and software for transmission and reception is also required. For this reason, the load on the CPU (central processing unit) in the electronic exchange may increase, technical problems may arise, and circuitry may be complicated due to the addition of new 5 hardware.

FIG. 4 is a block diagram showing a configuration of a conventional key telephone system adapted to U point of an ISDN line.

A key telephone system 50 includes an ISDN 10 interface unit (I/F unit) 51 for connecting with an ISDN network 60 and an ISDN terminal 70, and a control unit 52 for controlling the ISDN interface unit 51 and executing the calling process and the speech exchange process.

15 The -ISDN interface unit 51 and the control unit 52 exchange various signals such as speech data, 'a clock signal, a frame synchronization signal, a control signal, etc. via an internal bus 53.

FIG. 5 is a block diagram showing the structures 20 of the ISDN interface unit 51 and the control unit 52.

The ISDN interface unit 51 includes an interface LS1 80 for interfacing.(called NT) with the ISDN network 60, and an interface LSI 81 for interfacing (called LT) with the ISDN terminal 70. The interface 25 LS1 80 is fixed to the NT mode that allows the operation to be made in accordance with a clock signal extracted from the ISDV network 60. The interface LSI 6 - 81 is fixed to the LT mode that makes the terminal synchronous by using its own clock signal. A port corresponding to the NT mode is called a line port and a port corresponding to the LT mode is called an 5 extension port.

when the interface LSI 80 is set to extract clock signal CLK from the ISDN network 60, i.e. when the interface LSI 80 is set in the NT mode, a switch unit 82 is turned on and a switch unit 84 is turned off.

10 The interface LSI 80 extracts the clock signal CLK from the ISDN network 60 and outputs the signal through its own clock port.

The clock signal CLK that is output from the interface LSI 80 is input to a timing generation unit 15 85 of the control unit 52 as basic clock signal CLKb through the switch unit 82.

The timing generation unit 85 generates system clock signal CLKs in accordance with the basic clock signal CLKb and supplies this signal to both a time 20 switch unit 86 of the control unit 52 and a phase adjustment time switch unit 83 of the ISDN interface unit 51 to make synchronization in the system.

The timing generation unit 85 also generates a frame synchronization signal FS and outputs the signal to 25 the phase adjustment time switch unit 83 and the time switch unit 86.

Synchronization between the interface LSI 80 and the interface LSI 81 is made by the clock signal CLK that is output from the interface LSI 80 and the frame synchronization signal FS. The speech data of the interface LSI 80 and the interface LS1 81 is 5 transmitted to the phase adjustment time switch unit 83 in a single speech data highway DH1 and further transmitted to the time switch unit 86 in a speech data highway DB2 synchronized with the time switch unit 86.

When the interface LSI 80 is set not to extract 10 the clock signal CLK from the ISDN network 60, i.e.

when the interface LSI 80 is set in the LT mode, the switch unit 82 is turned off and the switch unit 84 is turned on. The interface LS1 80 and the interface LSI 81 are made synchronized with the system by the system 15 clock signal CLKs and the frame synchronization signal FS that are generated by the timing generation unit 85 of the control unit 52. At this time, the clock ports of the interfaces LSis 80 and 81 are set in the input state.

20 in the case of the conventional key telephone system constituted as described above, the interface LSIs 80 and 81 are fixed to either the NT mode or the LT mode and, therefore, the degree of freedom in the selection of the line is small. For example, if the 25 user requires two interfaces in the NT mode, it is necessary to prepare for another ISDN interface unit 51. For this reason, the circuitry of the system becomes larger and the miniaturization is prevented, and the manufacturing costs are increased.

FIG. 6 is a block diagram showing the configurations of an ISDN interface unit 56 and a 5 control unit 57 in the conventional key telephone system adapted to S and T points of the ISDN line.

The ISDN interface unit 56 includes an interface LSI 120 for interfacing (called TE) with the ISDN network 60 and an interface LSI 121 for interfacing 10 (called NT) with the ISDN terminal 70. The interface LSIs 120 and 121 are fixed to either the TE or the NT.

When the interface LSI 120 is set to extract the clock signal CLK from the ISDN network 60, i.e. when the interface LSI 120 is set in the TE, the interface 15 LSI 120 extracts the clock signal CLK from the ISDN network 60 and outputs the signal through the clock port. The clock signal CLK output from the interface LSI 120 is input to a timing generation unit 123 of the control unit 57.

20 The timing generation unit 123 generates the system clock signal CLKs in accordance with the clock signal CLK and supplies the signal to the interface LSI 121 that synchronizes with the timing generation unit 123 as a slave at the NT mode. The timing generation 25 unit 123 also generates a frame synchronization signal FS1. The frame synchronization signal FS1 is supplied to a phase adjustment time switch unit 122 together with a frame synchronization signal FS2 output from the interface CSI 120. Speech data DSI and DS2 of the interface LSIS 120 and 121 is supplied from the phase adjustment time switch unit 122 to the a time switch 5 unit 12 4 of the control unit 57 in a single speech highway HS.

In the interface LSI 121, the frame synchroniza tion is executed by using the frame synchronization signal FS1 generated by the timing generation unit 10 123 of the control unit 57, due to the slave synchronization.

In the case of this conventional key telephone system, like the above-described key telephone system, the interface LSIs 120 and 121 are fixed to either the 15 NT mode or the TE mode and," therefore, the degree of f reedom. in the selection of the line is small. If the user requires two NT functions, it is necessary to prepare for another ISDN interface unit 56. For this reason, the circuitry of the system becomes larger and 20 the miniaturization is prevented, and the manufacturing costs are increased.

The present invention is accomplished in consideration of such circumstances, and the object 25 thereof"is to provide an electronic exchange capable of certainly making forwarding to a telephone at the forwarding destination and a key telephone system with a high degree of freedom in the selection of the line.

To achieve the object, according to the first aspect of the present invention, an electronic exchange capable of controlling call reception from and call 5 transmission to other electronic exchanges is provided.

The electronic exchange comprises means for receiving a request for a forwarding from the other electronic exchanges, and prohibiting means for setting a telephone of forwarding destination connected to the 10 own electronic exchange to be in a state of prohibiting the call reception except for the forwarding or the call transmission at the time to make the telephone shift to a standby state for the forwarding in response to the request for the forwarding.

15 According to the present invention, the telephone of the forwarding destination is shifted from the idle state to the receiving standby state for the forwarding, in response to the request for forwarding from the other electronic exchange, so as to set the 20 call transmission and the call reception except for the forwarding at the telephone to be impossible.

Therefore, even if calling operations are executed at the telephone of the forwarding destination or there is a call from a different telephone, the calling is 25 invalid and thereby the forwarding of the call can be certainly accomplished. Further, the data traffic is not unnecessarily increased since an invalid signal is not transmitted into the network as seen in the prior art.

it is preferable that the electronic exchange is capable of controlling the call reception from and call 5 transmission to the other electronic exchanges under the QSIG protocol.

It is preferable that when the telephone of forwarding destination connected to the own electronic exchange is idle after receiving a request for the 10 forwarding, the telephone is made to shift to be in a standby state for the forwarding.

it is preferable that the electronic exchange further comprises announcement setting means for setting the telephone so as to announce to a user 15 of the telephone that the telephone is set in the prohibition state.

According to the present invention, it is announced to the user of the telephone that the call reception except for the forwarding and the call 20 transmission are prohibited.

Thus, the user of the telephone at the forwarding destination can recognize that the forwarding is to be made. Therefore, he can properly make further response without being confused or making a mistake in the 25 operations.

The announcement setting means may set the telephone so as to operate a sound source provided in the telephone, set the telephone so as to display predetermined information on a display unit provided on the telephone, or set the telephone so as to turn on a light of a display unit provided on the telephone.

5 In addition, the announcement setting means may set the telephone so as to operate a sound source provided in the telephone when a calling key of the telephone is pushed down in a period from the time of shifting to the standby state for the forwarding to the 10 time of receiving an incoming of call caused by the forwarding. The announcement setting means sets the telephone so as to display predetermined information on a display unit provided on the telephone when a calling key of the telephone is pushed down in the period from 15 the time of shifting to the standby state for the forwarding to the time of receiving an incoming of call caused by the forwarding.

Further, the announcement setting means may set the telephone so as to turn on a light of a display 20 unit provided on the telephone when a calling key of the telephone is pushed down in the period from the time of shifting to the standby state for the forwarding to the time of receiving an incoming of call caused by the forwarding. The announcement setting 25 means may also set the telephone so as not to accept input made by a dial key when a calling key of the telephone is pushed down in the period from the time of shifting to the standby state for the forwarding to the time of receiving an incoming of call caused by the forwarding.

According to another aspect of the present 5 invention, an electronic exchange capable of control ling call reception from and call transmission to other electronic exchanges is provided. The electronic exchange comprises means for receiving a request for a forwarding from the other electronic exchanges, and 10 announcement setting means for setting a telephone of forwarding destination connected to the own electronic exchange to announce to a user of the telephone that the telephone is set in a standby state for the forwarding at the time to make the telephone shift to 15 the standby state for the forwarding in response to the request for the forwarding.

According to the present invention, it is announced to the user of the telephone in response to the request for forwarding that the forwarding 20 destination is in the incoming standby state. The user of the telephone at the forwarding destination can thereby recognize that the forwarding is to be made and, therefore, he can properly make further response without being confused or making a mistake in the 25 operations.

According to the other aspect of the present invention, an electronic exchange for connecting calling from a telephone connected to other electronic exchange to an outside line connected to the own electronic exchange, under the QSIG protocol that is an international standard of digital lines. The electric 5 exchange comprises means for receiving information to restrict the calling from the other electronic exchange at the time of the calling from the telephone; and means for restricting the calling from the telephone to the outside line in response to the calling restriction 10 information. The calling restriction information is added to a caller number notification information element of the QSIG protocol.

According to the present invention, the calling restriction information can be transmitted technically 15 easily at low costs without using a specific information element, by adding the calling restriction information to the caller number notification information element of the QSIG protocol.

It is preferable that the electronic exchange 20 further comprises a table for storing calling restriction contents and the calling restricting means searches for the calling restriction contents on the table in response to the calling restriction information and restricts the calling in accordance 25 with the searched calling restriction contents.

According to the other aspect of the present invention, a key telephone system is provided. The key telephone system comprises interf ace means having a line interface function of transmitting digital data to an ISDN network via a U point of an ISDN line and an extension interface function of transmitting digital 5 data to an ISDN terminal, for selectively setting one of the functions; and control means for setting the interface means to implement one of the line interface function and the extension interface function in accordance with line setting information.

10 According to the present invention, one interface means can be freely set to implement the line interface function or the extension interface function.

Therefore, it is possible to implement a key telephone system with a high degree of freedom, in 15 which the number of the ISDN line ports and that of extension ports can be increased or decreased in accordance with the application.

According to the other aspect of the present invention, a key telephone system is provided. The key 20 telephone system comprises interface means having a line interface function of transmitting digital data to an ISDN network via a U point of an ISDN line and an extension'interface function of transmitting digital data to an ISDN terminal, for selectively setting 25 one of the functions; timing generating means for generating a system clock signal and a frame synchro nization signal in accordance with a clock signal output from the interface means when the interface means is set to implement the line interface function, and for generating the system clock signal and the frame synchronization signal in accordance with an 5 internal clock signal when the interface means is set to implement the extension interface function; first switch means interposed into a signal transmission path between a clock signal input/output terminal of the interface means and a clock signal input/output 10 terminal of the timing generating means; second switch means interposed into a signal transmission path between a system clock signal output terminal and a frame synchronization signal output terminal of the timing generating means, and a clock signal 15 input/output terminal and a frame synchronization signal input/output terminal of the interface means; and control means for setting the interface means to implement one of the line interface function and the extension interface function in accordance with line 20 setting information, for turning on the first switch means and turning off the second switch means when the interface means is set to implement the line interface function, and for turning off the first switch means and turning on the second switch means when the 25 interface means is set to implement the extension interface function.

According to the present invention at the U point of the ISDN line, the line interface function and the extension interface function of the interface means are set by the control means. When the interface means is set to implement the extension interface function, the 5 first switch means is turned off and the second switch means is turned on by the control means to use the internal clock signal of the timing generating means.

The control means sets the line interface function and the extension interface function of the interface means 10 in accordance with the line setting information.

Thus, the interface means can be freely set to implement either the line interface function or the extension interface function.

Therefore, it is possible to implement a key 15 telephone system with a high degree of freedom, in which the number of the ISDN line ports and that of extension ports can be preferably increased or decreased.

According to the other aspect of the present 20 invention, a key telephone system is provided.. The key telephone system comprises interface means having a line interface function of transmitting digital data to an ISDN network via S and T points of an ISDN line and an extension interface function of transmitting digital 25 data to an ISDN terminal, for selectively setting one of the functions; first switch means connected to the interface means, for changing a transmission line and a reception line respectively at the time of setting the line interface function and at the time of setting the extension interface function; second switch means interposed into signal transmission paths of a clock 5 signal and a frame synchronization signal to the interface means, for changing input/output of the clock signal and the frame synchronization signal to the interface means; and control means for setting the interface means to implement one of the line interface 10 function and the extension interface function in accordance with the line setting information, for changing the second switch means to the side of outputting the clock signal and the frame synchroniza tion signal when the interface means is set to 15 implement the line interface function, and for changing the second switch means to the side of inputting the clock signal and the frame synchronization signal when the interface means is set to implement the extension interface function.

20 According to the present invention, the first switch means for reversing the transmission line and the reception line is provided in front of the interface means so that the transmission line and the reception line are changed at the S and T points of the 25 ISDN line. The control means also sets to implement the line interface function and the extension interface function of the interface means, and controls the changing of the second switch means.

When the first switch means is changed to the line interface function side, the line setting information to be set to implement the line interface function is 5 input to the control means. on the other hand, when the second switch means is changed to the extension interface function side, the line setting information to be set to implement the extension interface function is input to the control means.

10 After inputting the line setting information to be set at the line interface function, the control means sets the interface means to implement the line interface function and changes the second switch means to the side of outputting the clock signal and the 15 frame synchronization signal.

when the control means is input the line setting information to be set at the extension interface function, the control means sets the interface means to implement the extension interface function and changes 20 the second switch means to the side of inputting the clock signal and the frame synchronization signal.

Therefore, the interface means can be freely set to implement either the line interface function or the extension interface function. For this reason, a key 25 telephone system with a high degree of freedom can be provided.

Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and 5 obtained by means of the instrumentalities and combina tions particularly pointed out hereinafter.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

The accompanying drawings, which are incorporated in and constitute a part of the specification, illust

10 rate presently preferred embodiments of the invention, and together with the general description given above and the detailed description of the preferred embodi ments given below, serve to explain the principles of the invention.

15 FIG. 1 is a diagram showing networking of conventional electronic telephones; FIG. 2 is a diagram showing exchange of message signals at the forwarding among the electronic exchanges in the networking of FIG. 1; 20. FIG. 3 is a flow chart showing the operations of the electronic exchanges in the networking of FIG. 1; FIG. 4 is a block diagram showing a configuration of a conventional key telephone system; FIG. 5 is a block diagram showing configurations 25 of an ISDN interface unit and a control unit in the conventional key telephone system of FIG. 4; FIG. 6 is a block diagram showing configurations of.an ISDN interface unit and a control unit in another conventional key telephone system; FIG. 7 is a block diagram showing an electronic exchange according to a first embodiment of the present 5 invention; FIG. 8 is a flow chart showing the operations of the electronic exchange according to the first embodiment; FIG. 9 is a block diagram showing the operation of 10 an electronic exchange according to a second embodiment of the present invention-, FIG. 10 is a block diagram showing the operation of an electronic exchange according to a third embodiment of the present invention; 15 FIG. 11 is a block diagram showing the operation of an electronic exchange according to a fourth embodiment of the present invention; FIG. 12 is a diagram showing an example of displaying information on a telephone by the electronic 20 exchange of the fourth embodiment; FIG. 13 is a block diagram showing an electronic exchange according to a sixth-embodiment of the present invention-, FIG. 14 is a diagram showing the transmitting 25 conditions of a signal transmitted from the electronic exchange of the sixth embodiment; FIG. 15 is a diagram showing a structure of "Setup message" defined by the QSIG protocol; FIG. 16 is a diagram showing calling number information under the QSIG protocol; FIG. 17 is a block diagram showing the operation 5 of the electronic exchange according to the sixth embodiment of the present invention; FIG. 18 is a block diagram showing configurations of anISDN interface unit and a control unit in a key telephone system according to a seventh embodiment of 10 the -pre sent --i-nvent ion; FIG. 19 is a block diagram showing a part in each of the configurations of the ISDN interface unit and the control unit in the key telephone system according to the seventh embodiment of the present invention; 15 FIG. 20 is a block diagram showing an application example of the key telephone system of the seventh embodiment; FIG. 21 is a block diagram showing a part in each of the configurations of the ISDN interface unit in a 20 key telephone system according to an eighth embodiment of the present invention; FIG. 22 is a diagram showing a detailed configuration of a T/R line switching unit in the key telephone system of the eighth embodiment; and 25 FIG. 23 is a diagram showing a detailed configuration of a CLK/FS switching unit in the key telephone system of the eighth embodiment.

Embodiments of the present invention will be explained below in detail with reference to the drawings.

5 (1) Electronic Exchange (a) First Embodiment FIG. 7 is a diagramshowing the networking of electronic exchanges according to the first embodiment of the present invention.' FIG - 8 is a f low chart 10 showing the process after the electronic exchanges of the first embodiment have received "Facility message".

In FIG. 7 the same portion-s as those of FIG. 1 are denoted by the same reference numerals.

In FIG. 7, electronic exchanges 30, 31 and 32 15 comprising call reception/ tran smis s ion prohibiting means 300, 310 and 320, and announcement setting means 301, 311 and 321 are connected to one another in digital lines 21, 22 and 23 employing the QSIG protocol, which is the international standard of the 20 digital dedicated lines.

it is assured now that the telephone I has communication with the telephone 2 via the electronic exchanges 30 and 31 and the telephone 2 forwards the call with the telephone 1 to the telephone 3 connected 25 to the electronic exchange 32 so as to allow the telephones I and 3 to make communication.

FIG. 8 is a flow chart showing the operations of the electronic exchanges according to the first embodiment of the present invention.

In this figure, when the electronic exchange 32 receives forward acknowledgement signal."Facility 5 message" from the electronic exchange 31 (S10), the electronic exchange 32 checks whether the telephone 3 to be called is idle or not (S12). If the telephone 3 is not idle, the electronic exchange 32 transmits a message to the electronic exchange 31 indicating 10 a rejection of forwarding acceptance (S14). On the other hand, if the telephone 3 is idle, the electronic exchange 32 makes the telephone 3 shift to the receiving standby state for the forwarding (S16).

The announcement setting means 321 turns on an 15 extension button in the telephone 3. The call reception/transmission prohibiting means 320 sets the call transmission and the call reception except for the forwarding to be impossible.

After having set the call transmission and the 20 call reception except for the forwarding to be impossible for the telephone 3, the electronic exchange 32 transmits "Call proceeding message" representing that the forwarding is acceptable to the electronic exchange 31 (S18).

25 When the electronic exchange 31 receives the "Call proceeding message" from the electronic exchange 32, the electronic exchange 31 recognizes that the telephone 3, which is the destination of a call to be forwarded, is idle and can accept the call. At this time, the electronic exchange 31 transmits the information about the forwarding included in the 5 OfFacility message" to the electronic exchange 30 so that the electronic exchange 30 transmits the calling request "Setup message" as a formal call start request to the electronic exchange 32.

Receiving the "Facility message', transmitted from 10 the electronic exchange 31, the electronic exchange transmits the calling request "Setup message,, to the electronic exchange 32 in accordance with the information included in the Facility message.

When the electronic exchange 32 receives the 15 "Setup message", the electronic exchange 32 checks again whether the telephone 3 is idle or not. If the telephone 3 is idle, the electronic exchange 32 transmits the "Call proceeding message" as the acknowledgement of acceptance for the call to the 20 electronic exchange 30. The electronic exchange 32 further transmits the calling signal to the telephone 3 and transmits "Alerting" representing that electronic exchange 32 is calling an extension to the electronic exchange 30.

25 When the user of the telephone 3 hooks off the telephone 3 after hearing the ringing tone, he can make communication with the telephone 1.

In the first embodiment, the telephone 32 receives the forwarding acknowledgement signal "Facility message" from the electronic exchange 31, and if the telephone 3 to be called is idle, the telephone 32 5 makes the telephone 3 shift to the receiving standby state for the forwarding, turns on the extension button of the telephone 3 and sets the call transmission and the call reception except for the forwarding to be impossible.

10 Thus, even if the calling operations are executed at the telephone 3 or if there is the call reception from a different telqphone until the call reception from the electronic exchange 30, they are invalid by setting the call transmission and the call reception 15 except for the forwarding to be impossible for the telephone 3. For this reason, the forwarding of the incoming call from the electronic exchange 30 can be certainly achieved. Further, no invalid signals are transmitted into the network as seen in the prior art

20 and, therefore, the data traffic is not increased unnecessarily.

(b) Second Embodiment FIG. 9 is a flow chart showing the process after the telephone of a second embodiment receives the 25 "Facility message". In this embodiment, the configura tion of the digital line network is the same as that of FIG. 7.

An announcement function (S20) is added to this embodiment in which the announcement setting means 321 in the electronic exchange 32 causes the telephone 3 of the forwarding destination output a specific tone to 5 announce to the user of the telephone 3 that the call transmission and the call reception except for the forwarding become impossible.. The announcement function step (S20) is executed after the step (S18) of making the electronic exchange 32 transmit the "Call 10 proceeding message" to the electronic exchange 31, but may be executed before the step (S18).

The user of the telephone 3 of the forwarding destination is informed that the call transmission and the call reception except for the forwarding become 15 impossible. He can therefore recognize that the forwarding is to be executed and properly make a further response without being confused or making a mistake in the operations.

(c) Third Embodiment 20 FIG. 10 is a flow chart showing the process after the telephone of a third embodiment receives the "Facility message". In this embodiment, the configuration of the digital line network is the same as that of FIG. 7.

25 An announcement function (S22) is added to this embodiment in which the announcement setting means 321 in the electronic exchange 32 causes the telephone 3 generate a specific tone to announce to the user of the telephone 3 that the call transmission and the call reception except for the forwarding become impossible when the user pushes down a call transmission key of 5 the telephone 3. The announcement function step (S22) is executed after the step (S18) of making the electronic exchange 32 transmit the "Call proceeding message" to the electronic exchange 31, but may be executed before the step (S18).

10 The user of the telephone 3 of the forwarding destination is informed that the call transmission and the call reception except for the forwarding become impossible. He can therefore recognize that the forwarding is to be executed and properly make 15 a further response without being confused or making a mistake in the operations.

in the third embodiment, when the call transmission key of the telephone 3 is pushed down a specific tone is generated therefrom. However, input 20 from the dial key can be rejected when the call transmission key is pushed shown. In this case, the specific tone can also be simultaneously generated.

(d) Fourth Embodiment FIG. 11 is a flow chart showing the process 25 after the telephone of a fourth embodiment receives the "Facility message". In this embodiment, the configuration of the digital line network is the same - 29 as that of FIG. 7.

An announcement function (S24) is added to this embodiment in which the announcement setting means 321 in the electronic exchange 32 causes the telephone 3 5 of the forwarding destination display predetermined information on a display unit such as an LCD of the telephone 3 to announce to the user of the telephone 3 that the call transmission and the call reception except for the forwarding become impossible.

10 The announcement function step (S24) is executed after the step (S18) of making the electronic exchange 32 transmit the "Call proceeding message" to the electronic exchange 31, but may be executed before the step (S18).

15 FIG. 12 shows an example of the display on the telephone 3 in a case where it shifts to the standby state for the forwarding. in this example, "Forward Reserved" is displayed.

The user of the telephone 3 of the forwarding 20 destination is informed that the call transmission and the call reception except for the forwarding become impossible. He can therefore recognize that the forwarding is to be executed and properly make a further response without being confused or making.

25 a mistake in the operations.

In the fourth embodiment, the predetermined information is displayed on the LCD display unit of the telephone 3 of the forwarding destination when the telephone 3 shifts to the standby state for the forwarding. However, the predetermined information may be displayed on the display unit when the call 5 transmission key of the telephone 3 is pushed down while the telephone 3 shifts to the standby state for the forwarding. In this case, the specific tone may be simultaneously output.

Further, when while the telephone 3 shifts to the 10 standby state for the forwarding, the display unit provided on the telephone 3 may be turned on to inform the user that the telephone 3 is in the standby state for the forwarding.

(e) Fifth Embodiment 15 When the telephone shifts to the standby state for the forwarding, the call transmission and the call reception except for the forwarding become impossible in the first to fourth embodiments. However, the call transmission and the forwarding may become possible by 20 informing that the telephone is in the standby state for the forwarding, from the aspect of raising the degree of freedom of the use. Thus, it is possible to make contact with the partner required with priority when an urgent contact is required.

25 (f) Sixth Embodiment FIG. 13 is a diagram showing the networking of electronic exchanges according to the sixth embodiment of the present invention.

In this figure, electronic exchanges 40 and 41 comprising call transmission restricting means 400 and 410 are connected to one another in a digital dedicated 5 line 45 employing the QSIG protocol, which is the international standard for the digital dedicated lines.

An extension telephone 46 is connected to the electronic exchange 40, and two extension telephones 47 and 48 are connected to t he electronic exchange 41.

10 The electronic exchange 40 is connected to a public telephone network 90.

It is assumed that extension telephone numbers 5000, 3000 and 4000 are assigned to the extension telephones 46, 47 and 48, respectively.

15 The characteristics of the electronic exchanges 40 and 41 in a case where a signal is transmitted from the extension telephone 47 through the digital line 45 to the public telephone network 90 will be explained.

FIG. 14 is a diagram showing the signal 20 transmission conditions when the signals are transmitted from the extension telephone 47 to the public telephone network 90.

The user of the extension telephone 47 off-hooks the extension telephone 47 and transmits a request for 25 call transmission to the electronic exchange 41. Thus, a dial tone signal is transmitted from the electronic exchange 41 to the extension telephone 47.

After confirming the dial tone, the user of the extension telephone 47 dials the telephone number of the communication partner. The dialing allows the electronic exchange 41 to transmit the calling request 5 defined by the QSIG protocol, i.e. "Setup message" through the digital line 45 to the electronic exchange 40. When the electronic exchange 40 receives the calling request "Setup message", it transmits the dial information to the public telephone network 90.

10 FIG. 15 is a diagram showing the structure of the "Setup message" defined by the QSIG protocol. it is basically formed by information items denoted by numbers 1 to 4, and information items denoted by numbers 5 to 13 are added thereto as occasion requires.

15 The information items in the "Setup message" are sequentially transmitted to the opposed electronic exchange 40 when the "Setup message" is transmitted.

In the sixth embodiment, calling restriction class number (for example, a two-digit numeric) is added into 20 caller number information (i.e. information informing the extension number of the calling telephone) of "MESSAGE TYPE" with item number 3 in the "Setup message", and the information is transmitted to the opposed electronic exchange 40. In this case, the 25 calling restriction class number is set at "11".

FIG. 16 is a diagram showing the caller number information. The information necessary for the caller number information elements is input to octets I to 4, and the extension number of the caller who has actually made a call is input to a reserved item, i.e. octet 5.

The caller telephone numbers or extension numbers to be 5 input to reserved items are input to the respective octets as "3", "0", 110" and 110" as shown in the figure.

Subsequently, a two-digit number I'll" of the calling restriction class number is input as I'll, and 111".

The total contents length of the caller number 10 information can be freely set in the item "caller number contents length" of octet 2, so that the calling restriction class number can be easily added.

Each octet is 1 byte long.

AS shown in FIG. 17, when the electronic exchange 15 41 receives a call from the extension telephone 47 of extension number "300011, the electronic exchange 41 add the calling restriction class number (i.e. a two-digit numeric, for example, 111111) to the caller number information carrying the extension number of the 20 extension telephone 47 and informs the opposed electronic exchange 40 of the information. The electronic exchange 40 detects calling restriction class number in the received caller number information, checks the calling restriction contents registered in 25 advance on an own table 401 of the electronic exchange 40, and executes restriction such as disconnecting the calling as occasion requires.

For example, when it is set on the table 401 of the electronic exchange 40 not to accept an international telephone call of the extension telephone 47, the extension telephone 47 is not connected by 5 the electronic exchange 40 even if there is an international telephone call from the extension telephone 47.

Thus, in the sixth embodiment, the calling restriction information is added to the caller number 10 information of "Setup message" defined by the QSIG protocol, which is the international standard of the digital line, and is announced to the opposed electronic exchange 40. For this reason, execution of the specific coding caused by using information element 15 unique to the manufacturer, or software for transmit ting and receiving information element unique to the manufacturer is unnecessary. When these are unnecessary, the load on the CPU can be limited to the minimum.

20 (11) Key Telephone System (g) Seventh Embodiment FIG. 18 is a block diagram showing the configurations of an ISDN interface unit and a control unit in the key telephone system according to the 25 seventh embodiment of the present invention. The same portions as those of FIG. 5 are denoted by the same reference numerals and their explanation is omitted.

An ISDN interface unit 55 of the present embodiment is adapted to U points (i.e. two pins) of the ISDN line.

Each of two interface LSIS 80 and 81 having the 5 same function is fixed at the NT mode or LT mode in the conventional key telephone system. In the seventh embodiment, however, setting at the NT mode or LT mode can be freely executed by using a microcomputer 100.

In this case, a hard ware setting control signal 10 SSI is used for the NT/LT setting port of the interface LSI 80 and a hardware setting control signal SS2 is used for the NT/LT setting port of the interface LSI 81, so that setting at the NT mode or LT mode can be executed by the microcomputer 100. A software setting control signal SS3, other than the control signals SS1 and SS2, is used for the interface LSIs 80 and 81 to inform the interface LSIs 80 and 81 that the hardware setting at the NT mode or LT mode has been made.

The microcomputer 100 sets both the interface LSIs 20 80 and 81 by the control signals SS1, SS2 and SS3, and controls turning on/off the switch units 82 and 84 by using a control signal SS4.

When the interface LS1 80 is set at the NT mode, the interface LSI 80 extracts the clock signal CLK from 25 the ISDN network 60 When the interface LSI 80 is set at the LT mode, the interface LSI 80 does not extract the clock signal. When the interface LSI 80 is set at the NT mode and the interface LSI 81 is set at the LT mode, the interface LSI 80 extracts the clock signal CLK from the ISDN network 60 and supplies the signal to the interface LSI 81. At this time, the switch unit 82 5 is controlled to be turned on and the switch unit 84 is controlled to be turned off.

The basic clock signal CLKb extracted from the ISDN network 60 by the interface LSI 80 is input to the timing generation unit 85 in the control unit 52 10 through the switch unit 82. The timing generation unit generates the clock signal CLKs for the system synchronization signal and the frame synchronization signal FS in accordance with the basic clock signal CLKb and transmits these signals to the time switch 15 unit 86 in the control unit 52 and the phase adjustment time switch unit 83 in the ISDN interface unit 55 so as to synchronize with the ISDN network.

The interface LSIs 80 and 81 are synchronized with the phase adjustment time switch unit 83 by the clock 20 signal CLK of the interface LSI 80 and the frame synchronization signal FS.

on the other hand, the speech data from the interface LSIs 80 and 81 is transmitted to the phase adjustment time switch unit 83 through the data highway 25 DH1. The speech data is further transmitted to the time switch unit 86 through the data highway DH2 synchronized with the time switch unit 86 in the control unit 52. Thus, the speech data can be handled as a sy stem- synchronized signal.

FIG. 19 is a diagram showing a specific example of using a three-state buffer at the switch units 82 5 and 84.

The switch unit 82 is turned on and the switch unit 84 is turned off by using the control signal SS4 of the microcomputer 100 so that the interface LSI 80 in the ISDN interface unit 55 extracts the clock signal 10 CL'K from the ISDN network 60. To make the system synchronized by this clock signal CLK.

The timing generation unit 85. in the control unit 52 generates the system clock signal CLKs and the frame synchronization signal FS in accordance with the basic 15 clock signal CLKb from the switch unit 82 as described above.

when the interface LSI 80 does not extract the clock signal CLK from the ISDN network 60, the switch unit 82 is turned off and the switch unit 84 is turned 20 on and internal clock generating means 851 in the timing generation unit 85 is used. The timing generation unit 85 in the control unit 52 generates the system clock signal CLKs and the frame synchronization signal FS in accordance with the clock signal generated 25 by the internal clock generating means 851.

Thus, the clock can be easily switched by using the three-state buffer for the switch units 82 and 84.

FIG. 20 shows an example of a key telephone system having three NT ports and one LT port. That is, three NT ports and one LT port are formed by two ISDN interface units 55 in a key telephone system 110.

5 The ISDN interface unit 55 can freely set the NT/LT modes as described above, and large convenience can be thereby provided to the user.

To provide three NT ports and one LT port, three ISDN interface units 51 need to be prepared in the 10 prior art, and two of the LT ports are unnecessary.

In the present invention, the NT mode or the LT mode can be freely set by one ISDN interface unit 55.

Therefore, the system can be rationally constituted and much advantage can be obtained in the manufacturing 15 costs.

Thus, in the seventh embodiment, the LT/NT modes of the interface LSIs 80 and 81 are set by the microcomputer 100, at the U points of the ISDN line.

When both the interface LSIs 80 and 81 are set at the 20 NT mode, the switch unit 82 is turned off and the switch unit 84 is turned on by the microcomputer 100 to use the clock signal generated by the internal clock generating means 851 in the timing generation unit 85.

The microcomputer 100 sets the LT/NT modes of the 25 interface LSIs 80 and 81 in accordance with the line setting data that is input from the control unit 52.

Therefore, since one interface unit 55 can be f reely set at either the NT mode or the LT mode, it is possible to provide the key telephone system with high degree of freedom where the number of ISDN line ports and the number. of extension ports can be increased or 5 decreased in accordance with the purpose.

(h) Eighth Embodiment FIG. 21 is a block diagram showing the essential portions of an ISDN interface unit 58 in the key telephone system -according to the eighth embodiment of 10 the present invention. The same portions as those of FIG. 6 are denoted by the same reference numerals, and their explanations are omitted. The control unit and portion other than the ISDN interface unit 58 shown in FIG. 21 are the same as the ISDN interface unit 55 and 15 the control unit 52 of FIG. 18.

The eighth embodiment is adapted to S and T points (i.e.- four pins) of the ISDN line, and two interface LSIs 120 and 121 that have been required in the prior art are reduced to one. To implement this, a T/R lines 20 change-over switch unit 130 for changing a transmission line (i.e. a T line) and a reception line (i.e. R line) at the NT and TE modes and a CLK/FS change-over unit 131 for changing the clock signal and the frame synchronization signal are added to the conventional 25 configuration.

Further, a control line from a microcomputer 132 for the changing of the NT/TE modes in the CLK/FS change-over unit 131 and the interface LSI 120 is also added.

FIG. 22 is a diagram showing a detailed configura tion of the T/R lines change-over switch unit 130.

5 The interface with the line is an eight-pin modular jack 133 usually called RJ45. The "third and sixth pins" are used for transmission and the "fourth and fifth pins" are used for reception at the TE mode.

The "fourth and fifth pins" are used for transmission 10 and the "third and sixth pins" are used for reception at the NT mode. These are mechanically changed by a manual switch of a change-over switch 134. An electric switch such as a relay, a semiconductor switch, etc.

can be used if the primary and secondary insulation can 15 be maintained by a transformer 140.

As shown in FIG. 21, the control unit 52 (in FIG. 18) transmits the setting contents of the line to the microcomputer 132 through the internal bus.

The microcomputer 132 instructs the interface LSI 120 20 and the CLK/FS change-over unit 131 to set the TE/NT modes in accordance with the setting contents of the line transmitted from the control unit 52.

A clock signal CLK and a frame synchronization signal FS are extracted from the ISDN network 60 at 25 the TE mode. Therefore, the signals flow from the interface LSI 120 to the control unit 52 and also to the phase adjustment time switch unit 83 (FIG. 18) in the ISDN interface unit 58. The entire system is operated in accordance with the clock signal CLK.

On the other hand, at the NT mode, circuit becomes in the slave-synchronizing state and the signals 5 therefore flow from the control unit 52 and the phase adjustment time switch unit 83 in the ISDN interface unit 58 to the interface LSI 120.

rIG. 23 is a diagram showing a detailed configura tion of the CLK/FS change unit 131. This can be easily 10 implemented by a three-state buffer as shown in the figure.

As described above, in the eighth embodiment, the T/R lines change-over switch unit 130 for reversing the T line and the R line is provided at-the front stage of is the interface LSI 120, at the S and T points of the ISDN line, so as to change the T line and the R line.

In addition, the microcomputer 132 is provided to set the TE/NT modes of the interface LSI 120 and control the CLK/FS change unit 131. When the T/R lines 20 change-over switch unit 130 is changed to the TE side, the line setting data to set the TE is input to the microcomputer 132. on the other hand, the T/R lines change-over switch unit 130 is changed to the NT side, the line setting data to set the.NT is input to the 25 microcomputer 132. Inputting the line setting data to set the TE, the microcomputer 132 sets the interface LSI 120 at the TE mode and also sets the CLK/FS change unit 131 at the TE side. The microcomputer 132, which is input the line setting data to set the NT mode, sets the interface LSI 120 at the NT mode and also sets the CLK/FS change unit 131 at the NT side. Thus, one ISDN 5 interface unit 58 can be freely set at either the TE side or the NT side and, therefore, the degree of freedom for the selection of the line is made higher.

If a number of such ISDN interface units 58 are used, the degree of freedom for the selection of the line is 10 made much higher and thereby a user-friendly key telephone system can be provided.

Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to 15 the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.

Claims

CLAIMS:

1. A key telephone system comprising:

interface means having a line interface function of transmitting digital data to an ISDN network via a U point of an ISDN line and an extension interface function of transmitting digital data to an ISDN terminal, for selectively setting one of the functions; and control means for setting said interface means to implement one of said line interface function and said extension interface function in accordance with line setting information.

2. A key telephone system comprising:

interface means having a line interface function of transmitting digital data to an ISDN network via a U point of an ISDN line and an extension interface function of transmitting digital data to an ISDN terminal, for selectively setting one of the functions; timing generating means for generating a system clock signal and a frame synchronisation signal in accordance with a clock signal output from said interface means when said interface means is set to implement the line interface function, and for generating the system clock signal and the frame synchronization signal in accordance with an internal clock signal when said interface means is set to implement the extension interface function; first switch means interposed into a signal transmission path between a clock signal input/output terminals of said interface means and a clock signal input/output terminal of said timing generating means; second switch means interposed into a signal transmission path between a system clock signal output terminal and a frame synchronization signal output terminal of said timing generating means, and a clock signal input/output terminal and a frame synchronization signal input/output terminal of said interface means; and control means for setting said interface means to implement one of said line interface function and said extension interface function in accordance with line setting information, for turning on said first switch means and turning off said second switch means when said interface means is set to implement the line interface function, and for 44 turning off said first switch means and turning on said second switch means when said interface means is set to implement the extension interface function.

3. A key telephone system comprising:

interface means having a line interface function of transmitting digital data to an ISDN network via S and T points of an ISDN line and an extension interface function of transmitting digital data to an ISDN terminal, for selectively setting one of the functions; first switch means connected to said interface means, for changing a transmission line and a reception line respectively at the time of setting the line interface function and at the time of setting the extension interface function; second switch means interposed into signal transmission paths of a clock signal and a frame synchronization signal to said interface means, for changing input/output of the clock signal and the frame synchronization signal to said interface means; and control means for setting said interface means to implement one of said line interface function and said extension interface function in accordance with the line setting information, for changing said second switch means to the side of outputting the clock signal and the frame synchronization signal when said interface means is set to implement said line interface function, and for changing said second switch means to the side of inputting the clock signal and the frame synchronization signal when said interface means is set to implement said extension interface function.

4. An electronic exchange and key telephone system, substantially as hereinbefore described with reference to Figures 18 to 23.