JPH0563829A - Private branch of digital exchange - Google Patents

Abstract

PURPOSE:To improve the convenience for the user by releasing the held state of a held call so as to make various services available. CONSTITUTION:When a 2nd extension reaches a held state (state 2) by holding operation of a 1st extension, a release means 2 releases the held state of a 2nd extension (a symbol B in the state 2) while keeping the 1st extension (a symbol A in the state 2) in the held state. Thus, the 2nd extension is released from the held state and makes various service requests. When a service request such as a holding request, a transfer request or a last number radial request comes from the 2nd extension, a service control means 3 offers a relevant service.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital private branch exchange, and more particularly to an extension service of a digital private branch exchange.

[0002]

2. Description of the Related Art Recently, in the field of telephone services,
Digital private branch exchanges (hereinafter referred to as digital PBXs) are becoming popular in place of conventional analog private branch exchanges. In the digital PBX, since the line switching connection is processed digitally, various extension services such as extension mutual call and office line call are compared with the conventional analog system.
The processing speed of the screw can be greatly increased.

An example of this type of digital PBX is disclosed in Japanese Patent Application Laid-Open No. 2-220546. In the one disclosed in this publication, when a hold-time call resumption request special number is input from the held digital telephone, the hold-side digital telephone issues a hold call resumption request sound. As a result, it is possible to convey the intention of resuming the call from the held party to the holding party.

[0004]

In the extension service of the conventional digital PBX, when one extension performs hooking or holding operation in the call state, the other extension is put on hold and the extension on the other side. He could not let go of the handset until he performed the hold release operation. In addition, there is a problem that the waiting line cannot be effectively used because other operations such as transfer cannot be performed on the extension which has been put on hold.

Further, in the one disclosed in the above publication, the intent to resume the call can be transmitted from the held party to the holding party, but in this case as well, the held party is in the held state. Therefore, there was a problem similar to the above.

An object of the present invention is to provide a digital PBX capable of releasing various services by releasing the held call state of the held call and improving the convenience of the user.

[0007]

In order to achieve the above object, in the first aspect of the invention, a speech path switch for establishing a speech path connection between extension lines and between an extension and a station line, and a control for controlling the speech path switch. In the digital private branch exchange having a section, the control section makes a second operation by a holding operation on the first extension side of the first extension and the second extension which are in a call state.
When the extension of the second extension is in the held state, the releasing means for releasing the held state of the second extension while keeping the first extension in the held state, and from the second extension after releasing the held state. When there is a service request of, the service control means for providing the corresponding service is provided.

According to a second aspect of the present invention, in a digital private branch exchange having a speech path switch for connecting speech paths between extension lines and between an extension and a station line, and a control section for controlling the speech path switch, the control section is provided. , First in a call
Of the second extension and the second extension that has been put on hold by the transfer operation on the side of the first extension, the second extension is transferred while keeping the first extension in the transfer state. It comprises a releasing means for releasing the state and a service control means for providing a corresponding service when there is a service request from the second extension after releasing the transferred state.

According to a third aspect of the present invention, in the first or second aspect of the invention, the service request includes a hold request for putting the second extension in a hold state, a third extension or a station. At least one of a transfer request for the line and a last number dial request for redialing to the destination indicated by the last stored dial number is included.

[0010]

According to the present invention, when the second extension is put on hold by the holding operation on the side of the first extension, the second extension is held by the releasing means while the first extension is kept on hold.
When the hold state of the extension is released and a service request is input from the second extension whose hold state has been released, the corresponding service is provided by the service control means. You are released from hold and can receive the requested service.

When the second extension is put on hold by the transfer operation on the first extension side, the releasing means
When the held state of the second extension is released while the first extension is maintained in the transfer state and a service request is input from the second extension whose held state has been released, the corresponding service is service-controlled. As provided by the means, the second extension is released from the held state and can receive the requested service.

Specifically, on the side of the second extension released from the held state, for example, a hold request for putting the second extension in the hold state, a transfer request for the third extension or office line, and a final stored dial number. By requesting at least one of the last number dial requests for redialing to the destination indicated by, the corresponding service can be received.

[0013]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

A first embodiment of the digital PBX according to the present invention will be described.

FIG. 1 shows a diagram for explaining the basic principle of the digital PBX of the present invention.

In the figure, an application service control means 1 is for realizing an extension service which is one of the service functions of the digital PBX, that is, various application services. The application service control means 1 includes a release means 2 and a service control means 3. The canceling means 2 puts the first extension in the hold state when the second extension of the first extension and the second extension in the call state is put on hold by the hold operation of the first extension. The held state of the second extension is released while maintaining. On the other hand, the service control means 3 provides a corresponding service when there is a service request from the second extension after the releasing means 2 releases the held state of the second extension. In FIG. 1, A and B indicate extensions, LCT indicates a line circuit trunk, and HDT indicates a holding tone.

Next, the basic operation of this embodiment will be described with reference to FIG.

In state 1, extension A and extension B are connected via their respective LCTs and are in a call state. From this state, the extension A performs a hold operation, and the state is changed to state 2. In this state 2, the connection between the extension A and the extension B is released, the HDT is connected to each extension, the extension A is put on hold, and the extension B is put on hold. The processing operation up to this point is the same as the processing operation by the conventional digital PBX.

In the present invention, when the state 1 is transited to the state 2, the releasing means 2 in the digital PBX is
While the extension A is kept in the hold state, the held state of the extension B is released and the fact is notified to the service control means 3. At this time, the extension B is released from the held state,
As a result, services such as a hold request, a transfer request, and a last number dial request can be requested. on the other hand,
After canceling the held state of the extension B by the canceling means 2, the service control means 3 monitors the operating state of the extension B and determines whether or not there is a service request.

Here, the hooking operation, the holding operation, and other operations from the extension B, for example, a feature key (function key)
When the button is pressed or the special number dial is operated, the service control unit 3 detects those operations and provides services such as hold, transfer, and last number dial according to the operation contents.

FIG. 2 shows a digital PBX according to the present invention.
FIG. 3 is a functional block diagram showing an embodiment of FIG.

Next, referring to FIG. 2, the digital PB
The structure of X10 will be described.

This digital PBX 10 realizes application service control means 11 for realizing various application services, call control means 12 for realizing call control (state transition), and exchange connection. Control means 15 which is a control means for executing and managing exchange connection control in response to a connection request from a user. And a time division switch 16 which is a connecting means for connecting lines. Further, the time division switch 16 is connected with a line circuit 21 for connecting with an extension line and a station line trunk 22 for connecting with a public communication network such as NTT. The application service control means 11 of the control unit 15 has a hold service control means 31 for realizing a hold service, a transfer service control means 32 for realizing a transfer service, and other components. It is composed of extension service control means 33 for realizing the service.

Among the first extension and the second extension in the call state, the holding service control means 31 puts the second extension into the on-hold state by hooking or holding the first extension. At this time, when a holding operation is performed from the second extension side, the second extension in the held state is shifted to the holding state,
An extension mutual holding service means 41 for holding the first extension and the second extension in the mutual holding state is included. Also,
Of the first extension and the second extension in a call state, the transfer service control means 32 notifies the second extension when the second extension is put on hold by hooking or holding on the side of the first extension.
When an operation of holding hooking is performed from the second extension side, the second extension in the held state is shifted to the hooking state, and a transfer request from the second extension to another extension or office line is accepted, A held call transfer service means 42 for performing processing according to a designated service is included.

Although not shown in FIG. 2, the digital PBX 10 shown in FIG. 2 has an interface between main control means for controlling program execution and memory area management, various tests, traffic measurement, and maintenance personnel. Maintenance and operation control means for performing processing are provided.

In this embodiment, the two control means and the control unit 15 not shown are the central processing unit (hereinafter, C).
A PU is used as a main component, and the above-described data processing is executed according to each control program written in a memory device (not shown) in the PBX. The hold service control means 31 and the transfer service control means 32 both have the functions of the releasing means 2 and the service control means 3 shown in FIG.

The basic operation of the digital PBX 10 shown in FIG. 2 is to input a connection request to the line circuit 21.
Through hardware control means 14, exchange connection means 1
3. The call control means 12 takes it into the application control means 11 and, after executing the processing according to the connection request, the switching connection means 13 and the hardware control means 14
The switching connection of the time divisional switch 16 is controlled via the.

Next, the processing procedure for performing the extension mutual holding service and the held call transfer service in the digital PBX 10 described above will be described based on the flowcharts of FIGS. 3 to 7. .. Here, the extension A in the call state
With respect to the extension B, hooking or holding is performed from the side of the extension A, and a processing procedure after the extension B is put on hold will be described.

The processing procedures of the extension mutual holding service and the held call transfer service which are the characteristic operations of the digital PBX according to the present invention are shown in FIGS. In addition, hooking and holding are performed from the extension B side, and the extension A
The processing procedure when the is put on hold is described in B below.
The operation of is replaced with A, and the description is omitted here. Further, although the processing is executed by the plurality of control means in the control unit 15 as described above, only the means that is the basis of the operation will be shown here to simplify the description.

First, in the flow chart of FIG. 3, the call control means 12 monitors the states of the extensions A and B (step 1
01), it is determined whether or not the states of the extensions A and B have changed (step 102). Here, when there is a change in the state, it is judged which extension has changed (in this case, the extension A is changed) (step 10).
3) Further, the type of change is judged (step 10).
4).

When the type of change in the extension A is on hold, the hold service control means 31 sends the HDT to the extensions A and B.
(Hold tone) is connected (step 105), and the hold timer is monitored (step 106). This allows extension A
Is on hold and extension B is on hold (step 10).
7). As shown in step 107, the barrel-shaped symbol frame in the flow chart represents the connection state of each extension. Since the processing of the broken line after this connection state (and the processing according to the designated service) is a normal extension processing, the description thereof is omitted here (other flowcharts are the same).

When the type of change is hooking in step 104, the transfer service control means 32 SDs the extension A.
Connect T (2nd dial tone) (Step 10
8) The HDT is connected to the extension B (step 109).
As a result, the extension A is hooked and the extension B is on hold (step 110).

When the type of change is on-hook in step 104, the call control means 12 disconnects the communication path (step 111) and connects the extension B with ROT (restricted sound) (step 112). As a result, the extension A becomes empty and the extension B becomes ROT connection (step 113).

When the type of change is other service designation in step 104, the extension service control means 33 performs a process according to the designated service (step 11).
4). Next, the processing after step 107 in FIG. 3 will be described with reference to the flowchart in FIG.

First, the call control means 12 monitors the states of the extensions A and B (step 201) and judges whether the states of the extensions A and B have changed (step 202). Then, when the state has changed, it is determined which extension has changed (step 203). Here, if the change is within the extension of A, the type of change is further determined (step 204). Here, when the type of change is hold timeout, the call control means 12 releases the HDT from the extensions A and B (step 205). Next, the extension A is connected to the RGT (ring tone) (step 206), and the extension B is connected to the RBT (call back tone) (step 20).
7). As a result, the extension A becomes ringing from the hold timeout and the extension B becomes the RBT connection (step 208). In step 204, when the type of change is hold release, the call control means 12 changes the extension A, B to HD.
T is released (step 209) and the speech path is connected (step 210). As a result, the extensions A and B are in a call (step 211). When the type of change is on-hook in step 204, the call control means 12 disconnects the communication path (step 212) and connects the ROT to the extension B (step 213). As a result, the extension A becomes empty and the extension B becomes ROT connection (step 214).

Next, in step 203 of FIG. 4, the process when the state change is on the extension side of B is the flow of FIG.
Explain by chart. FIG. 5 shows a processing procedure of the extension mutual holding service and the held call transfer service which are the most characteristic operations of the digital PBX according to the present invention.

First, the call control means 12 judges the type of change (step 301). Here, when the type of change is hooking, the held call transfer service means 42 of the transfer service control means 16 releases the HDT from the extension B (step 302). Then, the extension B of the held call is shifted to the hooking state, and the SDT is connected to the extension B (step 303). As a result, extension A is on hold, extension B is
Becomes hooking (step 304), and extension B can transfer from the held call to another extension or office line. In step 301, when the type of change is on hold, the extension mutual hold service means 4 of the hold service control means 15
1 shifts the extension B in the held call to the hold state, maintains the extensions A and B in the mutual hold state, and starts counting the hold timer (step 305). This allows extensions A and B
Both are put on hold (mutual hold) (step 306), and the extension B can leave the seat without being restricted by the call.

In step 301, when the type of change is another service designation (by a specific key operation), the extension designation service means (not shown) in the extension service control means 33 designates The processing corresponding to the service thus performed is performed (step 307). In the example of step 307, even if extension B is a held call, a service other than hooking or holding is used.
This indicates that screws can be designated.

In step 301, when the type of change is on-hook, the call control means 12 causes the extensions B to H to be changed.
The DT is released (step 308) and the communication path is disconnected (step 309). With this, extension A is on hold,
Extension B becomes empty (step 310).

Next, the processing after step 110 in FIG. 3 will be described with reference to the flowchart in FIG.

First, the call control means 12 monitors the states of the extensions A and B (step 401) and judges whether the states of the extensions A and B have changed (step 402). Then, when the state has changed, it is determined which extension has changed (step 403). If the change is within the extension of A, the type of change is further determined (step 404). Here, when the type of change is hooking or time-out, the call control unit 12 releases the SDT from the extension A (step 405) and releases the HDT from the extension B (step 406). Then, the communication path is connected (step 407). This allows extension A
And B are in a call (step 408). Step 40
4, the call control means 12 releases the SDT from the extension A when the change type is on-hook (step 4).
09), the HDT is released from the extension B (step 41)
0). Next, the RGT is connected to the extension A (step 41
1), the RBT is connected to the extension B (step 412).
As a result, extension A is being called from hooking,
The extension B becomes an RBT connection (step 413).

Next, in step 403 of FIG. 6, the processing when the state change is on the extension side of B is shown in the flow chart of FIG.
Explain by chart. Note that, like FIG. 5, FIG. 7 shows a processing procedure of an extension mutual holding service and a held call transfer service which are characteristic operations of the digital PBX according to the present invention.

First, the call control means 12 judges the type of change (step 501). When the type of change is hooking, the held call transfer service means 42 of the transfer service control means 32 releases the HDT from the extension B (step 502). Then, the extension B of the held call is shifted to the hooking state, and the SDT is connected to the extension B (step 503). As a result, both extensions A and B are hooked (mutual hooking) (step 504), and extension B can transfer the held call to another extension or office line.

In step 501, when the type of change is on hold, the extension mutual hold service means 41 of the hold service control means 31 shifts the extension B in the held call to the hold state and the extension A. , B are maintained in the mutual holding state and the holding timer starts counting (step 505). As a result, the extension A is hooked and the extension B is put on hold (step 506), and the extension B can leave the seat without being bound by the call.

In step 501, when the type of change is other service designation (by a specific key operation), the extension designation service means (not shown) in the extension service control means 33 Processing is performed according to the service provided (step 507). This example also shows that, as with step 307 in FIG. 5, even if extension B is a held call, it is possible to specify a service other than hooking or holding.

In step 501, if the type of change is on-hook, the call control means 12 causes the extensions B to H to be changed.
The DT is released (step 508) and the communication path is disconnected (step 509). As a result, extension A is hooked and extension B is empty (step 510).

The above-mentioned mutual extension hold service and held call transfer service are peculiar services between the extension lines in the digital PBX, so that the extension line or external line telephone from the telephone line call can be used. Does not apply to operations. The telephone used may be digital or analog.

As described above, according to this embodiment, when a holding operation is performed from the extension which is the held call, both extensions are put in the mutual holding state. The user can leave the seat regardless of whether the extension of the other party's extension is released.

Further, when a hooking operation is performed from the extension which is the held call, the extension of the held call is put in the hooking state and the transfer request from the extension is accepted, so that the held call is set. It is possible to transfer from one extension to another extension or office line.

Therefore, according to the digital PBX of the present invention, various services are opened to the held call side, so that the user of the held call can effectively use the waiting time. Therefore, the convenience can be further improved.

Next, a second embodiment of the digital PBX according to the present invention will be described.

FIG. 8 is a functional block diagram showing a second embodiment of the digital PBX according to the present invention.

In the figure, a digital PBX 800
Is an application service control unit 810 for realizing various application services, and a main control unit 82 for controlling program execution and memory area.
0, maintenance / operation control means 830 for performing various tests, traffic measurement, and interface processing with a maintenance person, call control means 840 for performing various analysis processing such as call state management for call state transition and dial digit analysis, Split switch 86
Call path control means 8 for controlling 0 blockage and capturing / release control
50, a time division switch 860 which is a connecting means for connecting a line, a line circuit 870 for connecting with an extension, and a station line trunk 880 for connecting with a public communication network such as NTT. It consists of

Application service control means 810
Includes a held call service means 811 for realizing various extension services to the held call, and the held call service means 811 realizes a last number dial (hereinafter referred to as LNR) service. A held call LNR service means 812 for storing the reserved number and an LNR storage circuit 813 for storing the last number are included.

In this embodiment, the control means is composed of a peripheral device having a central processing unit (CPU) as a main component, and has been described above according to each control program written in a memory device (not shown) in the PBX. Perform data processing. Further, the held call service means 811 is shown in FIG.
It has the functions of the releasing means 2 and the service controlling means 3 shown in FIG. Furthermore, the application service control means 8
Reference numeral 10 is the application service control means 1 described above.
1, and the communication path control means 850 corresponds to the switching connection means 13 and the hardware control means 14 described above.

In the digital PBX 800 having such a configuration, a processing procedure for servicing a held call will be described with reference to FIGS. 9 and 10.

FIG. 9 shows a flowchart of the processing procedure, and FIG. 10 shows a state transition diagram showing the flow of the processing. In FIG. 10, reference numeral 1
Reference numerals 010 to 1040 indicate state transitions in the flow of processing, and symbols A and B indicate extensions.

Here, the description will be made from the state where the extension A and the extension B are talking (that is, the processing from step 301 onward in FIG. 5), and as described above in the control means. Although the processing is executed by a plurality of control means, only the basic means of the operation will be shown here for the sake of simplicity.

Extension A and extension B are talking (state 1 in FIG. 10).
010). At this time, the call control means 840 monitors the states of the extension A and the extension B based on the output information from the line circuit 870.

Here, when the extension A performs a holding operation (operation of a holding function key or operation of a special number dial, hereinafter referred to as holding) from the state 1010, the line circuit 870 detects the change. This detection result is notified to the call control means 840 through the communication path control means 850.

When the call control means 840 analyzes the holding operation from the extension line B, the call path is temporarily disconnected, the HDT is connected to each of the extension lines A and B, and the call state is changed to on hold. At this time, the extension A is put on hold and the extension B is put on hold (state 1020 in FIG. 10) (step 901).

When the hooking operation by the extension B is performed from this state, the call control means 840 notifies the held call service means 811 that hooking is performed. In the held call service means 811, the extension B in the held state is held.
To release the HDT (step 902), shift the extension B to the hooking state, and connect the extension B to the SDT (step 903). With this, extension A is on hold,
Extension B becomes hooking (state 1030 in FIG. 10)
(Step 904) Extension B is released from the held call and can request a service.

In the conventional digital PBX,
Since the state of the hooked extension is the held state, the call control means has ignored the hooking. Therefore, the extension in the held state was still in the held state.

In the state 1030, the call control means 840 detects a change in the state of the extension B (step 90).
5) When there is a change in state, the held call service means 811 is notified of that fact.

The held call service means 811 checks whether the service request operation is a dial or a feature key (function key) (step 906), and in the case of a dial, analyzes the contents of the dial (step 907). Here, if the dial operation is a special number of the LNR, the held call service means 811 causes the held call LNR.
The service means 812 reads out the information last dialed by the extension B (here, the extension C number) from the LNR storage circuit 813 and dials the number. afterwards,
The SDT is released from the extension B (step 908), the RBT is connected to the extension B (step 909), and the extension C is further added.
RG (ringer) is connected to (step 910). As a result, extension A is on hold, extension B is ringing, and extension C is receiving a call (state 1040 in FIG. 10) (step 91).
1).

In this way, the call state of the extension B can be released from the held call state, and the state can be changed to the LNR calling state from the held call. This provides LNR service from the held call.

If it is the feature key in step 906, the held call service means 811 analyzes the content of the key. If the feature key is compatible with LNR, the same processing as steps 908 to 911 is performed.

If there is another service designation (specific key operation, for example, pressing the feature key) from extension B from the state 1020 of FIG. 10 (after completion of the above step 901), the held call LNR Service means 81
2 performs processing according to the designated service (step 912).

In each of the above-mentioned embodiments, when the second extension in the held state (extension B in the embodiment) performs the hooking operation or the holding operation, the held state of the second extension is changed. Although it is released, when the first extension (extension A in the embodiment) is on hold and the second extension is in the hold state, the second extension is held. The state may be canceled.

As described above, according to this embodiment, even when the second extension is put on hold by the holding operation on the first extension side, the second extension is operated for hooking. By performing a hold operation or a hold operation, the held state of the second extension is released and various services can be received.

[0071]

As described above, according to the present invention, when the second extension is put on hold by the holding operation on the first extension side, the releasing means holds the first extension. When the hold status of the second extension is released while the status is maintained and a service request is input from the second extension whose hold status has been released, the corresponding service is provided by the service control means. , The second extension is released from the held state and can receive the requested service.

When the second extension is put on hold by the transfer operation on the first extension side, the releasing means
When the held state of the second extension is released while the first extension is maintained in the transfer state and a service request is input from the second extension whose held state has been released, the corresponding service is service-controlled. As provided by the means, the second extension is released from the held state and can receive the requested service.

Specifically, on the side of the second extension released from the held state, for example, a hold request for putting the second extension in the hold state, a transfer request for the third extension or office line, and a final storage dial number. By requesting at least one of the last number dial requests for redialing to the destination indicated by, the corresponding service can be received.

Therefore, according to the digital PBX of the present invention, various services are opened to the held call side, and the user of the held call can effectively use the waiting time. Therefore, the convenience can be further improved.

[Brief description of drawings]

FIG. 1 is a diagram for explaining the basic principle of a digital PBX according to the present invention.

FIG. 2 is a functional block diagram showing a first embodiment of a digital PBX according to the present invention.

FIG. 3 is a flowchart showing a processing procedure for performing extension mutual holding service and held call transfer service in the digital PBX of the first embodiment.

FIG. 4 is a flowchart showing a processing procedure for performing extension mutual holding service and held call transfer service in the digital PBX of the first embodiment.

FIG. 5 is a flow chart showing a processing procedure for performing extension mutual holding service and held call transfer service in the digital PBX of the first embodiment.

FIG. 6 is a flowchart showing a processing procedure in the case of performing extension mutual holding service and held call transfer service in the digital PBX of the first embodiment.

FIG. 7 is a flowchart showing a processing procedure in the case of performing extension mutual holding service and held call transfer service in the digital PBX of the first embodiment.

FIG. 8 is a functional block diagram showing a second embodiment of the digital PBX according to the present invention.

FIG. 9 is a flowchart showing a processing procedure for performing a held call service in the digital PBX of the second embodiment.

FIG. 10 is a state transition diagram showing the flow of processing of a held call service according to the second embodiment.

[Explanation of symbols]

1, 11, 810 ... Application service control means, 2 ... Release means, 3 ... Service control means, 10, 810 ... Digital PBX, 12, 840 ... Call control means, 13 ... Switching connection means, 14 ... Hardware Control means, 15 ... Control unit, 16, 860 ... Time division switch, 31 ... Hold service control means, 32 ... Transfer service control means, 33 ... Extension service control means, 41 ... Mutual extension hold service Service means, 42 ... held call transfer service means 811, held call service means, 820 ... main control means, 830 ... maintenance / operation control means, 850 ... call path control means, 870 ... line circuit, 880 ... station line trunk

Claims (3)

[Claims] 1. A digital private branch exchange comprising a communication path switch for connecting communication paths between extension lines and between an extension line and a station line, and a control unit for controlling the communication path switch, wherein the control unit is in a communication state. Of the first extension and the second extension, when the second extension is put on hold by the holding operation on the side of the first extension, the second extension is kept on hold while the first extension is held. And a service control means for providing a corresponding service when there is a service request from the second extension after releasing the held state. Private branch exchange. 2. A digital private branch exchange having a call path switch for connecting call paths between extension lines and between an extension line and a station line, and a control unit for controlling the call path switch, wherein the control unit is in a call state. Of the first extension and the second extension, when the second extension is put on hold by the transfer operation on the side of the first extension, the second extension is kept in the transfer state. And a service control means for providing a corresponding service when there is a service request from the second extension after releasing the transferred state. Private branch exchange. 3. The service request includes a hold request for putting a second extension on hold, a transfer request for a third extension or an office line, and a last number dial for redialing to a destination indicated by a final stored dial number. At least one of the requests
3. A digital private branch exchange according to claim 1 or 2, characterized in that one is included.