JPH03181262A - Private branch of exchange - Google Patents

Abstract

PURPOSE:To improve the operability by using caller telephone number information and checking whether or not the information corresponds to a number reserved and registered and reaching the call to a reserved extension when the number is matched. CONSTITUTION:Opposite number information acquired from a digital network (ISDN network) is registered in a 1st storage means 7 corresponding to extension telephone set terminals 1a-1n in talking connection and when a re-incoming call reservation command is received from the extension telephone set terminals 1a-1n, the opposite telephone number information of a current talking destination of the extension telephone set terminals 1a-1n is acquired by the 1st storage means 7. Moreover, opposite telephone number information acquired by a 2nd storage means 7 is registered corresponding to the extension telephone set terminals 1a-1n. In the case of a call from the ISDN network, the information is collated with opposite telephone number information registered in the 2nd storage means 7 and when they are coincident, the opposite telephone number information is controlled to reach the registered extension. Thus, the registration of an incoming call retailed to be reached directly to the extension telephone set is implemented by a simple operation.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to an electronic private branch exchange used in connection with a digital communication network, for example, an I5DN network.

(Prior Art) Conventionally, in electronic private branch exchanges, it has been possible for the user to set in advance a relay stand or a specific extension telephone number for each central line boat number as the destination for incoming calls from the central office line. In a private branch exchange configured in this manner, when a call is received from a central office line, the call is controlled to be sent to the specified extension telephone number or relay stand.

In this case 1. 'li The call destination is not necessarily the caller's desired destination, so the operator of the extension that receives the call checks the extension telephone number specified by the caller, and then attempts to place the call to that extension telephone number. A transfer operation is performed, and only after this "handover" is the caller able to talk to the desired party.

On the other hand, in recent years, l5DN (digital integrated service network)
digitalnetwork) is now available for service.

This ISDN provides telephone, data, facsimile communications, and various communication processing services in one digital communication network, and this communication system is configured as shown in FIG. 6, for example.

In other words, this system includes a digital circuit switching network 11, a packet switching network 12, and a common line signaling network! What is the 15DN exchange 14 to which 3 etc. are connected?The subscriber line 19 is connected to the 15DN exchange 14 to the network termination device 18 in the user's home, and this network termination device 18 is connected to the home bus l5DN in the user's home.
A communication terminal device 6 such as a telephone device, a facsimile device, a personal computer, etc. can be connected to the home bus 10.

Then, a plurality of communication channels are selectively used for each subscriber line 19 to perform desired communication between communication terminal devices. For example, in a basic interface with a transmission rate of 192 to 717 seconds, there are two B channels with a transmission rate of 64 to 717 seconds, and one
8 bit/sec D channels are time-division multiplexed, and these channels are used to transmit data. In the case of the basic interface, the subscriber premises bus has l.
Up to eight 5DN terminals can be connected. A subaddress can be set for each terminal, and if an incoming call setup message has a subaddress, the call will arrive at the existing terminal corresponding to the subaddress, and if there is no subaddress, the call will arrive at the respective terminal.

Since the system is such that messages are sent, it is now possible to know the telephone number of the caller from this call setup message. Using this service, you can arbitrarily set a destination extension phone number for each caller's phone number on the electronic private branch exchange, and specify that incoming calls from the set caller will not be relayed. A call termination designation function has been implemented that allows calls to be received directly to an extension telephone, reducing transfer time.

By the way, for such a service in a private branch exchange, there are two methods for setting the calling party's telephone number and the corresponding extension telephone number of the called party: one is to register it at the time of order setting, and the other is to register it from an extension telephone terminal. In the former case, the settings are fixed and cannot be changed easily, but in the latter case, the settings can be made freely for the convenience of the user. This latter method can also be called a call-specific incoming call function. In this method, to register from an extension telephone terminal, for example, after capturing the extension number, dial the special code for calling number registration, and then enter the calling number. Registration can be performed by dialing, and in this case, the extension number captured in the calling number registration operation is selected as the destination extension number.

(Problem to be solved by the invention) As mentioned above, as a digital communication service, 15DN
In this ISDN service, when a call is received from the network, a call setup message including the caller's telephone number is sent. Now you can know the number.

Using this service, at an electronic private branch exchange,
Call-by-call reception allows you to arbitrarily set a destination extension phone number for each caller's phone number, and allows incoming calls from the set caller to be received directly to a designated extension phone without transfer. The specified function has been implemented, and the transfer time has been shortened.

In this way, in the conventional electronic private branch exchange used in the 15DN network, when a call arrives from the 15DN network, if the destination extension telephone number for the caller's telephone number has been set in advance, the extension telephone The incoming call can be placed at the number. Then, the incoming call can be registered to the designated extension by dialing the special number for calling number registration after capturing the extension number, and then dialing the calling number.

However, when setting the caller's phone number using this method,
You cannot register without knowing the caller's phone number, and
Setting operations were cumbersome as it required operations such as dialing a special number for calling party number registration and then dialing the calling party's number. In particular, I received a call from a caller whose calling number was not registered, and after passing through the call, I received a call from someone whose calling number was not registered. I When you are on a call with telephone A, if you hang up for some reason and have the other party call you back, in order to receive the call directly to extension A, the exchange must call the extension based on the call setup message. You must check the display information of the other party's phone number sent and displayed and register the settings.In other words, on an extension phone, the phone number sent from the private branch exchange side must be displayed on the built-in display of the phone. ), it is necessary to check and register the caller's phone number displayed on this display, and extension telephone A has a display that can display the caller's phone number. If you do not have one, you will have to go through extremely troublesome operations, such as having to ask the other party for their phone number and register it, and you will not be able to avoid mistakes in numbers or incorrect settings, which can be a problem especially when you are busy. be.

Also, once you register a caller's phone number, calls from that phone number will be fixed only to the registered extension number until you cancel it, and it is easy to forget to cancel it. This was a serious problem in terms of service.

Therefore, an object of the present invention is that when an extension telephone operator who is making a call via a digital network such as the 15DN network asks the other party to call back again, the incoming call from the other party is Registration for receiving calls directly to the extension telephone can be performed with a simple operation, and
An object of the present invention is to provide an electronic private branch exchange in which the function of specifying incoming calls for each call is improved so that the cancellation thereof is automated.

[Structure of the invention]

(Means for Solving the Problems) In order to achieve the above object, the present invention is configured as follows. That is, in a branch exchange connected to a digital network that transmits the telephone number information of the caller when a call is received, when a call is connected to the digital network, the number information of the other party is registered in correspondence with the extension telephone terminal connected to the call. a first storage means for registering the other party's number information in correspondence with the extension; and a second memory means for registering the other party's number information in correspondence with the extension; and the other party's number information or the calling party's extension obtained from the digital network when a call is connected to the digital network; The number information of the called party is registered in the first storage means corresponding to the extension telephone terminal to which the call is connected, and when a re-arrival order command is received from the extension telephone terminal, the current call destination of the extension telephone terminal is registered. obtain the telephone number information of the other party from the first storage means, register the obtained telephone number information in the second storage means in association with the extension telephone terminal, and when receiving a call from the digital network, , and control means for checking the telephone number information of the other party registered in the second storage means and controlling the call to be received on the extension in which the telephone number information is registered if the telephone number information matches the telephone number information of the other party. Furthermore, the control means is provided with a function of updating the second storage means so as to cancel the reservation registration for the extension for which the re-arrival reservation command is issued when the incoming call control based on the re-arrival reservation is completed.

(Function) In such a configuration, when the digital network and the extension are connected, the control means collects information about the telephone number of the other party (including the called subaddress) or the caller's extension from the originating extension via the extension and the digital network. The called party's number information is stored in the first storage means, and when a command to reserve a call again is received from the extension during a call, the control means reads out the stored telephone number information of the current called party. , a reservation is registered in the second storage means corresponding to the extension for which the re-arrival reservation command has been issued, and when a call arrives from the network from the other party having the telephone number information, the second storage means
Based on the information in the storage means, the extension for which the reservation-registered call re-arrival reservation command is issued is known and the call is received at the extension. Furthermore, when the incoming call control is completed, the reservation registration for the extension for which the re-incoming reservation command is issued is canceled.

In this way, when an extension is making a call over the network, simply by issuing a re-call reservation command from the connected telephone terminal of that extension, the exchange side will receive the telephone number information (including sub-address) of the other party. When a call is received from the network, it is automatically registered in accordance with the extension for which the incoming call reservation command has been issued, and the caller's phone number information is used to check whether or not this corresponds to the number registered for reservation. Control is performed so that the call is received on the reserved extension, so when the extension operator is making a call over the network and wants the other party to make a call again, all he or she needs to do is issue a re-reservation command to the other party. You can easily reserve and register a telephone number, and incoming calls from the set other party can be received directly to the designated extension phone terminal without transfer, and you can also make reservations for repeat calls. If there is, the reservation will be automatically canceled, so the extension telephone terminal can register the telephone number of the other party as the telephone number of the caller who will receive a call to the extension without being aware of the other party's telephone number. Since there is no need to perform any operations after the call has been completed, the operability is improved, and the caller side eliminates waiting time for handover, which improves the service provided to the caller.

(Example) Hereinafter, an example of the present invention will be described in detail based on the drawings.

FIG. 1 is a block diagram showing an embodiment of an electronic private branch exchange to which the present invention is applied. In the figure, reference numerals 1a to 1n indicate electronic key telephones, which are connected to the communication path network 3 via line circuits 2a to 2n as extension telephone terminals, respectively.

The line circuits 2a to 2n are for interfacing with extension lines, and the communication path network 3 is an 15DN interface that supports up to "layer 3 (network layer)".
It is connected to the 15DN network via bus circuits 4a to 4Il.

In addition, this communication path network 3, line circuits 2a to 2
The n and l5DN interface circuits 4a to 4m are connected to a central controller 6 via a control data bus line 5, and are connected to the central controller 6, which performs control operations using data stored in a storage device 7. It is configured to transmit and receive data to form a communication path between the extension telephone terminals 1a=In and between the extension telephone terminals 1a-In and the 15DN network via the communication path network 3.

The l5DN interface circuits 4a to 4m are connected to the l5DN network to provide an interface, and support up to "layer 3 (network layer)" and support "layer 1 (
physical layer) and layer 2 (data link layer), connection between the B channel of the 15DN network and the communication path network 3, and the ``layer 3'' between the D channel of the 15DN network and the ψ real control device 6. Send and receive information.

Next, the repeat call reservation function according to the present invention will be explained.

FIG. 2 is a diagram showing the structure of a memory that stores information used to control the call re-arrival reservation function. The re-arrival reservation function control information table is formed in the storage device 7 and is controlled by the central control unit 6. Writing/reading, erasing, etc. are performed and managed as follows.

MBI to MB3 in the re-arrival reservation function control information table in FIG. 2 indicate memory blocks, and among these, memory block MDI is 15DN.
Interface circuits 4a to 4+ (hereinafter referred to as TRKDNn
(where n is called 0.1.2.-'), and the currently connected extension D of each TRKDNn is
This is a trunk-by-trunk current call extension information holding area for storing Nn.

Furthermore, the memory block MB2 is a trunk-based current telephone number holding area for storing the telephone number of the other party currently connected to each TRKDNn via the 15DN network.

Extension DNn stored in the above memory block MBI
The information (where n is 0, 1, 2, etc.) is updated every time the extension DN connected to each TRKDNn changes due to call transfer, etc., and is cleared when the call ends.

In addition, the telephone number stored in the memory block MB2 corresponds to the called number and called subaddress sent to the l5DN network when making a call, and corresponds to the called number and subaddress sent to the l5DN network when receiving a call.
The calling number and calling subaddress received from the network correspond to
Use of the memory block MB2 when making a call from the extension to the 15DN network or when receiving a call from the 15DN network TRKD
The telephone number is stored in an area corresponding to Nn.

Furthermore, the memory block MB3 in FIG. 2 is a source called number information area for each extension that stores the calling number and calling sub-address (if any exist) for receiving a call to that extension DNn. , when there is an incoming call from the 15DN network, the central controller 6 reads the calling number and calling subaddress from the layer 3 message, and if the calling number and calling subaddress are registered in the memory block MB3, the registration is completed. The incoming call is terminated on extension DNn.

To register the calling number and calling subaddress in the memory block MB3, the extension DNn to be registered is l5.
During a call with the DN network, by executing a predetermined operation from the terminal of the extension DNn to activate the repeat call reservation function, the central control device 6
This is done by reading out the telephone number of the other party with whom the user is communicating via the 15DN network from the memory blocks MBI and MB2, and storing the read out telephone number information in the area corresponding to the extension DNn of the memory block MB3.

Next, the operation of this system having the above configuration will be explained with reference to FIGS. 3, 4 and 5. FIG. 3 is an example of a case where a call is made from an extension terminal to the 15DN network, and is a flowchart showing the sequence of operations when obtaining the information necessary for using the repeat call reservation function when making a call to the 15DN network.

When a call is made from an extension terminal to the l5DN network, the central control unit 6
First of all, the l5DN interface (TR
KDN) Find a vacant one among 4a-4■.

If a free TRKDN is found, the free TRKDN
n4n and the extension DNn of the originator, the line circuit of the extension DNn of the originator and the vacant TRKDNn 4n are controlled to be connected via the communication path network 3, and at the same time, the corresponding TRKDNn of the memory block MBI is 4
Information on the extension DNn of the caller is registered in the area corresponding to n (s301.5302).

Next, the called number and called sub-address are extracted from the called number information element and called sub-address information element included in the call setup message sent from the calling extension to the 15DN network, and the extracted called number and called sub-address are stored in the memory block. Register in the TRKDNn 4n compatible area of MB2 (s3H). In this way, the central control device B stores the telephone number of the other party to whom the extension DNn calls via the 15DN network in the memory block MB2.

FIG. 4 is a flowchart showing an example of call termination control including the case where necessary information for using the call re-arrival reservation function is collected when a call is received from the 15DN network.

When a call is received from the 15DN network, the central control unit 6 searches for a free TRKDNn in the exchange and determines the 15DN interface (TRKDN) to receive the call (s401). Assume that this is TRKDNn 4n, for example. Then, the central control device 6 enters incoming call control via this TRKDNn 4n. At this time, central controller B searches the calling number information element and calling subaddress information element from the call setup message received from the 15DN network, and reads the calling number and calling subaddress (5402). If there is a calling party number information element in the call setup message, the central controller 6 receives the incoming call T l? in the memory block MB2. K D N n 4
The calling number is registered in the area corresponding to n, and if a calling subaddress exists in the call setting message, the calling subaddress is also registered in the area (5403).

In this way, using the telephone number information of the other party obtained when receiving a call from the network or when making a call from an extension to the network, the ψ central control device 6 determines whether the incoming TRKDNn 4n is connected to the other party via the SDN network. User's phone number in memory block M
Store in B2.

Next, the central control unit B searches the memory block MB3 and checks whether the same 'Rh telephone number as the telephone number registered in the memory block MB2 in step 5403 is registered (404).

The details of the procedure for registering a telephone number in memory block MB3 will be described later, but by activating the repeat call reservation function, the caller's telephone number (calling number and calling subaddress) can be registered in the extension DN corresponding area of memory block MB3. register. When the repeat call reservation function is not working, the memory block MB
3 stores a specific value indicating that no re-arrival reservation is being made.

As a result of the check in step 5404, if the corresponding telephone number is registered in the memory block MB3, the central control device B reads the extension DNn for which the re-arrival reservation has been made for the telephone number from the memory block MB3,
An incoming call is made to the extension DNn. In addition, in order to connect the extension DNn and the incoming TRKDNn 4n, the extension DNn is registered in the area corresponding to the TRKDNn 4n of the memory block MBI, and furthermore, in order to cancel the re-arrival reservation function, the extension DNn is registered in the area corresponding to the TRKDNn 4n of the memory block MBI. A specific value indicating that a re-arrival reservation is not in progress is registered in the area corresponding to the extension DNn (s40B). That is, since the call reception based on the re-arrival reservation has been executed, the reservation has been completed, so the reservation is canceled so that this reservation will not be executed repeatedly in the future.

On the other hand, if it is determined in step 5402 that the calling number information element cannot be detected from the call setup message received from the I5DN network at the time of incoming call, and as a result of the check in step 5404, the calling number information element is detected from the call setup message received from the I5DN network in memory block MB3. If the calling number and sub-address are not registered, the incoming call will be processed normally.
The call is received on the pre-installed extension DN. At this time, the nuclear IDN is registered in the area corresponding to the incoming TRKDNn 4n of the memory block MBI (5405).

Next, the repeat call reservation function will be explained. This function can be used by executing it while talking with the other party from an extension line. FIG. 5 is a flowchart showing the operation of the repeat call reservation function. As described above, when the extension DNn is in a state of communication with the other user via the I5DN network after making a call to or receiving a call from the I5DN network, the memory block Ml'll,
MB2 is compatible with TRKDNn, which is used respectively.
Information on the connecting extension DNn and the telephone number of the other user are registered.

In this state, perform a predetermined operation from the key telephone of the extension in question to activate the repeat call reservation function, such as pressing the repeat call reservation function button on the key telephone or dialing the repeat call reservation function special number. By (5501)
, the repeat call reservation function of the central control device 6 is activated, and the central control device 6 is connected to the extension DNn that has instructed this function.
KDNn information is searched from memory block MHI (5502), and the telephone number of the user on the other end of the call is obtained from the area corresponding to the searched "Connected TRKDNnJ" in memory block MB2.Then, the obtained telephone number is stored in memory. It is registered in the area corresponding to the commanded extension DNn of block MB3 (5503).

' After this, if there is an incoming call from the other user via the ISDN network, the central control unit f! 8, as mentioned above, the extension DNn which activated the re-arrival reservation function receives the call preferentially. Then, once the reservation is executed, the reservation becomes obsolete, so as described in 540B, the reservation is canceled and unnecessary repeat calls thereafter are eliminated.

This automates the cancellation operation after the call reservation function is no longer used.

Therefore, according to this embodiment, when an extension operator who is making a call via the 15DN network wants the other party to make a call again, if the extension operator performs the predetermined operation to reserve a second call, , the telephone number of the person you are currently talking to can be reserved in the memory of the exchange. After this, when a call is received from a user with the same telephone number as the reserved telephone number, the call can be directly received to the extension DN for which the telephone number has been reserved.

In addition, the extension telephone terminal is an electronic key telephone, and an LED is installed on the electronic key telephone to display a repeat call reservation function, and when a repeat call is reserved, the LED is lit at all times, and when a second call is received from the reserved telephone number. By providing a display means that causes the L-ED to blink, usability is further improved. Also, when calling from an extension to the l5DN network,
The caller's number information included in the call setup message sent by the calling extension to the 15DN network is extracted as the caller's number and used to reserve a repeat call, but the dial operation information when making a dial call from the extension is You may also use it.

As explained in detail above, this device has the function of transmitting and receiving the caller's telephone number information etc. via the network when making a call.
In a private branch exchange connected to a digital network such as a DN network, when connecting the network and an extension, the other party's phone number information obtained from the L5DN network or the extension side is used, and this information is transmitted via the L5DN network that the extension is currently calling. The telephone number information (including the called subaddress) of the called party is stored in correspondence with that extension, and when a command to reserve a call again is given from the extension during a call, the stored telephone number information of the current called party is stored. read out and register the reservation in correspondence with the extension for which the re-arrival reservation command has been issued, and the incoming call from the party with that phone number information is 15.
When a call is received from a DN network, the exchange is provided with a function to allow a call to arrive at the registered extension for which a re-arrival reservation command is issued, and to cancel the reservation registration for the extension for which the re-arrival reservation command is issued when the incoming call control is completed.

Therefore, when an extension is making a call via the 15DN network, simply by issuing a re-arrival Ga reservation command from the connected telephone terminal of that extension, the exchange side will receive the telephone number information (including sub-address) of the other party. When there is an incoming F2 from the 15DN network, it is automatically registered in accordance with the extension for which the incoming T contract is issued.
Using the phone number information of the calling party, it is checked whether this corresponds to a registered number, and if so, the call is controlled to be received on the reserved extension, so the extension handler can
When making a call via a 5DN network, if you want the other party to call you again, you can easily set the other party's phone number by simply issuing a repeat call reservation command. Incoming calls from users can be directly routed to the designated extension phone without having to be relayed.Moreover, if a call is received due to repeat call reservation, the reservation is automatically canceled, so the extension phone can The phone number of the other party can be registered as the phone number of the caller who will receive the call on the extension phone without being aware of the other party's phone number, and there is no need to perform any operations after the call is finished, improving operability. At the same time, on the caller side, there is no waiting time for handover, and service to the caller can be improved.

[Effects of the Invention] As described in detail above, the present invention allows an extension to communicate with the other party by simply issuing a repeat call reservation command 8 from the connected telephone terminal of the extension. Telephone number information is automatically registered in correspondence with the extension for which the re-incoming reservation order has been issued, and when a call is received from the network, the telephone number information of the calling party is used to determine whether or not this corresponds to the number for which the reservation has been registered. If the call is checked, the call is controlled to be received on the reserved extension, so when the extension operator is making a call over the network,
If you want the other party to call you again, you can easily set it up without knowing the other party's phone number by simply issuing a repeat call reservation command, and you will not be able to pick up calls from the set party. You can receive calls directly to the designated extension phone, and the reservation will be automatically canceled if you receive a call due to the repeat call reservation, so you can receive calls directly to your designated extension phone. ! jl On the telephone terminal side, you can register the telephone number of the other party to receive the call on your own extension telephone terminal without having to be aware of the telephone number of the other party, and there is no need to perform any operations after the call is finished. It is possible to provide a private branch exchange with features such as improved operability, elimination of waiting time for callers, and improved service to callers.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of an electronic exchange according to the present invention, FIG. 2 is a diagram showing the structure of a memory that stores information used to control the re-arrival reservation function in the embodiment, and FIG.
Figure 4 is a flowchart showing the control of calling to the 15DN network in the embodiment, Figure 4 is the flowchart showing the control operation of receiving calls from the 15DN network in the embodiment, and Figure 5 is a flowchart showing the operation of controlling calls from the 15DN network in the embodiment. FIG. 6 is a flowchart showing registration control and is a diagram for explaining the outline of the I5DN network. 1a~In...Electronic key telephone, 2a~2n・
...Line circuit, 3...Call path network, 4a~
4m・-IS D N interface circuit (TRKD
N), 5... Control data bus line, 6... Central control unit, 7... Storage device.

Claims (4)

[Claims] (1) In a private branch exchange connected to a digital network that transmits the telephone number information of the caller when a call is received, when a call is connected to the digital network, the other party's number information is registered in correspondence with the extension telephone terminal connected to the call. a first storage means for registering the number information of the called party in correspondence with the extension; and a second storage means for registering the number information of the called party in correspondence with the extension telephone; In addition to registering in the first storage means corresponding to the terminal, when receiving a repeat call reservation instruction from the extension telephone terminal, obtains the telephone number information of the current destination of the extension telephone terminal from the first storage means, The obtained destination telephone number information is registered in the second storage means in association with the extension telephone terminal, and when a call is received from the digital network, the other party telephone number information registered in the second storage means and the other party telephone number information registered in the second storage means are registered. A private branch exchange comprising: control means for controlling the call to be received at the extension in which the telephone number information of the other party is registered when the telephone number information of the called party is registered. (2) In a private branch exchange connected to a digital network that transmits the telephone number information of the caller when a call is received, when a call is connected to the digital network, the other party's number information is registered in correspondence with the extension telephone terminal connected to the call. a first storage means for registering the number information of the called party in correspondence with the extension; and a second storage means for registering the number information of the called party in correspondence with the extension telephone; In addition to registering in the first storage means corresponding to the terminal, when receiving a repeat call reservation instruction from the extension telephone terminal, obtains the telephone number information of the current destination of the extension telephone terminal from the first storage means, The obtained destination telephone number information is registered in the second storage means in association with the extension telephone terminal, and when a call is received from the digital network, the other party telephone number information registered in the second storage means and the other party telephone number information registered in the second storage means are registered. When the call is checked and they match, the call is controlled to be received on the extension for which this called party's phone number information is registered, and when the call control based on the repeat call reservation is completed, the reservation registration for the extension for which the repeat call reservation command is issued is canceled. A private branch exchange comprising: control means having a function of rewriting and controlling the second storage means. (3) In a private branch exchange connected to a digital network that transmits the telephone number information of the caller when a call is received, when a call is connected to the digital network, the other party's number information is registered in correspondence with the extension telephone terminal connected to the call. a first storage means for registering the number information of the called party in correspondence with the extension; and a second storage means for registering the number information of the called party in correspondence with the extension number; The number information of the called party is registered in the first storage means corresponding to the extension telephone terminal to which the call is connected, and when a repeat call reservation command is received from the extension telephone terminal, the information of the current call destination of the extension telephone terminal is registered. Obtaining telephone number information from the first storage means, registering the obtained telephone number information in the second storage means in association with the extension telephone terminal, and when receiving a call from the digital network, A private branch exchange comprising: control means for checking the telephone number information of the other party registered in the second storage means and controlling the call to be received on the extension in which the telephone number information of the other party is registered when the telephone number information matches the telephone number information of the other party. (4) In a private branch exchange connected to a digital network that transmits the telephone number information of the caller when a call is received, when a call is connected to the digital network, the other party's number information is registered in correspondence with the extension telephone terminal connected to the call. a first storage means for registering the number information of the called party in correspondence with the extension; and a second storage means for registering the number information of the called party in correspondence with the extension number; The number information of the called party is registered in the first storage means corresponding to the extension telephone terminal to which the call is connected, and when a repeat call reservation command is received from the extension telephone terminal, the information of the current call destination of the extension telephone terminal is registered. Obtaining telephone number information from the first storage means, registering the obtained telephone number information in the second storage means in association with the extension telephone terminal, and when receiving a call from the digital network, When the telephone number information of the other party is checked against the telephone number information registered in the second storage means, the call is controlled to be received on the extension in which the telephone number information of the other party is registered;
A private branch exchange having a control means having a function of rewriting and controlling a second storage means so as to cancel the reservation registration for the extension for which the re-arrival reservation command is issued when the incoming call control based on the re-arrival reservation is completed.