IP telephone network system and telephone control device

Abstract

If a call fails due to insufficient line resources on the receiving telephone control unit, the system ensures that subsequent re-calls from the originating telephone control unit are successful. [Solution] If the calling fails due to insufficient line resources on the receiving telephone control device 20, the calling telephone control device 10 requests the receiving telephone control device 20 to secure line resources, and the receiving telephone control device 20 attempts to redial once it successfully secures the line resources. Furthermore, the procedure for requesting line resource allocation is communicated between the calling telephone control device 10 and the receiving telephone control device 20 via the IP communication network DN, rather than using the IP telephone network TN.

Description

Technical Field

[0001] The present invention relates to an IP telephone control technology for recalling when an error message due to insufficient line resources is returned in response to a transmitted call message.

Background Art

[0002] In an IP telephone network constructed on an IP communication network such as the Internet, call control related to VoIP (Voice over Internet Protocol) calls such as outgoing call, incoming call and hold can be performed by exchanging IP call control messages at a control server using an IP call control protocol such as SIP (Session Initiation Protocol).

[0003] In a telephone system such as a key telephone system or a PBA system that provides IP telephone services to a plurality of telephone terminals connected thereunder, a telephone control device such as a main device or a PBX device uses such an IP call control protocol to call a specified destination telephone terminal in response to a call message (INVITE) from the IP telephone network, and establishes a VoIP call in accordance with a response operation at the destination telephone terminal.

[0004] In this case, when the line resources of the called-side telephone control device are congested and insufficient, for example, the destination telephone terminal is in a call, a SIP response code (SIP Response Code) and a reason display code (Reason Header) are used to return the call failure and the reason therefor to the call control server via an error message, and notify the calling-side telephone control device of the same.

[0005] Conventionally, for example, Patent Document 1 proposes a technology that uses such an IP call control protocol to resend a call message from the originating telephone control unit at a fixed interval if it is unable to make a VoIP call with the called destination telephone terminal, and notifies the originating telephone terminal when the destination telephone terminal becomes available for a call. This allows the originating user to confirm that the destination telephone terminal is available for a call without having to repeatedly redial. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2005-45456 [Overview of the project] [Problems that the invention aims to solve]

[0007] In the conventional technology described above, if a call fails due to insufficient line resources at the receiving telephone control unit, for a successful re-call from the originating telephone control unit, the call message from the originating telephone control unit must reach the receiving telephone control unit at the same time that the line resource shortage at the receiving telephone control unit is resolved. However, if another call message arrives at the receiving telephone control unit between the time the line resource shortage is resolved and the time the call message from the originating telephone control unit arrives at the receiving telephone control unit, a line resource shortage will occur again, and the re-call will fail.

[0008] Therefore, the success of a redial depends on when the caller's telephone control unit resolves its line resource shortage. Furthermore, shortening the call interval increases the probability of a successful call, but this also increases the burden on the IP telephone network and the caller's telephone control unit. Consequently, according to the aforementioned conventional technology, it is difficult to reliably ensure a successful redial after a call fails due to insufficient line resources.

[0009] The present invention aims to solve these problems by providing an IP telephone control technology that can reliably ensure successful re-calls if a call fails due to insufficient line resources at the receiving telephone control device. [Means for solving the problem]

[0010] To achieve this objective, the IP telephone network system according to the present invention comprises an outgoing telephone control device and a receiving telephone control device that provide IP telephone services to telephone terminals connected under their respective systems by exchanging call control messages with an IP telephone network on an IP communication network. The outgoing telephone control device sends a call message to the IP telephone network to call a destination telephone terminal under the receiving telephone control device, and if an error message is returned due to insufficient line resources at the receiving telephone control device, it directly sends a resource allocation request to the receiving telephone control device via the IP communication network to request the allocation of line resources at the receiving telephone control device, and a resource allocation response indicating successful resource allocation is returned directly from the receiving telephone control device via the IP communication network. The receiving telephone control device is configured to retransmit the call message accordingly. The receiving telephone control device monitors its own line resources in response to the reservation request received directly from the originating telephone control device via the IP communication network. If a line resource is available, it reserves the receiving line resource from the line resource to be used for a VoIP call with the originating telephone control device. It then sends a reservation response indicating successful reservation directly back to the originating telephone control device via the IP communication network. In response to a call message originating from the originating telephone control device that arrives after the response, it calls the destination telephone terminal under its control specified in the call message, and establishes a VoIP call with the originating telephone control device using the receiving line resource in response to an answer operation at the destination telephone terminal.

[0011] Furthermore, in one example of the configuration of the IP telephone network system according to the present invention, the incoming telephone control device is configured to release the reserved incoming line resources if the call message to be retransmitted from the outgoing telephone control device does not arrive within a predetermined reservation time after the reservation response is returned.

[0012] Furthermore, the telephone control device according to the present invention comprises a network interface for data communication with an IP communication network, a terminal interface for data communication with telephone terminals connected to it via a communication line, and a control circuit that provides IP telephone services to the telephone terminals by exchanging call control messages with the IP telephone network on the IP communication network via the network interface. The control circuit is configured to monitor its own line resources in response to a reservation request for the reservation of line resources received directly from the originating telephone control device via the IP communication network, and if it confirms that there are available line resources, it reserves an incoming line resource from the line resources to be used for a VoIP call with the originating telephone control device, and sends a reservation response indicating successful reservation directly back to the originating telephone control device via the IP communication network. In response to a call message originating from the originating telephone control device that arrives after the response, it calls the incoming telephone terminal specified in the call message, and establishes a VoIP call with the originating telephone control device using the incoming line resource in response to an answer operation at the incoming telephone terminal.

[0013] Furthermore, another telephone control device according to the present invention comprises a network interface for data communication with an IP communication network, a terminal interface for data communication with telephone terminals connected to it via a communication line, and a control circuit that provides IP telephone services to the telephone terminals by exchanging call control messages with the IP telephone network on the IP communication network via the network interface. If an error message is returned after sending a call message due to insufficient line resources at the receiving telephone control device, the device is configured to directly send a resource allocation request to the receiving telephone control device via the IP communication network to request the allocation of line resources at the receiving telephone control device, and to resend the call message in response to a resource allocation response indicating successful allocation of line resources returned directly from the receiving telephone control device via the IP communication network. [Effects of the Invention]

[0014] According to the present invention, if a call fails due to insufficient line resources at the receiving telephone control device, subsequent re-calls from the originating telephone control device can be reliably made to succeed. [Brief explanation of the drawing]

[0015] [Figure 1] Figure 1 is a block diagram showing the configuration of the IP telephone network system according to this embodiment. [Figure 2] Figure 2 is a flowchart showing the operation of the outgoing telephone control device. [Figure 3] Figure 3 is a flowchart showing the operation of the incoming telephone control device. [Figure 4] Figure 4 is a sequence diagram illustrating the operation of an IP telephone network system. [Modes for carrying out the invention]

[0016] Next, one embodiment of the present invention will be described with reference to the drawings. [IP Telephone Network System] First, with reference to the block diagram in Figure 1, the IP telephone network system 1 according to this embodiment will be described.

[0017] This IP telephone network system 1 is a system comprising an originating-side telephone control device 10 and a terminating-side telephone control device 20, which exchange call control messages with an IP telephone network TN to provide IP telephone services to telephone terminals connected respectively under their control.

[0018] The originating-side telephone control device 10 and the terminating-side telephone control device 20 are telephone control devices such as main devices and PBX units used in telephone systems such as business phone systems and PBX systems. In the present invention, to facilitate understanding of the content of the invention, the telephone control device to which an originating telephone terminal 15 that is the origination source of a VoIP call is connected is referred to as the originating-side telephone control device 10, and the telephone control device to which a destination telephone terminal 25 that is the destination of a VoIP call is connected is referred to as the terminating-side telephone control device 20.

[0019] The IP telephone network TN has a plurality of call control servers (not shown) connected to an IP communication network DN such as the Internet, and is configured to relay and connect a VoIP call between the originating-side telephone control device 10 and the terminating-side telephone control device 20 by exchanging IP call control messages using an IP call control protocol such as SIP between the call control servers or between the call control servers and the telephone control devices 10, 20 via the IP communication network DN. The ENUM server 30 is a common server device that mutually converts telephone numbers and IP addresses, and is widely operated. In the present invention, since the line resource reservation request procedure executed between the originating-side telephone control device 10 and the terminating-side telephone control device 20 is executed using an IPv6 address, the IPv6 address corresponding to the telephone number of the terminating-side telephone control device 20 is acquired from the ENUM server 30.

[0020] [Principle of the Invention]

[0021] According to the configuration, similar to the aforementioned prior art, in which after a call failure caused by insufficient line resources of the called-side telephone control device 20, the calling-side telephone control device 10 performs recall at a fixed call interval, the success or failure of the recall depends on the timing at which the insufficient line resources of the called-side telephone control device 20 are resolved, and subsequent recalls cannot be reliably succeeded. The reason for this is that if the called-side telephone control device 20 has available line resources, it sequentially and equally allocates the resources to all call messages received from the IP telephone network TN.

[0022] The present invention focuses on such a method for allocating available line resources, and is configured such that when the calling-side telephone control device 10 fails to initiate a call due to insufficient line resources of the called-side telephone control device 20, the calling-side telephone control device 10 sends a line resource reservation request to the called-side telephone control device 20, and performs a recall in response to a reservation response indicating successful reservation of called-side line resources from the called-side telephone control device 20. Furthermore, since existing call control protocols do not provide a line resource reservation request procedure, the line resource reservation request procedure is configured to be exchanged between the calling-side telephone control device 10 and the called-side telephone control device 20 via the IP communication network DN instead of using the IP telephone network TN. Accordingly, when a call fails due to insufficient line resources of the called-side telephone control device 20, a subsequent recall initiated by the calling-side telephone control device 10 can be reliably succeeded.

[0023] [Detailed Configuration of Telephone Control Device] Next, the configurations of the calling-side telephone control device 10 and the called-side telephone control device 20 of the IP telephone network system 1 according to the present embodiment will be described in detail with reference to the block diagram of FIG. 1 described above.

[0024] [Calling-Side Telephone Control Device] The calling-side telephone control device 10 includes, as main circuit configurations, a network I / F 11, a terminal I / F 12, a storage circuit 13, and a control circuit 14.

[0025] The network interface 11 is configured to send and receive call control messages and voice data by communicating with the IP communication network DN and the IP telephone network TN.

[0026] The terminal I / F12 is configured to send and receive call control messages and voice data by communicating with the telephone terminal 15 via the communication line L1.

[0027] The memory circuit 13 consists of a storage device such as a semiconductor memory or a hard disk, and is configured to store various processing data and programs for realizing the call control processing executed by the control circuit 14.

[0028] The control circuit 14 has a CPU and its peripheral circuits, and is configured to execute call control processing by reading the program from the memory circuit 13 and cooperating with the CPU.

[0029] In this call control process, the control circuit 14 sends a call message to the IP telephone network TN to call the destination telephone terminal 25 under the control of the receiving telephone control device 20, and if an error message is returned due to insufficient line resources on the receiving telephone control device 20, the control circuit 14 is configured to directly send a resource allocation request to the receiving telephone control device 20 via the IP communication network DN to request the allocation of line resources on the receiving telephone control device 20, and in response to a resource allocation response indicating successful allocation of line resources returned directly from the receiving telephone control device 20 via the IP communication network DN, the control circuit 14 resends the call message to the destination telephone terminal 25 to the IP telephone network TN.

[0030] [Caller telephone control device] The incoming telephone control device 20 includes, as its main circuit configuration, a network interface 21, a terminal interface 22, a memory circuit 23, and a control circuit 24.

[0031] The network interface 21 is configured to send and receive call control messages and voice data by communicating with the IP communication network DN and the IP telephone network TN.

[0032] The terminal I / F22 is configured to send and receive call control messages and voice data by communicating with the telephone terminal 25 via the communication line L2.

[0033] The memory circuit 23 consists of a storage device such as a semiconductor memory or a hard disk, and is configured to store various processing data and programs for realizing the call control processing executed by the control circuit 24.

[0034] The control circuit 24 has a CPU and its peripheral circuits, and is configured to execute call control processing by reading the program from the memory circuit 23 and cooperating with the CPU.

[0035] In this call control process, the control circuit 24 monitors its own line resources in response to a reservation request received directly from the originating telephone control device 10 via the IP communication network DN. If availability is confirmed, it reserves the incoming line resources from the line resources to be used for a VoIP call with the originating telephone control device 10, and directly sends a reservation response indicating successful reservation back to the originating telephone control device 10 via the IP communication network. After sending the response, in response to a call message originating from the originating telephone control device 10, it calls the designated incoming telephone terminal 25 under its control, and establishes a VoIP call with the originating telephone control device 10 using the incoming line resources in response to an answer operation at the incoming telephone terminal 25.

[0036] [Operation of this embodiment] Next, the operation of the originating telephone control device 10 and the incoming telephone control device 20 will be described as part of the operation of the IP telephone network system 1 according to this embodiment. Here, the case in which a call is made from an originating telephone terminal 15 connected under the originating telephone control device 10 to an incoming telephone terminal 25 connected under the incoming telephone control device 20 will be described as an example.

[0037] [Operation of the calling telephone control device] First, the operation of the outgoing telephone control device 10 will be explained by referring to the flowchart in Figure 2. The control circuit 14 of the outgoing telephone control device 10, in response to an outgoing call request from the originating telephone terminal 15, sends a call message to the IP telephone network TN to call the destination telephone terminal 25 under the receiving telephone control device 20. If an error message is returned due to insufficient line resources on the receiving telephone control device 20, the control circuit 14 executes the call control process shown in the flowchart of Figure 2.

[0038] In response to a line reservation request from the originating telephone terminal 15, the control circuit 14 first secures an originating line resource from its own line resources to be used for the VoIP call of the originating telephone terminal 15 (step 100). At this time, in order to distinguish and maintain the secured originating line resource, the control circuit 14 generates resource identification information to identify this VoIP call and stores it in the memory circuit 13, linked to the secured originating line resource.

[0039] In step 100 described above, if there are no available line resources, the control circuit 14 should wait until a line resource becomes available and secure the originating line resource as soon as it becomes available. If the originating line resource cannot be secured within a predetermined waiting period from the start of the allocation process, the control circuit 14 should cancel the line reservation request from the originating telephone terminal 15 and terminate the series of call control processes.

[0040] When the allocated outgoing line resources are restricted to be used as line resources for VoIP calls corresponding to transmitted call messages, the resource identification information of the outgoing line resources must include outgoing identification information to identify the outgoing party of the VoIP call and incoming identification information to identify the incoming party of the VoIP call. The outgoing identification information may consist, for example, the extension number of the outgoing telephone terminal 15 included in the outgoing request from the outgoing telephone terminal 15. The incoming identification information may consist, for example, the incoming telephone number corresponding to the incoming telephone terminal 25 included in the outgoing request from the outgoing telephone terminal 15. This prevents the incorrect application of the allocated outgoing line resources to outgoing requests from telephone terminals 15 other than the outgoing telephone terminal 15, or to outgoing requests to telephone terminals other than the incoming telephone terminal 25.

[0041] (Obtain the destination IP address and send a resource allocation request to the destination.) Next, the control circuit 14 accesses the ENUM server 30 on the IP communication network DN from the network I / F 11 to obtain the telephone number of the receiving telephone control device 20 and the corresponding IPv6 address of the receiving telephone control device 20 (step 101). Using the obtained IPv6 address, it directly sends a reservation request to the receiving telephone control device 20 via the IP communication network DN from the network I / F 11 to request the reservation of line resources to be used for the VoIP call with the destination telephone terminal 25 (step 102). If the IPv6 address of the receiving telephone control device 20 could not be obtained in step 101, the control circuit 14 cancels the line reservation request and terminates the series of operations.

[0042] Subsequently, if the control circuit 14 receives a reservation response indicating successful allocation of line resources from the receiving telephone control device 20 via the IP communication network DN through the network interface 11 (step 103), it notifies the originating telephone terminal 15 of the completion of line allocation via the communication line L1 from the terminal interface 12 (step 104). As a result, the caller is notified of the completion of line allocation, for example, by the blinking of the line reservation button on the originating telephone terminal 15.

[0043] Next, if the control circuit 14 confirms that the caller has pressed the line reservation button and has performed a redial operation (step 105), it retransmits a call message from the network interface 11 to the IP telephone network TN to call the destination telephone terminal 25 (step 106), and terminates the series of call control processes.

[0044] Furthermore, if a reservation response indicating successful allocation of line resources in step 103 is not received within a predetermined waiting period from the transmission of the allocation request, the control circuit 14 cancels the line reservation request from the originating telephone terminal 15 and terminates the series of call control processes.

[0045] Furthermore, if the redial operation in step 105 described above is not confirmed within the predetermined waiting time elapsed from the transmission of the line reservation completion, the control circuit 24 cancels the line reservation request from the originating telephone terminal 15 and terminates the series of call control processes.

[0046] [Operation of the incoming telephone control device] Next, the operation of the incoming telephone control device 20 will be explained with reference to the flowchart in Figure 3.

[0047] When the control circuit 24 of the incoming telephone control device 20 receives a reservation request from the outgoing telephone control device 10 via the IP communication network DN at the network I / F 21, it executes the call control process shown in the flowchart of Figure 3.

[0048] The control circuit 24 first monitors its own line resources (step 110) and checks whether there are any available line resources (step 111).

[0049] If there is an available line resource for use in a VoIP call (Step 111: YES), the control circuit 24 secures a receiving line resource from the line resources to be used for a VoIP call with the originating telephone control device 10 (Step 113). In this case, in order to retain the secured receiving line resource, the control circuit 24 generates identification information to identify this VoIP call and stores the identification information in the storage circuit 23, linked to the secured originating line resource.

[0050] When the allocated incoming line resources are restricted to be used as line resources for VoIP calls corresponding to received call messages, the resource identification information of the incoming line resources must include caller identification information for identifying the initiating party of the VoIP call and incoming identification information for identifying the receiving party of the VoIP call. The caller identification information may consist, for example, the calling telephone number corresponding to the originating telephone terminal 15 included in the received call message. The incoming identification information may consist, for example, the receiving telephone number corresponding to the receiving telephone terminal 25 included in the received call message.

[0051] This prevents the incorrect application of reserved incoming line resources to call messages from telephone terminals other than the originating telephone terminal 15, and to call messages to telephone terminals other than the receiving telephone terminal 25.

[0052] Furthermore, if no available network resources are found in step 111 (step 111: NO), the control circuit 24 waits until network resources become available (step 112), and then proceeds to step 113 as described above.

[0053] Furthermore, if the incoming line resource cannot be secured between the receipt of the reservation request and the elapsed of a predetermined waiting time, the control circuit 24 cancels the reservation request from the outgoing telephone control device 10 and terminates the series of call control processes.

[0054] Next, the control circuit 24 sends a confirmation response indicating successful allocation of the incoming line resource back to the outgoing telephone control device 10 via the IP communication network DN from the network I / F 21 (step 114).

[0055] Subsequently, if the control circuit 24 receives a call message for calling the destination telephone terminal 25, which has been retransmitted from the originating telephone control device 10, via the IP telephone network TN to the network interface 21 (step 115), it calls the corresponding destination telephone terminal 25 via the communication line L2 from the terminal interface 22 (step 116). As a result, the destination telephone terminal 25 displays an incoming call notification.

[0056] Furthermore, if no call message to be retransmitted is received from the originating telephone control device 10 between the transmission of a reservation response indicating successful reservation and the elapsed of a predetermined reservation time, the control circuit 24 releases the reserved incoming line resource and terminates the series of call control processes.

[0057] If the recipient telephone terminal 25 confirms that an answer has been received (step 117), the control circuit 24 sends a response message to the IP telephone network TN from the network interface 21 for the received call message (step 118). Next, the control circuit 24 uses the reserved incoming line resources to establish a VoIP call with the outgoing telephone control device 10 (step 119), and terminates the series of call control processes.

[0058] [Example of operation of this embodiment] Next, with reference to the sequence diagram in Figure 4, an example of the operation of the IP telephone network system according to this embodiment will be described. Here, an example will be described in which a call is made from a source telephone terminal 15 connected under the control of the originating telephone control device 10 to a destination telephone terminal 25 connected under the control of the receiving telephone control device 20.

[0059] In response to a call request to call the destination telephone terminal 25, sent from the originating telephone terminal 15 by the originating user's call operation (step 200), the originating telephone control unit 10 sends a call message (INVITE) to call the destination telephone terminal 25 (step 201). The call message is then forwarded to the receiving telephone control unit 20 via the IP telephone network TN.

[0060] In response to this call message, the incoming telephone control unit 20 checks its own line resources and, if there are insufficient line resources for VoIP calls due to the destination telephone terminal 25 specified in the call message being on another call, it returns an error message indicating that the line is busy (486 Busy Here) (step 202). This error message is then forwarded to the outgoing telephone control unit 10 via the IP telephone network TN.

[0061] In response to this error message, the outgoing telephone control unit 10 notifies the originating telephone terminal 15 that the destination is busy (step 203). As a result, the originating telephone terminal 15 displays a busy message.

[0062] Subsequently, the calling telephone control device 10, in response to the line reservation request sent from the originating telephone terminal 15 by the calling user's line reservation operation (step 210), secures an originating line resource from its own line resources to be used for the originating telephone terminal 15's VoIP call (step 211). At this time, the calling telephone control device 10 generates resource identification information to identify this VoIP call and stores it in the memory circuit 13, linked to the secured originating line resource.

[0063] After this, the outgoing telephone control unit 10 sends a search request to the ENUM server 30 on the IP communication network DN to obtain the IPv6 address of the incoming telephone control unit 20 (step 212).

[0064] The calling telephone control unit 10 obtains the IPv6 address of the receiving telephone control unit 20 from the search response returned by the ENUM server 30 in response to this (step 213), and sends a reservation request to the receiving telephone control unit 20 from the IP communication network DN using the IPv6 address to request the reservation of a line for VoIP calling (step 214).

[0065] In response to this allocation request, the incoming telephone control unit 20 checks its own line resources, allocates incoming line resources to be used for the VoIP call with the outgoing telephone control unit 10 (step 215), and sends an allocation response to the outgoing telephone control unit 10 from the IP communication network DN using an IPv6 address, indicating that the allocation of the incoming line resources was successful (step 216). At this time, the incoming telephone control unit 20 generates identification information to identify this VoIP call and stores the identification information in the storage circuit 23, linked to the allocated outgoing line resources.

[0066] In response to this successful reservation response, the outgoing telephone control device 10 notifies the originating telephone terminal 15 that the line reservation is complete (step 217). As a result, the originating telephone terminal 15 displays that the line reservation is complete.

[0067] Subsequently, the outgoing telephone control unit 10, in response to the outgoing call request from the originating telephone terminal 15 (step 220) upon completion of the line reservation, resends a call message (INVITE) to the receiving telephone terminal 25 (step 221). The call message is then forwarded to the incoming telephone control unit 20 via the IP telephone network TN.

[0068] The incoming telephone control unit 20 calls the designated incoming telephone terminal 25 in response to this call message (step 222). As a result, the incoming call is displayed on the incoming telephone terminal 25.

[0069] Subsequently, the incoming telephone control unit 20, in response to the response from the receiving telephone terminal 25 that answered the call (step 223), sends back a response message (200 OK) to the call message (step 224). This response message is then forwarded to the outgoing telephone control unit 10 via the IP telephone network TN.

[0070] The outgoing telephone control device 10 notifies the originating telephone terminal 15 of the incoming response in response to this response message (step 226).

[0071] Subsequently, the outgoing telephone control device 10, in response to the outgoing call request from the originating telephone terminal 15, generates resource identification information to identify the VoIP call corresponding to this outgoing call request, confirms the outgoing line resource associated with this resource identification information using the storage circuit 13, and establishes a VoIP call with the incoming telephone control device 20 using that outgoing line resource.

[0072] Furthermore, the incoming telephone control device 20 generates resource identification information to identify the VoIP call corresponding to the received call message, confirms the incoming line resource associated with this resource identification information using the storage circuit 23, and establishes a VoIP call with the outgoing telephone control device 10 using that incoming line resource.

[0073] As a result, a VoIP call is initiated between the originating telephone terminal 15 under the control of the originating telephone control device 10 and the receiving telephone terminal 25 under the control of the incoming telephone control device 20 (step 226).

[0074] [Effects of this embodiment] As described above, in this embodiment, if the calling device 10 fails to make a call due to insufficient line resources on the receiving device 20, it requests the receiving device 20 to secure line resources, and the receiving device 20 attempts to make a call again upon receiving a confirmation response indicating successful allocation of line resources. Furthermore, the procedure for requesting line resource allocation is configured to be communicated between the calling device 10 and the receiving device 20 via the IP communication network DN, rather than using the IP telephone network TN.

[0075] This ensures that if a call fails due to insufficient line resources on the receiving telephone control device 20, subsequent re-calls from the originating telephone control device 10 are reliably successful.

[0076] [Expansion of the embodiment] Although the present invention has been described above with reference to embodiments, the present invention is not limited to the above embodiments. Various modifications to the configuration and details of the present invention can be made that will be understood by those skilled in the art within the scope of the present invention. [Explanation of Symbols]

[0077] 1...IP telephone network system, 10...Sender telephone control unit, 11...Network interface, 12...Terminal interface, 13...Memory circuit, 13...Control circuit, 15...Telephone terminal, 15...Originating telephone terminal, 20...Incoming telephone control unit, 21...Network interface, 22...Terminal interface, 23...Memory circuit, 24...Control circuit, 25...Telephone terminal, 25...Receiving telephone terminal, 30...ENUM server, L1...Communication line, L2...Communication line, DN...IP communication network, TN...IP telephone network.

Claims

1. It comprises an outgoing call control device and an incoming call control device that provide IP telephone services to telephone terminals connected under their respective networks by exchanging call control messages with an IP telephone network on an IP communication network. The outgoing telephone control unit is configured to send a call message to the incoming telephone terminal under the control of the incoming telephone control unit to the IP telephone network, and if an error message is returned due to insufficient line resources at the incoming telephone control unit, it sends a resource allocation request directly to the incoming telephone control unit via the IP communication network to request the allocation of line resources at the incoming telephone control unit, and to resend the call message in response to a resource allocation response indicating successful resource allocation returned directly from the incoming telephone control unit via the IP communication network. The receiving telephone control device is configured to monitor its own line resources in response to the allocation request received directly from the originating telephone control device via the IP communication network, and if an available line resource is confirmed, it allocates the receiving line resource from the line resource to be used for a VoIP call with the originating telephone control device, and sends the allocation response indicating successful allocation directly back to the originating telephone control device via the IP communication network, and in response to a call message originating from the originating telephone control device that arrives after the response, it calls the destination telephone terminal under its control specified in the call message, and establishes a VoIP call with the originating telephone control device using the receiving line resource in response to an answer operation at the destination telephone terminal. An IP telephone network system characterized by the following features.

2. In the IP telephone network system described in claim 1, The incoming telephone control device is configured to release the reserved incoming line resource if the call message to be retransmitted from the outgoing telephone control device does not arrive within a predetermined reservation time after the reservation response is returned. An IP telephone network system characterized by the following features.

3. IP communication network and network interface for data communication, A terminal interface that performs data communication with telephone terminals connected to it via a communication line, The system includes a control circuit that provides IP telephone services to the telephone terminal by exchanging call control messages with the IP telephone network on the IP communication network via the network interface, The control circuit is configured to monitor its own line resources in response to a resource allocation request received directly from the originating telephone control unit via the IP communication network, and if available line resources are found, to allocate the incoming line resources from the line resources for use in a VoIP call with the originating telephone control unit, and to send a resource allocation response indicating successful allocation directly back to the originating telephone control unit via the IP communication network. After the response, in response to a call message originating from the originating telephone control unit that arrives, it calls the recipient telephone terminal under its control specified in the call message, and establishes a VoIP call with the originating telephone control unit using the incoming line resources in response to an answer operation at the recipient telephone terminal. A telephone control device characterized by the following features.

4. IP communication network and network interface for data communication, A terminal interface that performs data communication with telephone terminals connected to it via a communication line, The system includes a control circuit that provides IP telephone services to the telephone terminal by exchanging call control messages with the IP telephone network on the IP communication network via the network interface, If an error message is returned after sending a call message due to insufficient line resources at the receiving telephone control unit, the system is configured to send a resource allocation request directly to the receiving telephone control unit via the IP network, requesting that the receiving telephone control unit allocate line resources. In response to the resource allocation response sent directly back from the receiving telephone control unit via the IP network indicating successful resource allocation, the system is configured to resend the call message. A telephone control device characterized by the following features.

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