JP5897439B2 - COMMUNICATION SYSTEM, NETWORK DEVICE, CALL CONTROL DEVICE, AND SYSTEM CONTROL METHOD - Google Patents

Description

  Embodiments described herein relate generally to a communication system, network device, call control apparatus, and system control method using VPN technology.

  Currently, there is a movement to replace an existing public network with an IP network by a next-generation IP network technology called NGN (Next Generation Network). Telecommunications carriers are promoting IP and optical communications, and the number of IP telephone subscribers is increasing year by year. In addition, as represented by cloud technology, there is an increasing demand to freely distribute devices on an IP network.

  On the other hand, in a system in which devices are distributed on an IP network, when the number of devices increases, it is assumed that many network devices simultaneously access the same gateway or the like. In particular, when a VPN (Virtual Private Network) is used for communication between a network device and a gateway, an increase in the number of VPN sessions of the gateway accompanying an increase in the number of devices becomes a problem. The gateway is provided with an upper limit value of the VPN session, and when VPN connection requests are received from a number of network devices exceeding the upper limit value, the VPN session cannot be established, which may lead to a loss of call of the network device. . Therefore, in a system in which devices are distributed on an IP network, the number of VPN sessions when the number of network devices increases is a major issue.

  Usually, in a cloud-type system that crosses networks, gateways are installed between the networks, and network devices access different networks via the gateways. When the gateway destination is a secure network, the network device generally establishes a VPN session with the gateway and enables access to the secure network by tunneling. At that time, there are two possible methods: a first method in which a network device establishes a VPN session when a call occurs, and a second method in which a VPN connection is always established with a gateway in advance.

JP 2011-228864 A

  However, in the first method, since the network device does not establish the VPN session with the gateway until the call is generated, the establishment of the VPN session fails when the number of VPN sessions of the gateway reaches the upper limit. In order to realize highly reliable communication, it is necessary to always make a VPN connection and guarantee the transmission and reception of call control messages as in the second method.

  However, the second method requires VPN sessions for the number of network devices. When the number of network devices increases, the VPN load of the gateway increases.

  Therefore, an object of the present embodiment is to provide a communication system, a network device, a call control apparatus, and a system control method that always connect a VPN between a network device and a gateway and reduce the number of VPN sessions. There is.

  According to the present embodiment, a communication system includes a plurality of network devices connected to a first network, a call control device connected to the first network and managing call control of the network devices, and the first And a gateway that connects the network device to a second network via one network. The call control device includes a call information management unit, a resource monitoring unit, an aggregation determination unit, and an operation mode instruction unit. The call information management unit manages call information for each network device. The resource monitoring unit monitors VPN resources based on the call information. The aggregation determination unit groups the network devices based on the VPN resource. The operation mode instructing unit is a normal mode for establishing a first VPN session alone for the grouped network devices, a representative mode for establishing a second VPN session and aggregating other network devices, and It is instructed to set one of the subordinate modes connected to the second network via the second VPN session as a subordinate of the network device in the representative mode. Further, the network device includes an operation mode control unit and a message relay unit. The operation mode control unit sets the operation mode based on an instruction from the operation mode instruction unit. The message relay unit relays a call control message from a subordinate network device when the representative mode is set by the operation mode control unit.

1 is a block diagram showing a configuration of a communication system according to a first embodiment. The figure which shows an example of the connection form according to operation mode of the network device which concerns on 1st Embodiment. The figure which shows an example of the monitoring operation | movement of the gateway which judges the necessity of grouping of the network which concerns on 1st Embodiment. The figure which shows an example of the aggregation determination operation | movement at the time of grouping the network device which concerns on 1st Embodiment. The block diagram which shows the structure of the communication system for showing an example of the aggregation determination operation | movement at the time of grouping the network device which concerns on 1st Embodiment. The figure which shows an example of the aggregation determination operation | movement in the case of using the number of sessions as the aggregation determination threshold value T which concerns on 1st Embodiment. The sequence diagram which shows an example of the communication sequence at the time of the network device aggregation which concerns on 1st Embodiment. The sequence diagram which shows an example of the communication sequence at the time of the network device aggregation cancellation | release based on 1st Embodiment. The block diagram which shows the structure of the communication system which concerns on 2nd Embodiment. The figure which shows an example of the monitoring operation | movement of gateway GW1 which judges the necessity of grouping of the network which concerns on 2nd Embodiment. The figure which shows an example of the aggregation determination operation | movement at the time of grouping the network device which concerns on 2nd Embodiment. The block diagram which shows the structure of the communication system for showing an example of the aggregation determination operation | movement at the time of grouping the network device which concerns on 2nd Embodiment. The figure which shows an example of the aggregation determination operation | movement in the case of using the number of sessions as the aggregation determination threshold value T which concerns on 2nd Embodiment. The sequence diagram which shows an example of the communication sequence at the time of the network device aggregation which concerns on 2nd Embodiment. The sequence diagram which shows an example of the communication sequence at the time of the network device aggregation cancellation | release which concerns on 2nd Embodiment.

  Hereinafter, embodiments will be described with reference to the drawings. Detailed description of overlapping parts is omitted.

[First Embodiment]
FIG. 1 is a block diagram showing a configuration of a communication system according to the first embodiment.

  The communication system according to the first embodiment includes network devices PS1 to PSn (n is a natural number), a gateway GW1, a control device S1, and a location registration server S2.

  The network devices PS1 to PSn are connected to the IP network / public communication network NW1, and access the backbone network NW2 via the gateway GW1. The network device PS ′ is also arranged in the backbone network NW2, and the network devices PS1 to PSn connected to the IP network / public communication network NW1 establish a VPN session with the gateway GW1 to Communication with the network device PS ′ is performed. Furthermore, the gateway GW1 is connected to the control device S1 and the location registration server S2 via the backbone network NW2 so that they can communicate with each other.

  The network devices PS1 to PSn are ISDN routers or the like, and connect at least one terminal TM to the IP network / public communication network NW1. The network devices PS1 to PSn include a path forming unit 101, an operation mode control unit 102, a message relay unit 103, and a location registration unit 104. The network devices PS1 to PSn hold telephone number information used for outgoing / incoming calls between other network devices.

  The path forming unit 101 establishes a VPN session with the gateway GW1.

  The operation mode control unit 102 establishes the VPN session VP1 by itself, the representative mode for establishing the VPN session VP2 and aggregating other network devices, and the subordinates of the network devices in the representative mode via the VPN session VP2. Thus, the operation mode is switched to one of the subordinate modes connected to the backbone network NW2.

  When operating in the representative mode, the message relay unit 103 relays call control messages from the subordinate network devices PS1 to PSn.

  When the location registration unit 104 operates in the representative mode, the location registration unit 104 registers the location of the phone number information notified from the network device in the subordinate mode as its own phone number information. Further, when returning from the representative mode or the subordinate mode to the normal mode, the location registration unit 104 establishes a VPN session with the gateway GW1 and registers the location of telephone number information held by the network device itself.

  Here, when operating in the subordinate mode, the network device determines the destination of the call control message from the gateway GW1 based on the network device information in the representative mode included in the operation mode change instruction received from the control device S1 described later. The network device is changed to a representative mode network device, and its own telephone number information is notified to the representative mode network device.

  The gateway GW1 is connected to the IP network / public communication network NW1 and the backbone network NW2, and the network devices PS1 to PSn connected to the IP network / public communication network NW1 are network devices PS ′ and the control device S1 in the backbone network NW2. When communicating with the location registration server S2, a VPN session is established with the network devices PS1 to PSn, and communication between networks is relayed.

  The control device S1 manages call control of the network devices PS1 to PSn. The control device S1 includes a call information management unit 105, a resource monitoring unit 106, an aggregation determination unit 107, and an operation mode instruction unit 108.

  The call information management unit 105 acquires call statistical information of the network devices PS1 to PSn and manages the call information database DB1.

  The resource monitoring unit 106 manages VPN session resource information (for example, the number of VPN sessions and control channel throughput information) related to the VPN session of the gateway GW1.

  The aggregation determination unit 107 performs determination for grouping the network devices PS1 to PSn based on the VPN session resource information.

  The operation mode instruction unit 108 instructs the operation mode change (normal mode / representative mode / subordinate mode) of the aggregation candidate network devices grouped by the aggregation determination unit 107.

  That is, the control device S1 changes the operation mode of the network device in response to an operation mode change instruction from the operation mode instruction unit, aggregates the network form in which the network device individually connects to the gateway GW1 and the VPN, and the network device. The network device switches between the gateway GW1 and the network configuration for VPN connection.

  The location registration server S2 performs location registration of the telephone number information of the network devices PS1 to PSn.

(Network device operation mode)
FIG. 2 is a diagram illustrating an example of a connection mode for each operation mode of the network devices PS1 to PSn. In FIG. 2, a case where four network devices PS1 to PS4 are installed in the IP network / public communication network NW1 will be described as an example.

  The network device PS1 operating in the normal mode establishes a VPN session VP1 directly with the gateway GW1, sends a call control message such as an SIP message to the gateway GW1 via the VPN session VP1, and within the backbone network NW2. Enables communication.

  The network device PS2 operating in the representative mode establishes a VPN session VP2 directly with the gateway GW1, transmits its own call control message to the gateway GW1 via the VPN session VP2, and communicates within the backbone network NW2. Establish. The call control message received from the subordinate mode network devices PS3 and PS4 is converted into its own call control message and transmitted to the gateway GW1 via the VPN session VP2, and the subordinate mode network devices PS3 and PS4 and the backbone network are transmitted. Communication with the NW2 is enabled.

  The network devices PS3 and PS4 operating in the subordinate mode do not establish a VPN session with the gateway GW1, but transmit / receive a call control message to / from the network device PS2 operating in the representative mode.

  As described above, the network devices PS1 to PSn adopt the operation mode to establish communication individually in the normal mode, and in the representative mode, SIP that aggregates a plurality of network devices and converts the call control message. By operating like a server and operating like a SIP client that communicates via the representative mode in the subordinate mode, the connection form with the gateway GW1 can be dynamically changed.

(Gateway monitoring operation)
FIG. 3 is a diagram illustrating an example of an operation of monitoring the gateway GW1 in which the control device S1 determines whether or not network grouping is necessary.

  The resource monitoring unit 106 of the control device S1 inquires of the VPN resource of the gateway GW1 and acquires VPN session resource information such as the number of VPN sessions. Based on the acquired VPN session resource information, the resource monitoring unit 106 compares the number of VPN sessions with a predetermined VPN session threshold N, and determines that the VPN session load of the gateway GW1 is high if the number is greater than the threshold. Executes an aggregate judgment operation for grouping. If the number of VPN sessions is less than the VPN session threshold N, an aggregation determination operation for canceling grouping of network devices connected to the gateway GW1 is performed.

  The VPN session threshold N can be arbitrarily changed according to a request from the system administrator, so that the VPN session load can be controlled according to the performance of the gateway GW1. In addition, the control device S1 can monitor the load status such as the CPU usage rate of the gateway GW1, and can dynamically change the VPN session threshold N according to the load status.

(Aggregation determination operation: Example 1)
The aggregation determination operation in the case of grouping network devices based on the control channel throughput will be described with reference to FIGS. 4 and 5.

  As shown in FIG. 4, the call information management unit 105 of the control device S1 holds a call information database DB1 that manages call information of each network device PS1 to PSn. In this call information database DB1, for example, the operation mode (normal / representative / subordinate), VPN connection destination information (VPN connection destination gateway), control channel throughput, and number of sessions are stored for each network device. Based on this call information database DB1, the aggregation determination unit 107 evaluates the call connection frequency of the network devices PS1 to PSn and determines an aggregation target candidate. In the case of a system in which throughput is held as the aggregation determination threshold T1, the throughput information of the control channel that performs VPN connection is set as an evaluation target, and the aggregation target candidate network device is selected so that the control channel throughput is equal to or less than the aggregation determination threshold T1.

  In the example of FIG. 4, the aggregation determination threshold T1 is set to 64 kbps, the network devices PS4, PS1, and the network devices PS4, PS1, and the like are connected in order from the network device having the smallest control channel throughput to the aggregation gateway. Select PS5. In the present embodiment, as shown in FIG. 5, the network device PS4 with the lowest control channel throughput is set as the representative mode, and the other network devices PS1 and PS5 are set as the subordinate mode and are aggregated into the network device PS4.

(Aggregation determination operation: Example 2)
In the second embodiment, an example in which the aggregation determination operation is performed based on the number of sessions will be described with reference to FIGS. 6 and 7.

  In the case of a system in which the number of sessions is held as the aggregation determination threshold T2, the aggregation target candidates are selected so that the number of sessions in the call information database DB1 is an evaluation target and the number of sessions is equal to or less than the aggregation determination threshold T2. In the example of FIG. 6, the aggregation determination threshold T2 is set to 20 sessions, connected to the same gateway, and the network devices PS4 and PS1 are connected in order from the network device with the smallest number of sessions in the range where the total number of sessions does not exceed the aggregation determination threshold T2. Select. In the present embodiment, the network device PS4 having the smallest number of sessions is set as the representative mode, and the other network devices PS1 are set as the subordinate mode and are aggregated in the network device PS4.

  In addition to the aggregation determination operations of the first and second embodiments, aggregation target candidates are selected in order from the network device with the lowest failure rate. Among the selected network devices, the network device with the lowest failure rate is set as the representative mode, and the other network devices are set as the subordinate mode and are aggregated into the network device with the lowest failure rate.

  In this way, network devices with a relatively small processing load are grouped and aggregated, and a network device with the smallest processing load is assigned to a representative mode that requires a call control message conversion process, thereby enabling a VPN session. It is possible to suppress the load and guarantee a stable operation of call connection processing.

  Also, it manages call information of network devices that operate in the representative mode. When the call connection from the network device in the representative mode exceeds the aggregation determination threshold, the network device that is the aggregation target candidate is reselected and aggregated. Change the combination dynamically.

  Note that the method of selecting the network device in the representative mode is not limited to the method of the present embodiment, and the aggregation determination threshold value can be made variable and can be arbitrarily selected according to the system requirements.

(Communication sequence: when network devices are consolidated)
FIG. 7 shows an example of a communication sequence at the time of network device aggregation. FIG. 7 shows a case where the network devices PS1 to PS3 make a VPN connection to the gateway GW1.

  The network devices PS1 to PS3 operate in the normal mode in the initial state, and establish a VPN path with the gateway GW1 (S101). The resource monitoring unit 106 of the control device S1 acquires the VPN session number information of the gateway GW1 by the VPN resource acquisition request (S102) (S103), and the aggregation determination unit 107 performs the aggregation determination operation based on the number of VPN sessions (S104). To implement. As a result, the aggregation determination unit 107 selects the network devices PS1 to PS3 as aggregation target candidates.

  The operation mode instruction unit 108 selects, for example, the network device PS3 having the smallest number of sessions as the representative mode from the aggregation target candidates, and transmits an operation mode change instruction_representation (S105) to the network device PS3. Upon receiving this instruction, the network device PS3 is switched to the representative mode by the operation mode control unit 102 and starts the operation as the representative mode (S106, S107). Further, the operation mode instruction unit 108 transmits an operation mode change instruction_subordinate (S108) to the network devices PS1 and PS2, so that the operation mode control unit 102 switches to the subordinate mode and starts the operation as the subordinate mode. (S109, S111). The operation mode change instruction_subordinate (S108) includes connection destination information of the network device PS3 associated as the representative mode, and establishes a call control path with the network device PS3 in the representative mode (S110). ).

  The network devices PS1 and PS2 that have started the operation in the subordinate mode notify their representative telephone number information to the network device PS3 in the representative mode (S111), and the network device PS3 adds the subordinate mode to the subordinate mode. The location information of the network device PS1 and PS2 is registered in the location registration server S2 (S112).

  Upon receiving the location registration completion notification (S113), the network device PS3 operating as the representative mode instructs the network devices PS1 and PS2 in the subordinate mode to release the VPN path (S114). The network device in the subordinate mode releases the VPN path with the gateway GW1 (S115, S116), and starts a call connection operation via the network device PS3 in the representative mode.

  In this way, the control device S1 instructs the network devices PS1 to PS3 to shift to the operation mode from the normal mode to the representative mode and the subordinate mode, and releases the VPN path of the gateway GW1, whereby the VPN of the gateway GW1. Session load can be suppressed.

(Communication sequence (when canceling network device aggregation))
FIG. 8 is a sequence diagram illustrating an example of a communication sequence at the time of canceling network device aggregation.

  In the example of FIG. 8, the network devices PS1 and PS2 operate in the subordinate mode, and the network device PS3 operates in the representative mode. The network devices PS1 and PS2 establish a call control path with the network device PS3 (S201), and establish a VPN path with the gateway GW1 (S202). The resource monitoring unit 106 of the control device S1 acquires the VPN session number information of the gateway GW1 by the VPN resource acquisition request (S203) (S204), and performs the aggregation determination operation (S205) based on the number of VPN sessions. As a result, when the number of VPN sessions of the gateway GW1 is less than or equal to the threshold value, the operation mode of the network devices PS1 to PS3 is changed to the normal mode. The control device S1 instructs the operation mode change instruction_normal (S206) to the network devices PS1 and PS2 that are in the subordinate mode, and the operation mode control unit 102 switches to the normal mode and starts operation in the normal mode. At the same time (S207), the VPN path with the gateway GW1 is re-established (S208, S209). After the establishment of the VPN path (S210), location registration is performed with respect to the location registration server S2 based on its own telephone number information (S211 and S212), and the completion of the operation mode change is notified to the control device S1 upon completion of location registration. (S213). The control device S1 transmits an operation mode change instruction_normal (S214) to the network device PS3 operating as the representative mode at the timing when all the network devices PS1 and PS2 in the subordinate mode are switched to the normal mode. . The network device PS3 is switched to the normal mode by the operation mode control unit 102, starts operation in the normal mode (S215, S216), and is established with the network devices PS1 and PS2 that have been operating as the subordinate mode. The call control path is released (S217, S218).

  In this way, when the control device S1 instructs the network devices PS1 to PS3 operating in the representative mode and the subordinate mode to change the operation mode, the network devices PS1 to PS3 individually set the gateway GW1 and the VPN path. It becomes possible to shift to an established network form.

[Second Embodiment]
FIG. 9 is a block diagram showing a configuration of a communication system according to the second embodiment.

  The communication system shown in the second embodiment has a configuration in which the function of the control device S1 shown in the first embodiment is provided in the gateway GW1. In addition, about FIGS. 10-13, it is the same as that of FIGS. 3-6 of 1st Embodiment.

(Communication sequence (when network devices are consolidated))
FIG. 14 is a sequence diagram showing an example of a communication sequence at the time of network device aggregation.

  Similarly to FIG. 7, the network devices PS1 to PS3 operate in the normal mode in the initial state, and establish a VPN path with the gateway GW1 (S301). The gateway GW1 performs an aggregation determination operation (S302) based on its VPN session number information. As a result, the network devices PS1 to PS3 are selected as candidates for aggregation, and the network device PS3 transmits the operation mode change instruction_representative (S303) to the network device PS3 selected as the representative mode, so that the network device PS3 performs the operation mode control. The unit 102 switches to the representative mode and starts the operation as the representative mode (S304, S305). Furthermore, by transmitting the operation mode change instruction_dependent (S306) to the network devices PS1 and PS2, the operation mode control unit 102 switches to the dependent mode and starts the operation as the dependent mode (S307, S309). The operation mode change instruction_subordinate (S306) includes connection destination information of the network device PS3 associated as the representative mode, and establishes a call control path with the network device in the representative mode (S308). .

  The network devices PS1 and PS2 that have started the operation in the subordinate mode notify the network device PS3 that is the representative mode of its own telephone number information (S310), and the network device PS3 adds to its own telephone number information, The telephone number information of the network devices PS1 and PS2 in the subordinate mode is registered in the position registration server S2 (S311).

  The network device PS3 operating as the representative mode receives the location registration completion notification (S312), and instructs the network devices PS1 and PS2 in the subordinate mode to release the VPN path (S313). The network device in the subordinate mode releases the VPN path to the gateway (S314, S315), and starts a call connection operation via the representative mode.

  In this way, the gateway GW1 instructs the network devices PS1 to PS3 to shift to the operation mode from the normal mode to the representative mode and the subordinate mode, and releases the VPN path of the gateway GW1, thereby reducing the VPN session load of the gateway. It becomes possible to suppress.

(Communication sequence (when canceling network device aggregation))
FIG. 15 is a sequence diagram showing an example of a communication sequence when releasing network device aggregation.

  In the example of FIG. 15, as in FIG. 8, the network devices PS1 and PS2 operate in the subordinate mode, and the network device PS3 operates in the representative mode. The network devices PS1 and PS2 establish a call control path with the network device PS3 (S401), and the network device establishes a VPN path with the gateway GW1 (S402). The gateway GW1 performs an aggregation determination operation (S403) based on the number of VPN sessions of the gateway GW1. As a result, when the number of VPN sessions of the gateway GW1 is less than or equal to the threshold value, the operation mode of the network devices PS1 to PS3 is changed to the normal mode. The gateway GW1 instructs the operation mode change instruction_normal (S404) to the network devices PS1 and PS2 that are in the subordinate mode, and the operation mode control unit 102 switches the network devices PS1 and PS2 to the normal mode and operates in the normal mode. (S405) and re-establish the VPN path with the gateway GW1 (S406, S407). After establishing the VPN path (S408), the location registration is performed with respect to the location registration server S2 based on its own telephone number information (S409, S410), and the completion of the operation mode change is notified to the gateway GW1 upon completion of the location registration. (S411). The gateway GW1 transmits the operation mode change instruction_normal (S412) to the network device PS3 operating as the representative mode at the timing when all the network devices PS1 and PS2 in the subordinate mode are switched to the normal mode. The network device PS3 is switched to the normal mode by the operation mode control unit 102, starts operation in the normal mode (S413, S414), and is established with the network devices PS1 and PS2 that have been operating as the subordinate mode. The call control path is released (S415, S416).

  In this way, when the gateway device GW1 instructs the network devices PS1 to PS3 operating as the representative mode and the subordinate mode to change the operation mode, the network devices PS1 to PS3 individually establish the VPN path with the gateway GW1. It is possible to shift to a network form that does this.

  As described above, in the above embodiment, the control device S1 that manages the resources of the network devices PS1 to PSn groups a plurality of network devices PS1 to PSn based on the resource information, and selects the representative network devices PS1 to PSn. To do.

  As a result, only the representative mode network device establishes a VPN session with the gateway GW1, and the other network devices transmit and receive call control messages via the representative mode network device. Reduction can be realized.

  Therefore, it is possible to provide a communication system, a network device, a control apparatus, and a system control method that always connect the VPN between the network device and the gateway and can reduce the number of VPN sessions.

  As mentioned above, although some embodiment of this invention was described, these embodiment is shown as an example and is not intending limiting the range of invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the invention described in the claims and equivalents thereof as well as included in the scope and gist of the invention.

  PS1 to PSn: Network device, 101: Path formation unit, 102: Operation mode control unit, 103: Message relay unit, 104: Location registration unit, GW1 ... Gateway, S1 ... Control device, 105 ... Call information management unit, 106 ... Resource management unit 107 ... aggregation determination unit 108 ... operation mode instruction unit S2 ... location registration server TM TM terminal NW1 IP network / public communication network NW2 backbone network

Claims (15)

A plurality of network devices connected to a first network, a call control device connected to the first network and managing call control of the network device, and the network device via the first network A communication system comprising a gateway connected to the network of two,
The call control device includes:
A call information management unit for managing call information for each network device;
A resource monitoring unit that monitors VPN resources based on the call information;
An aggregation determination unit that groups the network devices based on the VPN resource;
A normal mode for establishing a first VPN session alone for the grouped network devices, a representative mode for establishing a second VPN session and aggregating other network devices, and a network device in the representative mode An operation mode instructing unit for instructing to set one of the subordinate modes connected to the second network via the second VPN session
The network device is
An operation mode control unit that sets an operation mode based on an instruction from the operation mode instruction unit;
And a message relay unit that relays a call control message from a subordinate network device when the representative mode is set by the operation mode control unit. The network device is
When the normal mode is set by the operation mode control unit, a VPN session is established with the gateway to transmit / receive its own call control message,
When the representative mode is set by the operation mode control unit, a VPN session is established with the gateway to transmit / receive its own call control message, and the call control message of the subordinate network device is relayed to the gateway. Send and receive,
When the subordinate mode is set by the operation mode control unit, a VPN session with the gateway is released, and a call control message is transmitted / received to / from the gateway via a network device in a representative mode. Item 12. The communication system according to Item 1.   The network device further includes a location registration unit that, when the representative mode is set by the operation mode control unit, representatively registers the location number information notified from the network device in the subordinate mode as its own phone number information. The communication system according to claim 1.   The location registration unit establishes a VPN session with the gateway when the operation mode control unit changes the setting from the state set to the representative mode or the subordinate mode to the normal mode. 4. The communication system according to claim 3, wherein the telephone number information held by itself is registered as a location.   When the subordinate mode is set by the operation mode control unit, the network device changes the transmission destination of the call control message from the gateway to the representative mode network device based on the operation mode change instruction received from the control device. The communication system according to claim 1, further comprising notifying the network device in the representative mode of own telephone number information.   The call control device changes the operation mode of the network device in accordance with an instruction from the operation mode instruction unit, aggregates the network device in which the network device individually connects to the gateway and the VPN, and the representative mode. 2. The communication system according to claim 1, wherein the network device switches between the gateway and the network form in which VPN connection is established.   2. The resource monitoring unit according to claim 1, wherein the resource monitoring unit detects the number of VPN sessions of the gateway, and performs aggregation of the network devices when the detected number of VPN sessions is a predetermined value or more. Communications system.   The communication system according to claim 1, wherein the aggregation determination unit selects aggregation target candidates such that a total of control channel throughputs of the network devices managed by the call control device is equal to or less than a predetermined value.   The communication system according to claim 1, wherein the aggregation determination unit selects an aggregation target candidate such that a total number of connection sessions of the network device managed by the call control device is equal to or less than a predetermined value.   The aggregation determination unit manages call information of network devices set to the representative mode, and reselects and aggregates the aggregation target candidate network devices when a call connection from the network device exceeds an aggregation determination threshold. The communication system according to claim 1, wherein a combination of network devices is dynamically changed.   The operation mode instruction unit transmits an instruction to change the setting to the representative mode to the aggregation target candidate network device selected by the aggregation determination unit, and to the other network target candidate network device The communication system according to claim 1, wherein an instruction to change the setting to the subordinate mode is transmitted.   The communication system according to claim 1, wherein the gateway has a function of the call control device. In a network device in which call control is managed by a call control device provided in a communication system,
Based on an instruction from the call control device, a normal mode in which a first VPN session is established alone, a representative mode in which a second VPN session is established and other network devices are aggregated, and subordinates of the network devices in the representative mode An operation mode control unit configured to set one of the subordinate modes connected to the second network via the second VPN session;
And a message relay unit that relays a call control message from a subordinate network device when the representative mode is set by the operation mode control unit. A call control apparatus that manages call control of a plurality of network devices connected to a network,
A call information management unit for managing call information for each network device;
A resource monitoring unit that monitors VPN resources based on the call information;
An aggregation determination unit that groups the network devices based on the VPN resource;
A normal mode for establishing a first VPN session alone for the grouped network devices, a representative mode for establishing a second VPN session and aggregating other network devices, and a network device in the representative mode A call control device comprising: an operation mode instructing unit for instructing setting to any one of subordinate modes connected to the second network via the second VPN session. In a communication system control method for managing call control of a network device,
Manages call information for each network device, monitors VPN resources based on the call information, groups the network devices based on the VPN resources, and sets a single unit for the grouped network devices. In the normal mode for establishing the first VPN session, the representative mode for establishing the second VPN session and aggregating other network devices, and the subordinate of the network device in the representative mode via the second VPN session. Instructing to set to one of the subordinate modes connected to the second network;
A control method for a communication system, comprising: relaying a call control message from a subordinate network device when a representative mode is set in the network device based on the instruction.

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