JP2007336178A - Call control server and call control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide call control servers capable of individually performing the flow control of communication control messages without making them cooperate with one another. <P>SOLUTION: In a call control server 1, address information being addresses of communication control messages and line numbers of lines being next transmission destinations are stored in a line information storage part 1-3 in association with one another. Upper limit values of the number of call connection which are predetermined per line are stored in a line state storage part 1-5 in association with the address information and the line numbers. A line determination part 1-4 detects a line number being the next transmission destination on the basis of address information included in a communication control message and information stored in the line information storage part 1-3. A flow control processing part 1-6 determines whether or not the number of connection of the line having the detected line number exceeds the upper limit value and transmits the communication control message to the line when determination that it doesn't exceed the upper limit value and doesn't transmit the communication control message as a call loss when determining that it exceeds the upper limit value. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a call control server that performs call control between terminals in a communication system, and a call control method.

  Conventionally, in a system that controls communication between terminals by sending a communication request message to the call control server at the start of communication from the subscriber's terminal, the call control server becomes congested even if there is a sufficient communication path between the terminals. As a result, communication between terminals could not be performed. In addition, when the destination call control server is congested, communication cannot be performed even when the processing capacity of the calling side call control server is sufficient.

  In such a system, a technique for regulating congestion has been proposed (see, for example, Patent Document 1). In this technology, first, the calling side call control server monitors its own congestion state, and when congestion occurs, it restricts outgoing calls from the terminal. In addition, when the called side call control server is congested, the called side call control server issues an instruction to the calling side call control server to regulate the call, and the calling side call control server sends the call from the terminal. And the callee server on the called side is protected from congestion.

  Specifically, the prior art described in Patent Document 1 will be described with reference to FIGS. FIG. 5 is a block diagram showing an outline of the congestion control apparatus 101 in the prior art. In the congestion control device 101, the own server originating load measuring unit 105 measures the load of the call control server directly connected to the own device, and the other server originating load measuring unit 106 passes through the own call control server. Then, the load of the other call control server connected is measured, and the restriction is started when the restriction control unit 104 determines that it is necessary based on the measurement result. Then, the restriction request transmission unit 107 transmits the transmission restriction to the other call control server, thereby causing the other call control server to start the transmission restriction and protecting the own call control server. In addition, when the restriction request receiving unit 109 receives a call restriction from another congestion control apparatus 101, the restriction request receiving unit 109 starts the call restriction on the own call control server.

  FIG. 6 is a diagram showing an outline of the configuration of the communication system 100 of the prior art described in Patent Document 1. In FIG. 6, congestion control apparatuses 110a and 110b having the same configuration as the apparatus shown in FIG. 5 are connected to the call control servers 102a and 102b, and the call control servers 102a and 110b are connected by the congestion control apparatuses 110a and 110b. Transmission restriction is performed on 102b.

For example, the call control servers 102a and 102b monitor the congestion state of their own devices, and the congestion control devices 110a and 110b installed on the network constantly monitor the load of each call control server in the network. When the congestion control devices 110a and 110b determine that the monitoring destination call control servers 102a and 102b are congested, the congestion control devices 110a and 110b accommodate the transmission source terminal to restrict communication toward the congested call control server. That is, a call restriction instruction is transmitted to a call control server directly connected to the caller terminal. The call control server that terminates the caller terminal receives the call restriction instruction and restricts communication toward the call control server that is congested. When the terminal is directly transmitting to a congested call control server, the congested call control server regulates communication from the terminal. Call restriction for a terminal that makes a direct call is realized by the call control server limiting the number of communication processes to a preset number according to the restriction level and not processing communication exceeding the limit.
JP 2005-167769 A

  However, in the technique described in Patent Document 1, congestion control devices must cooperate to perform congestion control, and the source terminal that causes the congestion is a terminal accommodated in the own call control server. If not, outgoing restrictions to other call control servers need to be sent. At this time, there is a problem that the intermediate call control server and the call control server as the caller have to process a call request that does not require processing.

  The present invention has been made to solve the above-described problem, and its purpose is to provide a call control server that enables flow control of communication control messages in each call control server without performing cooperation between the call control servers, And providing a call control method.

  In order to solve the above problem, the present invention includes a terminal used by a subscriber and a plurality of call control servers to which identification information uniquely identifiable in advance is provided, based on a communication control message transmitted and received. Identification information of a call control server in a communication system for performing call control between terminals, the destination information serving as the destination of the communication control message, and the next destination of the communication control message including the destination information And a storage means for storing the predetermined upper limit value of the number of call control states between the call control server and the own server in association with each other, and receiving a communication control message from the terminal or another call control server If the communication control message received by the receiving means and the receiving means is a communication start request, the destination included in the communication control message Detection means for detecting a call control server as a next transmission destination based on the information and information stored in the storage means, and a current predetermined call control state between the detected call control server and the own server It is determined whether the number exceeds the upper limit value stored in the storage means in association with the detected call control server, and the current predetermined call control state number does not exceed the upper limit value. If it is determined, the communication control message is transmitted to a call control server as a next transmission destination, and if it is determined that the current predetermined number of call control states exceeds the upper limit value, the communication control message is transmitted. And a call control server that performs predetermined processing without performing the above process.

  According to the present invention, in the above-described invention, the storage unit has, for one destination information, identification information of a plurality of call control servers that are the next transmission destinations of a communication control message including the destination information, A predetermined upper limit value of the number of call control states between the call control server and the own server is stored in association with each other, and the call control means is configured so that the current predetermined call control state number is equal to the upper limit value. If it is determined that the value exceeds the value, the communication control message is not transmitted to the call control server as the next transmission destination, and the detection means detects the detection of another call control server as the next transmission destination. If the detection means cannot detect a call control server as the next transmission destination, the communication control message is not transmitted and the call is lost.

  According to the present invention, in the invention described above, the plurality of call control servers include at least a calling / calling side call control server connected directly to at least two or more terminals and at least connected to only another call control server. Two or more relay call control servers, and at least two or more relay call control servers are connected to one of the destination call control servers, The storage means, for one destination information, for the identification information of at least two or more relay call control servers to be the next transmission destination of the communication control message including the destination information, and one destination information An upper limit value that is larger than the case where one call control server is associated is stored in association with each other.

  The present invention includes a terminal used by a subscriber and a plurality of call control servers to which identification information uniquely identifiable in advance is provided, and performs communication control between terminals based on transmitted and received communication control messages A call control method for a call control server in a system, the destination information serving as a destination of the communication control message, the identification information of the call control server serving as the next transmission destination of the communication control message including the destination information, and predetermined Storing the storage means in association with an upper limit value of the predetermined number of call control states between the call control server and the own server, and receiving a communication control message from the terminal or another call control server; When the received communication control message is a communication start request, the destination information included in the communication control message, A step of detecting a call control server as a next transmission destination based on information stored in the storage means, and a current predetermined number of call control states between the detected call control server and the own server are detected. Determining whether or not an upper limit value of a predetermined number of call control states stored in the storage unit in association with the call control server is exceeded; and When it is determined that the communication control message is not exceeded, the step of transmitting the communication control message to a call control server as a next transmission destination, and when it is determined that the current predetermined call control state number exceeds the upper limit value, And a predetermined process without transmitting the communication control message.

  According to this invention, the call control server includes destination information that is a destination of the communication control message, identification information of the call control server that is the next transmission destination of the communication control message including the destination information, and the predetermined call. When a predetermined communication control message between the control server and its own server is associated with the upper limit value of the number of call control states and stored in the storage means, and the received communication control message is a communication start request, it is included in the communication control message A call control server as a next transmission destination is detected based on the destination information and the information stored in the storage means, and the current predetermined number of call control states between the detected call control server and the own server is When it is determined that the upper limit value is exceeded, a predetermined process is performed without transmitting a communication control message. As a result, it is possible to perform outgoing call restriction based on the communication control message only by each call control server without performing cooperation between the call control servers, and it is possible to reduce communication control messages that do not require processing.

  Further, according to the present invention, the call control server stores, in the storage unit, for one destination information, identification information of a plurality of call control servers that are the next transmission destination of the communication control message including the destination information, A predetermined upper limit value of the number of call control states between the call control server and the own server is stored in association with each other, and it is determined that the current predetermined number of call control states exceeds the upper limit value In this case, the communication control message is not transmitted to the call control server that is the next transmission destination, and another call control server that is the next transmission destination is detected. And when the call control server used as the next transmission destination cannot be detected, it is set as the call loss without transmitting a communication control message. Thus, by setting a plurality of call control servers as destinations in advance, it is possible to reduce the probability of call loss.

  According to the present invention, the plurality of call control servers in the communication system include at least two call control servers that are directly connected to at least two or more terminals, and at least two that are connected only to other call control servers. Two or more relay call control servers, and at least two or more relay call control servers are connected to one destination, and the call control server on the destination side stores the call control server. As a means, for one destination information, identification information of at least two or more call control servers for relay that will be the next transmission destination of the communication control message including the destination information, and one destination information. The upper limit value that is larger than the case where two call control servers are associated with each other is stored in association with each other. In this configuration, since a plurality of call control servers for relaying can be set for one destination, the number of connections between the call control servers can be reduced as a whole, thereby increasing the upper limit between the call control servers. A value can be set.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram illustrating a communication system 50 according to the present embodiment. The communication system 50 includes a plurality of call control servers 1, 2, 3, 11, 12, and 13 and a plurality of subscriber terminals 20A to 20A. 20F. In FIG. 1, call control servers 1, 2, and 3 are call control servers that accommodate subscriber terminals, that is, callers that are directly connected to the terminals, or callees. In FIG. 1, for the following explanation, the call control server 1 is shown as the calling side, and the call control servers 2 and 3 are shown as the called side. The call control servers 11, 12, 13 for relay are connected to the call control servers 1, 2, 3 on the calling side or the called side, and relay communication control messages between these call control servers. If the call control servers 11, 12, and 13 for relay are directly connected to the call control servers 1, 2, and 3 that connect the subscriber terminals 20 </ b> A to 20 </ b> F when the network is large, the number of routes This is a server that is distributed to reduce the number of routes. Also, each call control server 1, 2, 3, 11, 12, 13 is assigned a server number, which is identification information that can be identified in the communication system 50. Here, reference numerals shown in FIG. It is assumed that a server number corresponding to is assigned.

  The call control servers 1, 2, and 3 store therein information on a route that is a transmission route of the communication control message in association with the call control servers 11, 12, and 13 for relay. For the call control server 1, information on the route 1, the route 2, and the route 3 is stored for each of the call control servers 11, 12, and 13. In a general communication system, there are a plurality of routes between incoming and outgoing call control servers in order to improve the reliability of the transfer route. The call control server 1 in FIG. The route 1 and the route 2 are set, and the route 2 and the route 3 are set for the call control server 3. The route may correspond to the physical line itself connected to the call control server, but is set within one physical line when the network is an IP (Internet Protocol) network or the like. It may correspond to each of the logical lines. In addition, a route number is assigned to each route in advance for each call control server, and here, a route number corresponding to the code shown in FIG. 1 is assigned.

  When making a call, each of the subscriber terminals 20A to 20F first transmits a communication control message for a call start request to the directly connected call control server. The communication control message of the start request is received and a call (call) is established. Further, when the subscriber terminals 20A to 20F are disconnected, the subscriber terminals 20A to 20F transmit a communication control message of a communication release request to the directly connected call control server, and when the subscriber terminals 20A to 20F are disconnected from other terminals, The communication release message is received from the server and the communication call is disconnected.

  Here, when SIP (Session Initiation Protocol) is applied as a protocol for performing communication control, the destination information included in the above-described communication control message is 03xxxxyyy @ sip. domain. It is described in an address format such as jp. This destination information is given to each of the subscriber's terminals 20A to 20F. If the granting method corresponds to the arrangement method of the call control servers 1, 2, and 3 in the network, The connected call control server can be associated with the domain name and the number zone of the 03xxxyyyy part, and the call control server connected to the route or destination terminal can be detected from the destination information. In the case of SIP, an INVITE message and a BYE message are applied to the communication start request message and the communication release request message, respectively.

  FIG. 2 is a diagram showing an internal configuration of the call control server according to the present embodiment. Since the call control servers 1, 2, 3, 11, 12, and 13 shown in FIG. 1 are servers having the same internal configuration, FIG. 2 shows the call control server 1 as a representative example thereof, and the internal configuration thereof. This will be described below.

  In the call control server 1 shown in FIG. 2, the communication control message processing unit 1-1 is connected to other call control servers 11, 12, 13 or subscriber terminals 20A, 20B, and the other call control servers 11, 12 are connected. 13 or the communication control message transmitted from the subscriber's terminals 20A and 20B is processed according to the communication control protocol. As shown in FIG. 3A, the call state storage unit 1-2 stores call identification information indicating a call in communication and information on a route to which the call is connected. When SIP is applied to the communication control protocol, the call identification information is represented by Call-ID.

  The route information storage unit 1-3, as shown in FIG. 3B, the “destination server number” that is the transmission destination of the communication control message and the next transfer destination when the communication control message is transmitted to the destination Destination / route correspondence information in which a “route number” indicating the route is associated with a “next transfer destination server number” indicating a call control server for relay existing at the transfer destination of the route is stored. . The destination / route correspondence information shown in FIG. 3 (b) shows an example of setting in the caller side call control server 1 in FIG. 1, and the terminals 20A and 20B connected to the call control server 1; Communication control messages between the terminals 20C and 20D connected to the call control server 2 are transferred via the relay call control server 11 or the call control server 12 corresponding to the route 1 or the route 2, respectively. Is set to Further, the communication control messages between the terminals 20A and 20B connected to the call control server 1 and the terminals 20E and 20F connected to the call control server 3 are relayed corresponding to the route 2 or the route 3, respectively. Are set in advance so as to be transferred via the call control server 12 or the call control server 13.

  The route determination unit 1-4 determines whether the destination information of the communication control message exists in the “destination server number” of the destination / route correspondence information stored in the route information storage unit 1-3. If it exists, the route number of the route to which the communication control message stored corresponding to the destination information is transferred next is detected. As shown in FIG. 3 (c), the route state storage unit 1-5, for each “route number” assigned to each route, the “number of connected calls” in the route, and the route The correspondence information of “maximum allowable number of calls” indicating the upper limit value of the number of calls that can be connected is stored. When the communication control message received by the communication control message processing unit 1-1 is a communication start request message, the flow control processing unit 1-6 determines whether or not a call can be connected based on the message. 1 is added to the value of the “number of calls in connection” of the corresponding route in the route state storage unit 1-5, and the communication control message processing unit In 1-1, connection permission for the call is input. In addition, when the received communication control message is a communication release request message, the flow control processing unit 1-6 performs a call release process based on the message, and executes “call” of the corresponding route in the route state storage unit 1-5. 1 is subtracted from the value of the “number of connected calls”.

  Next, call flow control processing performed in the communication system 50 shown in FIG. 1, that is, outgoing call restriction processing, will be described with reference to the flowchart of FIG. In the call control server 1, the relationship between the destination information of the received communication control message and the route to be transferred next is stored in advance in the route information storage unit 1-3 as destination / route correspondence information. The route state storage unit 1-5 of the call control server 1 stores in advance an upper limit value of the number of connections for each route.

  Assume that the terminal 20A makes a call to the terminal 20C of the call control server 2. The communication control message processing unit 1-1 of the call control server 1 receives the communication control message and inputs the received communication control message to the flow control processing unit 1-6 (step S1). The flow control processing unit 1-6 determines whether the input communication control message is a communication start request message or a communication release request message (step S2). Here, since the call is being made, it is determined that the message is a communication start request message, the information included in the received communication control message is analyzed, the destination information is read from the analyzed communication control message, and the read destination information is It inputs into the route determination part 1-4 (step S3). As described above, for example, the route determination unit 1-4 detects the destination server number from a part of the destination information, and the route information storage unit 1-3 stores the destination server number based on the detected destination server number. Based on the destination / route correspondence information, one route number of the route to be transferred next is detected, and the detected route number is input to the flow control processing unit 1-6 (step S4). Here, as shown in FIG. 3B, since the route 1 or the route 2 is set as the route to the call control server 2, the route 1 described first is detected. And

  The flow control processing unit 1-6 is connected to the route 1 detected by the route determination unit 1-4 from the route state storage unit 1-5 and stored corresponding to the route 1 The number of calls n and the upper limit value N are read (step S5). Here, as shown in FIG. 3C, the number n1 of connected calls and the upper limit value N1 are read out. Then, the flow control processing unit 1-6 determines whether or not the read number of calls n is less than the upper limit value N (step S6). When the number of calls n is less than the upper limit value N (step S6: Yes), a value obtained by adding 1 to the number n of connected calls on the route 1 corresponds to the route 1 in the route state storage unit 1-5. Is recorded in the item “number of calls being connected” (step S7). And the information which permits connection with respect to the path 1 is input with respect to the communication control message process part 1-1 (step S8). The communication control message processing unit 1-1 connects to the call control server 11 connected to the route 1 based on the communication start request message when information permitting connection is input. The state of the connected call, for example, call identification information given for each call, and the route used for connection, that is, the information of the route 1 are recorded in the state storage unit 1-2 (step S20). The communication control message is also processed in the transferred call control server 11 of the next stage, finally reaches the call control server 2, and a call is established between the terminal 20A and the terminal 20C. become.

  On the other hand, when the number of calls n is equal to the upper limit value N or the number of calls n exceeds the upper limit value N1 in step S6 (step S6: No), the route detected by the route determination unit 1-4 is determined. Since the communication control message cannot be transferred using the flow control processing unit 1-6, the flow control processing unit 1-6 requests the route to the route determination unit 1-4 again. The route determination unit 1-4 determines whether there is another route based on the destination / route correspondence information stored in the route information storage unit 1-3. The process from step S4 is performed (step S9: Yes). Since the route 2 exists to the call control server 2, the route number of the route 2 is detected here, and the processing from step S5 is performed.

  On the other hand, in step S9, when the route determination unit 1-4 determines that there is no other route in the route information storage unit 1-3, that is, the number n of connected calls for all the available routes. Has reached the upper limit value N, the flow control processing unit 1-6 inputs connection impossible to the communication control message processing unit 1-1 (step S10), and the communication control message processing unit 1-1 The call is processed as a call loss (step S20).

  Next, when the call connected from the terminal 20A is disconnected, the communication control message processing unit 1-1 of the call control server 1 receives the communication control message and sends the received communication control message to the flow control processing unit. Input to 1-6 (step S1). The flow control processing unit 1-6 determines whether the input communication control message is a communication start request message or a communication release request message (step S2). Here, since disconnection has been performed, the communication control message is determined to be a communication release request message, and the flow control processing unit 1-6 determines the destination information and call identification information of the communication control message. Input to part 1-4.

  The route determination unit 1-4 detects information indicating which route the call is using from the call state storage unit 1-2 (step S15). Here, the route number of the route 1 is detected. The route determination unit 1-4 inputs the detected route number of the route 1 to the flow control processing unit 1-6, and the flow control processing unit 1-6 receives the number of connected calls of the inputted route 1 The number n1 is read from the route state storage unit 1-5, and the value of the number n1 of connected calls that have been read out is subtracted by 1, and the value obtained by subtracting the subtracted value of the route state storage unit 1-5 Recorded in the item “number of middle calls” (step S16). Then, the flow control processing unit 1-6 inputs a disconnection request to the communication control message processing unit 1-1 (Step S17). The communication control message processing unit 1-1 that has received the input of the disconnection request performs the disconnection processing of the call, and deletes information corresponding to the call identification information of the call that has disconnected from the call state storage unit 1-2 ( Step S20).

  When the configuration of the above embodiment is compared with the prior art shown in FIG. 5, in the prior art shown in FIG. 5, when the call control server on the called side is congested, the aggregation device arranged in the communication system 50. Via 120, the call control server on the calling side is notified of the congestion state and the processing of the communication control message is restricted, thereby avoiding congestion on the call control server on the called side. On the other hand, in this embodiment, it is possible to avoid the occurrence of congestion at the destination call control server by providing an upper limit value for the number of connections by the communication control message transferred to the destination call control server in advance. .

  In the above embodiment, when the number of call control servers in the communication system 50 increases, the number of calling side call control servers that transmit communication control messages to one called side call control server also increases. In order to surely avoid congestion at the called side call control server, it is necessary to keep the upper limit of the number of connected calls of each calling side call control server low. For example, when the number of call control servers in the communication system 50 is 10 and the communication control message processing amount of the call control server is 100, in order to avoid congestion of the called side call control server, each incoming call at the calling side call control server It is necessary to set the upper limit of the number of connected calls transferred to the control server to an average of 10. For this reason, when the number of calls that are connected only between certain specific incoming / outgoing call control servers increases, the outgoing call control even when the processing amount of the incoming call control server is 10, that is, 1/10 of the upper limit value. There are cases where outgoing calls are restricted by the server. In the present embodiment, as described above, in addition to the call control servers 1, 2, and 3 connecting the subscribers to the terminals 20A to 20F, the call control servers 11 and 12 for relay for relaying communication control messages are also provided. , 13, it is possible to aggregate the transfer routes of communication control messages and set the upper limit value for restriction on one route high.

  As described above, the call control servers 2, 3, 11, 12, and 13 have the same internal configuration as the call control server 1, and the above-described call flow control processing is performed in all call control servers. It will be.

  In the above embodiment, when the number of connected calls n is equal to the upper limit value N or when the number of calls n exceeds the upper limit value N, other routes are detected. You may make it perform the process which makes the said call call loss as it is, without detecting another route.

  In the configuration of the above embodiment, the call flow control method using the number of connected calls as the predetermined number of call control states described in the present invention has been described. However, the present invention is not limited to this, and the predetermined call control As the number of states, the number of communication start requests within a certain time, the number of communication control messages within a certain time, or the like may be applied.

  In the above embodiment, the configuration is described in which processing is performed based on the route set in the call control server as the transmission destination of the communication control message. However, the present invention is not limited to this, and the call control server of the transmission destination. Such identification information may be set in each call control server, and processing may be performed based on the identification information of the call control server.

  The storage means described in the present invention corresponds to a combination of the route information storage unit 1-3 and the route state storage unit 1-5, and the reception unit receives the communication control message processing unit 1-1. Corresponding to the function configuration, the detection means corresponds to the route determination unit 1-4, and the call control means corresponds to the transmission function configuration of the flow control processing unit 1-6 and the communication control message processing unit 1-1. To do.

It is a schematic block diagram which shows the communication system by this embodiment. It is the block diagram which showed the internal structure of the call control server of the embodiment. It is the figure which showed the data structure of the memory | storage part with which the call control server of the embodiment is equipped. It is the flowchart which showed the call flow control processing by the call control server of the same execution form. It is the block diagram which showed the internal structure of the congestion control apparatus in a prior art. It is the schematic block diagram which showed the communication system in a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Call control server 1-1 Communication control message process part 1-2 Call state memory | storage part 1-3 Route information memory | storage part 1-4 Way determination part 1-5 Path state memory | storage part 1-6 Flow control process part

Claims (4)

Call control in a communication system comprising a terminal used by a subscriber and a plurality of call control servers to which identification information uniquely identifiable in advance is provided, and performing call control between terminals based on communication control messages transmitted and received A server,
Destination information that is the destination of the communication control message, identification information of the call control server that is the next transmission destination of the communication control message that includes the destination information, and predetermined between the call control server and the local server that are determined in advance Storage means for associating and storing an upper limit value of the number of call control states of
Receiving means for receiving a communication control message from a terminal or another call control server;
When the communication control message received by the receiving means is a communication start request, a call control server to be a next transmission destination based on the destination information included in the communication control message and the information stored in the storage means Detecting means for detecting;
It is determined whether the current predetermined number of call control states between the detected call control server and the own server exceeds an upper limit value stored in the storage unit in association with the detected call control server. When it is determined that the current predetermined call control state number does not exceed the upper limit value, the communication control message is transmitted to a call control server as a next transmission destination, and the current predetermined call control state number Is determined to exceed the upper limit, call control means for performing a predetermined process without transmitting the communication control message;
A call control server comprising: The storage means
For one destination information, identification information of a plurality of call control servers that are the next transmission destination of the communication control message including the destination information, and a predetermined call between the call control server and the own server, which are determined in advance. The upper limit value of the number of control states is stored in association with it,
The call control means includes
If it is determined that the current predetermined number of call control states exceeds the upper limit value, the communication control message is not transmitted to the call control server that is the next transmission destination, and the detection means Requesting the detection means to detect another call control server, and if the detection means cannot detect a call control server to be a next transmission destination, call failure without transmitting the communication control message. The call control server according to claim 1, wherein: The plurality of call control servers include at least two call control servers that are directly connected to at least two terminals, and at least two relay call control servers that are connected only to other call control servers. The call control server on the calling side is connected to at least two relay call control servers for one destination,
The storage means of the calling / calling side call control server includes:
For one piece of destination information, identification information of at least two or more call control servers for relay serving as the next transmission destination of the communication control message including the destination information, and one call control for one piece of destination information The call control server according to claim 1, wherein an upper limit value larger than a value associated with the server is stored in association with each other. Call control in a communication system comprising a terminal used by a subscriber and a plurality of call control servers to which identification information uniquely identifiable in advance is provided, and performing call control between terminals based on communication control messages transmitted and received A server call control method comprising:
Destination information that is the destination of the communication control message, identification information of the call control server that is the next transmission destination of the communication control message that includes the destination information, and predetermined between the call control server and the local server that are determined in advance Storing in the storage means in association with the upper limit value of the number of call control states,
Receiving a communication control message from a terminal or other call control server;
If the received communication control message is a communication start request, detecting a call control server as the next transmission destination based on the destination information included in the communication control message and the information stored in the storage means; ,
The current predetermined number of call control states between the detected call control server and the own server exceeds the upper limit value of the predetermined number of call control states stored in the storage means in association with the detected call control server. Determining whether or not
If it is determined that the current predetermined number of call control states does not exceed the upper limit, the communication control message is transmitted to a call control server as a next destination;
If it is determined that the current predetermined number of call control states exceeds the upper limit, performing a predetermined process without transmitting the communication control message;
A call control method comprising:

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