Abstract:
[Problem] To provide a communication route control device, a communication route control system, a storage medium storing a communication route control program, and a communication route control method, with which the operating efficiency of a communication network can be increased and a decrease in communication quality can be satisfactorily prevented. [Solution] A communication means ( 11 ) is connected to each of multiple information transmission devices, including a first information transmission device connected to a first session initiation protocol (SIP) server and a second information transmission device connected to a second SIP server, with communication paths being set between the information transmission devices. On the basis of available capacity information, which indicates the available capacity of the communication paths between the information transmission devices and is obtained from each information transmission device by the communication means ( 11 ), a control means ( 12 ) sets a new route so as to avoid the communication path having the least available capacity.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a communication route control device, a communication route control system, a storage medium storing a communication route control program, and a communication route control method for controlling a route for transmitting and receiving a speech packet. 
       BACKGROUND ART 
       [0002]    A Voice over Internet Protocol (VoIP) is provided as a call service by an Internet Protocol (IP) technique using a communication system. Further, there is a communication system in which a Session Initiation Protocol (SIP) is employed as a call control protocol. 
         [0003]      FIG. 7  is a block diagram illustrating an example of a communication system in which an SIP is employed as a call control protocol. The communication system illustrated in  FIG. 7  includes switches  2   a  and  2   b , routers  3   a ,  3   b , and  3   c , and SIP servers  4   a  and  4   b . The switch  2   a  to be connected to IP phones la and lb is connected to the router  3   a.    
         [0004]    The router  3   a  is connected to the SIP server  4   a  and to the routers  3   b  and  3   c,  and transmits and receives a packet to and from the router  3   b  according to an instruction of the SIP server  4   a.  The switch  2   b  to be connected to IP phones  1   c  and  1   d  is connected to the router  3   b.  The router  3   b  is connected to the SIP server  4   b  and to the routers  3   a  and  3   c,  and transmits and receives a packet to and from the router  3   a  according to an instruction of the SIP server  4   b.    
         [0005]    For instance, when the IP phone  1   a  sends a call request to the IP phone  1   d  to perform a call, first of all, a call control packet for establishing a call on the basis of an SIP is transmitted from the IP phone  1   a  to the IP phone  1   d  via the SIP servers  4   a  and  4   b.  Specifically, a call control packet is transmitted from the IP phone  1   a  to the IP phone  1   d  via the switch  2   a,  the router  3   a,  the SIP server  4   a,  the router  3   a,  the router  3   b , the SIP server  4   b,  the router  3   b,  and the switch  2   b.    
         [0006]    Thereafter, when the call is established, a speech packet is transmitted and received between the IP phones  1   a  and  1   d  via the switch  2   a , the router  3   a,  the router  3   b,  and the switch  2   b.    
         [0007]    PTL 1 describes a system, in which a priority is set in advance for each of communication terminals using a VoIP. 
         [0008]    PTL 2 describes a method for deciding a route for transmitting and receiving a packet on the basis of a traffic amount and a band width between nodes of a communication network. 
       CITATION LIST 
     Patent Literature 
       [0009]    [PTL 1] Japanese Laid-open Patent Publication No. 2008-92257 
         [0010]    [PTL 2] Japanese Laid-open Patent Publication No. 2011-97656 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0011]    In the communication system illustrated in  FIG. 7 , however, when the traffic amount between the routers  3   a  and  3   b  increases, and congestion occurs, communication of a speech packet being transmitted and received during a call may stagnate, and speech quality may deteriorate. This may adversely affect the call. The reason for this is described as follows. A speech packet to be transmitted and received between the IP phones (e.g. IP phones connected by a same Local Area Network (LAN), or IP phones using a same SIP server)  1   a  and  1   b  of one of the segments, and a speech packet to be transmitted and received between the IP phones  1   c  and  1   d  of another one of the segments pass a same route. Therefore, the speech packet to be transmitted and received between the IP phones  1   a  and  1   b , and the speech packet to be transmitted and received between the IP phones  1   c  and  d  pass the same routers  3   a,    3   b,  and the like. This may cause an excessive load on the routers  3   a  and  3   b.  The reason why a speech packet to be transmitted and received between the IP phones  1   a  and  1   b , and a speech packet to be transmitted and received between the IP phones  1   c  and  1   d  pass the same routers  3   a  and  3   b  or the like is because routing tables of the routers  3   a  and  3   b  are set such that the routers  3   a  and  3   b  are adjacent to each other on a communication circuit. Therefore, transmitting and receiving a speech packet via the router  3   c  is not performed. 
         [0012]    The system described in PTL 1 is configured to discard a packet whose priority is low when a communication network is congested. Then, a speech packet being transmitted and received during a call may be discarded, or speech quality may deteriorate. This may also adversely affect the call. 
         [0013]    Further, in the method described in PTL 2, IP phones also employ a symmetrical routing for reducing the amount of management data, and packets are transmitted and received on a same route (see paragraphs [0030 ]and [0069] of PTL 2). In an SIP, whereas a call control packet is transmitted and received via the SIP servers  4   a  and  4   b,  a speech packet is transmitted and received without via the SIP servers  4   a  and  4   b.  When a symmetrical routing is applied to the call control packet and to the speech packet, a route passing the SIP servers  4   a  and  4   b  is also selected in transmitting and receiving the speech packet. Then, this may increase the traffic amount of a communication network, and may cause congestion in the communication network. 
         [0014]    In view of the above, an object of the present invention is to provide a communication route control device, a communication route control system, a storage medium storing a communication route control program, and a communication route control method that enable to advantageously prevent lowering of speech quality by enhancing the operating efficiency of a communication network. 
       Solution to Problem 
       [0015]    A communication route control device, according to the present invention, comprises: 
         [0016]    a communication means connected to each of a plurality of information transmission devices including a first information transmission device connected to a first SIP server, and a second information transmission device connected to a second SIP server, with communication paths set between the information transmission devices; and 
         [0017]    a control means which sets a new route while avoiding a communication path whose vacant capacity is smallest on the basis of vacant capacity information indicating vacant capacities of the communication paths between the information transmission devices, the vacant capacity information being acquired from each of the information transmission devices by the communication means. 
         [0018]    A communication route control system comprises: 
         [0019]    any one of aspects of the communication route control device; 
         [0020]    the first SIP server; 
         [0021]    the second SIP server; and 
         [0022]    the plurality of the information transmission devices. 
         [0023]    A storage medium storing a communication route control program, according to the present invention, which causes a computer to execute: 
         [0024]    a communication process of communicating with each of a plurality of information transmission devices including a first information transmission device connected to a first SIP server, and a second information transmission device connected to a second SIP server, with communication paths set between the information transmission devices; and 
         [0025]    a control process of setting a new route while avoiding a communication path whose vacant capacity is smallest on the basis of vacant capacity information indicating vacant capacities of the communication paths between the information transmission devices, the vacant capacity information being acquired from each of the information transmission devices by the communication process. 
         [0026]    A communication route control method, according to the present invention, comprises: 
         [0027]    a communication step for communicating with each of a plurality of information transmission devices including a first information transmission device connected to a first SIP server, and a second information transmission device connected to a second SIP server, with communication paths set between the information transmission devices; and 
         [0028]    a controlling step for setting a new route while avoiding a communication path whose vacant capacity is smallest on the basis of vacant capacity information indicating vacant capacities of the communication paths between the information transmission devices, the vacant capacity information being acquired from each of the information transmission devices. 
       Advantageous Effects of Invention 
       [0029]    According to the present invention, it is possible to enhance the operating efficiency of a communication network. Further, it is possible to advantageously prevent lowering of speech quality. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0030]      FIG. 1  is a block diagram illustrating an example of a communication network connected to a control server in a first exemplary embodiment of the present invention. 
           [0031]      FIG. 2  is a block diagram illustrating a configuration example of the control server in the first exemplary embodiment of the present invention. 
           [0032]      FIG. 3  is a sequence diagram illustrating an operation until a session is established between an IP phone and another IP phone in a communication network connected to the control server in the first exemplary embodiment of the present invention. 
           [0033]      FIG. 4  is a flowchart illustrating an operation of changing a speech packet route by the control server in the first exemplary embodiment of the present invention. 
           [0034]      FIG. 5  is a block diagram illustrating an example of a communication route control device in a second exemplary embodiment of the present invention. 
           [0035]      FIG. 6  is a block diagram illustrating an example of a communication route control system in a third exemplary embodiment of the present invention. 
           [0036]      FIG. 7  is a block diagram illustrating an example of a communication system in which an SIP is used as a call control protocol. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
     First Exemplary Embodiment 
       [0037]    The first exemplary embodiment of the present invention is described referring to the drawings.  FIG. 1  is a block diagram illustrating an example of a communication network connected to a control server (communication route control device)  100  in the first exemplary embodiment of the present invention. As illustrated in  FIG. 1 , the control server  100  in the first exemplary embodiment of the present invention is connected to each of routers  3   a,    3   b,  and  3   c,  and SIP servers  4   a  and  4   b.    
         [0038]    The control server  100  controls transmission destinations of speech packets in the routers  3   a,    3   b,  and  3   c  in cooperation with the SIP servers  4   a  and  4   b.  In other words, the control server  100  controls transmission routes of speech packets in cooperation with the SIP servers  4   a  and  4   b . Note that speech packets and call control packets are also generically and simply referred to as packets. 
         [0039]    Note that the control server  100  acquires in advance connection statuses between the routers  3   a,    3   b,  and  3   c,  and the SIP servers  4   a  and  4   b  on the basis of an Address Resolution Protocol (ARP) or a Link Layer Discovery Protocol (LLDP). Then, the control server  100  causes a storage means (not illustrated) to store the acquired information in advance. Further, the control server  100  causes a storage means to store in advance information indicating each of the routes along which a packet may pass when a call using the SIP server  4   a  and the SIP server  4   b  is performed. Furthermore, the control server  100  causes a storage means to store in advance information indicating a router which relays a packet for each of the routes along which the packet may pass, and information indicating an allowable communication amount of a communication path between the routers on each route. 
         [0040]    The switch  2   a  to be connected to IP phones la and lb is connected to the router  3   a.  The router  3   a  is connected to the control server  100 , the SIP server  4   a,  and the routers  3   b  and  3   c.  Then, the router  3   a  decides a transmission destination of a received packet depending on whether the received packet is a speech packet or a call control packet and according to the transmission destination, in accordance with at least one of controls by the control server  100  and the SIP server  4   a.  Specifically, the router  3   a  transmits a received packet to either one of the SIP server  4   a,  the routers  3   b  and  3   c,  and the switch  2   a.    
         [0041]    The switch  2   b  to be connected to IP phones  1   c  and  1   d  is connected to the router  3   b.  The router  3   b  is connected to the control server  100 , the SIP server  4   b,  and the routers  3   a  and  3   c.  Then, the router  3   b  decides a transmission destination of a received packet depending on whether the received packet is a speech packet or a call control packet and according to the transmission destination, in accordance with at least one of controls by the control server  100  and the SIP server  4   b.  Specifically, the router  3   b  transmits a received packet to either one of the SIP server  4   b,  the routers  3   a  and  3   c,  and the switch  2   b.    
         [0042]    The router  3   c  is connected to the routers  3   a  and  3   b,  transmits a speech packet received from the router  3   a  to the router  3   b,  and relays the transmission of a speech packet received from the router  3   b  to the router  3   a.    
         [0043]      FIG. 2  is a block diagram illustrating a configuration example of the control server  100  in the first exemplary embodiment of the present invention. As illustrated in  FIG. 2 , the control server  100  in the first exemplary embodiment of the present invention includes a communication unit  110  and a control unit  120 . The control unit  120  transmits and receives information to and from the SIP servers  4   a  and  4   b,  and the routers  3   a,    3   b,  and  3   c  via the communication unit  110 . Specifically, the communication unit  110  acquires information on the traffic amount from the routers  3   a,    3   b,  and  3   c  in accordance with an instruction of the control unit  120 , and instructs a transmission destination of a speech packet to the routers  3   a,    3   b,  and  3   c.  Further, the communication unit  110  transmits and receives information to and from the SIP servers  4   a  and  4   b  in accordance with an instruction of the control unit  120 . 
         [0044]    Next, an operation of a communication network connected to the control server  100  in the first exemplary embodiment of the present invention is described. First of all, an operation until a session is established between the IP phone  1   a  and the IP phone  1   c  after the IP phone  1   a  sends a call request to the IP phone  1   c  is described.  FIG. 3  is a sequence diagram illustrating an operation until a session is established between the IP phone  1   a  and the IP phone  1   c  in a communication network connected to the control server  100  in the first exemplary embodiment of the present invention. 
         [0045]    As illustrated in  FIG. 3 , first of all, when the phone number of the IP phone  1   c  is input as a phone number of a call destination, the IP phone  1   a  performs the following process. Specifically, the IP phone  1   a  transmits an INVITE message, which is a call control packet indicating that the IP phone  1   a  is calling the IP phone  1   c , to the SIP server  4   a,  which is associated with the IP phone  1   a  (Step S 101 ). 
         [0046]    The INVITE message transmitted by the process of Step S 101  is transmitted to the SIP server  4   a  via the switch  2   a  and the router  3   a  (Steps S 102  and S 103 ). 
         [0047]    The SIP server  4   a  that receives the INVITE message transmitted by the process of Step S 101  performs the following process. Specifically, the SIP server  4   a  transmits the INVITE message to the SIP server  4   b , which is associated with the IP phone  1   c , on the basis that the call destination is the IP phone  1   c  as indicated in the INVITE message (Step S 104 ). The INVITE message transmitted by the process of Step S 104  is transmitted to the SIP server  4   b  via the routers  3   a  and  3   b  (Steps S 105  and S 106 ). 
         [0048]    Further, the SIP server  4   a  that transmits the INVITE message to the SIP server  4   b  in the process of Step S 104  transmits a Trying message, which is a call control packet indicating that a call process is being executed, to the IP phone  1   a  (Step S 107 ). The Trying message transmitted by the process of Step S 107  is transmitted to the IP phone  1   a  via the router  3   a  and the switch  2   a  (Steps S 108  and S 109 ). 
         [0049]    The SIP server  4   b  that receives the INVITE message transmitted by the process of Step S 104  performs the following process. Specifically, the SIP server  4   b  transmits the INVITE message to the IP phone  1   c  on the basis that the call destination is the IP phone  1   c  as indicated in the INVITE message (Step S 110 ). The INVITE message transmitted by the process of Step S 110  is transmitted to the IP phone  1   c  via the router  3   b  and the switch  2   b  (Steps S 111  and S 112 ). 
         [0050]    Further, the SIP server  4   b  that transmits the INVITE message to the IP phone  1   c  in the process of Step S 110  transmits a Trying message, which is a call control packet indicating that a call process is being executed, to the SIP server  4   a  (Step S 113 ). The Trying message transmitted by the process of Step S 113  is transmitted to the SIP server  4   a  via the routers  3   b  and  3   a  (Steps S 114  and S 115 ). 
         [0051]    The IP phone  1   c  that receives the INVITE message transmitted by the process of Step S 110  performs a call operation such as outputting a ringtone. Then, the IP phone  1   c  transmits a Ringing message, which is a call control packet indicating that the IP phone  1   c  is being called, to the IP phone  1   a  on the basis that the call source of the received INVITE message is the IP phone  1   a  (Step S 116 ). The Ringing message transmitted by the process of Step S 116  is transmitted to the IP phone  1   a  via the switch  2   b , the router  3   b,  the SIP server  4   b,  the router  3   b,  the router  3   a,  the SIP server  4   a,  the router  3   a,  and the switch  2   a  (Steps S 117  to S 124 ). 
         [0052]    The IP phone  1   a  that receives the Ringing message transmitted by the process of Step S 116  performs an incoming call waiting operation such as outputting a ringback tone. 
         [0053]    Further, when a user performs a receiving operation with use of the IP phone  1   c , the IP phone  1   c  transmits an OK message, which is a call control packet indicating that start of a call session is accepted, to the IP phone  1   a  (Step S 125 ). The OK message transmitted by the process of Step S 125  is transmitted to the IP phone  1   a  via the switch  2   b,  the router  3   b , the SIP server  4   b,  the router  3   b,  the router  3   a,  the SIP server  4   a,  the router  3   a,  and the switch  2   a  (Steps S 126  to S 133 ). 
         [0054]    The IP phone  1   a  that receives the OK message transmitted from the IP phone  1   c  by the process of Step S 125  transmits an ACK response, which is a call control packet indicating that the OK message is received, to the IP phone  1   c  (Step S 134 ). The ACK response transmitted by the process of Step S 134  is transmitted to the IP phone  1   c  via the switch  2   a,  the router  3   a,  the router  3   b,  and the switch  2   b  (Steps S 135  to S 138 ). 
         [0055]    By the processes of Steps S 101  to S 138 , a speech packet route via the switch  2   a,  the router  3   a,  the router  3   b,  and the switch  2   b  is set between the IP phone  1   a  and the IP phone  1   c , and a session is established (Step S 139 ). Then, the SIP server  4   a  causes each of the storage means (not illustrated) to store the set speech packet route on the basis that the OK message transmitted by the process of Step S 125  is received by the process of Step S 130 . Further, the SIP server  4   b  causes each of the storage means (not illustrated) to store the set speech packet route on the basis that the OK message transmitted by the process of Step S 125  is received by the process of Step S 127 . Further, the SIP servers  4   a  and  4   b  transmit route information indicating the set speech packet routes to the control server  100 , and notifies that a session is established (Steps S 140  and S 141 ). 
         [0056]    Then, the SIP server  4   a  sets a routing table of the router  3   a  in such a manner that the router  3   a  transmits a packet transmitted to the IP phone  1   c  to the router  3   b.  Further, the SIP server  4   a  sets a routing table of the router  3   a  in such a manner that the router  3   a  transmits a packet transmitted to the IP phone  1   a  to the switch  2   a.    
         [0057]    The SIP server  4   b  sets a routing table of the router  3   b  in such a manner that the router  3   b  transmits a packet transmitted to the IP phone la to the router  3   a.  Further, the server  4   b  sets a routing table of the router  3   b  in such a manner that the router  3   b  transmits a packet transmitted to the IP phone  1   c  to the switch  2   b.    
         [0058]    Next, an operation of changing a speech packet route which is initially set by the processes in the steps illustrated in  FIG. 3 , after the control server  100  in the first exemplary embodiment of the present invention performs the processes on the basis of a traffic amount between the routers  3   a,    3   b,  and  3   c,  is described. In this example, an initially set route along which the router  3   a  and the router  3   b  transmit and receive a speech packet without via the router  3   c  is changed to a route along which the router  3   a  and the router  3   b  transmit and receive a speech packet via the router  3   c.    FIG. 4  is a flowchart illustrating an operation of changing a speech packet route by the control server  100  in the first exemplary embodiment of the present invention. 
         [0059]    As illustrated in  FIG. 4 , first of all, the control server  100  performs the following process on the basis of route information received by the communication unit  110  from the SIP servers  4   a  and  4   b  by the processes of Steps S 140  and S 141 . Specifically, the control unit  120  in the control server  100  specifies a speech packet route between the IP phones  1   a  and  1   c  (Step S 201 ). In this example, the control unit  120  in the control server  100  specifies that the router  3   a  and the router  3   b  directly transmit and receive a speech packet. 
         [0060]    Next, the communication unit  110  in the control server  100  reads a routing table from the routers  3   a  and  3   b  (Step S 202 ). Then, the control unit  120  in the control server  100  searches another speech packet route between the IP phones  1   a  and  1   c  on the basis of the routing table read from the routers  3   a  and  3   b  by the communication unit  110  by the process of Step S 202  (Step S 203 ). In this example, it is assumed that the control unit  120  in the control server  100  finds a route for transmitting and receiving a speech packet between the router  3   a  and the router  3   b  via the router  3   c  by the search in the process of Step S 203 . 
         [0061]    The communication unit  110  in the control server  100  acquires vacant capacity information indicating a vacant capacity of a communication path between the routers  3   a  and  3   b,  between the routers  3   b  and  3   c,  and between the routers  3   c  and  3   a  from each of the routers  3   a,    3   b , and  3   c  on the basis of a search result by the control unit  120  (Step S 204 ). Specifically, for instance, the communication unit  110  in the control server  100  requests each of the routers  3   a,    3   b,  and  3   c  to transmit vacant capacity information indicating vacant capacities of communication paths between the routers  3   a  and  3   b,  between the routers  3   b  and  3   c,  and between the routers  3   c  and  3   a.  Then, the communication unit  110  in the control server  100  receives the vacant capacity information transmitted by each of the routers  3   a,    3   b,  and  3   c  in response to the request. 
         [0062]    The control unit  120  in the control server  100  compares the vacant capacities of communication paths between the routers  3   a  and  3   b,  between the routers  3   b  and  3   c,  and between the routers  3   c  and  3   a  on the basis of the vacant capacity information acquired by the process of Step S 204  (Step S 205 ). Specifically, for instance, it is assumed that the vacant capacity of a communication path between the router  3   a  and the router  3   b,  which is indicated by vacant capacity information received from at least one of the router  3   a  and the router  3   b  is 10 Mbps (bits per second). Further, it is assumed that the vacant capacity of a communication path between the router  3   a  and the router  3   c,  which is received from at least one of the router  3   a  and the router  3   c  is 20 Mbps. Furthermore, it is assumed that the vacant capacity of a communication path between the router  3   b  and the router  3   c,  which is received from at least one of the router  3   b  and the router  3   c  is 30 Mbps. 
         [0063]    Then, it is clear that the vacant capacity of a communication path between the router  3   a  and the router  3   b  via the router  3   c  is larger than the vacant capacity of an initially set communication path for directly connecting between the routers  3   a  and  3   b.  Accordingly, in this example, the control unit  120  in the control server  100  decides to change the speech packet route from the initially set route to the route via the router  3   c  (Y in Step S 206 ). In other words, the control unit  120  in the control server  100  avoids a communication path whose vacant capacity is smallest (in this example, a communication path between the routers  3   a  and  3   b ), and changes the speech packet route to a new route. According to the aforementioned configuration, it is possible to advantageously prevent speech packet loss, and to advantageously prevent lowering of speech quality due to speech packet loss. 
         [0064]    The control unit  120  in the control server  100  sets a routing table of the router  3   a  in such a manner that the router  3   a  transmits a packet transmitted to the IP phone  1   c  to the router  3   c.  Further, the control unit  120  in the control server  100  sets a routing table of the router  3   b  in such a manner that the router  3   b  transmits a packet transmitted to the IP phone  1   a  to the router  3   c.  Furthermore, the control unit  120  in the control server  100  sets a routing table of the router  3   c  in such a manner that the router  3   c  transmits a packet transmitted to the IP phone  1   a  to the router  3   a,  and transmits a packet transmitted to the IP phone  1   c  to the router  3   b  (Step S 207 ). 
         [0065]    When the vacant capacity of an initially set route is larger than the vacant capacity of a newly searched route (N in Step S 206 ), the process is terminated without changing the route. 
         [0066]    Note that when there is no vacant capacity in an initially set route, and a newly searched route does not have a vacant capacity capable of transmitting and receiving a speech packet, the control server  100  notifies an error to the SIP servers  4   a  and  4   b.  Then, the SIP servers  4   a  and  4   b  disconnect the call in response to a notification of an error from the control server  100 . 
         [0067]    The control server  100  executes each of the processes illustrated in  FIG. 4  when receiving route information that is transmitted in response to receiving an OK message by the SIP servers  4   a  and  4   b,  and periodically executes each of the processes illustrated in  FIG. 4 . Note that the control server  100  may execute each of the processes illustrated in  FIG. 4  at other timings. Specifically, for instance, the another timing is a time when a processing load of one of the routers  3   a,    3   b,  and  3   c  excessively increases, or a time when transmitting and receiving a call control packet is started. 
         [0068]    By causing the control server  100  to periodically execute each of the processes illustrated in  FIG. 4 , it is possible to flexibly change a speech packet route in response to a change in the communication amount in each of the routes. 
         [0069]    According to the exemplary embodiment, the control server  100  uses a route whose vacant capacity is relatively large among a plurality of routes between the routers  3   a  and  3   b  for transmitting and receiving a speech packet. Accordingly, it is possible to increase the operating efficiency of a communication network. Further, it is possible to avoid use of a route whose vacant capacity is relatively small in transmitting and receiving a speech packet. This makes it possible to advantageously prevent lowering of speech quality due to speech packet loss. 
       Second Exemplary Embodiment 
       [0070]    The second exemplary embodiment of the present invention is described referring to the drawing.  FIG. 5  is a block diagram illustrating an example of a communication route control device  10  in the second exemplary embodiment of the present invention. As illustrated in  FIG. 5 , the communication route control device (corresponding to the control server  100  illustrated in  FIG. 1 )  10  in the second exemplary embodiment of the present invention includes a communication means (corresponding to the communication unit  110  illustrated in  FIG. 2 )  11 , and a control means (corresponding to the control unit  120  illustrated in  FIG. 2 )  12 . 
         [0071]    The communication means  11  is connected to a first information transmission device connected to a first SIP server. Further, the communication means  11  is connected to a second information transmission device, which is connected to a second SIP server and to the first information transmission device for transmitting and receiving a speech packet to and from the first information transmission device. Further, the communication means  11  is connected to another information transmission device, which is connected to the first information transmission device and to the second information transmission device. 
         [0072]    Note that the first SIP server corresponds to the SIP server  4   a  illustrated in  FIG. 1 . The first information transmission device corresponds to the router  3   a  illustrated in  FIG. 1 . The second SIP server corresponds to the SIP server  4   b  illustrated in  FIG. 1 . The second information transmission device corresponds to the router  3   b  illustrated in  FIG. 1 . The another information transmission device corresponds to the router  3   c  illustrated in  FIG. 1 . 
         [0073]    The control means  12  sets a new route while avoiding a communication path whose vacant capacity is smallest on the basis of vacant capacity information indicating vacant capacities of communication paths between the information transmission devices, which is acquired by the communication means  11 . 
         [0074]    According to the exemplary embodiment, it is possible to enhance the operating efficiency of a communication network. Further, it is possible to advantageously prevent lowering of speech quality. 
       Third Exemplary Embodiment 
       [0075]    The third exemplary embodiment of the present invention is described referring to the drawing.  FIG. 6  is a block diagram illustrating an example of a communication route control system in the third exemplary embodiment of the present invention. As illustrated in  FIG. 6 , the communication route control system in the third exemplary embodiment of the present invention includes a communication route control device  200 , information transmission devices  300   a,    300   b , . . . , and  300   z,  a first SIP server  400   a,  and a second SIP server  400   b.    
         [0076]    The communication route control device  200  in the exemplary embodiment corresponds to the control server  100  in the first exemplary embodiment illustrated in  FIG. 1 , or to the communication route control device  10  in the second exemplary embodiment. The information transmission devices  300   a,    300   b , . . . , and  300   z  in the exemplary embodiment correspond to the routers  3   a,    3   b,  and  3   c  illustrated in  FIG. 1 . The first SIP server  400   a  and the second SIP server  400   b  in the exemplary embodiment correspond to the first SIP server  4   a  and the second SIP server  4   b  illustrated in  FIG. 1 , respectively. 
         [0077]    In the exemplary embodiment, the information transmission device  300   a  is connected to the first SIP server, and the information transmission device  300   z  is connected to the second SIP server. Further, a communication path is set between the information transmission devices  300   a,    300   b , . . . , and  300   z.    
         [0078]    According to the exemplary embodiment, it is possible to enhance the operating efficiency of a communication network. Further, it is possible to advantageously prevent lowering of speech quality. 
         [0079]    While the invention has been particularly shown and described with reference to exemplary embodiments thereof, the invention is not limited to these embodiments. It will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the claims. 
         [0080]    This application is based upon and claims the benefit of priority from Japanese patent application No. 2014-046448, filed on Mar. 10, 2014, the disclosure of which is incorporated herein in its entirety by reference. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           1   a ,  1   b ,  1   c ,  1   d  IP phone 
           2   a,    2   b  Switch 
           3   a,    3   b,    3   c  Router 
           4   a,    4   b  SIP server 
           10 ,  200  Communication route control device 
           11  Communication means 
           12  Control means 
           100  Control server 
           110  Communication unit 
           120  Control unit 
           300   a,    300   b,    300   z  Information transmission device 
           400   a  First SIP server 
           400   b  Second SIP server