Patent Publication Number: US-9906570-B2

Title: Session control system, communication terminal, communication system, session control method, and medium

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The disclosures herein generally relate to controlling establishing a session between communication terminals to transmit the contents data in a communication system that includes multiple relay management devices to manage relaying the contents data transmitted from the communication terminals. 
     2. Description of the Related Art 
     In recent years, demand for reducing the cost and time spent for business trips has risen, and a communication system has become popular that is for calls and conferences in which communication is made via a communication network such as the Internet, dedicated lines, and the like. In such a communication system, once a communication is started between communication terminals, contents data such as image data and sound data is transmitted and received so that participants can communicate with each other. 
     Also, in a communication system for a video conference, other than communication terminals, MCUs (Multipoint Control Units) and a management device to manage the MCUs are provided. An MCU relays contents data, such as image data and sound data, among communication terminals at multiple sites by receiving contents data transmitted from a communication terminal, and transmitting the data to one or more other communication terminals under management by the management device. 
     SUMMARY OF THE INVENTION 
     According to an embodiment of the present invention, a session control system controls establishing a session to transmit contents data between communication terminals, in a communication system including multiple relay management devices managing relaying the contents data transmitted from the communication terminals. The session control system includes a selection unit configured to select one of the relay management devices to manage relaying the contents data, every time the session is to be established; and a transmitter unit configured to transmit selection information representing the relay management device selected by the selection unit, at least to the communication terminals being connected with the relay management devices different from the relay management device selected by the selection unit, among the communication terminals to be participating in the session to be established. 
     According to at least one embodiment of the present invention, when establishing a session to transmit contents data between communication terminals by using multiple relay systems, an effect is obtained that a load can be reduced for a communication terminal on the starting side of a communication, to execute a starting process. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other objects and further features of embodiments will be apparent from the following detailed description when read in conjunction with the accompanying drawings, in which: 
         FIG. 1  is an overview of a communication system according to an embodiment of the present invention; 
         FIG. 2  is an example of an external view of a terminal; 
         FIG. 3  is a hardware configuration diagram of a terminal; 
         FIG. 4  is a hardware configuration diagram of a call control device; 
         FIG. 5  includes functional block diagrams of a terminal, a call control device, and a session management device; 
         FIGS. 6A-6B  are conceptual diagrams that illustrate management tables managed by a session management device; 
         FIG. 7  is a conceptual diagram that illustrates a state of transmission and reception of contents data and various management information in a communication system; 
         FIG. 8  is a sequence chart that illustrates a process where a terminal logs in on a call control device; 
         FIG. 9  is a sequence chart that illustrates a process where a session for contents data is established; and 
         FIG. 10  is a sequence chart that illustrates a process where a terminal participates in a session for contents data “sed”. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the following, embodiments of the present invention will be described with reference to the drawings. 
     &lt;&lt;Overall Configuration of Embodiment&gt;&gt; 
       FIG. 1  is an overview of a communication system  1  according to an embodiment of the present invention. As illustrated in  FIG. 1 , the communication system  1  is configured to include call terminals ( 10   aa ,  10   ab ,  10   ba ,  10   bb ), for example, video-conference terminals, relay systems ( 3   a ,  3   b ), and a management system  5 . In the following, the call terminals are simply referred to as the “terminal(s)”, and when referring to an arbitrary one of the call terminals or the terminal ( 10   aa ,  10   ab ,  10   ba ,  10   bb ), it will be referred to as the “terminal  10 ”. 
     The relay system  3   a  is configured to include relay devices ( 30   aa ,  30   ab ), and a relay management device  40   a . On the other hand, the relay system  3   b  is configured to include relay devices ( 30   ba ,  30   bb ), and a relay management device  40   b . In the following, when referring to an arbitrary one of the relay devices ( 30   aa ,  30   ab ,  30   ba ,  30   bb ), it will be referred to as the “relay device  30 ”. When referring to an arbitrary one of the relay management devices ( 40   a ,  40   b ), it will be referred to as the “relay device  40 ”. 
     The relay device  30  relays contents data such as image data and sound data among multiple terminals  10 . Note that an image of image data may be a moving picture or a still picture, or images may include both moving pictures and still pictures. 
     The relay management device  40  is a computer having a server function. The relay management device  40  manages the relay devices  30  at a site which it belongs to. 
     The management system  5  is configured to include call control devices ( 50   a ,  50   b ), and a session management device  60 . In the following, when referring to an arbitrary one of the call control devices ( 50   a ,  50   b ), it will be referred to as the “call control device  50 ”. 
     The call control device  50  is a computer having a server function. The call control device  50  controls establishing a session (session for contents data “sed”) to transmit contents data among the terminal  10  in the communication system  1 . 
     The session management device  60  manages various information items relating to the session for contents data “sed”. 
     The relay devices ( 30   aa ,  30   ab ), the relay management device  40   a , and the call control device  50   a  are connected with a LAN  2   a  (Local Area Network) at a site A to communicate with each other. For example, the site A is a data center in Tokyo. 
     On the other hand, the relay devices ( 30   ba ,  30   bb ), the relay management device  40   b , and the call control device  50   b  are connected with a LAN  2   b  (Local Area Network) at a site B to communicate with each other. For example, the site B is a data center in New York. 
     The devices at the site A and the devices at the site B are connected with the devices at the other site, the session management device  60 , and terminals  10  to communicate with each other, via respective routers ( 70   a ,  70   b ) and a communication network  2 . The communication network  2  may be the Internet, a cellular phone network, or dedicated lines. For example, by having the devices at the site A and the devices at the site B connected via the communication network  2  constituted by dedicated lines, a communication between the relay devices  30 , or between the call control devices  50  can be stabilized. 
     Note that the session management device  60  may be installed at the site A or the site B, and may be connected with one of the LAN  2   a  and LAN  2   b.    
     By this communication system  1 , users of the terminals  10  can make calls with each other. A call may be implemented with sound, video (images), or sound and video (images). 
     Although to simplify the description, two sites (A, B) and four terminals ( 10   aa ,  10   ab ,  10   ba ,  10   bb ) are illustrated in  FIG. 1 , the communication system  1  may include three or more sites, and may be configured to include five or more terminals  10 . 
     &lt;&lt;Hardware Configuration of Embodiment&gt;&gt; 
     Next, a hardware configuration of the present embodiment will be described.  FIG. 2  is an external view of the terminal  10  according to the present embodiment. As illustrated in  FIG. 2 , the terminal  10  includes a chassis  1100 , an arm  1200 , and a camera housing  1300 . On a front side surface  1110  of the chassis  1100 , an air intake surface having multiple air intake holes is provided. On a rear side surface  1120  of the chassis  1100 , an air outlet surface having multiple air outlet holes is provided. This structure makes it possible to take in outside air through the air intake holes by driving a cooling fan built in the chassis  1100 , and then to exhaust the air on the rear side of the air outlet holes  1121 . On a right side surface  1130  of the chassis  1100 , a sound pickup hole  1131  is formed, through which voice sound, other sound, noise, and the like are captured by a built-in microphone  114 , which will be described later. 
     On a top surface of the chassis  1100  closer to the right side surface  1130 , an operation panel  1150  is formed. On the operation panel  1150 , multiple operational buttons  108   a - 108   e , a power switch  109 , and an alarm lamp  119  are provided, which will be described later, and a sound output surface  1151  is formed having multiple sound output holes, through which sound output from a built-in loudspeaker  115  goes to the outside, which will be described later. On the top surface of the chassis  1100  closer to a left side surface  1140 , a concave-shaped housing part  1160  is formed to accommodate the arm  1200  and the camera housing  1300 . On the right side surface  1130  of the chassis  1100 , multiple connectors  1132   a - 1132   c  are provided to have an external device connection I/F (Interface)  118  electrically connected with a cable, which will be described later. On the other hand, on the left side surface  1140  of the chassis  1100 , a connector is provided to have the external device connection I/F  118  electrically connected with a cable  120   c  for a display  120 . 
     Noted that in the following description, when referring to an arbitrary one of the operational buttons  108   a - 108   e , it will be referred to as the “operational button  108 ”, and when referring to an arbitrary one of the connectors  1132   a - 1132   c , it will be referred to as the “connector  1132 ”. 
     Next, the arm  1200  is attached to the chassis  1100  via a torque hinge  1210 , and is configured so that the arm  1200  can rotate vertically up to 135 degrees of the tilt angle θ 1  relative to the chassis  1100 .  FIG. 2  illustrates a state of the tilt angle θ 1  set at 90 degrees. The camera housing  1300  has a built-in camera  112 , which will be described later, to take a picture of a user, a document, and a room. The camera housing  1300  also has a torque hinge  1310  formed. The camera housing  1300  is attached to the arm  1200  via the torque hinge  1310 . The camera housing  1300  can rotate vertically up to ±180 degrees of the pan angle θ 2 , and horizontally up to ±45 degrees of the tilt angle θ 3 , relative to the state of angles formed by the camera housing  1300  and the arm  1200  in  FIG. 2  defined as 0 degrees. 
     Note that the external view in  FIG. 2  is just an example, and the embodiment is not restricted to this appearance. The terminal  10  may be, for example, a PC of general use, a smart phone, or a tablet-type terminal. The camera and the microphone do not necessarily need to be built in, but may be attached externally. 
     Note that the relay device  30 , the relay management device  40 , the call control device  50 , and the session management device  60  have an external view similar to that of a general-purpose server computer, and description of their external view is omitted. 
       FIG. 3  is a hardware configuration diagram of the terminal  10  according to the present embodiment. As illustrated in  FIG. 3 , the terminal  10  in the present embodiment includes a CPU (Central Processing Unit)  101  to control the overall behavior of the terminal  10 , a ROM (Read-Only Memory)  102  to store programs to drive the CPU  101  such as an IPL (Initial Program Loader), a RAM  103  used as a work area for the CPU  101 , a flash memory  104  to store various programs and data such as image data, audio data, and the like for the terminal  10 , an SSD (Solid State Drive)  105  to control writes/reads of various data on the flash memory  104  under control of the CPU  101 , a media I/F  107  to control writes/reads of data on a recording media  106  such as a flash memory or an IC (Integrated Circuit) card, operational buttons  108  operated when selecting an address or the like, the power switch  109  to turn on and off the power of the terminal  10 , and a network I/F  111  to transmit data by using the communication network  2 . 
     The terminal  10  also includes the built-in camera  112  to capture image data by taking a picture of an object under control of the CPU  101 , an imaging device I/F  113  to control the camera  112 , the built-in microphone  114  to input sound, the built-in loudspeaker  115  to output sound, a sound input/output I/F  116  to input/output audio signals between the microphone  114  and the loudspeaker  115  under control of the CPU  101 , a display I/F  117  to transfer image data to the external display  120  under control of the CPU  101 , the external device connection I/F  118  to have various external devices connected, and the alarm lamp  119  to indicate abnormalities of various functions in the terminal  10 , and a bus line  110  including an address bus, a data bus, and the like to have the above elements electrically connected with each other as illustrated in  FIG. 3 . 
     The display  120  is a display unit constituted with an LCD or an organic electroluminescence display to show images of an object, operational icons, and the like. Also, the display  120  is connected with the display I/F  117  via the cable  120   c . The cable  120   c  may be a cable for analog RGB (VGA) signals, a cable for component video, or a cable for HDMI (High-Definition Multimedia Interface) or DVI (Digital Video Interactive). 
     The camera  112  includes a solid-state imaging device to convert light into electric charge to obtain an electronic image of an object. As a solid-state imaging device, a CMOS (Complementary Metal Oxide Semiconductor) or a CCD (Charge Coupled Device) may be used. 
     The external device connection I/F  118  may be connected with an external camera, an external microphone, an external loudspeaker, or the like, via a USB (Universal Serial Bus) cable or the like plugged into the connector  1132  on the chassis  1100 . If having an external camera connected, the external camera is driven under control of the CPU  101 , with priority over the built-in camera  112 . Similarly, if having an external microphone or an external loudspeaker connected, the external microphone or loudspeaker is driven under control of the CPU  101 , with priority over the built-in microphone  114  or the built-in loudspeaker  115 , respectively. 
     Note that the recording media  106  can be easily attached to or detached from the terminal  10 . Also, instead of the flash memory  104 , an EEPROM (Electrically Erasable and Programmable ROM) or the like may be used, as long as it is a non-volatile memory with which reads/writes of data can be executed under control of the CPU  101 . 
       FIG. 4  is a hardware configuration diagram of the call control device  50 . The call control device  50  includes a CPU  501  to control the overall behavior of the call control device  50 ; a ROM  502  to store programs to drive the CPU  501  such as an IPL; a RAM  503  used as a work area for the CPU  501 ; an HD (Hard Disk)  504  to store various data of programs for the call control device  50 ; an HDD (Hard Disk Drive)  505  to control writes/reads of various data on the HD  504  under control of the CPU  501 ; a media drive  507  to control writes/reads of the data on a recording medium  506  such as a flash memory, a display  508  to display various information items including cursors, menus, windows, characters, and images; a network I/F  509  to transmit data using the communication network  2 ; a keyboard  511  having multiple keys to enter characters, numerals, various commands, etc.; a mouse  512  for various selections and executions, selection of an object, and moving the cursor; a CD-ROM drive  514  to control writes/reads of data on a CD-ROM (Compact Disc Read-Only Memory)  513 , which is an example of a recording medium attached/detached easily; and a bus line  510  including an address bus, a data bus, and the like to have the above elements electrically connected with each other as illustrated in  FIG. 4 . 
     The relay device  30 , the relay management device  40 , the call control device  50 , and the session management device  60  have substantially the same hardware configuration as the call control device  50 , and their description is omitted. 
     &lt;&lt;Functional Configuration of Embodiment&gt;&gt; 
     Next, functional units of the present embodiment will be described.  FIG. 5  includes functional block diagrams of the terminal  10 , the call control device  50 , and the session management device  60  that constitute a part of the communication system  1  according to the present embodiment. In FIG.  5 , the terminal  10  and the call control device  50  are connected with each other via the communication network  2  for data communication. 
     &lt;Functional Configuration of Terminal&gt; 
     The terminal  10  includes a transceiver unit  11 , an operational input reception unit  12 , a display control unit  13 , and a storage/read unit  19 . Functions of these units are implemented by one or more of the elements illustrated in  FIG. 3  that operate on instructions from the CPU  101  running a program loaded on the RAM  103  from the flash memory  104 . The terminal  10  also includes a storage unit  1000  constituted with the ROM  102 , the RAM  103 , and the flash memory  104  illustrated in  FIG. 3 . 
     (Functional Units of Terminal) 
     Next, using  FIG. 3  and  FIG. 5 , functional units of the terminal  10  will be described in detail. Note that in describing functional units of the terminal  10  in the following, main units illustrated in  FIG. 3  will be also described that are relevant to implement the functional units of the terminal  10 . 
     The transceiver unit  11  of the terminal  10  illustrated in  FIG. 5  is implemented by instructions from the CPU  101 , and the network I/F  111 , to transmit and receive various data (or information) to/from the other terminals, the devices, or the systems via the communication network  2 . 
     The operational input reception unit  12  is implemented by instructions from the CPU  101 , the operational buttons ( 108   a ,  108   b ,  108   c ,  108   d ,  108   e ), and the power switch  109 , to receive various inputs from a user, and to receive various selections from the user. 
     The display control unit  13  is implemented by instructions from the CPU  101 , and the display I/F  117 , to control transmitting image data received from the counterpart of a call, to the display  120 . 
     The storage/read unit  19  is executed by instructions from the CPU  101 , and the SSD  105 , or is implemented by instructions from the CPU  101 , to store various data in the storage unit  1000 , or to extract various data stored in the storage unit  1000 . 
     &lt;Functional Configuration of Call Control Device&gt; 
     The call control device  50  includes a transceiver unit  51 , an authentication unit  52 , a management unit  53 , a session control unit  58 , and a storage/read unit  59 . Functions of these units are implemented by one or more of the elements illustrated in  FIG. 4  that operate on instructions from the CPU  501  running a program loaded on the RAM  503  from the HD  504 . The call control device  50  also includes a storage unit  5000  that is constituted with the HD  504 . 
     (Functional Units of Call Control Device) 
     Next, functional units of the call control device  50  will be described in detail. Note that in describing functional units of the call control device  50  in the following, main units illustrated in  FIG. 4  will be also described that are relevant to implement the functional units of the call control device  50 . 
     The transceiver unit  51  is executed by instructions from the CPU  501 , and the network I/F  509 , to transmit and receive various data (or information) to/from the other terminals, the devices, or the systems via the communication network  2 . 
     The authentication unit  52  is implemented by instructions from the CPU  501 , to look up in an authentication management table (see  FIG. 6A ) by a search key of a communication ID and a password received by the transceiver unit  51 , to determine whether the same communication ID and password are managed in this authentication management table, to authenticate a terminal  10 . 
     The management unit  53  is implemented by instructions from the CPU  501 , to manage terminals  10  in a terminal management table (see  FIG. 6B ) by having pairs of communication IDs and terminal names of the respective terminals  10  associated with operational states and the like of the terminals  10 . 
     The session control unit  58  is implemented by instructions from the CPU  501 , to control a communication session “sed” in which contents data is transmitted among terminals  10 . The control includes control for establishing a communication session, control for having a terminal  10  participate in the established communication session, and control for disconnecting the communication session. 
     The storage/read unit  59  is executed by instructions from the CPU  501 , and the HDD  505 , or is implemented by instructions from the CPU  501 , to store various data in the storage unit  5000 , or to extract various data stored in the storage unit  5000 . 
     &lt;Functional Configuration of Session Management Device&gt; 
     The session management device  60  includes a transceiver unit  61 , and a storage/read unit  69 . Functions of these units are implemented by one or more of the elements illustrated in  FIG. 4  that operate on instructions from the CPU  501  running a program loaded on the RAM  503  from the HD  504 . The session management device  60  also includes a storage unit  6000  that is constituted with the HD  504 . This storage unit  6000  stores an authentication management DB  6001  including the authentication management table, and a terminal management DB  6002  including the terminal management table, as will be described later in detail. 
     (Authentication Management Table) 
       FIG. 6A  is a conceptual diagram that illustrates the authentication management table. In this authentication management table, to identify a terminal  10  as a communication destination, a communication ID and a password are managed by being associated with each other. Note that a communication ID here may be an ID stored in a terminal  10  in advance, or an ID input by a user on the terminal  10 . Also, it may be an ID read out of a recording medium such as an IC card connected with the terminal  10 . If the communication ID is to be input on the terminal  10 , the terminal  10  can be identified based on the communication ID, by having the communication ID transmitted from terminal  10  on a login request, associated with the terminal  10  as a requestor of the login request, and managing the association in the management system  5 . Note that it is assumed in the following description that the terminals ( 10   aa ,  10   ab ,  10   ba ,  10   bb ) have communication IDs “01aa, 01ab, 01ba, 01bb” associated, respectively. 
     (Terminal Management Table) 
       FIG. 6B  is a conceptual diagram that illustrates the terminal management table. In this terminal management table, the communication ID of a terminal  10  is managed by being associated with the terminal name, an operational state of this terminal  10 , a communication state of this terminal  10 , a session ID of a session for contents data in which this terminal  10  is participating, domain information of a relay management device  40  that manages relaying contents data as a whole in this session, and information representing a site which the call control device  50  or the relay management device  40  connected with this terminal  10  belongs to. 
     The transceiver unit  61  is executed by instructions from the CPU  501 , and the network I/F  509 , to transmit and receive various data (or information) to/from the other terminals, the devices, or the systems via the communication network  2 . 
     The storage/read unit  69  is executed by instructions from the CPU  501 , and the HDD  505 , or is implemented by instructions from the CPU  501 , to store various data in the storage unit  6000 , or to read out various data stored in the storage unit  6000 . 
     &lt;&lt;Processes or Operations of Embodiment&gt;&gt; 
     Next, processes or operations of the terminal  10 , the relay system  3 , and the management system  5  will be described that constitute the communication system  1  in the present embodiment. First, using  FIG. 7 , an overview of processes or operations in the communication system  1  will be described.  FIG. 7  is a conceptual diagram that illustrates a state of transmission and reception of contents data and various management information in the communication system  1 . 
     As illustrated in  FIG. 7 , in the communication system  1 , a session for management information, referred to as “sei”, is established between the terminals  10 , via one or more of the call control devices  50 , or between the terminal  10  and the call control device  50 , to transmit and receive various management information items. Also, between the terminals  10 , via one or more of the relay devices  30 , a session is established to transmit and receive contents data (image data and sound data). Here, these sessions are collectively referred to as the session for contents data “sed”. Namely, the session for contents data “sed” is a session(s) used in a video conference. Based on the session information transmitted from the call control device  50 , the relay management device  40  manages the relay device  30  to have the relay device  30  relay contents data through a predetermined path. 
     Next, processes or operations will be described in detail for the terminal  10 , the relay system  3 , and the management system  5  that constitute the communication system  1  in the present embodiment. First, using  FIG. 8 , a process will be described where the terminal  10  logs in on the call control device  50 .  FIG. 8  is a sequence chart that illustrates a process where the terminal  10  logs in on the call control device  50 . 
     In the communication system  1 , the terminal  10  can make a login request to an arbitrary one of the call control devices  50 . A method of selecting a call control device  50  as the destination of a login request is not specifically restricted, but possibly adopted among a method that selects a call control device  50  based on information input on the terminal  10 , a method that selects the closest call control device  50  based on physical positional information of the terminal  10 , a method that selects a call control device  50  by using GSLB (Global Server Load Balancing), and the like. 
     The terminal  10  has the transceiver unit  11  make a login request to an arbitrary one of the call control devices  50  (Step S 1 ). This login request includes a communication ID and a password to identify the terminal  10  as the requestor of the login request. Then, the transceiver unit  51  of the call control device  50  receives the login request, and the communication ID and password. 
     Next, the authentication unit  52  authenticates the terminal  10  as the requestor of the login request, by making a query to the session management device  60  to determine whether the same pair of communication ID and password received by the transceiver unit  51  is managed in the authentication management table (see  FIG. 6A ) (Step S 2 ). In this case, the transceiver unit  51  of the call control device  50  transmits the communication ID and password transmitted from the terminal  10  as the requestor of the login request, to the session management device  60 . The storage/read unit  69  of the session management device  60  looks up in the authentication management table, to confirm whether the pair of communication ID and password transmitted from the call control device  50  is managed in the authentication management table. The transceiver unit  61  of the session management device  60  transmits the confirmation result to the call control device  50 . 
     If the terminal  10  is determined to be valid by this authentication, the management unit  53  makes a request to the session management device  60  via the transceiver unit  51 , to manage the communication ID of the requestor of the login request in the terminal management table (see  FIG. 6B ) to have an operational state of “Online”, and the connection destination set (Step S 3 ). Note that in the communication system  1 , the terminal  10  is connected with a relay management device  40  that is in the same site as the call control device  50  connected with the terminal  10 . Therefore, for example, if the call control device  50  having received the login request is the call control device  50   a  that is installed in a data center in Tokyo, the management unit  53  makes a request to manage “Tokyo” as the connection destination. In response to the above request, the storage/read unit  69  of the session management device  60  updates the terminal management table. 
     Next, the transceiver unit  51  transmits an authentication result to the terminal  10  as the requester of the login request (Step S 4 ). 
     Next, using  FIG. 9 , a process will be described that establishes a session for contents data “sed” between the terminals  10 .  FIG. 9  is a sequence chart that illustrates a process to establish a session for contents data “sed”. In the following, a case will be described where the terminal  10   aa , which has been connected with the call control device  50   a  by the above login process, makes a request for starting a communication with the terminal  10   ba , which has been connected with the control device  50   b  by a login process. 
     In response to an operation on the operational buttons  108  by a user, the terminal  10   aa  has the transceiver unit  11  make a request for starting a communication, to the call control device  50   a  (Step S 21 ). This request for starting a communication includes the communication ID “01aa” of the terminal  10   aa  as the requestor of starting communication, and the communication ID “01ba” of the terminal  10   ba  as the destination. 
     The transceiver unit  51  of the call control device  50   a  receives the request for starting a communication. Next, the management unit  53  of the call control device  50   a  makes a request to the session management device  60  via the transceiver unit  51 , to manage the communication IDs of the terminals ( 10   aa ,  10   ba ) as the requestor of starting communication, and the destination, respectively, in the terminal management table (see  FIG. 6B ), to have communication states set to “Busy” representing that a communication is being executed (Step S 22 ). In response to the request by the call control device  50   a , the storage/read unit  69  of the session management device  60  updates the terminal management table. 
     Next, the session control unit  58  of the call control device  50   a  makes a query to the session management device  60  via the transceiver unit  51 , about the connection destination associated with the communication ID of the terminal  10   ba  as the destination in the terminal management table (see  FIG. 6B ) (Step S 23 ). In response to the request, the storage/read unit  69  of the session management device  60  reads the connection destination “New York” associated with communication ID “01ba” of the terminal  10   ba  as the destination in the terminal management table. The transceiver unit  61  of the session management device  60  transmits the read out connection destination to the call control device  50   a.    
     Next, based on the connection destination transmitted from the session management device  60 , the transceiver unit  51  of the call control device  50   a  transmits a request for starting a communication to the call control device  50   b  that is installed in a data center in New York (site B) as the connection destination (Step S 24 - 1 ). This request for starting a communication includes the communication IDs of the terminals ( 10   aa ,  10   ba ) as the requestor of starting communication, and the destination. The transceiver unit  51  of the call control device  50   b  transmits the received request for starting a communication to the terminal  10   ba  as the destination (Step S 24 - 2 ). 
     Having received the request for starting a communication, and depending on input to start the communication by a user, the terminal  10   ba  as the destination has the transceiver unit  11  transmit a response to indicate permission to start the communication to the call control device  50   b  (Step S 25 - 1 ). This response includes the communication IDs of the terminals ( 10   bb ,  10   aa ) as the requestor of starting communication, and the destination. The transceiver unit  51  of the call control device  50   b  transmits the received response to the call control device  50   a  (Step S 25 - 2 ). 
     Having received the response by the transceiver unit  51  of the call control device  50   a , the session control unit  58  selects one of the relay management devices  40  installed in the communication system  1 , to manage relaying contents data as a whole in a session to be established based on this request for starting the communication (Step S 26 ). A method of selecting a relay management device  40  is not specifically restricted, but possibly adopted among a method that selects a relay management device  40  installed at the site with which the terminal  10  as the requestor of starting the communication is connected, a method that selects a relay management device  40  installed at the site with which the terminal  10  as the communication destination is connected, a method that selects a relay management device  40  installed at an intermediate position between the site with which the terminal  10  as the requestor of starting the communication is connected, and the site with which the terminal  10  as the communication destination is connected, a selection method by a round robin method, a selection method based on a load balancing viewpoint, and the like. In the following description, it is assumed that the relay management device  40   a  installed at the site A is selected where the site A is connected with the terminal  10   aa  as the requestor of starting communication. 
     The transceiver unit  51  of the call control device  50   a  transmits session information about the session for contents data “sed” that is to be established between the terminals ( 10   aa ,  10   ba ) in response to the request by the terminal  10   aa , to the relay management device  40   a  of the relay system  3   a . This session information includes at least the communication IDs of the terminals ( 10   bb ,  10   aa ) as the requestor of starting communication, and the destination. Having received the session information, the relay management device  40   a  generates a session ID “S001” to identify the session. Also, the relay management device  40   a  associates the generated session ID with domain information “tokyo.conf.example.com” that represents the device itself, and transmits the associated session ID to the call control device  50   a  (Step S 28 ). Note that to make it easier for a user to understand at a terminal  10  to which the session ID is transmitted later, the “session (ID, information)” may be changed to an arbitrary term such as “conference (ID, information)”, “conference room (ID, information)”, or the like in the communication system  1 . 
     In the call control device  50   a  having received the session ID and domain information, the management unit  53  makes a request to the session management device  60  via the transceiver unit  51 , to manage the communication IDs of the terminals ( 10   bb ,  10   aa ) as the requestor of starting communication and the destination to have the session ID and domain information “S001@tokyo.conf.example.com” in the terminal management table (see  FIG. 6B ) (Step S 29 ). In response to the request from the call control device  50   a , the storage/read unit  69  of the session management device  60  updates the terminal management table. 
     Next, the call control device  50   a  transmits the session ID “S001” received at Step S 28  to the terminal  10   aa  as the requestor for starting the communication (Step S 30 ). Also, the call control device  50   a  transmits the session ID and domain information “S001@tokyo.conf.example.com” received at Step S 28 , and the communication ID of the terminal  10   ba  as the destination, to the call control device  50   b  connected with the terminal  10   ba  as the destination (Step S 31 - 1 ). 
     The transceiver unit  51  of the call control device  50   b  transmits the session ID and domain information “S001@tokyo.conf.example.com”, transmitted from the call control device  50   a , to the terminal  10   ba  as the destination (Step S 31 - 2 ). Also, the transceiver unit  51  of the call control device  50   b  transmits the communication ID of the terminal  10   ba  as the destination transmitted from the call control device  50   a , to the relay management device  40   b  constituting the relay system  3   b  (Step S 32 ). 
     In the communication system  1 , a terminal  10  connects with a relay management device  40  at the site which the call control device  50  belongs to, with which the terminal is connected. Namely, the terminal  10   aa  as the requestor for starting the communication makes a connection with the relay management device  40   a , by transmitting the communication ID of its own to the relay management device  40   a  that is installed at the site A which the call control device  50   a  belongs to, with which the terminal  10   aa  is connected. Next, the transceiver unit  11  of the terminal  10   aa  transmits the session ID transmitted from the call control device  50   a  and the communication ID of its own, to the relay management device  40   a , to make a request for participating in the session for contents data “sed” identified by this session ID (Step S 33 ). 
     Having received the request for participation, the relay management device  40   a  allocates a relay device  30  to relay contents data in this session among the relay devices  30  under its management, and has the allocated relay device  30  (referred to as the “relay device  30   aa ”, below) connected with the terminal  10   aa  as the requestor of the participation. This makes it possible for the terminal  10   aa  to transmit contents data generated by itself to the relay device  30   aa.    
     On the other hand, the terminal  10   ba  as the destination transmits the communication ID of its own to the relay management device  40   b  that is installed at the site B which the call control device  50   b  belongs to, with which the terminal  10   ba  is connected. The relay management device  40   b  permits the connection if the communication ID transmitted from the terminal  10   ba  is the same as the communication ID transmitted from the call control device  50   b . After having been connected, the transceiver unit  11  of the terminal  10   ba  transmits the session ID and domain information transmitted from the call control device  50   b  and the communication ID of its own, to the relay management device  40   b , to make a request for participating in the session for contents data “sed” identified by this session ID (Step S 34 ). 
     Having received the request for participation, the relay management device  40   b  allocates a relay device  30  to relay contents data in this session among the relay devices  30  under its management, and has the allocated relay device  30  (referred to as the “relay device  30   ba ”, below) connected with the terminal  10   ba  as the destination. This makes it possible for the terminal  10   ba  to transmit contents data generated by itself to the relay device  30   ba.    
     Next, the relay management device  40   b  transmits a request for participation to the relay device  40   b  based on the domain information included in the request for participation transmitted from the terminal  10   ba  (Step S 35 ). This request for participation includes the communication ID and session ID of the terminal  10   ba  included in the request for participation transmitted from the terminal  10   ba , and the relay device ID of the relay device  30   ba  that has been allocated by itself. 
     The relay management device  40   a  transmits relay management information used for managing relaying contents data, to the relay management device  40   b . This relay management information includes information about a relay destination of contents data to be relayed by the relay device  30   ba  allocated by the relay management device  40   b . Based on the relay management information, the relay management device  40   b  manages the relay device  30   ba  to transmit the contents data transmitted from the relay device  30   aa  to the terminal  10   ba , and to transmit the contents data transmitted from the terminal  10   ba  to the relay device  30   aa.    
     On the other hand, based on the relay device ID transmitted from the relay management device  40   b , the relay management device  40   a  manages the relay device  30   aa  to transmit contents data transmitted from the relay device  30   ba  to terminal  10   aa , and to transmit contents data transmitted from terminal  10   aa  to the relay device  30   ba.    
     The process described above establishes the session for contents data “sed” to transmit contents data between the terminals ( 10   aa ,  10   ba ) via the relay devices ( 30   aa ,  30   ba ). 
     Next, a process will be described using FIG.  10  in which the terminal  10   bb  participates in the session for contents data “sed” established between the terminals ( 10   aa ,  10   ba ). Note that  FIG. 10  is a sequence chart illustrating a process in which the terminal  10   bb  participates in the session for contents data “sed”. In the following, a case will be described where the terminal  10   bb  has been connected with the call control device  50   b  by a login process. 
     In response to an operation on the operational buttons  108  by a user, the terminal  10   bb  has the transceiver unit  11  make a request for starting a communication, to the call control device  50   b  (Step S 41 ). This request for starting a communication includes the communication ID “01ba” of the terminal  10   bb  as the requestor of starting communication, and the communication ID “01aa” of the terminal  10   aa  as the destination. 
     The transceiver unit  51  of the call control device  50   b  receives the request for starting a communication. Next, the management unit  53  of the call control device  50   b  makes a request to the session management device  60  via the transceiver unit  51 , to manage the communication IDs of the terminals ( 10   aa ,  10   bb ) as the requestor of starting communication, and the destination, respectively, in the terminal management table (see  FIG. 6B ), to have a communication state of “Busy” (Step S 42 ). In response to the request by the call control device  50   b , the storage/read unit  69  of the session management device  60  updates the terminal management table. 
     Next, the session control unit  58  of the call control device  50   b  makes a query to the session management device  60  via the transceiver unit  51 , about the connection destination associated with the communication ID of the terminal  10   aa  as the destination in the terminal management table (see  FIG. 6B ) (Step S 43 ). In response to the request, the storage/read unit  69  of the session management device reads the connection destination “Tokyo” associated with communication ID “01aa” of the terminal  10   aa  as the destination in the terminal management table. The transceiver unit  61  of the session management device  60  transmits the read out connection destination to the call control device  50   b.    
     Next, based on the connection destination transmitted from the session management device  60 , the transceiver unit  51  of the call control device  50   b  transmits a request for starting a communication to the call control device  50   a  that is installed in a data center in Tokyo (site A) as the connection destination (Step S 44 - 1 ). This request for starting a communication includes the communication IDs of the terminals ( 10   bb ,  10   aa ) as the requestor of starting communication, and the destination. The transceiver unit  51  of the call control device  50   a  transmits the received request for starting a communication to the terminal  10   aa  as the destination (Step S 44 - 2 ) Having received the request for starting a communication, and depending on input to start the communication by a user, the terminal  10   aa  as the destination transmits a response to indicate permission to start the communication to the call control device  50   a  (Step S 45 - 1 ). 
     Having received the response indicating the permission to start, the transceiver unit  51  of the call control device  50   a  transmits the session ID generated by the relay management device  40   a  managing contents data, the domain information of the relay management device  40   a  (see Step S 28 ), and the communication ID of the terminal  10   bb  as the requestor for starting the communication, to the call control device  50   b , in the session for contents data participates (Step S 46 - 1 ). 
     The transceiver unit  51  of the call control device  50   b  transmits the session ID and domain information “S001@tokyo.conf.example.com”, transmitted from the call control device  50   a , to the terminal  10   bb  as the destination (Step S 46 - 2 ). Also, the transceiver unit  51  of the call control device  50   b  transmits the communication ID of the terminal  10   bb  transmitted from the call control device  50   a , to the relay management device  40   b  constituting the relay system  3   b  (Step S 47 ). 
     The terminal  10   bb  as the requestor for starting the communication transmits the communication ID of its own to the relay management device  40   b  that is installed at the site B which the call control device  50   b  belongs to. The relay management device  40   b  permits the connection if the communication ID transmitted from the terminal  10   bb  is the same as the communication ID transmitted from the call control device  50   b . After having been connected, the transceiver unit  11  of the terminal  10   bb  transmits the session ID and domain information transmitted from the call control device  50   b  and the communication ID of its own, to the relay management device  40   b , to make a request for participating in the session for contents data “sed” identified by this session ID (Step S 48 ). 
     Having received the request for participation, the relay management device  40   b  allocates a relay device  30   ba  among the relay devices under its management, to relay contents data in this session for contents data “sed”, and has the relay device  30   ba  connect with the terminal  10   bb  as the destination. This makes it possible for the terminal  10   bb  to transmit contents data generated by itself to the relay device  30   ba.    
     Next, the relay management device  40   b  transmits a request for participation to the relay device  40   b , based on the domain information included in the request for participation transmitted from the terminal  10   bb  (Step S 49 ). This request for participation includes the communication ID and session ID of the terminal  10   bb  included in the request for participation transmitted from the terminal  10   bb , and the relay device ID of the relay device  30   ba.    
     The relay management device  40   a  transmits relay management information used for managing relaying contents data, to the relay management device  40   b . This relay management information includes information about a relay destination of contents data to be relayed by the relay device  30   ba  allocated by the relay management device  40   b . Based on the relay management information, the relay management device  40   b  manages the relay device  30   ba  to transmit contents data transmitted from the relay device  30   aa  to the terminals ( 10   ba ,  10   bb ), to transmit contents data transmitted from the terminal  10   ba  to the relay device  30   aa  and terminal  10   bb , and to transmit contents data transmitted from the terminal  10   bb  to the relay device  30   aa  and terminal  10   ba . On the other hand, in response to the request for participation transmitted from the relay management device  40   b , the relay management device  40   a  manages the relay device  30   aa  to transmit contents data transmitted from the relay device  30   ba  to terminal  10   aa , and to transmit contents data transmitted from the terminal  10   aa  to the relay device  30   ba.    
     The process described above establishes the session for contents data “sed” to transmit contents data among the terminals ( 10   aa ,  10   ba ,  10   bb ) via the relay devices ( 30   aa ,  30   ba ). 
     &lt;&lt;Effects of Embodiment&gt;&gt; 
     Next, major effects of the above embodiments will be described. 
     The management system  5  (an example of a session control system) controls establishing a session for contents data “sed” to transmit contents data in the communication system  1  including multiple relay management devices  40  to manage relaying contents data transmitted from terminals  10 . The session control unit  58  (an example of a selection unit) of the call control device  50  constituting the management system  5  selects a relay management device  40  to manage relaying contents data among multiple relay management devices  40  for every session for contents data “sed” to be established. The transceiver unit  51  (an example of a transmitter unit) of the call control device  50  transmits domain information of the relay management device  40  selected by the session control unit  58  (an example of selection information representing a selected relay management device), to at least a terminal  10  connected with a relay management device  40  different from the relay management device  40  selected by the session control unit  58 , among terminals  10  participating in the session for contents data “sed” to be established. 
     The terminal  10  having the domain information received can start a session, without receiving information representing a selected relay management device  40  as input from a user, even if not connected with the relay management device  40  selected by the call control device  50 , and hence, the load can be reduced for the starting process. 
     The terminal management DB  6002  (an example of connection information management unit) of the session management device  60  constituting the management system  5  manages a site (an example of connection information representing a relay management device) which the relay management device  40  connected with this terminal  10  belongs to, by associating it with the communication ID of the terminal  10 . If the relay management device  40  selected by the session control unit  58  is different from the relay management device  40  represented by the connection destination in the terminal management DB  6002 , having been associated with the communication ID of the terminal  10  participating in the session for contents data “sed”, the transceiver unit  51  transmits the domain information of the relay management device  40  selected by the session control unit  58  to the terminal  10  participating in the session for contents data “sed”. 
     Thus, even if the terminal  10  is connected with a relay management device  40  that may differ every time a session is to be established, the call control device  50  can transmit domain information appropriately, based on the connection destination managed in the terminal management DB  6002 . 
     The respective transceiver units  51  (an example of multiple login request reception units) of the call control devices ( 50   a ,  50   b ) receive login requests from terminals  10 , respectively. 
     Depending on a transceiver unit ( 50   a ,  50   b ) that has received a login request by a terminal  10 , the management unit  53  (an example of connection information management unit) manages a site (for example, Tokyo or New York) which the relay management device  40  belongs to, as the connection destination of the terminal  10  in the terminal management DB  6002 . 
     Thus, even if the terminal  10  is connected with a relay management device  40  that may differ every time a session is to be established, the call control device  50  can transmit domain information to an appropriate terminal  10 , based on the connection destination managed in the terminal management DB  6002 . 
     The terminal management DB  6002  (an example of a relay management unit) associates the communication ID (an example of identification information) of the terminal  10 , with domain information of the relay management device  40  selected by the session control unit  58 , to manage them. The transceiver unit  51  (an example of a start-request reception unit) receives a request for starting a communication between a terminal  10  as a requestor of starting the communication, and a terminal  10  as a destination. 
     If the relay management device  40  represented by domain information of the relay management device that is managed in the terminal management DB  6002  by having been associated with the communication ID of the terminal  10  as the destination, is different from the relay management device  40  represented by the connection destination that is managed in the terminal management DB  6002  by having been associated with the communication ID of the terminal  10  as the requestor of starting communication terminal  10 , the transceiver unit  51  transmits domain information representing the relay management device  40  selected by the session control unit  58  to the terminal  10  as the requestor for starting the communication. 
     Thus, when receiving a request for starting communication that specifies a terminal  10  participating in a session for contents data “sed” as the destination, the transceiver unit  51  can transmit a request for starting the communication, with the domain information of the relay management device  40  that manages relaying contents data in the session for contents data “sed”. 
     The transceiver unit  11  (an example of a selection information receiver unit) of the terminal  10  receives domain information transmitted by the call control device  50 . The transceiver unit  11  (an example of a participation request unit and a selection information transmitter unit) of the terminal  10  transmits domain information to the relay management device  40 , with which the terminal  10  itself is connected, when making a request for participating in a session for contents data “sed” to the connected relay management device  40 . Thus, the connected relay management device  40  can transmit the request for participation to the relay management device  40  designated by the domain information. 
     &lt;&lt;Supplementary Features of Embodiment&gt;&gt; 
     The programs for the terminal  10  and the call control device  50  may be recorded on computer-readable recording media, such as the recording medium  106 , to be distributable and as files installable or executable on a computer. Other examples of the recording media include CD-R (Compact Disc Recordable), DVD (Digital Versatile Disk), and Blu-ray Disc. 
     Also, the call control device  50  in the above embodiments may be installed on a single computer, or may be divided into parts (functional units) to be installed on multiple computers. 
     Also, the call control device  50  and the session management device  60  may be installed on a single computer. 
     A recording medium, such as a CD-ROM, or a hard disk that stores the programs according to the embodiments can be offered as a program product domestically or overseas. 
     Also, although a video-conference terminal has been described as a call terminal as an example of the terminal  10 , it is not limited to that as long as mutual communication is possible. For example, the terminal  10  may be an IP (Internet Protocol) telephone, an Internet telephone, or a PC (Personal Computer). Also, the terminal  10  may be a projector, an electronic signboard (digital signage), or an interactive whiteboard. 
     Furthermore, although the above embodiments have been described about a call made by a terminal (an intermediate concept) such as a video-conference terminal (a subordinate concept), it is not limited to that as long as communication can be made, based on a broader concept including a call. For example, it may be applicable when an application autonomously accesses a server at a data center to transmit or obtain various data. In this case, the counterpart may not be a terminal, but a server. Also, terminals include a game machine and a car navigation device. 
     The present invention can be implemented in any convenient form, for example using dedicated hardware, or a mixture of dedicated hardware and software. The present invention may be implemented as computer software implemented by one or more networked processing apparatuses. The network can comprise any conventional terrestrial or wireless communications network, such as the Internet. The processing apparatuses can be comprised of any suitably programmed apparatuses such as a general purpose computer, a personal digital assistant, a mobile telephone (such as a WAP or 3G-compliant phone) and so on. Since the present invention can be implemented as software, each and every aspect of the present invention thus encompasses computer software implementable on a programmable device. (For EP) The computer software can be provided to the programmable device using any conventional carrier medium. The carrier medium can be comprised of a transient carrier medium such as an electrical, optical, microwave, acoustic or radio frequency signal carrying the computer code. An example of such a transient medium is a TCP/IP signal carrying computer code over an IP network, such as the Internet. The carrier medium can also be comprised of a storage medium for storing processor readable code such as a floppy disk, a hard disk, a CD ROM, a magnetic tape device or a solid state memory device. (FOR US) The computer software can be provided to the programmable device using any storage medium for storing processor readable code such as a floppy disk, a hard disk, a CD ROM, a magnetic tape device or a solid state memory device. 
     The hardware platform includes any desired kind of hardware resources including, for example, a central processing unit (CPU), a random access memory (RAM), and a hard disk drive (HDD). The CPU may be implemented by any desired kind of any desired number of processors. The RAM may be implemented by any desired kind of volatile memory or both volatile and non-volatile memory. The HDD may be implemented by any desired kind of non-volatile memory capable of storing a large amount of data. The hardware resources may additionally include an input device, an output device, or a network device, depending on the type of the apparatus. Alternatively, the HDD may be provided outside of the apparatus as long as the HDD is accessible. In this example, the CPU, such as a cache memory of the CPU, and the RAM may function as a physical memory or a primary memory of the apparatus, while the HDD may function as a secondary memory of the apparatus. 
     RELATED-ART DOCUMENTS 
     Patent Documents 
     [Patent Document 1] Japanese Patent No. 4378651 
     The present application is based on and claims the benefit of priority of Japanese Priority Application No. 2014-190681 filed on Sep. 19, 2014, with the Japanese Patent Office, the entire contents of which are hereby incorporated by reference.