Abstract:
The present invention provides a communication system, a control apparatus, a program and a recording medium that controls participation in a session using presence information on participation member and information of the session itself. A communication system in which a plurality of communication terminals are connected to each other through a network to establish communication between the communication terminals has a presence information registering section that registers presence information of the communication terminals, a participation condition setting section that sets a participation condition for participating in the communication, a communication information managing section that manages communication information related to a state of the communication, and a communication control section that controls participation in and separation from the communication of the communication terminals.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a communication system, a control device, a control method, a program, and a recording medium in a form in which a plurality of users participate in one session like a PoC service or a PoC extended service, and more particularly, to a communication system, a control device, a control method, a program, and a recording medium that administer comings and goings of users based on a state of a session. 
         [0003]    2. Description of the Related Art 
         [0004]    In recent years, provision of the PoC (Push-to-talk over Cellular) service has been started. Users of the service gradually are increasing. The PoC service is a voice communication service. The voice communication indicates such a communication over transceivers. In the voice communication service, a plurality of users participates in one session, one of the users who obtains a speech right transmits voice, and the voice is transmitted to the other users. The service is well received at the following points. That is, a band is efficiently used, and communication among a plurality of persons is appropriately performed because voices are not mixed with each other. 
         [0005]    Some carriers advance the extension of the PoC service, for example, incorporating a multimedia PoC service. The OMA (Open Mobile Alliance), which is an international standard-setting organization, also begins to discuss the extension of services (for example, MA-RD-PoC-V2 — 0-20060112-D). 
         [0006]    Other than the PoC or the PoC extension, another communication service that is built on a session and lumps a plurality of users as participants in one session is spreading from an on-line game. 
         [0007]    Methods of selecting session members are roughly classified into three categories. The first method names members at the start point of a session. This method is often called an ad-hoc method. The second method selects a member in advance. This method is often called a pre-arranged method. The third method describes conditions to become a member. These three methods are used separately or combined. 
         [0008]    The third method often uses user information or presence information as a condition for participating in a session. For example, in a session for a user support, an employee corresponding to another user at that time is not accepted as a member of the session. When a response to the user ends, i.e., when the presence information changes, the employee is accepted as a member. 
         [0009]    As the above-mentioned conventional technique related to a communication service, the methods disclosed in Japanese Patent Application Laid-Open Nos. 2004-178000 (document 1), 2005-115537 (document 2), and 2005-309524 (document 3) are known. Document 1 discloses a reservation system, a reservation device, a reservation method, and a reservation program that automatically display reservation information, depending on an attribute of a user, on a screen, thereby accepting a reservation under a condition relating to the attribute. 
         [0010]    Document 2 describes a fire-monitoring system that sets a communication means or a warning means depending on various situations of family members and supports an observer&#39;s decision where to make a contact in an emergency. 
         [0011]    Furthermore, Document 3 describes an application server, a presence information providing method, and a program that protect privacy and establish real-time communication when presence information is provided. 
         [0012]    However, the methods of selecting and designating a session member in conventional communication based on a session as shown in documents 1 to 3 utilize user information such as a name (address). However, information of the session itself is not used. For this reason, in order to establish a session for playing a mah-jong game (a game usually played by four persons), a target session must be started after members are adjusted by another sub-system or the like to gather four members. 
       SUMMARY OF THE INVENTION 
       [0013]    In consideration of the above problems, it is an objective of the present invention to provide a communication system, a control device, a program and a recording medium that control participation in and separation from communication by using communication information and presence information. 
         [0014]    In order to achieve the above objective, provided is a communication system in which a plurality of communication terminals are connected to each other through a network to establish communication between the communication terminals, including presence information registering section that registers presence information of communication terminals, participation condition setting section that sets a participation condition for participating in the communication, communication information managing section that manages communication information related to a state of the communication, and communication control section that controls participation in and separation from the communication of the communication terminals. 
         [0015]    The communication control section may control participation in and separation from communication based on the presence information, the participation condition, and the communication information. 
         [0016]    When the presence information is changed in the communication system, the communication control section may control participation in and separation from the communication of the communication terminals with reference to the participation condition again. 
         [0017]    The communication control section may suspend the communication when the participation condition is not satisfied after the presence information is changed. 
         [0018]    When the participation condition is satisfied after the presence information is changed while the communication is suspended, the communication may be resumed. 
         [0019]    The participation condition setting section may add a participation condition to the communication already established. 
         [0020]    The communication control section may control participation in the communication based on the added new participation condition, the presence information, and the communication information. 
         [0021]    There is also provided a communication control device for controlling communication between communication terminals, comprising a participation condition setting section that sets a participation condition for participating in the communication, the communication information managing section that manages communication information related to a state of the communication, and the communication control section that controls participation in and separation from the communication of the communication terminals. 
         [0022]    The communication control section may control participation in and separation from the communication based on the presence information, the participation condition, and the communication information. 
         [0023]    When the presence information is changed, the communication control section may control participation in and separation from the communication of the communication terminals by referring to the participation condition again. 
         [0024]    The communication control section may suspend the communication when the participation condition is not satisfied after the presence information is changed. 
         [0025]    The communication may be resumed when the participation condition is satisfied after the presence information is changed while the communication is suspended. 
         [0026]    The participation condition setting section may add a new participation condition to the communication already established. 
         [0027]    The communication control section may control participation in the communication based on the added new participation condition, the presence information, and the communication information. 
         [0028]    There is also provided a method for controlling a communication system in which a plurality of communication terminals, a presence server that registers presence information of the communication terminals, and a communication control device that controls communication between the communication terminals are connected to each other through a network, comprising a participation condition setting step of setting a participation condition for participating in the communication, a communication information managing step of managing communication information related to a state of the communication, and the communication control step of controlling participation in and separation from the communication of the communication terminals. 
         [0029]    In the communication control step, participation in and separation from the communication may be controlled based on the presence information, the participation condition, and the communication information. 
         [0030]    When the presence information is changed, in the communication control step, participation in and separation from the communication of the communication terminals may be controlled by referring to the participation condition again. 
         [0031]    In the communication control step, when the participation condition is not satisfied after the presence information is changed by referring to the participation condition again, the communication may be suspended. 
         [0032]    The communication may be resumed when the participation condition is satisfied after the presence information is changed while the communication is suspended. 
         [0033]    In the participation condition setting step, a new participation condition may be added to the communication already established. 
         [0034]    In the communication control step, participation in the communication may be controlled based on the added new participation condition, the presence information, and the communication information. 
         [0035]    There is also provided a computer program for establishing communication between a plurality of communication terminals, causing a computer to perform a participation condition setting process of setting a participation condition for participating in the communication, a communication information managing process of managing communication information related to a state of the communication, and a communication control process of controlling participation in and separation from the communication of the communication terminals. 
         [0036]    In the communication control process, participation in and separation from the communication may be controlled based on the presence information, the participation condition, and the communication information. 
         [0037]    When the presence information is changed, in the communication control process, participation in and separation from the communication of the communication terminals may be controlled by referring to the participation condition again. 
         [0038]    In the communication control process, when the participation condition is not satisfied after the presence information is changed to refer to the participation condition again, the communication may be suspended. 
         [0039]    When the participation condition is satisfied after the presence information is changed while the communication is suspended, the communication may be resumed. 
         [0040]    In the participation condition setting process, a new participation condition may be added to the communication already established. 
         [0041]    In the communication control process, participation in the communication may be controlled based on the added new participation condition, the presence information, and the communication information. 
         [0042]    There is also provided a computer readable recording medium storing the program above. 
         [0043]    In this manner, according to the communication system, the control device, the control method, the program, and the recording medium of the present invention, since participation in and separation from communication are controlled with communication information and presence information, entries into communication can be more flexibly controlled. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0044]      FIG. 1  is a block diagram showing a communication system; 
           [0045]      FIG. 2  is a block diagram of an example of the communication system; 
           [0046]      FIG. 3  is a diagram showing an example of information registered in a presence server; 
           [0047]      FIG. 4  is a diagram showing an example of rules set in a participation rule control unit; 
           [0048]      FIG. 5  is a diagram showing session information obtained immediately after the start of a session; 
           [0049]      FIG. 6  is a diagram showing session information when users B and C participate in a session; 
           [0050]      FIG. 7  is a flow chart showing an operation of the communication system; 
           [0051]      FIG. 8  is a diagram showing the communication system when user B cannot come to work; 
           [0052]      FIG. 9  is a diagram showing session information obtained when user B is separated from the session; 
           [0053]      FIG. 10  is a diagram showing session information obtained when user D participates in the session; 
           [0054]      FIG. 11  is a flow chart showing an operation of the communication system when user B cannot come to work; 
           [0055]      FIG. 12  is a block diagram showing another example of the communication system; 
           [0056]      FIG. 13  is a diagram showing another example of information registered in a presence server; 
           [0057]      FIG. 14  is a diagram showing another example of a rule set in a participation rule control unit; 
           [0058]      FIG. 15  is a diagram showing another example of session information obtained immediately after the start of the session; 
           [0059]      FIG. 16  is a diagram showing a case in which a new rule is added to the rules set in  FIG. 14 ; 
           [0060]      FIG. 17  is a diagram showing session information obtained when user A is separated from the session; 
           [0061]      FIG. 18  is a diagram showing an example of a state of a session when a session is suspended; 
           [0062]      FIG. 19  is a diagram showing session information obtained when user B participates in a session; 
           [0063]      FIG. 20  is a flow chart showing anther example of the operation of the communication system; 
           [0064]      FIG. 21  is a block diagram showing another example of the communication system; 
           [0065]      FIG. 22  is a diagram showing still another example of rules set in a participation rule control unit; 
           [0066]      FIG. 23  is a diagram showing an example of session information in which a response order is set; and 
           [0067]      FIG. 24  is a flow chart showing still another example of the operation of the communication system. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0068]    A communication system, a control device, a control method, a program, and a recording medium according to this embodiment perform session control of participation of a member by combining session information related to a state of a session and presence information (user information) related to information of a participant in the session. 
         [0069]    The communication system, the control device, the control method, the program, and the recording medium will be described below with reference to the accompanying drawings. The embodiments are not limited to the following description and can be variably changed without departing from the spirit and scope of the embodiments. The presence information in the embodiments also includes general user information. 
         [0070]      FIG. 1  is a block diagram showing the communication system according to the embodiment. 
         [0071]    As shown in  FIG. 1 , the communication system includes a session control device  1 , a presence server  2 , and user terminals  3 A,  3 B,  3 C, and  3 D. The session control device  1  includes a participation control rule unit  11 , a session information managing unit  12 , and a session participation member control unit  13 . The presence server  2  includes a user information registering unit  21  that registers information of each of the user terminals  3 A,  3 B,  3 C, and  3 D. The user terminals  3 A to  3 D each include rule setting units  31   a  to  34   a  and terminal control units  31   b  to  34   b.    
         [0072]    The unit  11  controls rules related to a session. The participation into a session is controlled based on rules related to a session set by each of the user terminals  3 A to  3 D, each user information registered by the unit  21  of the presence server  2 , and information related to a present session state from the unit  12 . The rule set here may be directly set by each of the user terminals  3 A to  3 D or may be selected from rules set in advance in the session control device  1  by each of the user terminals  3 A to  3 D. 
         [0073]    The unit  12  is to manage session information. When a session state changes, the unit  12  notifies the participation control rule unit of the change. The unit  13  calls each of the user terminals  3 A to  3 D on the basis of a designation from the unit  11  to perform participation/nonparticipation, stoppage, continuation, or the like of the session. 
         [0074]    The presence server  2  includes the unit  21  and registers pieces of unique information of the user terminals  3 A to  3 D, respectively. When information (state) of a user terminal changes during a session, the change information is registered in the unit  21 . Depending on the registered change information, the unit  11  instructs the unit  13  to suspend or continue a session, or call a new session participant. 
         [0075]    Information unique to a user registered in the unit  21  may be provided from a communication terminal having a GPS (Global Positioning System) function, a security function, and the like. In case of the GPS function, user position information is updated and registered at any time by the unit  21  of the presence server  2  and then transmitted to the session control device  1  (unit  11 ). In case of the security function, for example, when a terminal goes through a security gate, the information that the terminal has gone through the gate is registered in the unit  21  and transmitted to the session control device  1 . In this manner, the user information is multilaterally updated at any time, so that the information of the session participant can be obtained in real time. 
         [0076]    The units  31   a  to  34   a  of the user terminals  3 A to  3 D set rules for regulating a session member to participate in a session. The rules may be set on the user terminals  3 A to  3 D, or may be selected by the user terminals  3 A to  3 D from rules set in advance in the unit  11  depending on a desired session format. 
         [0077]    An operation of the communication system will be described below with reference to the accompanying drawings. 
         [0078]      FIG. 2  is a block diagram showing an example of the communication system. In  FIG. 2 , four user terminals  3 A to  3 D are arranged, and pieces of information of the user terminals  3 A to  3 D are registered in a user information storing unit in the presence server  2 . Here, users A, B, C, and D (user terminals  3 A,  3 B,  3 C, and  3 D) are present. User A is assumed to be a manager of a shop, and users B, C, and D off-duty part-timers. 
         [0079]    An example of information registered in the presence server  2  is shown in  FIG. 3 . As the presence information, user&#39;s name, standing, today&#39;s plan, a present state, and the number of working days for this month are registered for each user. 
         [0080]    It is assumed that user A is notified that two part-timers on duty on that day cannot come. In this case, workers are short by two. Therefore, in order to find two workers, user A starts a session.  FIG. 7  is a flow chart showing an operation of the communication system. 
         [0081]    User A set a rule for the unit  11  (step S 101 ). Here, as the rule set by user A, it is designated (set) that “two part-timers who are not busy at present are called” and the session starts (step S 102 ). An example of a rule set at this time is shown in  FIG. 4 . Session information obtained immediately after the start is shown in  FIG. 5 . 
         [0082]    As shown in  FIG. 4 , rules are set as follows: [1] oneself (user A in this case) must be included; [2] as a condition for a member except for oneself, (i) the standing is a part-timer, (ii) today&#39;s schedule is off-duty, and (iii) the present state is “free”; and [3] the number of participants except for oneself=2, (a) an employee who works for many days is prioritized. As shown in  FIG. 5 , examples of session information immediately after the start of the session are the start time of the session, information of a session starter, and information of participants. 
         [0083]    In the unit  11 , information related to a rule designated by the user terminal  3 A is compared with information related to a session state in the unit  12  (step S 103 ) to determine whether the pieces of information match (step S 104 ). When the pieces of information match (Yes at step S 104 ), the session is terminated. 
         [0084]    When the pieces of information do not match (No at step S 104 ), the session control device  1  detects rules that are not fulfilled (step S 105 ). In this case, the rules [2] and [3] are not fulfilled. For this reason, a process to fulfill the rules [2] and [3] is started. 
         [0085]    In order to list up users who satisfy the rule [2], information of each user (user terminal) registered in the unit  21  of the presence server  2  is checked (step S 106 ). In this case, three persons B, C, and D correspond to users who satisfy “standing: part-timer, today&#39;s schedule: off-duty, and present state: free”. 
         [0086]    According to the rule [3], the condition designated by user A is that two participants except for oneself (A) participate. When the present session information from the unit  12  is viewed, “the number of participants in the present session except for (A)” is 0. Two more must be added. For this reason, two users are selected from the three users (B, C, and D). 
         [0087]    According to the condition (a) of the rule [3], users who work for many days in this month are preferentially selected. In this case, as the information of the unit  21 , the number of working days of the users are given by B: 8 days, C: 6 days, and D: 5 days. This time users B and C are selected (step S 107 ). 
         [0088]    When the users are selected in this manner, the unit  11  instructs the unit  13  to allow users B and C to enter the session (step S 108 ). The unit  13  calls users B and C (step S 109 ). It is checked whether users B and C give some response (step S 110 ). 
         [0089]    When there are responses (Yes at step S 110 ), the unit  13  notifies the unit  11  of the end of calling (step S 111 ). When users B and C participate in the session, as shown in  FIG. 6 , the number of participants in the session except for user A is two, and the condition of the rule [3] is satisfied. Therefore, the unit  13  temporarily stops the operation (step S 112 ). When users B and C accept coming to work (Yes at step S 113 ), user A ends the session. 
         [0090]    On the other hand, when there is no response from user B or C (No at step S 110 ), or when users B and C do not accept coming to work, i.e., when members are not determined (No at step S 113 ), the flow goes to step S 106  to re-check information of members (users). 
         [0091]    An operation performed when user B cannot come to work will be described.  FIG. 8  is a diagram showing a communication system according to an embodiment when user B cannot come to work.  FIG. 11  is a flow chart showing an operation of the communication system when user B cannot come to work. 
         [0092]    When user B is not available, the rules in the unit  11  of user A are not changed, and the unit  13  separates user B from the session (step S 201 ). The unit  13  may separate user B from the session, or user B may voluntarily disengage from the session. 
         [0093]    When user B is separated from the session, as shown in  FIG. 9 , the session state in the unit  12  changes, the number of called users except for user A is one, i.e., only user C. At this point, the unit  13  restarts the process (step S 202 ). 
         [0094]    The process performed after the restart by the unit  13  is almost the same as the process started from step  105  described above. More specifically, the unit  11  detects rules that are not satisfied (step S 203 ). In this case, it is detected that rule [3] is not satisfied. Therefore, the process to satisfy the rule [3] is started. 
         [0095]    When a user who satisfies the rule [2] is sought according to the information of the unit  21 , users B, C, and D meet the requirement. However, when session information from the unit  12  is checked, it is found that user B has disengaged from the session, and user C is being in the session. Therefore, the remaining candidate for the members is user D. 
         [0096]    Therefore, the unit  13  selects user D as a user to be newly called (step S 204 ). The unit  11  instructs the unit  13  to call user D (step S 205 ). The unit  13  calls user D (step S 206 ). It is checked whether there is some response from user D (step S 207 ). 
         [0097]    When there is a response from user D (Yes at step S 207 ), the unit  13  notifies the unit  11  of the end of calling (step S 208 ). When user D participates in the session, as shown in  FIG. 10 , the number of participants in the session except for user A is two, and the condition of the rule [3] is satisfied. Therefore, the unit  13  temporary stops the operation (step S 209 ). When user D accepts to come to work (Yes at step S 210 ), user A ends the session. 
         [0098]    On the other hand, when there is no response from user D (No at step S 207 ), or when user D does not accept coming to work, i.e., when the members are not determined (No at step S 210 ), the flow goes to step S 204  to select members (users) again. 
         [0099]    In this manner, according to the communication system, the session can be maintained in a state desired by user A. 
         [0100]    Another operation of the communication system will be described below. 
         [0101]      FIG. 12  is a block diagram showing another example of the communication system. In the following explanation, it is assumed that users A, B, C, and D (user terminals  3 A,  3 B,  3 C, and  3 D) are present and that users A and B are in administrative position, and users C and D are regular employees. An example of information registered in the presence server  2  is shown in  FIG. 13 . As presence information, a user name, a rank, and a present state are registered for each user. 
         [0102]    It is assumed that user A wishes to hold a meeting by members of a group. Further, it is assumed a member who is seeing his/her customer is not called until the member ends a meeting with his/her customer. 
         [0103]      FIG. 20  is a flow chart showing anther example of the operation of the communication system. 
         [0104]    First, user A sets rules to the unit  11  (step S 301 ). In this case, a condition that “a user is a group member and is not meeting his/her customer” is set in the unit  11  to start a session (step S 302 ). An example of the rules is shown in  FIG. 14 . Session information obtained immediately after the start is shown in  FIG. 15 . 
         [0105]      FIG. 14  shows rules: [1] four users A, B, C, and D are targeted, [2] as a condition for a member, (i) the present state is not “in-meeting”. As shown in  FIG. 15 , the start time of a session, information of a session starter, and information of session participants are used. 
         [0106]    In the unit  11 , information related to a rule designated by the user terminal  3 A is compared with information related to a session state in the unit  12  to check users A, B, C, and D (step S 303 ). User A has participated in the session, and user B is seeing his/her customer. Therefore, in order to satisfy the above condition, users C and D must participate in the session. Therefore, the unit  11  instructs the unit  13  to call users C and D. In response to this instruction, the unit  13  calls users C and D (step S 304 ). The operation until now is almost the same as that of the above embodiments. 
         [0107]    It is assumed that while the meeting is continued by users A, C, and D, discussion about budget starts. It is also assumed that in this group, a person in an administrative position (executive) must be involved in any decision concerning the budget. As shown in  FIG. 16 , user A adds a rule that [3] at least one of session participants is “rank=executive”, (i) when the condition is satisfied, the session continues, (ii) when the condition is not satisfied, the session suspended (step S 305 ). 
         [0108]    On the basis of the rule changed as described above, the session control device  1  acquires a list of session participants in the session information from a session information managing device  4  (step S 306 ). In this case, a list of three users A, C, and D are obtained. Registration information of users A, C, and D is acquired from the presence server  2  to check rules and conditions. Since user A is “rank=executive”, the conditions in the rule [3] are satisfied, and the session continues. 
         [0109]    It is assumed that user A is to meet his/her customer. User A changes his/her presence information into “in-meeting” (step S 307 ). The unit  11  is notified that registration information of user A in the unit  21 , i.e., the presence information has changed, and the unit  11  re-checks information related to the rule and information related to the session state on the basis of the notification from the unit  21  (step S 308 ). 
         [0110]    As a result of the re-checking, user A the present state of which is “in-meeting” is separated from the session on the basis of the rule [2], and the unit  11  instructs the unit  13  to separate user A from the session (step S 309 ). The unit  13  separates user A from the session (step S 310 ). 
         [0111]    Users remaining in the session are two, i.e., users C and D, and the session information shown in  FIG. 17  is obtained. The unit  11  acquires a list of session participation users from the unit  12  (step S 311 ). Two users C and D appears in the list. Registration information of users C and D is acquired from the unit  21  to check the rule and the condition (step S 312 ). Both users C and D are “rank=regular employee”, and “rank=executive” is not present. Therefore, on the basis of the condition of the rule [3], the unit  11  instructs the unit  13  to stop the session to put the unit  13  in abeyance (step S 313 ). The state of the session at this point is shown in  FIG. 18 . 
         [0112]    Furthermore, it is assumed that meeting between a customer and user B is over and that presence information of user B becomes “normal” (step S 314 ). The unit  11  is notified that the registration information of user B in the unit  21 , i.e., the presence information, has changed. On the basis of the notification from the unit  21 , the unit  11  re-checks information related to the rule and information related to the session information (step S 315 ). 
         [0113]    As a result of the re-checking, user B the present state of which is “normal” is to participate in the session on the basis of the rule [2]. The unit  11  instructs the unit  13  to put user B in the session (step S 316 ). The unit  13  puts user B in the session (step S 317 ). 
         [0114]    As a result, users participating in the session are three, i.e., users B, C, and D, and the session information shown in  FIG. 19  is obtained. The unit  11  acquires a list of session participation users from the unit  12  (step S 318 ). Three users B, C, and D appear in the list. Registration information of users B, C, and D is acquired from the unit  21  to check the rule and the condition (step S 319 ). 
         [0115]    Since user B is “rank=executive”, the session is resumed on the basis of the condition of the rule [3]. More specifically, the unit  11  instructs the unit  13  to resume the session to set the unit  13  in a continuation state (step S 320 ). 
         [0116]    In this manner, user A maintains a session in a desired state. Furthermore, when necessary conditions are not satisfied, the session is temporarily stopped. When the conditions are satisfied, the session can be resumed. 
         [0117]    Still another operation of a communication system will be described below. 
         [0118]      FIG. 21  is a block diagram showing another example of a communication system. It is assumed that users A, B, C, and D (user terminals A, B, C, and D) and a customer (terminal of customer)  4  are present, user A is a team leader, and users B, C, and D are regular members. 
         [0119]    When a customer requests a session, user A arranges that one of the members see the customer. An order is determined in consideration of factors such as a degree of busyness, a situation of another work, and the like. 
         [0120]      FIG. 24  is a flow chart showing still another example of the operation of a communication system. 
         [0121]    First, user A sets rules to the unit  11  (step S 401 ). Here user A sets a rule that “when a customer requests a session to be started, a member to participate in the session is one who is not seeing a customer and has the highest rank in a response order set by a presence server”. At the same time, a response order is set in the unit  21 .  FIG. 22  shows an example of rules.  FIG. 23  shows a relationship between presence information of each user and a “response order”. 
         [0122]    As shown in  FIG. 22 , rules for responding members are: [1] the present state is not “in-meeting”; [2] one person is needed; and [3] a response order is arranged according to a response order setting in the unit  21  of the presence server  2 . As the presence information in the unit  21 , user names, present information of each user, and response order settings are registered. 
         [0123]    When the customer terminal  4  requests a session (step S 402 ), the unit  12  notifies the unit  11  that the customer terminal  4  requested a session (step S 403 ). The unit  11  chooses participants by using the information of the unit  21  according to the rules shown in  FIG. 22  (step S 404 ). 
         [0124]    A user who is not seeing his/her customer is selected according to the rule [1], and appropriate users are “users A, B, and C”. According to the rule [3], an order decided based on the response order setting is by “D, C, B, and A”. According to the rule [2], since one person is needed, user C is selected. 
         [0125]    When the unit  11  determines that user C participates in a session, the unit  11  instructs the unit  13  to allow user C to participate in the session (step S 405 ). The unit  13  invites user C to participate in a session with the customer terminal  4  (step S 406 ). 
         [0126]    In this manner, user A can start a session under desired conditions. When user A changes an order (ranking), priorities of members who respond to customers can be changed without changing rules. 
         [0127]    As described above, the communication system, the control device, the control method, the program, and the recording medium of the embodiments use information of a session to control participants in a session and the session itself, and realize a flexible and useful session. More specifically, since not only the presence information of members but also information of a session itself is used to control group members, a participation control rule unit can use the session information to set conditions. In this way, more flexible group member participation control can be performed. 
         [0128]    The embodiments are not limited to the above explanations. For example, the number of users may be five or more. In the embodiments, a business scene is considered. However, general consumers may be targeted. In the embodiments, user information, presence information, and preference information (response order) are stored in a presence server. However, these pieces of information each may be stored in different servers. 
         [0129]    The presence information, the response order, and the like registered in the unit  21  of the presence server  2  are not limited to those explained in the embodiments. The information and the response order can be properly changed by a user depending on a desired session. This is also applied to rules to be set, and various rules corresponding to modes of sessions can be chosen. 
         [0130]    A communication system, a control device, a control method, a program, and a recording medium according to the present invention can also be applied to a general-purpose communication operator, a business communication device manufacturers, service suppliers, and the like.