Abstract:
A method for notifying block information applicable to an instant messaging (IM) system employing Session Initiation Protocol (SIP)/SIP for Instant Messaging and Presence Leveraging Extensions (SIMPLE) is disclosed. The method includes: a new user joining an activated instant messaging system; a server obtaining a user block list, and determining a block relationship between the new user and an existing user; sending a message to the existing user notifying that a blocked user has joined the instant messaging system, or a message to the new user notifying that a blocked user is in the instant messaging system. With the method, a client of the SIP/SIMPLE IM system is able to obtain the block relationship between users in the IM system, so that the IM system may be improved.

Description:
[0001]    This application claims priority of Chinese Application No. 200610006587.2 submitted on Jan. 11, 2006, entitled by “A METHOD FOR NOTIFYING BLOCK INFORMATION IN A CHAT ROOM”, the content of which is incorporated herein by reference. 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates to communications, information and Internet technologies, and particularly, to a method for determining whether a user blocks other users and for notifying the user in an Instant Messaging system. More particularly, the present invention relates to a method and system for instant notification of communication block information. 
       BACKGROUND OF THE INVENTION 
       [0003]    The present invention relates to Instant Messaging (IM) services over mobile communication networks and Internet. The mobile communication networks include existing 2G (2nd Generation) and 2.5G mobile networks, future 3G (3rd Generation) mobile communication network and IP Multimedia Subsystem (IMS) etc. 
         [0004]    The IM service is a mobile data service of person-to-person or person-to-group message-type based on presence service. 
         [0005]    An international standard organization, Open Mobile Alliance (OMA), has developed a standard for mobile IM. There are two types of IM systems in the standard of current version. The first type is Wireless Village (WV)-based IM system, the WV-based IM system is based on protocols borne over Hyper Text Transfer Protocol/Wireless Access Protocol/Short Message Service (HTTP/WAP/SMS) and supports 2.5G/3G networks. The second type is Session Initiation Protocol (SIP)/SIP for Instant Messaging and Presence Leveraging Extensions (SIMPLE)-based IM system, which is based on protocols borne over SIP/SIMPLE and supports IMS-based IP networks. 
         [0006]    In an SIP/SIMPLE-based IM system, particularly in a chat room system in SIMPLE IM system, there may be such a scenario: assuming there is a chat room of SIMPLE IM which is activated, and a new user is joining the chat room, if user M in the chat room has blocked the new user, the chat room will notify the user M that the new user which he has blocked has joined the chat room. On the other hand, if the new user has blocked a user which is already in the chat room, the chat room will notify the new user that the user which he has blocked is present in the chat room. 
         [0007]    In this application document, the “block” is similar to a blacklist. When a user A lists a user B in user A&#39;s block list, the user B is not able to send instant messages to the user A. In this situation, the user A is called a blocking party and the user B is called a blocked party. The concept of the “block”, put forward in the WV-based IMPS, is of similar meaning as that of the “block” in the SIP/SIMPLE IM. 
         [0008]    In the IMPS system based on WV protocol and SIP/SIMPLE IM standard, there is a related block technology mainly including: a user A may arrange and manage its own block list at a server, and the server controls users contained in the block list so that these users in the list can not interchange instant messages with the user A. But the technology for notifying a blocking party in a chat room has not been mentioned in the IMPS system based on WV protocol and SIP/SIMPLE IM standard. 
         [0009]    In the prior art, the instant messaging system conforming to the SIP/SIMPLE IM standard does not provide a method for determining block relationship between users and notifying block information in a chat room system. 
       SUMMARY OF THE INVENTION 
       [0010]    Embodiments of the present invention provide a method for determining block relationship between users and notifying block information in an instant communication system, so as to determine the block relationship between the users and notifying the block information. 
         [0011]    An embodiment of the present invention provides a method for notifying block information. The method includes: 
         [0012]    obtaining, by an instant messaging control server, a block relationship between the a new user and an existing user when the new user joins an instant messaging system; 
         [0013]    determining, by the instant messaging control server, whether to sending a notification message containing block information to a client of blocking party according to the obtained block relationship, and sending the notification message if there is a block relationship between the new user and the existing user. 
         [0014]    Preferably, the block relationship between the new user and the existing user is contained in a user block list in the instant messaging control server. A method for notifying block information includes: 
         [0015]    determining, by a user home instant messaging server, whether there is a block relationship between the new user and an existing user when the new user joins an instant messaging system according to a user block list stored in the user home instant messaging server, and sending a notification message containing block information to a client of blocking party if there is a block relationship between the new user and the existing user. Another method for notifying block information includes: 
         [0016]    determining whether the new user or an existing user is blocked according to a stored or obtained user block list by a client of a user when the new user joins an instant messaging system, and if the new user or an existing user is blocked, presenting block information to the client, the user being one of the new user or the existing user. 
         [0017]    The client determines whether there is a block relationship according to a received state change notification message of the instant messaging system, the state change notification message is sent from a control server to the client of the user in the instant messaging system after the new user joins the instant messaging system, and the state change notification message is subscribed by the user. 
         [0018]    An instant messaging system is provided, the system includes: 
         [0019]    an instant messaging terminal, for joining an instant messaging system, and for receiving a notification message containing block information; 
         [0020]    an instant messaging control server, for accepting a new user corresponding to the instant messaging terminal to join the activated instant messaging system, obtaining a block relationship between the new user and an existing user, sending the notification message containing the block information to a client of blocking party according to the obtained block relationship, and sending the notification message if there is a block relationship between the new user and the existing user. 
         [0021]    In summary, in the technical solution according to an embodiment of the present invention, the IM control server determines whether to send a notification message containing the block information to the client of the blocking party according to the block relationship between the new user and the existing user. If there is a block relationship between the new user and the existing user, the IM control server sends the notification message. The client may determine whether the new user or the existing user is blocked according to a stored or obtained user block list. If the new user or the existing user is blocked, the client presents the block information. In this way, when a SIP/SIMPLE IM user joins an IM system (for example, a chat room), the newly joined user or an existing user may be notified whether a blocked user is in the chat room. Accordingly, the SIP/SIMPLE IM system is enabled to support the whole solution with respect to the chat room service, and the user experience may be improved. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]      FIG. 1  is a schematic diagram illustrating the structure of a chat room system according to an embodiment of the present invention; 
           [0023]      FIG. 2  is a schematic diagram illustrating an overall flow of an exemplary embodiment of the present invention; 
           [0024]      FIG. 3  is a flow diagram illustrating a client joining a chat room according to an embodiment of the present invention; 
           [0025]      FIG. 4  is a flow diagram illustrating a control server sending block information to a user already in the chat room according to an embodiment of the present invention; 
           [0026]      FIG. 5  is a flow diagram illustrating the home IM server of a user sending block information to a user already in the chat room according to an embodiment of the present invention; 
           [0027]      FIG. 6  is a flow diagram illustrating a control server sending block information to a newly joined user according to an embodiment of the present invention; 
           [0028]      FIG. 7  is a flow diagram illustrating the home IM server of a user sending block information to a newly joined user according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0029]    For a better understanding of the principle, features of the invention would be given in detailed description below by way of examples of a chat room system. 
         [0030]    Embodiments of the present invention provide a process and method for determining block relationship between users and notifying block information in a SIP/SIMPLE-based instant messaging communication system. In a SIP/SIMPLE chat room system, a control server is used for managing and processing chat room services. The messages from a member in the chat room are sent to the control server of the chat room first, and then the control server of the chat room distributes the messages to other members in the chat room. 
         [0031]      FIG. 1  shows a schematic diagram illustrating a network structure of a chat room system. In the chat room system: 
         [0032]    Client A represents a client of a user about to join the chat room system of SIMPLE IM. 
         [0033]    Client B represents a client of a user having joined the chat room system of SIMPLE IM. 
         [0034]    Server X represents a control server of SIMPLE IM in the chat room system. The server X plays a role of controlling (control function). 
         [0035]    IM Server Sa represents home SIMPLE IM server of the client A. Since the server X is assumed to be the server of the chat room, the IM Server Sa plays a role of participating (participation function). 
         [0036]    IM Server Sb represents home SIMPLE IM server of the client B. Since the server X is supposed to be the server of the chat room, the IM Server Sb plays a role of participating (participation function). 
         [0037]    Instant Message XML Document Management Server (IM XDMS) represents a server for storing IM related information of the users using the IM servers, such as block lists and control strategies of the users. 
         [0038]    In the networking shown in  FIG. 1 , the control server of the chat room, i.e., the server X, and the IM Server Sa or Sb are different logic entities, which may be located in one physical entity or two different physical entities. In addition, the server X, the IM XDMS, the IM Server Sa, the IM Server Sb, the client A and the client B may be located in different SIP/IP Cores. If they are located in different SIP/IP Cores, signaling forwarding is required between different SIP/IP Cores. Regardless of the different networking structures, the principles of the signaling flows are similar. This has no substantial effect on the technical solution of the present invention and the understanding of those skilled in the art. 
         [0039]    The SIP/IP Core in the present invention belongs to the core network of Multimedia Subsystem (for example, CSCF) or IP network defined in 3GPP and 3GPP2. 
         [0040]      FIG. 2  is a schematic diagram illustrating the overall flow of an exemplary embodiment of the present invention. The flow includes processes as follows: 
         [0041]    S 201 . A new user joins a chat room which is activated. 
         [0042]    S 202 . A control server of the chat room obtains a user block list. 
         [0043]    S 203 . The control server of the chat room determines whether a block relationship exists between the new user and a user which is joined in the chat room earlier than the new user according to the user block list. If a block relationship exists, perform process of S 204 . Otherwise, the flow is ended. 
         [0044]    S 204 . The control server of the chat room sends a notification message containing block information to client of the new user, i.e., the client of the blocking party. 
         [0045]    Embodiments of the present invention will be described as follows, with the chat room system shown in  FIG. 1  as an example. 
         [0046]      FIG. 3  shows a process a client A joins an activated chat room according to an embodiment of the invention. The process includes the process as follows: 
         [0047]    S 301 . The client A requests to join the chat room, so the client A sends a SIP INVITE request to IM Server Sa (the server a). Request-URI in the SIP INVITE request contains a chat room identifier, and Accept-Contact in the SIP INVITE request contains a Feature code of SIP/SIMPLE service, for example “+g.oma.sip-im” etc. In addition, the SIP INVITE request carries transmission capability and negotiation parameters such as IP address, port number, supported transmission media type and the like of the client A in SDP parameters. 
         [0048]    S 302 . The IM Server Sa reads the chat room identifier carried in the SIP INVITE and determines that the chat room corresponding to the chart room identifier belongs to server X, and initiates a new SIP INVITE request to the server X. The Request-URI of the new SIP INVITE request contains the chat room identifier, and the Accept-Contact contains the Feature code of SIP/SIMPLE service, for example, “+g.oma.sip-im” etc. In addition, the new SIP INVITE request carries transmission capability and negotiation parameters such as IP address, port number, supported transmission media type and the like of the IM Server Sa in the SDP parameters. 
         [0049]    S 303 . The server X performs authorization to the client A according to the new SIP INVITE request. If the authorization is passed and the client A is permitted to join the chat room, the server X sends a SIP  200  “OK” response to the IM Server Sa. The SDP parameters in the SIP  200  “OK” response carry the transmission capability and negotiation parameters such as IP address, port number, supported transmission media type and the like of the server X, which may be used by the IM Server Sa for establishing Message Session Relay Protocol (MSRP). 
         [0050]    The processes of S 301 -S 303  accomplish a negotiation for establishing an MSRP channel between the IM Server Sa and the server X, i.e., the control server of the chat room. 
         [0051]    S 304 . The IM Server Sa sends a new SIP  200  “OK” to the client A. The SDP parameters in the new SIP  200  “OK” carry the transmission capability and negotiation parameters such as IP address, port number, supported transmission media type and the like of the IM Server Sa, which may be used by the client A for establishing MSRP. 
         [0052]    The processes of S 301 -S 304  accomplish a negotiation for establishing an MSRP channel between the client A and the IM Server Sa. 
         [0053]    S 305 . The client A sends a first acknowledge message SIP ACK to the IM Server Sa, acknowledging the receipt of the new SIP  200  “OK” sent from the IM Server Sa. 
         [0054]    S 306 . The IM Server Sa sends a second acknowledge message SIP ACK to the server X, acknowledging the receipt of the SIP  200  “OK” response sent from the server X. 
         [0055]    With the above-mentioned process, the MSRP channel between the client A and the IM Server Sa, and the MSRP channel between the IM Server Sa and the server X are established. Similarly, a direct MSRP channel may also be established between the client A and the server X. 
         [0056]    In an embodiment as shown in  FIG. 4 , some users (e.g. User B) which are already in the chat room have added a user A in their block lists. The control server of the chat room, i.e., the server X, makes a query to the IM XDMS for the block relationship and sends a notification to these users in the chat room notifying that the user A has joined the chat room. In this embodiment, only the process of sending the notification to a user B is described, and the processes for other users are similar. The procedure is as follows: 
         [0057]    S 401 . The server X sends a SIP SUBSCRIBE message to the IM XDMS of the user B. In the SIP SUBSCRIBE message, Request-URI is the URI (Uniform Resource Identifier) of the chat room, Event is sip-profile or ua-profile or the like, and Expires is 0. 
         [0058]    S 402 . The IM XDMS sends a first SIP  200  “OK” response to the server X, indicating the receipt of the SIP SUBSCRIBE message. 
         [0059]    S 403 . The IM XDMS retrieves a block list of the user B from its memory and sends an SIP NOTIFY message to the server X. The SIP NOTIFY message contains the block list of the user B. 
         [0060]    S 404 . The server X sends a second SIP  200  “OK” response to the IM XDMS, indicating the receipt of the SIP NOTIFY message. 
         [0061]    S 405 . The server X determines whether the user B has blocked the user A according to the SIP NOTIFY message, and if the user B has blocked the user A, sends to the IM Server Sb an SIP MESSAGE containing the URI of the user A blocked by the user B. If the user B has not blocked the user A, the procedure is ended. 
         [0062]    S 406 . When receiving the SIP MESSAGE, the IM Server Sb determines that the destination party is client B, and forwards the SIP MESSAGE to the client B. 
         [0063]    S 407 . The client B sends a third SIP  200  “OK” response to the IM Server Sb, indicating the receipt of the SIP MESSAGE. 
         [0064]    S 408 . When receiving the third SIP  200  “OK” response, the IM Server Sb determines that the third SIP  200  “OK” response is a response to the server X, and forwards the third SIP  200  “OK” response to the server X. 
         [0065]    The client B analyzes the SIP MESSAGE, and learns the user A blocked by the user B has joined the chat room. 
         [0066]    Another embodiment of the present invention is similar to the embodiment as shown in  FIG. 4 , and the difference between the two embodiments is process of S 403 , i.e., the server IM XDMS determines whether the user B has blocked the user A directly according to the block list of the user B stored in the IM XDMS, and returns the result of block by using the SIP NOTIFY Accordingly, the rule content of Filter should be included in the SIP SUBSCRIBE message sent from the server X to the IM XDMS in the process of S 401 . 
         [0067]    Similar to the embodiment shown in  FIG. 4 , in another embodiment of the present invention, the control server X of the chat room communicates with the IM XDMS by using XML (Extensible Markup Language) Configuration Access Protocol (XCAP). Particularly, the process of S 401 -S 404  as shown in the  FIG. 4  are simplified into the following process: 
         [0068]    1. The server X sends to the IM XDMS of the user B (using HTTP GET) a XCAP message containing the URI of the user B; 
         [0069]    2. The IM XDMS retrieves the block list of the user B from the memory and returns to the server X a XCAP message (HTTP  200  OK) containing the block list. 
         [0070]    The subsequent process is the same as the process S 405 -S 408  of the embodiment as shown in  FIG. 4 . 
         [0071]    Similarly, in another embodiment of the present invention, the IM XDMS may determine whether the user B has blocked the user A directly according to the block list of the user B stored in the IM XDMS. The result whether the user B has blocked the user A is contained in a XCAP message HTTP  200  OK. 
         [0072]    Similar to the embodiment as shown in  FIG. 4 , in another embodiment of the present invention, the block list of the user B is not stored in the server IM XDMS, but stored in the IM Server Sb of the user B. Particularly, the process of S 401 -S 404  as shown in  FIG. 4  are modified into following process: 
         [0073]    S 411 . The server X sends a SIP SUBSCRIBE message to the IM Server Sb. In the SIP message, Request-URI is URI of the chat room, Event is sip-profile or ua-profile etc., and Expires is 0. 
         [0074]    S 412 . The IM Server Sb sends a first SIP  200  “OK” response to the server X, indicating the receipt of the SIP SUBSCRIBE message. 
         [0075]    S 413 . The IM Server Sb retrieves a block list of the user B from the memory and sends a SIP NOTIFY message to the server X. The SIP NOTIFY message contains the block list of the user B. 
         [0076]    S 414 . The server X sends a second SIP  200  “OK” response to the IM Server Sb, indicating the receipt of the SIP NOTIFY message. 
         [0077]    The subsequent process is the same as the process of S 405 -S 408  of the embodiment as shown in  FIG. 4 . 
         [0078]    Similarly, in another embodiment of the present invention, the IM Server Sb may determine whether the user B has blocked the user A directly according to the block list of user B stored in the IM Server Sb. The result whether the user B has blocked the user A is contained in a returned NOTIFY message. 
         [0079]    Similar to the embodiment as shown in  FIG. 4 , in another embodiment of the present invention, the block list of user B is not stored in the server IM XDMS, but directly stored in the server X of the chat room. When client B joins the chat room, the IM Server Sb has brought the block list of the user B into the chat room. When the IM Server Sb forwards the SIP INVITE request, XML MIME BODY in the INVITE contains the block list of the user B. Thus the process of S 401 -S 404  of the embodiment as shown in  FIG. 4  may be omitted, the server X determines whether the user B has blocked user A according to the block list of user B stored in the server X, and executes process of S 405 -S 408  of the embodiment as shown in  FIG. 4 . 
         [0080]    Similar to the embodiment as shown in  FIG. 4 , in another embodiment of the present invention, the block list of user B is stored in the IM Server Sb, and the user B has subscribed to a state change notification of the chat room. In other words, when a new user joins the chat room, the control server of the chat room has to notify the user B that a new user has joined the chat room. So, the server X of the chat room may send a SIP MOTIFY message to the IM Server Sb, then to the client B. The home IM server, i.e., IM Server Sb, determines whether user A is blocked. As shown in  FIG. 5 , the implementation process is as follows: 
         [0081]    S 501 . The server X of the chat room sends a SIP NOTIFY message to the IM Server Sb. The SIP NOTIFY contains the URI of user A. 
         [0082]    S 502 . The IM Server Sb forwards the SIP NOTIFY message to the client B. 
         [0083]    S 503 . The client B returns a SIP  200  “OK” to the IM Server Sb, indicating the receipt of the SIP NOTIFY message. 
         [0084]    S 504 . The IM Server Sb forwards the SIP  200  “OK” to the server X. 
         [0085]    S 505 . The IM Server Sb determines whether the user B has blocked the user A according to the block list of user B stored in the IM Server Sb, and if the user B has blocked the user A, sends a SIP MESSAGE to the client B. The SIP MESSAGE contains the URI of user A. If the user B has not blocked the user A, the process is ended. 
         [0086]    S 506 . The client B sends a SIP  200  “OK” response to the IM Server Sb, indicating the receipt of the SIP MESSAGE. 
         [0087]    In a similar way, the client B analyzes the SIP MESSAGE, and learns that the user A blocked by the user B has joined the chat room. 
         [0088]    In an embodiment as shown in  FIG. 6 , if a user (e.g. user B) which is already in the chat room is listed in the block list of the user A, the control server of the chat room, i.e., the server X, makes a query to the IM XDMS about the block relationship and sends a notification to user A notifying that a blocked user is in the chat room. This embodiment describes the case in which the user B which is already in the chat room is blocked. Other cases are similar to this one. The embodiment includes the process as follows: 
         [0089]    S 601 . The server X sends a SIP SUBSCRIBE message to the IM XDMS of the user A. In the SIP message, Request-URI is URI of the chat room, Event is sip-profile or ua-profile etc., and Expires is 0. 
         [0090]    S 602 . The IM XDMS sends a first SIP  200  “OK” response to the server X, indicating the receipt of the SIP SUBSCRIBE message. 
         [0091]    S 603 . The IM XDMS retrieves a block list of the user A from the memory and sends a SIP NOTIFY message to the server X. The SIP NOTIFY message contains the block list of the user A. 
         [0092]    S 604 . The server X sends a second SIP  200  “OK” response to the IM XDMS, indicating the receipt of the SIP NOTIFY message. 
         [0093]    S 605 . The server X determines whether the user A has blocked a user which is already in the chat room according to the SIP NOTIFY message. If the user A has blocked a user which is already in the chat room, for example, user B, the server X sends a SIP MESSAGE to the IM Server Sa. The SIP MESSAGE contains a list of users blocked by the user A. If the user A has not blocked a user which is already in the chat room, the process is ended. 
         [0094]    S 606 . When receiving the SIP MESSAGE, the IM Server Sa determines that the destination party is client A, and forwards the SIP MESSAGE to the client A. 
         [0095]    S 607 . The client A sends a third SIP  200  “OK” response to the IM Server Sa, indicating the receipt of the SIP MESSAGE. 
         [0096]    S 608 . When receiving the third SIP  200  “OK” response, the IM Server Sa determines that the third SIP  200  “OK” response is a response to the server X, and forwards the third SIP  200  “OK” response to the server X. 
         [0097]    The client A analyzes the received SIP MESSAGE, and learns that the user B blocked by the user A is already in the chat room. 
         [0098]    Similar to the embodiment as shown in  FIG. 6 , in another embodiment of the present invention, at process of S 603 , the IM XDMS determines whether the user A has blocked a user which is already in the chat room directly according to the block list of the user A stored in the IM XDMS, and returns a list of users which are already in the chartroom and blocked by the user A by using an SIP NOTIFY message. Accordingly, the rule content of Filter needs to be included in the SIP SUBSCRIBE message sent from the server X to the IM XDMS in process of S 601 . 
         [0099]    Similar to the embodiment shown in  FIG. 6 , in another embodiment of the present invention, the server X of the chat room communicates with the IM XDMS by XML Configuration Access Protocol (XCAP). Particularly, process of S 601 -S 604  as shown in the  FIG. 6  is simplified into the following process: 
         [0100]    S 611 . The server X sends a XCAP message to the IM XDMS of the user A (using HTTP GET). The XCAP message contains the URI of user A. 
         [0101]    S 612 . The IM XDMS retrieves the block list of the user A from the memory and returns a XCAP message (HTTP  200  OK) to the server X. The HTTP  200  OK contains the block list of the user A. 
         [0102]    The subsequent process is the same as process of S 605 -S 608  of the embodiment as shown in  FIG. 6 . 
         [0103]    Similarly, in another embodiment of the present invention, the server IM XDMS may determine whether user A has blocked a user which is already in the chat room directly according to the block list of the user A stored in the IM XDMS, and carries a list of users blocked by the user A in the XCAP message HTTP  200  OK. 
         [0104]    Similar to the embodiment as shown in  FIG. 6 , in another embodiment of the present invention, the block list of user A is not stored in the server IM XDMS, but stored in the IM Server Sa of the user A. Particularly, process of S 601 -S 604  as shown in  FIG. 6  are modified to the process of S 621 - 624  as follows: 
         [0105]    S 621 . The server X sends a SIP SUBSCRIBE message to the IM Server Sa. In the SIP message, Request-URI is URI of the chat room, Event is sip-profile or ua-profile etc., and Expires is 0. 
         [0106]    S 622 . The IM Server Sa sends a first SIP  200  “OK” response to the server X, indicating the receipt of the SIP SUBSCRIBE message. 
         [0107]    S 623 . The IM Server Sa retrieves a block list of the user A from the memory, and sends a SIP NOTIFY message to the server X. The SIP NOTIFY message contains the block list of the user A. 
         [0108]    S 624 . The server X sends a second SIP  200  “OK” response to the IM Server Sa, indicating the receipt of the SIP NOTIFY message. 
         [0109]    The subsequent process is the same as process of S 605 -S 608  of the embodiment as shown in  FIG. 6 . 
         [0110]    Similarly, in another embodiment of the present invention, the IM Server Sa may determine whether the user A has blocked a user which is already in the chat room according to the block list of user A stored in the IM Server Sa, and carries a list of users which is already in the chat room and blocked by the user A in a returned NOTIFY message. 
         [0111]    Similar to the embodiment as shown in  FIG. 6 , in another embodiment of the present invention, the block list of the user A is not stored in the server IM XDMS, but stored in the control server X of the chat room. When client A joins the chat room, the IM Server Sa has brought the block list of the user A into the chat room. When the IM Server Sa forwards the SIP INVITE request, XML MIME BODY in the SIP INVITE request contains the block list of the user A. Thus, the process of S 601 -S 604  of the embodiment as shown in  FIG. 6  may be omitted. The server X determines whether user A has blocked a user which is already in the chat room according to the block list of user A stored in the server X, and executes the process of S 605 -S 608  of the embodiment as shown in  FIG. 6 . 
         [0112]    Similar to the embodiment shown in  FIG. 6 , in another embodiment of the present invention, the block list of user A is stored in the IM Server Sa. So, the control server X of the chat room may send a SIP MOTIFY message to the IM Server Sa, then to the client A. The IM Server Sa determines a list of users which are already in the chat room and blocked by the user A. As shown in  FIG. 7 , the embodiment includes the process as follows: 
         [0113]    S 701 . The control server X of the chat room sends a SIP NOTIFY message to the IM Server Sa. The SIP NOTIFY contains a list of users in the chat room. 
         [0114]    S 702 . The IM Server Sa forwards the SIP NOTIFY message to the client A. 
         [0115]    S 703 . The client A returns a SIP  200  “OK” to the IM Server Sa, indicating the receipt of the SIP NOTIFY message. 
         [0116]    S 704 . The IM Server Sa forwards the SIP  200  “OK” to the server X. 
         [0117]    S 705 . The IM Server Sa determines whether the user A has blocked a user which is already in the chat room according to the block list of the user A stored in the IM Server Sa. If the user A has blocked a user which is already in the chat room, for example, user B, the IM Server Sa sends a SIP MESSAGE to the client A. The SIP MESSAGE contains a list of users blocked by the user A. If the user A has not blocked a user which is already in the chat room, the process is ended. 
         [0118]    S 706 . The client A sends a response SIP  200  “OK” to the IM Server Sa, indicating the receipt of the SIP MESSAGE. 
         [0119]    In a similar way, the client A analyzes the received SIP MESSAGE, and learns that the user B blocked by the user A is already in the chat room. 
         [0120]    Similar to the above embodiment, in another embodiment of the present invention, the MSRP may be used for sending messages between the server X of the chat room and IM servers Sa and Sb, and between a client and a home IM server. The MSRP channels are established during the process of the client joining the chat room. The messages include MSRP SEND message and MSRP  200  OK response message carrying message content. 
         [0121]    In the above-mentioned embodiments, the block relationship between the users is determined by the servers. In another embodiment of the present invention, the block relationship may also be determined by a client. The block list of a user may be stored in the client of the user, or may be obtained from the HTTP/XCAP message sent from the client to the IM XDMS. 
         [0122]    For an chat room having multiple users (e.g. user B), after a user A joins the chat room, if the user B subscribed the state change notification of the chat room (the state change notification may be subscribed by sending a SIP SUBSCRIBE message from the client to the control server of the chat room), the control server of the chat room sends a notification message (using SIP NOTIFY) to the client B notifying that the user A has joined the chat room. The notification message contains the URI of the user A. When receiving the notification message, the client B directly determines whether the user B has blocked the user A. If the user B has blocked the user A, the client B notifies the user B that the blocked user A has newly joined the chat room via a certain interface form (such as text, pop-up dialog box and small animation etc.). 
         [0123]    After the user A joins the chat room, if the user A has subscribed the state change notification of the chat room (the state change notification may be subscribed by sending a SIP SUBSCRIBE message from the client to the control server of the chat room, or by adding a subscription mark in the SIP INVITE message sent when joining the chat room). The control server of chat room, i.e., the server X, sends a notification message containing the block lists in the chat room to the client A. When receiving the notification message, the client A determines whether the user A has blocked a user which is already in the chat room (e.g. user B). If the user A has blocked a user which is already in the chat room, the client A notifies the user A that a blocked user (e.g. user B) is in the chat room via a certain interface form. 
         [0124]    In addition to subscribing the state change notification of the chat room, the client of a user may send a query message to the control server of the chat room periodically or only one time. The query message may use an SIP SUBSCRIBE message, in the SIP SUBSCRIBE message, message header Expire is set to 0. “Periodically” means that the client sends an SIP SUBSCRIBE message to the control server of the chat room periodically, for example, once every 10 minutes. When receiving the query message, the control server of the chat room returns an SIP NOTIFY message to the client. The SIP NOTIFY message contains a list of users in the chat room. The client determines whether a blocked user is in the current chat room according to the list of users and a block list stored in the client. 
         [0125]    While the present invention has been illustrated and described with reference to some preferred embodiments, the present invention is not limited to these. Those skilled in the art should recognize that various variations and modifications can be made without departing from the spirit and scope of the present invention as defined by the accompanying claims and their equivalents.