Patent Publication Number: US-2010125744-A1

Title: Method and system for providing presence service

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) AND CLAIM OF PRIORITY 
     The present application is related to and claims priority to an application entitled “METHOD AND SYSTEM FOR PROVIDING PRESENCE SERVICE” filed in the Korean Intellectual Property Office on Nov. 20, 2008 and assigned Serial No. 10-2008-0115614 the contents of which are incorporated herein by reference. 
     TECHNICAL FIELD OF THE INVENTION 
     The present invention relates to a presence service and, in particular, to a method and system for providing a presence service with reduction of resource and energy waste. 
     BACKGROUND OF THE INVENTION 
     The traditional circuit switching networks used for voice service have migrated to Internet Protocol (IP)-based packet data network for providing data service as well as voice service. IP Multimedia subsystem (IMS) is one of the advanced IP-based network architectures. Recently, IMS has made various IP-based services available to users, and a messaging service is a very popular service using the IMS. The IMS messaging can be provided in two modes: page mode messaging and session-mode messaging. In the page mode messaging service, a short message or a short media message is delivered over a Session Initiation Protocol (SIP) message that is transmitted for a SIP session. Whereas, in the session-mode messaging service, the message is delivered over a Message Session Replay Protocol (MSRP) message for the MSRP session established using the SIP session. 
     A presence service is one of the basic services supported by the IMS. The presence service provides presence information such as status information of terminals registered for a specific service. The presence information includes presence status of the registered terminal or user, such as online, offline, busy, do-not-disturb, and mood. The presence information is transmitted over a presence message in response to a subscriber&#39;s request such that the subscriber can acquire the current present information about a registered user&#39;s terminal. In the current presence service, the presence server transmits the presence information whenever the presence information of the registered terminal is updated even when the subscriber does not want to receive. Particularly when a plurality of user terminals are registered, the number of times that the updated presence information is received increases exponentially, whereby this causes traffic overhead in the network, resulting in wastes of resource and power for processing the unnecessary presence service message. There is therefore a need of a method for improving the network efficiency by preventing unnecessary presence information from being transmitted. 
     SUMMARY OF THE INVENTION 
     To address the above-discussed deficiencies of the prior art, it is a primary object to provide a method and system for providing a presence service that is capable of improving the system throughput by preventing unnecessary presence information from being transmitted. 
     In accordance with an exemplary embodiment of the present invention, a method for providing a presence service includes receiving, at a presence server, a message requesting suspension of a delivery of presence information of presentities subscribed by a watcher, the suspension request message being transmitted by the watcher of which a sleep mode condition is satisfied; receiving a changed part of the presence information from one of the presentities; retaining the changed part of the presence information; receiving a message requesting restart of the delivery of presence information from the watcher; and sending the changed part of the presence information to the watcher in response to the restart request message. 
     In accordance with another exemplary embodiment of the present invention, a system for providing a presence service includes at least one presentity that provides presence information; a watcher that requests initiation of the presence service when a sleep mode condition is satisfied and suspension of the presence service when the sleep mode condition is dissatisfied; and a server that receives and stores the presence information provided by the at least one presentity and delivers the presence information to the watcher or retains the presence information according to the requests of the watcher. 
     The described features, advantages, and characteristics of the invention may be combined in any suitable manner in one or more embodiments. One skilled in the relevant art will recognize that the invention may be practiced without one or more of the specific features or advantages of a particular embodiment. In other instances, additional features and advantages may be recognized in certain embodiments that may not be present in all embodiments of the invention. These features and advantages of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter. 
     Before undertaking the DETAILED DESCRIPTION OF THE INVENTION below, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document: the terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation; the term “or,” is inclusive, meaning and/or; the phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like; and the term “controller” means any device, system or part thereof that controls at least one operation, such a device may be implemented in hardware, firmware or software, or some combination of at least two of the same. It should be noted that the functionality associated with any particular controller may be centralized or distributed, whether locally or remotely. Definitions for certain words and phrases are provided throughout this patent document, those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior, as well as future uses of such defined words and phrases. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present disclosure and its advantages, reference is now made to the following description taken in conjunction with the accompanying drawings, in which like reference numerals represent like parts: 
         FIG. 1  illustrates a schematic diagram for a presence system according to an exemplary embodiment of the present invention; 
         FIG. 2  illustrates a sequence diagram for operations of the entities composing the presence system of  FIG. 1  for providing a presence service according to an exemplary embodiment of the present invention; 
         FIG. 3  illustrates a sequence diagram for operations of the entities composing the presence system of  FIG. 1  for providing a presence service according to another exemplary embodiment of the present invention; 
         FIG. 4  illustrates a flowchart for a method for providing a presence service according to an exemplary embodiment of the present invention from the viewpoint of a watcher; and 
         FIG. 5  illustrates a flowchart for a method for providing a presence service according to an exemplary embodiment of the present invention from the viewpoint of a presence server. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIGS. 1 through 5 , discussed below, and the various embodiments used to describe the principles of the present disclosure in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the disclosure. Those skilled in the art will understand that the principles of the present disclosure may be implemented in any suitably arranged communication network. 
       FIG. 1  illustrates a schematic diagram for a presence system according to an exemplary embodiment of the present invention. A presence service is one of the basic services provided along with instant messaging service in the IMS-based network. The presence service is a system that accepts, stores and distributes presence information on the terminals registered by a user. The presence service allows people to locate the registered users and availability of the users with their presence status. The presence system for providing the presence service can be composed of two different types of clients and a server. The first type of client is a presentity that provides the presence information to the presence service, and the second type of client is a watcher that accepts the presence information distributed by the presence service. The server is presence server that accepts and stores the presence information provided by the presentity and distributes the presence information to the watcher. Here, the presence information includes the status information of the presentity, i.e., the terminal. The watcher can register a plurality of presentities with the presence server. In the example of  FIG. 1 , the watcher has registered two presentities with the presence server  120 . 
     As shown in  FIG. 1 , the presence system includes a watcher  110 , a presence server  120 , and two presentities: presentity 1   130  and presentity 2   131 . The operations of the watcher  110 , the presence server  120 , and the presentities  130  and  131  within the presence system are described in detail with reference to  FIGS. 2 and 3 . 
       FIG. 2  illustrates a sequence diagram for operations of the entities composing the presence system of  FIG. 1  for providing a presence service according to an exemplary embodiment of the present invention. 
     Referring to  FIG. 2 , when the watcher wants to know the presentities&#39; presence status, the watcher  110  sends a SUBSCRIBE request message  205  to the presence server  120 . The presentities can be subscribed to an ISM server deployed in the IMS network supporting presence service. Here, it is assumed that the presentity 1   130  and the presentity 2   131  previously have been subscribed to the IMS server through a presentity registration procedure. The SUBSCRIBE request message is a SIP-based message and formatted as shown in Table 1. 
     
       
         
           
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
             
            
               
                   
                 SUBSCRIBE sip:joe@example.com SIP/2.0 
               
               
                   
                   Via: SIP/2.0/UDP pc34.example.com;branch=z9hG4bKnashds7 
               
               
                   
                   From: sip:joe@example.com;tag=123aa9 
               
               
                   
                   To: sip:joe@example.com 
               
               
                   
                   Call-ID: 9987@pc34.example.com 
               
               
                   
                   CSeq: 9887 SUBSCRIBE 
               
               
                   
                   Contact: sip:joe@pc34.example.com 
               
               
                   
                   Event: presence.winfo 
               
               
                   
                 Expires: 3600 
               
               
                   
                   Max-Forwards: 70 
               
               
                   
                 Operation-Mode: Active 
               
               
                   
                   
               
            
           
         
       
     
     In Table 1, the start line of the message indicates that the SIP method is SUBSCRIBE and which version of SIP the message conforms to. The following fields carry information about session. The head fields include a “From” field carrying the SIP URI of the initiator of the request; a “To” field for carrying the desired recipient of the request; and “Contact” field for carrying the SIP URI that can be used for requests; a “Call ID” field for carrying the unique identifier of the session; a “CSeq” field for carrying the sequence number and method name; an “Event” field for carrying the event information; an “Expire” field for carrying the valid time for subscription; a “Max-Forwards” field for carrying the maximum number of hops the message can traverse on its way to the destination; and an “Operation-Mode” field for carrying the operation mode. It is noted that the SUBSCRIBE request message can include the Operation-Mode field. When no presence information is needed, the watcher  100  sends the SUBSCRIBE request message including the Operation-Mode field is set to “Active” as shown in Table 1 in order for the presence server  120  to suspend the transmission of the presence information. The operations of the presence system when the presence information is not required are described later with reference to  FIG. 3 . The SUBSCRIBE request message can be composed of a Header without message body as shown in table 1. Typically the body of the message is written in Extensible Markup language (XML). If the SUBSCRIBE request message is authenticated and accepted, then the presence server  120  sends a 200 OK response message  210  to the watcher  110 . The authentication and acceptance to the SUBSCRIBE request is performed by the presence server  120 . Since the authentication and acceptance process is out of the scope of the present invention, detailed description on the authentication and acceptance process is omitted. Upon receipt of the SUBSCRIBE request message, the presence server  120  stores the SUBSCRIBE request message along with the operation mode of the watcher  110 . 
     Next, the presence server  120  sends a NOTIFY message  215  containing presence Information about presentities subscribed by the watcher  110  to the watcher  110 . Here, it is assumed that the presentity 1   130  and presentity 2   131  are the presentities subscribed by the watcher  110 . Upon receipt of the NOTIFY message, the watcher  110  sends a 200 OK message  220  to the presence server  120 . The presentity 1   130  and the presentity 2   131  send PUBLISH messages containing changed part of their presence information to the presence server  120  whenever the presence information is changed. If the presence status of the first presentity 1   130  changes, the first presentity 1   130  sends the PUBLISH message  225  containing the changed part of the presence information to the presence server  120 . Upon receipt of the PUBLISH message transmitted by the first presentity 1   130 , the presence server  130  sends the 200 OK message  230  to the first presentity 1   130 . 
     Once the changed part of the presence information of the first presentity 1   130  is received, the presence server  120  stores the changed part of the presence information of the first presentity 1   130  and checks the operation mode of the watcher  110  to notify of the change of the presence information of the first presentity 1   130 . Although there can be more than one watchers subscribed to the presence information of the first presentity 1   130 , it is assumed that only one watcher, i.e., the watcher  110  has subscribed the presence information of the first presentity 1   130 . Since the operation mode of the watcher  110  is active, the presence server  120  sends a NOTIFY message  235  for notifying the watcher  110  of the change of the presence information of the first presentity 1   130 . Here, the NOTIFY message  235  carries the changed part of the presence information of the first presentity 1   130 . The presence information contained in the body of the NOTIFY message includes at least one tuple, and each tuple can contain a basic status and optionally communication address and other presence markup. More than one tuple can compose a Presence Information Data Format (PIDF) as a minimum unit for expressing presence information. The NOTIFY message including the Full presence information delivers the PIDF, and the NOTIFY message including the changed part of the presence information delivers the presence information in units of tuple. The watcher  110  that received the NOTIFY message sends the 200 OK message  240  to the presence server  120 . 
     In case when the presence status of the second presentity  131 , the second presentity 2   131  sends the changed presence information to the presence server  120 . In detail, if the presence information of the second presentity 2   131  is changed, the second presentity 2   131  sends a PUBLISH message  245  containing the changed part of the presence information to the presence server  120 . Upon receipt of the PUBLISH message  245  transmitted by the second presentity 2   131 , the presence server  120  sends the 200 OK message  250  to the second presentity 2   131 . Once the changed presence information of the second presentity 2   131  is received, the presence server  120  stores the changed presence information of the second presentity 2   131  and checks the operation mode of the watcher  110  to provide the presence information of the second presentity 2   131 . Since the operation mode of the watcher  110  is active, the presence server  120  sends a NOTIFY message  255  for notifying the watcher  110  of the change of the presence information of the second presentity 2   131 . The NOTIFY message carries the changed part of the presence information of the second presentity 2   131 . Upon receipt of the NOTIFY message, the watcher  110  sends the 200 OK message  260  to the presence server  120 . Although the watcher  110  is configured to receive the presence information continuously in the example of  FIG. 2 , the delivery of the presence information can be suspended. For instance, when the terminal, i.e., the watcher, does not detect any user input for requesting the presence information or operates in sleep mode, the presence information request is not initiated. In this case, the watcher  110  can send a message requesting the presence server  120  to suspend the delivery of the presence information. How to suspend the presence service is explained in another exemplary embodiment described with reference to  FIG. 3 . 
       FIG. 3  illustrates a sequence diagram for operations of the entities composing the presence system of  FIG. 1  for providing a presence service according to another exemplary embodiment of the present invention. 
     Referring to  FIG. 3 , in case that the watcher wants to know the presentities&#39; presence status, the watcher  110  sends a SUBSCRIBE request message  305  to the presence server  120 . The presentities can be subscribed to the IMS server deployed in the IMS network supporting the presence service already through a presentity registration process. Here, it is assumed that the first presentity 1   130  and the second presentity 2   131  previously have been subscribed to the IMS server through a presentity registration procedure. The SUBSCRIBE request message is a SIP-based message and formatted as shown in table 1. The structure of the SUBSCRIBE message is identical with that described in the description of the embodiment of  FIG. 2 . If the SUBSCRIBE request message is authenticated and accepted, then the presence server  120  sends a 200 OK message  310  to the watcher  110 . 
     Upon receipt of the 200 OK message  310 , the presence server  120  sends a NOTIFY message  315  containing the Full presence information of the requested presentities to the watcher  100 . Here, it is assumed that the first presentity 1   130  and second presentity 2   131  are the presentities subscribed by the watcher  110 . Upon receipt of the NOTIFY message  315 , the watcher  110  sends a 200 OK message  320  to the server  120 . In case that the presence information of the first presentity 1   130 , the first presentity 1   130  sends a PUBLISH message  325  containing a changed part of its presence information to the presence server  120 . If the PUBLISH message  325  transmitted by the first presentity 1   130 , the presence server  120  sends the 200 OK message  330  to the presence server  120 . 
     Upon receipt of the changed part of the presence information of the first presentity 1   130 , the presence server  120  stores the changed part of the presence information of the first presentity 1   130  and checks the operation mode of the watcher  110  to notify of the change of the presence information of the first presentity 1   130 . Since the operation mode of the watcher  110  is active, the presence server  120  sends a NOTIFY message  335  for notifying the watcher  110  of the change of the presence information of the first presentity 1   130 . Here, the NOTIFY message  335  is a message carrying the partial information of the changed presence information of first presentity 1   130 . Upon receipt of the NOTIFY message  335 , the watcher  110  sends the 200 OK message  340  to the presence server  120 . 
     In case that the watcher  110  wants to suspend the presence information, e.g., when the watcher  110  does not detect any user request for the presence information or operates in sleep mode, the watcher  110  can notify the presence server  120  that it operates in sleep mode such that the presence server suspends the transmission of the presence information. That is, the watcher  110  sends a SUBSCRIBE request message  345  including an Operation-Mode field set to ‘sleep’ to the presence server  120 . This SUBSCRIBE request message  345  is a SIP-based message and is formatted as shown in Table 2. 
     
       
         
           
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
             
            
               
                   
                 SUBSCRIBE sip:joe@example.com SIP/2.0 
               
               
                   
                   Via: SIP/2.0/UDP pc34.example.com;branch=z9hG4bKnashds7 
               
               
                   
                   From: sip:joe@example.com;tag=123aa9 
               
               
                   
                   To: sip:joe@example.com 
               
               
                   
                   Call-ID: 9987@pc34.example.com 
               
               
                   
                   CSeq: 9887 SUBSCRIBE 
               
               
                   
                   Contact: sip:joe@pc34.example.com 
               
               
                   
                   Event: presence.winfo 
               
               
                   
                 Expires: 3600 
               
               
                   
                   Max-Forwards: 70 
               
               
                   
                 Operation-Mode: Sleep 
               
               
                   
                   
               
            
           
         
       
     
     The SUBSCRIBE request message shown in Table 2 is identical with that of Table 1 except that the Operation-Mode field is set to ‘sleep’ to indicate that the watcher request to suspend the transmission of the presence information. If the SUBSCRIBE request message  345  including an Operation-Mode field is set ‘sleep’ is received, the presence server  120  updates the operation mode of the watcher  110  and sends the 200 OK message  350  to the watcher  110 . 
     After the operation mode of the watcher  110  is updated into sleep at the presence server  120 , the second presentity 2   131  sends a PUBLISH message  355  including changed presence information to the server  120 . Upon receipt of the PUBLISH message indicating the change of the presence information of the second presentity 2   131 , the presence server  120  sends the 200 OK message  360  to the second presentity 2   131 . Next, the presence server  120  stores the changed presence information of the second presentity 2   131  and checks the operation mode of the watcher  110 . In case that the operation mode of a watcher is ‘sleep’, the presence server  120  suspends the transmission of the presence information to the watcher. Since the operation mode of the watcher  110  has been updated into ‘sleep’, the presence server  120  does not send the NOTIFY message informing the watcher  110  of the change of the presence information of the second presentity 2   131  but retains the changed presence information of the second presentity 2   131 . 
     Also, if the presence information of the first presentity 1   130  is changed, the first presentity 1   130  sends a PUBLISH message  365  including the changed presence information to the presence server  120 . Upon receipt of the PUBLISH message  365  from the first presentity 1   130 , the presence server  120  sends the 200 OK message  370  to the first presentity 1   130 . Next, the presence server  120  stores the changed presence information of the first presentity 1   130  carried by the PUBLISH message  365  and checks the operation mode of the watcher  110 . Since the operation mode of the watcher is ‘sleep’ yet, the presence server  120  suspends the transmission of the NOTIFY message to inform the watcher  110  of the change of the presence information of the first presentity 1   130  but retains the change presence information of the first presentity 1   130 . 
     If the watcher  110  wants to know the presentities&#39; presence status, the watcher  110  sends a SUBSCRIBE request message  375  indicative of the release of its sleep mode to the presence server  120 . The SUBSCRIBE request message is identical with that of Table 1. If the SUBSCRIBE request message indicative of the release of the sleep mode, the presence server  120  sends the OK message  380  to the watcher  110 . At this time, the presence server  120  can accept the request by performing an authentication and acceptance procedure. Once the operation mode of a watcher is updated into ‘active’, the presence server checks whether there is any change of presence information of the presentities subscribed by the watcher while the watch is in sleep mode and sends, if any, a NOTIFY message containing the retained presence information to the watcher. Since the presence information of the first presentity 1   130  and second presentity 2   131  has been changed while the watcher  110  is in sleep mode, the presence server  120  sends the watcher  110  a NOTIFY message  385  including the changed presence information of the first presentity 1   130  and second presentity 2   131 . The changed presence information carried by the NOTIFY message is the changed parts of the presence information (i.e., partial presence information) of the first presentity 1   130  and second presentity 2   131 . Upon receipt of the NOTIFY message, the watcher  110  sends the 200 OK message  390  to the presence server  120 . In this manner, the presence server  120  suspends the transmission of the changed presence information of the presentities subscribed by the watcher when the watcher is in sleep mode, thereby reducing unnecessary resource waste. The method for providing a presence service according to an exemplary embodiment of the present invention is described from the viewpoints of the watcher and the presence server separately with reference to  FIGS. 4 and 5 . 
       FIG. 4  illustrates a flowchart for a method for providing a presence service according to an exemplary embodiment of the present invention from the viewpoint of a watcher. 
     Referring to  FIG. 4 , the watcher  110  (see  FIG. 1 ) first detects a user request for presence service (block  405 ). If the user request for presence service is detected, the watcher  110  generates a SUBSCRIBE request message and sends the subscriber request message to the presence server  120  (block  410 ). The SUBSCRIBE request message is formatted as shown in Table 1. It is noted that all the operations of the watcher at every step actually can be performed or controlled by a controller of the watcher  110 . After transmitting the SUBSCRIBE request message, the watcher  110  determines whether a NOTIFY message containing the presence information of the presentities subscribed by the watcher  110  (block  415 ). If no NOTIFY message is received in the predetermined time, the procedure goes to step  450 . If a NOTIFY message is received in a predetermined time, the watcher  110  acquires the presence information of the subscribed presentities from the NOTIFY message (block  420 ). Although not depicted in  FIG. 4 , the watcher  110  can send a response message to the presence server  120  in response to the NOTIFY message. 
     After acquiring the presence information, the watcher  110  monitors to determine whether a sleep mode condition is satisfied (block  425 ). The sleep mode condition can be set with various parameters by the user. In this embodiment of the present invention, the sleep mode condition is a time duration for which no user input is detected and the watcher is in idle state, e.g., the off-time of the display unit of the watcher. The time duration can be set to a value to some extent that does not cause resource waste to transmit SUBSCRIBE request message having the operation mode field. In order to count the time duration, a time can be started at the time when the display unit switches off. If the sleep mode condition is satisfied, the watcher  110  generates a SUBSCRIBE request message indicative of sleep mode and sends the SUBSCRIBE request message to the presence server  120  (see message  345  of  FIG. 3 ) (block  430 ). The SUBSCRIBE request message indicative of sleep mode has the operation mode field set to ‘sleep’ as shown in table 2. If the sleep mode condition is not satisfied at step  425 , the procedure goes to block  415 . After transmitting the SUBSCRIBE request message indicative of sleep mode at block  430 , the watcher  110  monitors to determine whether the sleep mode condition becomes dissatisfied (block  435 ). This means that the sleep mode condition satisfied at block  425  returns to be dissatisfied due to an event such as switching on the display unit. 
     If the sleep mode condition does not become dissatisfied, the procedure goes to block  450 . Otherwise, if the sleep mode condition become dissatisfied at block  435 , the watcher  110  generates a SUBSCRIBE request message indicative of active mode and sends the SUBSCRIBE request message to the presence server  120  (see step  375  of  FIG. 3 ) (block  440 ). The SUBSCRIBE request message indicative of active mode has the operation mode field set to ‘active’ as shown in Table 1. In case that there is any presence information of the subscribed presentities that is retained in the presence server  120  while the watcher  110  is in sleep mode, the watcher  110  receives the presence information from the presence server  120  (see step  385  of  FIG. 3 ) (block  445 ). After acquiring the presence information retained in the presence server  120 , the watcher  110  determines whether a presence service termination event is detected (block  450 ). If a presence service termination event is detected, the watcher  110  finishes the presence service. Otherwise, if no presence service termination event is detected, the procedure goes to block  415 . The presence service termination event can be occurred when the time set in an Expire field of a REGISTER message sent to the IMS server expires or by transmitting a REGISTER message of which Expire field set to zero to the IMS server to release the connection with the IMS server. Although not illustrated in  FIG. 4 , the watcher  110  can send response message (e.g. 200 OK message) to the presence server  120  in response to the message transmitted by the presence server  120 . 
       FIG. 5  illustrates a flowchart for a method for providing a presence service according to an exemplary embodiment of the present invention from the viewpoint of a presence server. 
     Referring to  FIG. 5 , the presence server  120  (see  FIG. 1 ) receives a SUBSCRIBE request message transmitted by the watcher  110  (see  FIG. 1 ) (block  510 ). If a SUBSCRIBE request message is received, the presence server  120  checks the presentities which the watcher  110  has subscribed to the IMS server, generates a NOTIFY message containing the presence information of the subscribed presentities, and sends the NOTIFY message to the watcher  110  (block  520 ). Here, the NOTIFY message can contain the full presence information (see message  215  of  FIG. 2  and block  315  of  FIG. 3 ). After transmitting the NOTIFY message, the presence server  120  monitors to determine whether a PUBLISH message indicative of a change of the presence information is received from any of the presentities subscribed by the watcher  110  (block  530 ). It is assumed that the presentities subscribed by the watcher  110  include the first presentity 1   130  and second presentity 2   131  of  FIGS. 2 and 3 . If a PUBLISH message indicative of the presence information change is received from one of the first presentity 1   130  and second presentity 2   131 , the presence server  120  checks whether the operation mode of the watcher  110  is registered as sleep mode (block  540 ). If the operation mode of the watcher  110  is registered as sleep mode, the presence server  120  suspends a transmission of the changed presence information carried by the PUBLISH message to the watcher  110  and retains the changed presence information (block  550 ). Otherwise, if the operation mode of the watcher  110  is not set to ‘sleep’, the procedure goes to block  570 . Here, the operation mode of the watcher  110  can be indicated by the operation mode field of the SUBSCRIBE request message transmitted by the watcher  110  as shown in Tables 1 and 2. The operation mode field of the SUBSCRIBE request message can be set to ‘active’ or ‘sleep’. 
     While retaining the charged presence information, the presence server  120  monitors to determine whether a SUBSCRIBE request message indicative of release of the sleep mode (block  560 ). If no SUBSCRIBE request message indicative of release of the sleep mode, the presence server  120  determines whether a presence service termination event is detected (block  570 ). If a presence service termination event is detected, the presence server  120  terminates the presence service to the watcher  110 . If a SUBSCRIBE request message indicative of release of the sleep mode at block  560 , the presence server  120  generates a NOTIFY message containing the presence information retained while the watcher  110  is in sleep mode and sends the NOTIFY message to the watcher  110  (see step  385  of  FIG. 3 ) (block  580 ). Here, the SUBSCRIBE request message indicative of release of the sleep mode can be formatted to have the operation mode field set to ‘active’ as shown in Table 1. Returning to block  540 , if the operation mode of the watcher  110  is not registered as sleep mode (i.e., if the operation mode of the watcher  110  is registered as active mode), the presence server  120  generates a NOTIFY message containing the change presence information and sends the NOTIFY message to the watcher  110  (block  590 ) and then the procedure goes to block  570 . Here, the NOTIFY message can carry only the changed part of the presence information, i.e., partial presence information, (see message  235  of  FIG. 2  and block  335  of  FIG. 3 ). Although not described in  FIG. 5 , the presence server  120  can send a response message (e.g. 200 OK message) in response to the SUBSCRIBE request message transmitted by the watcher  110  (see  FIGS. 2 and 3 ). In this manner, the presence server can suspend the transmission of the presence information of the presentities subscribed by the watcher when the watcher is in sleep mode, thereby preventing the presence information from being transmitted unnecessarily and thus reducing waste of resources. 
     As described above, the method and system for providing presence service according to the present invention allows the presence server to send the presence information of the presentities subscribed by a watcher only when the watcher is operating in active mode, resulting in reduction of resource waste. Since the presence service is suspended when presence information of the subscribed presentities is out of user&#39;s interest, it is possible to reduce the processing overhead and power consumption of the terminal. 
     Although the present disclosure has been described with an exemplary embodiment, various changes and modifications may be suggested to one skilled in the art. It is intended that the present disclosure encompass such changes and modifications as fall within the scope of the appended claims.