Abstract:
A method for managing information on user equipments (UEs) in a mobile communication system supporting an MBMS (Multimedia Broadcast/Multicast Service) service. A radio network controller (RNC) provides a packet switched (PS) service and a circuit switched (CS) service to the UEs. A UE that is in a Packet Mobility Management-Idle (PMM-Idle) mode after joining at least one MBMS service, transmits MBMS service-related information thereof to the RNC, and the RNC stores the MBMS service-related information in a first service context for the MBMS service held in the RNC, together with information on the UE.

Description:
PRIORITY  
         [0001]    This application claims priority under 35 U.S.C. § 119 to an application entitled “Method for Managing Service Context for Paging User Equipment in a Multimedia Broadcast/Multicast Service” filed in the Korean Intellectual Property Office on Feb. 12, 2003 and assigned Serial No. 2003-8934, an application entitled “Method for Managing Service Context for Paging User Equipment in a Multimedia Broadcast/Multicast Service” filed in the Korean Intellectual Property Office on Mar. 31, 2003 and assigned Serial No. 2003-20275, an application entitled “Method for Managing Service Context for Paging User Equipment in a Multimedia Broadcast/Multicast Service” filed in the Korean Intellectual Property Office on Apr. 14, 2003 and assigned Serial No. 2003-23355, an application entitled “Method for Managing Service Context for Paging User Equipment in a Multimedia Broadcast/Multicast Service” filed in the Korean Intellectual Property Office on May 16, 2003 and assigned Serial No. 2003-31354, the contents of all of which are incorporated herein by reference.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates generally to a Multimedia Broadcast/Multicast Service (MBMS), and in particular, to a method for managing an MBMS service context for an MBMS.  
           [0004]    2. Description of the Related Art  
           [0005]    Recently, due to the development of communication technology, a service provided in a Wideband Code Division Multiple Access (WCDMA) mobile communication system is developing into multimedia broadcast/communication capable of supporting an existing voice service and also packet service and multimedia service that transmit mass data, such as packet data and circuit data. In order to support the multimedia broadcast/communication, an MBMS service has been proposed, in which a particular service is provided from one or several data sources to a plurality of user equipments (UEs).  
           [0006]    The “MBMS service” refers to a service for transmitting the same multimedia data to a plurality of recipients through a radio network. In the MBMS service, recipients can share one radio channel to save radio transmission resources. The MBMS service supports transmission of multimedia data such as real-time image and voice, still image, and text, and can simultaneously transmit voice data and image data according to a type of the multimedia transmission. As such, the MBMS service requires massive transmission resources. Further, because the same data must be transmitted to a plurality of cells where users are located, connections are made on a point-to-point (PtP) basis or a point-to-multipoint (PtM) basis, based on the number of users located on each cell.  
           [0007]    [0007]FIG. 1 is a diagram schematically illustrating nodes joining an MBMS service in a mobile communication network. Referring to FIG. 1, UEs  161 ,  162 ,  163 ,  171 , and  172  are terminal equipments or subscribers for receiving an MBMS service, and a cell #1  160  and a cell #2  170  are controlled by their own base station apparatuses or Node Bs, which wirelessly transmit MBMS-related data to subscribers. A radio network controller (RNC)  140  controls the cells  160  and  170 , selectively transmits multimedia data to a particular cell, and controls a radio channel set up to provide an MBMS service. Connection between the RNC  140  and the UEs  161  and  172  are called “radio resource control (RRC) interfaces.” 
           [0008]    The RNC  140  is connected to a packet switched or packet service (PS) network such as the Internet by a serving GPRS (General Packet Radio Service) support node (SGSN)  130 . Communication between the RNC  140  and the PS network is achieved by packet switched (PS) signaling. Particularly, a connection between the RNC  140  and the SGSN  130  is called an “Iu-PS interface.” 
           [0009]    The SGSN  130  controls an MBMS service for each subscriber. For example, typical functions of the SGSN  130  include managing service accounting-related information of each subscriber and selectively transmitting multimedia data to the particular RNC  140 .  
           [0010]    A transit network (NW)  120  provides a communication path between a broadcast multicast service center (BM-SC)  110  and the SGSN  130 , and can be connected to an external network via an undepicted gateway GPRS support node (GGSN). The BM-SC  110  is a source of MBMS data, and controls scheduling of MBMS data.  
           [0011]    The RNC  140  is connected to a circuit switched (CS) network by a mobile switching center (MSC)  150 . The “CS network” is a connection-based voice-oriented legacy communication network. Communication between the RNC  140  and the MSC  150 , and is achieved by circuit switched (CS) signaling. Particularly, a connection between the RNC  140  and the MSC  150  is called an “Iu-CS interface.” An MBMS data stream is transferred to the UEs  161 ,  162 ,  163 ,  171 , and  172  via the transit network  120 , the SGSN  130 , the RNC  140 , and the Node Bs  160  and  170 .  
           [0012]    Although not illustrated in FIG. 1, for one MBMS service, a plurality of SGSNs and a plurality of RNCs for each SGSN can be used. Each of the SGSNs selectively transmits data to its RNCs, and each of the RNCs selectively transmits data to its cells. A list of nodes to which a data stream should be transmitted is stored in the SGSN and RNC (i.e., a list of RNCs is stored in each SGSN, and a list of cells is stored in each RNC), to later selectively transmit MBMS data only to the nodes stored in the list.  
           [0013]    In order for UEs to access a network and receive a service therefrom, a context, which is a set of information necessary for providing the corresponding service, must be first created between the UEs and network nodes. A UE context and an MM (Mobility Management) context are conventional examples of a context.  
           [0014]    An RNC creates a UE context for UEs after setting up RRC connection. The UE context includes fundamental information such as a UE identity (ID), position information of a UE, RRC state information of the UE, and information on a radio resource assigned to the UE. Further, the UE context is managed by an RNC while RRC connection is activated.  
           [0015]    The MM context is used to manage a position of a UE in a core network (CN). In order for a UE to receive a PS service, an MM context of the UE must be first created in an SGSN and a GGSN through a GPRS Attach procedure. Particularly, an MM context of the SGSN includes UE ID such as IMSI (International Mobile Subscriber Identity), P-TMSI (Temporary Mobile Subscriber Identity), IMEI (International Mobile Equipment Identity), and MS-ISDN (Mobile Subscriber ISDN (Integrated Switched Data Network)) Number, position information such as RA (Routing Area) and SAC (Service Area Code), authentication/encryption-related information, accounting information, and DRX (Discontinuous Reception) parameters.  
           [0016]    Network nodes, such as an RNC, an MSC, and an SGSN manage a state of a UE for efficient signaling transmission and data transmission. In particular, the RNC manages an RRC state of a UE, and the RRC state is determined according to an RRC connection of the UE being set up. A state in which the RRC connection is set up is called an “RRC-Connected state,” and a state in which RRC connection is not set up is called an “RRC-Idle state.” 
           [0017]    The SGSN manages a PMM (Packet Mobility Management) state of a UE. A UE for which an MM context is not created in an SGSN is identified as a UE in a PMM-Detached state. A UE for which an MM context is created in an SGSN through a GPRS Attach procedure is divided into a UE in a PMM-Connected state and a UE in a PMM-Idle state. A state in which a UE has Iu-PS signaling connection and is in an RRC-Connected state is called a “PMM-Connected state.” A state in which a UE does not have Iu-PS signaling connection or is in an RRC-Idle state is called a “PMM-Idle state.” The MSC manages a CMM (Circuit Mobile Management) state of a UE. A state in which a UE has Iu-CS signaling connection and is in an RRC-Connected state is called a “CMM-Connected state, and a state in which a UE does not have Iu-CS signaling connection or is in an RRC-Idle state is called a “CMM-Idle state.” 
           [0018]    For UEs requesting an MBMS service, an MBMS service context and an MBMS UE context are used in network nodes for the MBMS service. Because the MBMS service simultaneously transmits the same information to a plurality of UEs, an MBMS service context is uniquely created for each MBMS service or each session in an MBMS service, rather than being individually created for each UE. The MBMS UE context stores information on an MBMS service that each UE joined.  
           [0019]    In order to perform an MBMS service, an MBMS service context must first be created in UEs and a BM-SC, which are front-end points of the MBMS service. Also, an MBMS service context is created in an RNC, SGSN, and GGSN, which are network nodes used for transmitting MBMS data.  
           [0020]    In a PS network represented by an RNC and an SGSN, because information related to a UE in a PMM-Idle mode is not included in an MBMS service context of an RNC, the UE may fail to receive an MBMS paging from the PS network. This phenomenon can occur when although RRC connection for a circuit switched (CS) service is set up between a UE and an RRC, the PS network does not recognize this fact.  
           [0021]    [0021]FIG. 2 is a diagram illustrating an operation occurring when a UE is in a PMM-Idle mode while managing RRC connection set up to an RNC (RRC-Connected state) in a conventional MBMS system. In FIG. 2, reference numeral  202  represents a UE receiving an MBMS service, reference numeral  204  represents a serving RNC (SRNC) for an MBMS service, which is associated with the UE  202 , and reference numeral  206  represents an SGSN of a CN for the MBMS service.  
           [0022]    The UE  202  is in a PMM-Idle mode where it joined an MBMS service but does not have a PS signaling. Referring to FIG. 2, in step  210 , the UE  202  sets up an RRC connection for receiving a CS service, and transitions to a Cell-FACH (Forward Access Channel) or Cell-DCH (Dedicated Channel) state of an RRC-Connected mode. In step  220 , the SGSN  206  detects start of an MBMS service through an MBMS Session Start message received via a BM-SC. The MBMS Session Start message includes MBMS service ID, multicast area information, and QoS (Quality of Service) information.  
           [0023]    In step  230 , the SGSN  206  searches for an MBMS service context corresponding to the MBMS service identified by an MBMS service ID included in the MBMS Session Start message, and transfers the MBMS. Session Start message to RNCs belonging to an RNC list included in the MBMS service context, and all RNCs belonging to RA (Routing Area) to which UEs in a PMM-Idle state belong, in order to inform the RNCs that transmission of MBMS data is started.  
           [0024]    In step  240 , the RNC  204  analyzes an MBMS service ID in the MBMS Session Start message received from the SGSN  206  in order to page UEs that are requesting the MBMS service. Here, because the MBMS Session Start message transmitted in step  230  does not include a UE ID, the SRNC  204  detects IDs of UEs joined the MBMS service using the MBMS service ID included in the MBMS Session Start message.  
           [0025]    In an MBMS paging procedure, the SRNC  204  calculates the same PO (Paging Occasion) and PI (Paging Instance) values using the MBMS service ID (for example, TMGI) and a DRX parameter. The SRNC  204  turns on or off a pilot indication channel (PICH) for a time period indicated by the PI and the PO to indicate whether a related paging channel (PCH) for UEs is received, and pages the UEs through a related PCH that starts a predetermined time after the PICH. Here, in order to page UEs in a Cell-DCH state, a Paging Type 2 message transmitted over a dedicated control channel (DCCH) is used.  
           [0026]    However, if the SRNC  204  deletes information on a relation between a certain UE  202  and the MBMS service as illustrated in step  240 , while the UE  202  switches to a PMM-Idle mode, the SRNC  204  cannot transmit the Paging Type 2 message to the UE  202  as illustrated in step  250 .  
           [0027]    That is, the SRNC  204  uses a common channel (CCH) to page UEs in a PMM-Idle mode. However, because the UE  202  actually has a dedicated channel for a CS service with a CS network, it cannot receive an MBMS paging over the common channel. Undesirably, therefore, the UE  202  cannot receive MBMS data although it has requested an MBMS service.  
         SUMMARY OF THE INVENTION  
         [0028]    It is, therefore, an object of the present invention to provide a method for performing MBMS paging on UEs in all states in order to provide an MBMS service in a mobile communication system.  
           [0029]    It is another object of the present invention to provide a method for performing MBMS paging on UEs in a CS service to provide an MBMS service in a mobile communication system.  
           [0030]    It is further another object of the present invention to provide a method for managing an MBMS service context for UEs in a PMM-Idle/RRC-Connected mode in an RNC.  
           [0031]    It is yet another object of the present invention to provide a method for managing an MBMS service context for UEs in a PMM-Idle/RRC-Connected mode in an SGSN.  
           [0032]    In accordance with one aspect of the present invention, there is provided a method for managing information on user equipments (UEs) in a mobile communication system including a Node B, a plurality of the UEs capable of communicating with the Node B in a cell occupied by the Node B, and a radio network controller (RNC) for controlling communication of the Node B and the UEs to provide a packet switched (PS) service and a circuit switched (CS) service to the UEs, the system providing an MBMS (Multimedia Broadcast/Multicast Service) service to the UEs. The method comprises the steps of: transmitting MBMS service-related information of a UE that is in a Packet Mobility Management-Idle (PMM-Idle) mode after joining at least one MBMS service, from the UE to the RNC; and storing the MBMS service-related information in a first service context for the MBMS service held in the RNC, together with information on the UE.  
           [0033]    In accordance with another aspect of the present invention, there is provided a method for managing information on user equipments (UEs) in a mobile communication system including a Node B, a plurality of the UEs capable of communicating with the Node B in a cell occupied by the Node B, a radio network controller (RNC) for controlling communication of the Node B and the UEs to provide a packet switched (PS) service or a circuit switched (CS) service to the UEs, and a serving node for managing the RNC, the system providing an MBMS (Multimedia Broadcast/Multicast Service) service to the UEs. The method comprises the steps of: transmitting MBMS service-related information of a UE that is in a Packet Mobility Management-Idle (PMM-Idle) mode after joining at least one MBMS service, from the UE to the serving node; and linking the MBMS service-related information with information on the UE, and storing the MBMS service-related information linked to the information on the UE in a first service context for the MBMS service in held the serving node. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0034]    The above and other objects, features, and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which:  
         [0035]    [0035]FIG. 1 is a diagram schematically illustrating a network configuration for a Multimedia Broadcast/Multicast Service (MBMS) service,  
         [0036]    [0036]FIG. 2 is a diagram illustrating a PMM-Idle UE having RRC connection in a conventional MBMS system;  
         [0037]    [0037]FIG. 3 is a diagram illustrating a procedure for performing an MBMS service;  
         [0038]    [0038]FIG. 4 is a diagram illustrating MBMS service contexts for an MBMS service;  
         [0039]    [0039]FIG. 5 is a detailed diagram illustrating a Joining procedure for an MBMS service;  
         [0040]    [0040]FIG. 6 is a diagram illustrating a procedure for releasing signaling with a PS network by a UE that joined an MBMS service;  
         [0041]    FIGS.  7  to  9  are diagrams illustrating procedures for transmitting MBMS service-related information from a UE to an RNC according to a first embodiment of the present invention;  
         [0042]    FIGS.  10  to  12  are flowcharts illustrating operation of a UE according to the first embodiment of the present invention;  
         [0043]    FIGS.  13  to  15  are flowcharts illustrating operation of an RNC according to the first embodiment of the present invention;  
         [0044]    [0044]FIGS. 16 and 17 are flowcharts illustrating an operation of updating an MBMS service context by an SGSN according to the first embodiment of the present invention;  
         [0045]    FIGS.  18  to  21  are diagrams illustrating procedures for transmitting MBMS service-related information to an RNC and an SGSN when a UE joining an MBMS service performs RRC connection setup, according to a second embodiment of the present invention;  
         [0046]    [0046]FIG. 22 is a diagram illustrating a procedure for releasing RRC connection by an RNC and an SGSN according to another preferred embodiment of the present invention;  
         [0047]    [0047]FIG. 23 is a diagram illustrating a procedure for requesting an RNC and an SGSN to leave an MBMS service according to another preferred embodiment of the present invention;  
         [0048]    [0048]FIG. 24 is a flowchart illustrating an SGSN&#39;s operation for storing MBMS service-related information according to the second embodiment of the present invention; and  
         [0049]    [0049]FIG. 25 is a flowchart illustrating a UE&#39;s operation for transmitting MBMS service-related information according to the second embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0050]    Several preferred embodiments of the present invention will now be described in detail with reference to the annexed drawings. In the drawings, the same or similar elements are denoted by the same reference numerals even though they are depicted in different drawings. In the following description, a detailed description of known functions and configurations incorporated herein has been omitted for conciseness.  
         [0051]    [0051]FIG. 3 is a diagram illustrating an MBMS service procedure between a user equipment (UE) and a network. In FIG. 3, a BM-SC  306  communicates with a UE  302  via an RNC  304 . The RNC  304  communicates with the BM-SC  306  via an SGSN (not shown). Although one RNC  304  and one UE  302  are illustrated in FIG. 3 for simplicity, the same procedure can also be applied to a plurality of UEs requesting an MBMS service and a plurality of RNCs.  
         [0052]    Referring to FIG. 3, in a Subscription step  310 , a user, or the UE  302 , requesting an MBMS service is subscribed (or registered) in a service provider, or the BM-SC  306 . In the Subscription step  310 , the user exchanges fundamental information related to accounting or service reception with the service provider.  
         [0053]    In an Announcement step  320 , UEs detect fundamental information on an MBMS service, such as IDs (MBMS service IDs) of MBMS services available in the BM-SC  306 , and their service start time and duration. For example, the MBMS service ID includes a multicast address and an access point name (APN). In the Announcement step  320 , nodes interposed between the BM-SC  306  and the UE  302 , i.e., the RNC  304 , an SGSN and a transit network, detect the UE  302  and the nodes connected to the UE  302 . For example, the SGSN analyzes a list of UEs desiring to receive the MBMS service and a list of RNCs where the UEs are located, and transmits MBMS data to only the RNCs where the UEs are located by consulting the lists.  
         [0054]    After acquiring the fundamental MBMS service information, the UE  302  performs a Joining step  330  in order to receive its desired MBMS service data. In the Joining step  330 , the UE  302  sends at least one of the MBMS service IDs obtained in the Announcement step  320  to the BM-SC  306 .  
         [0055]    A Notification step  340  is for paging the UE  302  in order to inform that the MBMS service joined by the UE  302  will be initiated soon. In the step  340 , multiple UEs joining the MBMS service are paged on a group paging basis.  
         [0056]    A Radio Resource Allocation step  350  is a step for actually allocating a radio resource between the UE  302  and the RNC  304  for providing the MBMS service, and then notifying the information to related nodes. In the step  350 , the RNC  304  can select a point-to-multipoint (PtM) or a point-to-point (PtP) connection method based on information on the number of UEs belonging to each of its cells and a radio resource management function.  
         [0057]    In a Data Transfer step  360 , actual MBMS data is transferred to the UE  302  via the RNC  304 . In step  360 , for example, if a ciphering key for the MBMS service must be changed, the RNC  304  delivers a new ciphering key to all UEs receiving the MBMS service.  
         [0058]    If the MBMS service is ended (or suspended), in a Radio Resource Release step  370 , the allocated radio resource is released and the UE  302  is notified that the MBMS radio resource is released. Though not illustrated, while receiving the MBMS service (in step  350 ), the UE  302  can spontaneously request suspension of the MBMS service and then suspend reception of the MBMS service.  
         [0059]    In order to perform an MBMS service as described above, an MBMS service context (or MBMS context) must be stored in network nodes related to the corresponding MBMS service, particularly in an SGSN and an RNC. The MBMS service context is created by the network nodes in the Joining step  330 . A time when the MBMS service context is generated and a method of managing the MBMS service context are determined depending on functions of the network nodes.  
         [0060]    [0060]FIG. 4 is a diagram illustrating MBMS service contexts created by an RNC and an SGSN. In FIG. 4, a serving RNC (SRNC) for managing RRC connections of UEs is separated from a control RNC (CRNC) for managing cells where the UEs are actually located.  
         [0061]    Referring to FIG. 4, a first MBMS service context stored in an SGSN  406  includes an MBMS service ID (or Temporary MBMS Group Identity (TMGI)), a UE List (or UE ID list), an RNC List (or RNC ID list), SAC (Service Access Control) List, Multicast Area List, QoS (Quality of Service) information, and MBMS PDP (Packet Data Protocol) Context information, for a plurality of UEs.  
         [0062]    The MBMS service ID can be an identity (Multicast address/APN or MBMS Group Identity (IMGI)) permanently allocated to the corresponding MBMS service, or an identity (Temporary MBMS Group Identity (TMGI)) temporarily allocated to identify an MBMS service by a corresponding SGSN (or GGSN). The SGSN (or GGSN) allocates the TMGI value when it first creates an MBMS service context for the MBMS service.  
         [0063]    The UE ID list has IDs of UEs belonging to a corresponding SGSN among UEs joining a corresponding MBMS service. A UE ID in the MBMS service context is used as a pointer pointing an MM context in the SGSN  406 . Because a mapping relation between an MBMS service context and an MM context is held by the UE ID, the MM context (e.g., MM state information) necessary for an MBMS service is not repeatedly stored in the MBMS service context.  
         [0064]    The RNC ID list is a set of RNCs to which UEs included in the UE ID list belong. By using the RNC ID list, the SGSN can transmit MBMS data only to RNCs to which UEs actually requesting an MBMS service belong, rather than transmitting the MBMS data to all of its RNCs.  
         [0065]    The SAC list and the multicast area list represent service areas where the MBMS service is available. The QoS information includes such attributes as traffic class, date rate, SDU (Service Data Unit) format information, and SDU error rate of MBMS data to be transmitted.  
         [0066]    MBMS service contexts of RNCs  404   a  and  404   b  have a different format according to whether they are a serving RNC (SRNC)  404   a  for managing RRC connection of a UE or a control RNC (CRNC)  404   b  where the UE is physically located.  
         [0067]    An MBMS service context of the SRNC  404   a  includes an MBMS service ID (or Temporary MBMS Group Identity (TMGI)) and a UE ID list (or UE List), and an MBMS service context of the CRNC  404   b  includes an MBMS service ID (or Temporary MBMS Group Identity (TMGI)), a UE ID list (or UE List), and MBMS barer-related information, i.e., MBMS radio access bearer (RAB) INFO.  
         [0068]    As indicated above, the MBMS bearer-related information includes information on an RAB between the CRNC  404   b  and the SGSN  406 , and information on a radio bearer (RB) between the CRNC  404   b  and UEs. The RAB information exists for each MBMS service of each RNC for a single QoS, and the RB information exists for each MBMS service of each cell for a single QoS.  
         [0069]    The Joining step  330  of FIG. 3 will now be described in detail with reference to FIG. 5. In FIG. 5, reference numeral  402  represents a UE receiving an MBMS service, reference numeral  404  represents an RNC for an MBMS service, associated with the UE  402 , and reference numeral  406  represents an SGSN of a core network (CN) for the MBMS service. As already described in FIG. 3, the UE  402  acquires IDs of MBMS services available in its cell through the MBMS Service Announcement step  320 . If an RRC connection is not set up between the UE  402  and the RNC  404 , the UE  402  sets up an RRC connection to the RNC  404  in step  410 , in order to join a desired MBMS service.  
         [0070]    In step  412 , the UE  402  transmits an ID of a desired MBMS service among MBMS services in a corresponding cell, acquired through the MBMS Service Announcement step  320 , to the SGSN  406  via the RNC  404 , along with an Activate MBMS Context Request message based on a NAS (Non-Access Stratum) interface between the UE  402  and the SGSN  406 . In order to transmit the Activate MBMS Context Request message, initial direct transfer is used between the UE  402  and the RNC  404 , and an initial UE message is used between the RNC  404  and the SGSN  406 . However, the initial direct transfer and the initial UE message depart from the scope of the present invention, so a detailed description thereof will be omitted.  
         [0071]    Upon receiving the Activate MBMS Context Request message, the SGSN  406  authenticates the UE  402  in step  414  through a Security Function procedure for inquiring of an authentication center about whether the UE  402  is a valid user. If the authentication on the UE  402  is successful, the SGSN  406  adds in step  416  information on the UE  402  to an MBMS service context corresponding to the MBMS service. If the UE  402  is a first UE that requests the MBMS service, the SGSN  406  preferentially performs an operation of generating the MBMS service context for the MBMS service.  
         [0072]    In step  418 , the SGSN  406  transmits an Activate MBMS Context Accept message to the UE  402  to inform that a request for joining the MBMS service is successfully accepted. The Activate MBMS Context Accept message can include the MBMS service ID and a DRX parameter. The MBMS service ID transmitted along with the Activate MBMS Context Accept message is a temporary MBMS service identity, i.e., TMGI, allocated to an activated MBMS service.  
         [0073]    Because the Activate MBMS Context Request message and the Activate MBMS Context Accept message transparently pass through the RNC  404  when they are transferred between the UE  402  and the SGSN  406 , the RNC  404  cannot know whether the UE  402  has requested the MBMS service. Therefore, in step  420 , the SGSN  406  instructs the RNC  404  to update the MBMS service context through a Create MBMS Context Request message. The Create MBMS Context Request message is also called an MBMS UE Linking Request message.  
         [0074]    The Create MBMS Context Request message includes a UE ID and an MBMS service ID. The MBMS service ID in the Create MBMS Context Request message is an identity permanently allocated to a service, such as an MBMS Multicast address, or a temporary identity (TMGI) allocated to the MBMS service. Herein, it should be understood that the MBMS service ID corresponds to both of the two identities.  
         [0075]    In step  422 , the RNC  404  adds information on the UE  402  to a corresponding MBMS service context, and in step  424 , the RNC  404  sends a Create MBMS Context Response message to the SGSN  406 . If the UE  402  is a first UE that requested the MBMS service, the RNC  404  preferentially performs an operation of creating the MBMS service context for the MBMS service.  
         [0076]    [0076]FIG. 6 is a diagram illustrating PS signaling being released because MBMS data transmission is not initiated yet even though a predetermined time has passed after a UE joined an MBMS service through the procedure illustrated in FIG. 5. Referring to FIG. 6, in step  430 , the SGSN  406  determines to release PS signaling connection upon detecting no message exchange with the UE  402  for a predetermined time. In step  432 , through a Delete MBMS Context Request message, the SGSN  406  requests the RNC  404  to delete the UE  402  from a UE ID list in the MBMS service context. The Delete MBMS Context Request message is also called an MBMS UE Delinking Request message. In step  434 , the RNC  404  deletes information on the UE  402  from the MBMS service context, and in step  436 , the RNC  404  responds to the SGSN  406  through a Delete MBMS Context Response message.  
         [0077]    In step  438 , the SGSN  406  releases Iu-PS signaling through an Iu release procedure. Therefore, the RNC  404  and the SGSN  406  determine that the UE  402  is in a PMM-Idle mode in which there is no PS signaling. If the UE  402  does not use RRC connection even for a CS service, RRC connection between the UE  402  and the RNC  404  can also be released in step  440 . In step  442 , the UE  402  transitions to a PMM-Idle mode by simply releasing the Iu-PS signaling regardless of whether RRC connection is released or not.  
         [0078]    If the UE  402  is a last UE that joined the MBMS service, the RNC  404  deletes the MBMS service context after transmitting the Delete MBMS Context Response message, and transmits in step  446  an MBMS Service Deregister message to the SGSN  406 . In step  448 , the SGSN  406  deletes the RNC  404  from an RNC list in the MBMS service context. The MBMS service contexts in the SGSN  406  and the RNC  404  can be created, updated, and released through the procedures illustrated in FIGS. 5 and 6.  
         [0079]    However, when information on only a UE in a PMM-Connected state that joined the MBMS service is stored in the MBMS service context in an RNC, as described in connection with FIGS. 5 and 6, if a UE requests RRC connection setup for a CS service in step  210  of FIG. 2 after transitioning to the PMM-Idle mode in step  442 , information on the UE  402  is not stored in the MBMS service context of the RNC  404 . As a result, the RNC  404  informs the UE  402  of initiation of the MBMS service through a common channel, and the UE  402  in an RRC-Connected state does not monitor the common channel. Therefore, the UE  402  cannot receive a Notification indicating initiation of the MBMS service and thus cannot receive the MBMS service.  
         [0080]    In order to solve this problem, in a first embodiment of the present invention, for a PMM-Idle/RRC-Connected UE, UE information is linked with MBMS service information and managed in an MBMS context so that an RNC can detect that the UE is a terminal that has successfully joined the MBMS service. It is also possible to manage a separate context by linking the UE information with the MBMS service information. In addition, an SGSN can prevent an unsynchronized phenomenon of MBMS service contexts in the SGSN and the RNC by managing UEs in a CMM-Connected mode in the MBMS service contexts.  
         [0081]    In a second embodiment of the present invention, if a PMM-Idle/RRC-Connected UE transitions to a PMM-Connected mode after setting up RRC connection, an SGSN and an RNC can manage a UE in a PMM-Connected mode using an MBMS service context. Herein below, information transmitted from the UE to link the UE information with the MBMS service information will be referred to as MBMS service-related information.  
         [0082]    The first embodiment and the second embodiment will now be separately described in detail.  
         [0083]    1. Management of a Service Context in an RNC  
         [0084]    In a first embodiment of the present invention, in order to enable an RNC to manage information on a UE that joined an MBMS service but is in a PMM-Idle mode, MBMS service-related information indicating that the UE is a terminal that successfully joined the MBMS service is transmitted to the RNC along with a predetermined message. Then, the RNC updates information on the terminal in a corresponding MBMS service context requested by the terminal among MBMS service contexts managed by the RNC.  
         [0085]    By transmitting the MBMS service-related information, it is possible to enable an RNC to link a list of UEs that have set up RRC connection for a CS service with MBMS service information so as to manage the UE list and the MBMS service information together. The RNC can link only IDs of the UEs with the MBMS service information before storing them, or link state information indicating that the UEs have set up an RRC connection for a CS service with the MBMS service information before storing them. Herein, both the IDs of UEs and the state information of UEs will be referred to as UE information. The MBMS service-related information corresponds to an MBMS service ID indicating an MBMS service that the terminal joined, or an MBMS service activation indicator.  
         [0086]    In transmitting the MBMS service ID, authenticating a terminal as a valid terminal for an MBMS service corresponding to the MBMS service ID is required. When the terminal transmits an MBMS service activation indicator, the terminal must receive, from an SGSN, information on at least one MBMS service requested by the terminal. The MBMS service-related information is transmitted using an RRC Connection Setup message or a dedicated RRC message.  
         [0087]    FIGS.  7  to  9  illustrate procedures for adding information on a UE to an MBMS service context of an RNC associated with the UE that joined an MBMS service but is in a PMM-Idle mode. In FIGS.  7  to  9 , reference numeral  502  represents a UE receiving an MBMS service, reference numeral  504  represents an RNC serving the UE  502 , and reference numeral  506  represents an SGSN of a CN for the MBMS service. In addition, an MBMS service context of the SGSN  506  will be referred to as a “first MBMS service context,” and an MBMS service context of the RNC  504  will be referred to as a “second MBMS service context.” 
         [0088]    [0088]FIG. 7 is a diagram illustrating a method of inserting an MBMS service ID into an RRC Connection Setup Request message when transmitting a message for an RRC connection setup procedure between a UE and an RNC, to manage an MBMS service context of the RNC. Referring to FIG. 7, steps  510 ,  512 , and  514  are performed to set up an RRC connection between the UE  502  and the RNC  504 . More specifically, if the UE  502  transmits in step  510  an RRC connection Setup Request message for a PS service or a CS service to the RNC  504 , the RNC  504  responds thereto in step  512 , using an RRC Connection Setup message. In step  514 , the UE  502  transmits an RRC Connection Setup Complete message, completing setup of RRC connection between the UE  502  and the RNC  504 .  
         [0089]    In the RRC connection setup process for a PS service or a CS service in the steps  510  to  514 , the UE  502  inserts at least one MBMS service ID indicating a desired MBMS service in the RRC Connection Setup Request message or the RRC Connection Setup Complete message, before transmission. Then the RNC  504  changes a second MBMS service context of an MBMS service corresponding to the MBMS service ID in step  524 . That is, the RNC  504  adds UE information to the second MBMS service context, indicating that the UE  502  has an RRC connection.  
         [0090]    Through the above-described procedure, the RNC  504  can store information on UEs that have set up an RRC connection for a PS service or a CS service among UEs that requested the MBMS service, in a corresponding MBMS service context. Here, the MBMS service context corresponds to separate information for PMM-Idle/RRC-Connected UEs or an existing MBMS service context for each MBMS service.  
         [0091]    Updating an MBMS service context by the RNC  504  can be performed immediately after the RRC connection setup procedure of  510  to  514 , or performed after validity of the UE  502  is determined as illustrated in FIG. 7.  
         [0092]    In step  516 , the RNC  504  uses an MBMS UE Validate Request message to determine whether the UE  502  is valid for the requested MBMS service. The MBMS UE Validate Request message includes a UE ID of the UE  502 , an MBMS service ID acquired in the RRC connection setup procedure of steps  510  to  514 , and an RNC ID of the RNC  504 . Further, the MBMS UE Validate Request message is transferred from the RNC  504  to the SGSN  506 .  
         [0093]    In transmitting the MBMS UE Validate Request message, if the UE  502  is in a PMM-Idle state, a dedicated signaling bearer allocated for the UE  502  does not exist between the RNC  504  and the SGSN  506 . Therefore, the MBMS UE Validate Request message can be transmitted using a common signaling bearer created for a corresponding MBMS service, or transmitted using a connectionless signaling transmission method.  
         [0094]    When the MBMS UE Validate Request message is transmitted using a common signaling bearer for an MOMS service, the SGSN  506  can distinguish the MBMS service and the RNC  504  by checking a signaling bearer over which the MBMS UE Validate Request message is transmitted. Therefore, the MBMS service ID and the RNC ID are selectively excluded from the message. However, when the MBMS UE Validate Request message is transmitted using a connectionless signaling transmission method, the MBMS service ID and the RNC ID must be included in the message.  
         [0095]    Upon receiving the MBMS UE Validate Request message, the SGSN  506  adds information on the RNC  504  to which the UE  502  that has RRC connection and requested an MBMS service belongs, to a first MBMS service context in step  518 , if the first MBMS service context corresponding to an MBMS service ID included in the message of the step  516  exists and a UE ID included in the message of the step  516  exists in the first MBMS service context. The SGSN  506  can also store state information in the first MBMS service context so as to indicate that a corresponding UE is in a CMM-Connected state. In this case, if the first MBMS service context already has information on the RNC  504 , the SGSN  506  is not required to add the information on the RNC  504  again.  
         [0096]    If the UE  502  is valid for the MBMS service, an MBMS UE Validate Response message is transmitted from the SGSN  506  to the RNC  504  in step  520 . The MBMS UE Validate Response message includes information on an area where the MBMS service is available.  
         [0097]    For example, the information on an area where the MBMS service is available represents a service area code (SAC) or multicast area information. If it is determined, based on the service area information, that the UE  502  is located in a cell not belonging to an area where the MBMS service is available, the RNC  504  can request the UE  502  to move to another cell.  
         [0098]    When updating an MBMS service context by the RNC  524  is performed after a UE authentication procedure in steps  516  to  520 , the RNC  504  adds information on the UE  502  to its second MBMS service context, after receiving the MBMS UE Validate Response message in step  521 . If the second MBMS service context corresponding to the MBMS service ID does not exist in the RNC  504 , the RNC  504  first creates the second MBMS service context.  
         [0099]    If the SGSN  506  fails to determine whether the UE  502  is valid in receiving the MBMS service, although the RNC  504  requested in step  516  the SGSN  506  to determine whether the UE  502  is valid for the MBMS service, the SGSN  506  transmits an MBMS UE Validate Failure message to the RNC  504  in step  522  to inform that the UE  502  has not joined the MBMS service via the SGSN  506 . The MBMS UE Validate Failure message can be defined as an MBMS UE Validate Response message into which a particular parameter value ‘Cause Value’ is inserted.  
         [0100]    [0100]FIG. 8 is a diagram illustrating a method of transmitting an MBMS service ID from the UE  502  to the RNC  504  after the RRC connection setup procedure. In the procedure illustrated in FIG. 8, unlike in the procedure illustrated in FIG. 7, the UE  502  transmits an MBMS Service Request message to the RNC  504  to inform that it has requested the MBMS service.  
         [0101]    Referring to FIG. 8, the UE  502  sets up RRC connection to the RNC  504  through an RRC connection setup procedure  530 . The RRC connection setup procedure  530  exchanges RRC Connection Setup Request, RRC Connection Setup, and RRC Connection Setup Complete messages between the UE  502  and the RNC  504 . In the RRC connection setup procedure  530 , MBMS service-related information is not transferred.  
         [0102]    In step  532 , the UE  502  delivers an MBMS service ID to the RNC  504  through an MBMS Service Request message. The MBMS Service Request message includes at least one MBMS service ID indicating an MBMS service the UE  502  desires to receive.  
         [0103]    An operation performed after the RNC  504  receives the MBMS service ID through the MBMS Service Request message is similar to the corresponding operation illustrated in FIG. 7. That is, in step  534 , the RNC  504  transmits an MBMS UE Validate Request message to the SGSN  506  in order to determine whether the UE  502  is valid for the MBMS service. The MBMS UE Validate Request message includes the MBMS service ID, a UE ID and an RNC ID.  
         [0104]    If it is determined that the UE  502  has joined the MBMS service, the SGSN  506  adds information on the RNC  504  to its MBMS service context in step  536 , and transmits an MBMS UE Validate Response message to the RNC  504  in response to the MBMS UE Validate Request message in step  538 . In the step  536 , the SGSN  506  can also store state information in the first MBMS service context created by the SGSN  506  so as to indicate that the UE  502  is in a CMM-Connected state.  
         [0105]    The RNC  504  adds information on the UE  502  to its MBMS service context in response to the MBMS UE Validate Response message in step  542 . In an alternate embodiment, the RNC  504  adds information on the UE  502  to its MBMS service context immediately after the MBMS Service Request message is received.  
         [0106]    In step  544 , the RNC  504  transmits an MBMS Service Response message to the UE  502  to inform that an MBMS service context is created by the RNC  504 . If a cell to which the UE  502  currently belongs does not support an MBMS service, the RNC  504  includes a cell ID indicating a cell where the MBMS service is available, in the MBMS Service Response message in order to instruct the UE  502  to more to another cell in order to receive the MBMS service.  
         [0107]    If the SGSN  506  fails to authenticate the UE  502  in step  534 , although the RNC  504  inquired of the SGSN  506  about whether the UE  502  is valid for the MBMS service, the SGSN  506  transmits an MBMS UE Validate Failure message  540  to the RNC  504  to inform that the UE  502  has not joined the MBMS service via the SGSN  506 . The RNC  504  then does not add information on the UE  502  in the second MBMS service context, and informs the UE  502  of unavailability of the MBMS service through an MBMS Service Failure message in step  546 .  
         [0108]    [0108]FIG. 9 is a diagram illustrating a method of adding an MBMS service activation indicator to an RRC Connection Setup Request message before transmission. The procedure illustrated in FIG. 9 is identical to the procedure illustrated in FIG. 7 in that an RRC Connection Setup Request message is used, but different from the procedure illustrated in FIG. 7 in that an MBMS service activation indicator is transmitted instead of an MBMS service ID.  
         [0109]    The MBMS service activation indicator can be added to an RRC message (RRC Connection Setup Request message or RRC Connection Setup Complete message) as a new information element (IE), or added to the RRC message as a Cause Value (for example, Cause=“MBMS Service Activation”).  
         [0110]    In this case, if the UE  502  requested a plurality of MBMS services, the UE  502  can update information on all MBMS services by transmitting an MBMS service activation indicator only once rather than transmitting separate messages for all the MBMS services.  
         [0111]    Referring to FIG. 9, through steps  550 ,  552 , and  554 , the UE  502  sets up an RRC connection for a PS service or a CS service with the RNC  504 . Here, the UE  502  inserts an MBMS service activation indicator indicating availability of a desired MBMS service into an RRC Connection Setup Request message or an RRC Connection Setup Complete message transmitted to the RNC  504 , to inform that the UE  502  has joined the MBMS service. The MBMS service activation indicator can be inserted into the RRC message, i.e., the RRC Connection Setup Request message or the RRC Connection Setup Complete message, as an IE or a Cause Value.  
         [0112]    More specifically, each of the RRC messages includes a UE ID capable of identifying the UE  502  and a Cause Value indicating the cause that the RRC connection is necessary. The Cause Value constitutes one IE in the RRC message, and the reason that the message is necessary can be determined based on a previously set value of the Cause Value. Therefore, it is possible to assign a value indicating the MBMS service activation to the Cause Value (for example, Cause=“MBMS Service Activation”) before transmission.  
         [0113]    Preferably, when the UE  502  has joined one or more MBMS services, the MBMS service activation indicator can be used together with the above-stated MBMS service ID to inform the RNC  504  and the SGSN  506  that the UE  502  has joined the MBMS service.  
         [0114]    If an RRC connection is successfully set up between the UE  502  and the RNC  504  through steps  550  to  554 , in step  556 , the RNC  504  transmits an MBMS Service List Request message to the SGSN  506  in order to determine whether the UE  502  has joined a certain MBMS service. The MBMS Service List Request message includes a UE ID and an RNC ID.  
         [0115]    If the UE  502  is in a PMM-Idle state, a dedicated signaling bearer allocated for the UE  502  does not exist between the RNC  504  and the SGSN  506 . Therefore, the MBMS Service List Request message is transmitted using a connectionless signaling transmission method.  
         [0116]    In step  558 , if the RNC  504  does not exist in an MBMS service context in the SGSN  506 , the SGSN  506  adds to the MBMS service context information on the RNC  504 . In the step  558 , state information can be stored in the MBMS service context in the SGSN  506  so as to indicate that the UE  502  is in a CMM-Connected state.  
         [0117]    In step  560 , the SGSN  506  transmits information on an MBMS service currently joined by the UE  502  corresponding to a UE ID included in the MBMS Service List Request message, i.e., transmits an MBMS service ID list, to the RNC  504  along with an MBMS Service List Response message. The MBMS service ID list is extracted from a UE context stored in the SGSN  506 . The UE context can be either an existing UE context or a UE context newly defined for an MBMS service.  
         [0118]    The MBMS service ID list can further include information on an area where an MBMS service is currently available, with respect to each of the MBMS services that the UE  502  has joined. For example, the information on an area where the MBMS service is available represents a service area code (SAC) or multicast area information. If, based on the service area information, it is determined that the UE  502  is located in a cell not belonging to an area where the MBMS service is available, the RNC  504  can request the UE  502  to move to another cell.  
         [0119]    In step  564 , the RNC  504  adds information on the UE  502  to an MBMS service context corresponding to the MBMS service ID list included in the MBMS Service List Response message. If a second MBMS service context corresponding to the MBMS service ID included in the MBMS Service List Response message does not exist in the RNC  504 , the RNC  504  first creates a new second MBMS service context. In addition, if the UE  502  is simultaneously joining N MBMS services, i.e., if the number of MBMS service IDs included in the MBMS service ID list is N, the RNC  504  adds information on the UE  502  to each of N second MBMS service contexts.  
         [0120]    Although not illustrated in FIG. 9, in a modified embodiment of the present invention, a may UE transmit an MBMS Service Request message containing an MBMS service activation indicator to an RNC after RRC connection setup is completed. In response to the MBMS Service Request message, the RNC then requests an SGSN for MBMS service ID(s) of MBMS service(s) that the UE is joining, receives from the SGSN an MBMS service ID list including MBMS service ID(s) of the MBMS service(s) that the UE is joining, and adds information on the UE to its MBMS service context(s).  
         [0121]    Through the above-described procedure, the RNC  504  detects that the UE  502  having an RRC connection is joining an MBMS service, and pages the UE  502  using a Paging Type 2 message through a dedicated channel, when a session of an MBMS service joined by the UE  502  is started.  
         [0122]    FIGS.  10  to  12  are flowcharts illustrating operations of the UE  502  according to the procedures illustrated in FIGS.  7  to  9 , respectively. Referring to FIGS.  10  to  12 , in steps  602 ,  610 , and  620 , the UE  502  joins an MBMS service through the procedure described in connection with FIG. 5. In steps  604 ,  612 , and  622 , the UE  502  monitors whether an RRC connection exists. If it is determined that no RRC connection exists, the UE  502  monitors in steps  606 ,  614 , and  624  whether there is an RRC connection reconfiguration request. If it is determined that there is an RRC connection reconfiguration request, the UE  502  sends an MBMS service ID indicating the MBMS service joined by the UE  502  to the RNC  504  to which the RRC connection is to be set up, along with an RRC message, and then proceeds to steps  608 ,  616 , and  626 , respectively.  
         [0123]    In step  608  of FIG. 10, the UE  502  inserts an MBMS service ID into an RRC Connection message, i.e., an RRC Connection Setup Request message or an RRC Connection Setup Complete message, before transmission. In step  616  of FIG. 11, the UE  502  inserts an MBMS service ID into a dedicated message such as an MBMS Service Request message, before transmission.  
         [0124]    In step  626  of FIG. 12, the UE  502  inserts an MBMS service activation indicator into an RRC connection message, i.e., an RRC Connection Setup Request message or an RRC Connection Setup Complete message, before transmission. According to the modified embodiment of the present invention, in step  626 , the UE  502  inserts an MBMS service activation indicator into a dedicated message such as an MBMS Service Request message, before transmission.  
         [0125]    FIGS.  13  to  15  are flowcharts illustrating operations of the RNC  504  that manages a second MBMS service context, according to the procedures illustrated in FIGS.  7  to  9 , respectively. Referring to FIG. 13, in step  702 , the RNC  504  receives an RRC Connection Setup Request message (or an RRC Connection Setup Complete message) from the UE  502 . In step  704 , the RNC  504  determines whether an MBMS service ID is included in the RRC Connection Setup Request message.  
         [0126]    If no MBMS service ID is included in the RRC Connection Setup Request message, the RNC  504  performs an RRC connection setup procedure for a general service (not shown). However, if an MBMS service ID is included in the RRC Connection Setup Request message, in step  706 , the RNC  504  transmits an MBMS UE Validate Request message to the SGSN  506  in order to determine through the SGSN  506  whether the UE  502  is valid for the MBMS service. In step  708 , the RNC  504  determines whether a validate response for the MBMS UE Validate Request message is received. If a validate response for the MBMS UE Validate Request message is received, the RNC  504  proceeds to step  712  in order to update an MBMS service context for the UE  502 . However, if a validate response for the MBMS UE Validate Request message is not received, the RNC  504  transmits an MBMS Service Failure message to the UE  502  in step  710 .  
         [0127]    In step  712 , the RNC  504  searches for an MBMS service context corresponding to the MBMS service ID. If it is determined in step  714  that there is no MBMS service context corresponding to the MBMS service ID, the RNC  504  generates a new MBMS service context corresponding to the MBMS service ID in step  720 . Thereafter, in step  722 , the RNC  504  adds an ID of the UE  502  to the newly created MBMS service context, and in step  724 , the RNC  504  links the UE ID added to the MBMS service context with a corresponding UE context.  
         [0128]    However, if it is determined in step  714  that there is an MBMS service context corresponding to the MBMS service ID, the RNC  504  searches in step  716  for the ID of the UE  502  stored in the searched MBMS service context. If it is determined in step  718  that the UE ID exists in the MBMS service context, the RNC  504  is not required to newly add the UE ID. However, if the UE ID does not exist in the MBMS service context, the RNC  504  adds the UE ID in step  722 , and links the added UE ID with a corresponding UE context in step  724 .  
         [0129]    Referring to FIG. 14, if an RRC connection setup between the UE  502  and the RNC  504  is completed in step  730 , the RNC  504  receives an MBMS Service Request message containing an MBMS service ID from the UE  502  in step  732 . In step  734 , the RNC  504  transmits an MBMS UE Validate Request message in order to inquire of the SGSN  506  about whether an MBMS service requested by the UE  502  is valid, in response to the MBMS Service Request message.  
         [0130]    If it is determined in step  736  that a validate response for the MBMS UE Validate Request message is received, the RNC  504  proceeds to step  740  in order to update an MBMS service context in the RNC  504  for the UE  502 . However, if it is determined in step  736  that a validate response for the MBMS UE Validate Request message is not received, the RNC  504  proceeds to step  738  where it transmits an MBMS Service Failure message to the UE  502 .  
         [0131]    In step  740 , the RNC  504  searches for an MBMS service context corresponding to the MBMS service ID. If it is determined in step  742  that there is no MBMS service context corresponding to the MBMS service ID, the RNC  504  proceeds to step  748  where it creates a new MBMS service context corresponding to the MBMS service ID. Thereafter, the RNC  504  adds an ID of the UE  502  to the newly created MBMS service context in step  750 , and links the UE ID added to the MBMS service context with a corresponding UE context in step  752 .  
         [0132]    However, if it is determined in step  742  that there is an MBMS service context corresponding to the MBMS service ID, the RNC  504  determines in step  744  whether an ID of the UE  502  is stored in the searched MBMS service context. If it is determined in step  746  that the UE ID exists in the MBMS service context, the RNC  504  is not required to newly add the UE ID. However, if the UE ID does not exist in the MBMS service context, the RNC  504  adds the UE ID to the MBMS service context in step  750 , and links the added UE ID with a corresponding UE context in step  752 .  
         [0133]    Referring to FIG. 15, in step  760 , the RNC  504  receives an RRC Connection Setup Request message from a UE  502  that has released PS signaling after joining an MBMS service. In step  762 , the RNC  504  monitors whether an MBMS Service Request message, which is an RRC connection message or a dedicated RRC message, including an MBMS service activation indicator is received from the UE  502 .  
         [0134]    If the MBMS service activation indictor is received, in step  764 , the RNC  504  transmits an MBMS Service List Request message to the SGSN  506  in order to request an MBMS service list including MBMS services the UE  502  has joined.  
         [0135]    In step  766 , the RNC  504  monitors whether an MBMS Service List Response message is successfully received from the SGSN  506  in response to the MBMS Service List Request message. If the RNC  504  fails to successfully receive the MBMS Service List Response message from the SGSN  506 , in step  768 , the RNC  504  transmits an MBMS Service Failure message to the UE  502  and then ends the operation.  
         [0136]    However, if it is determined in step  766  that an MBMS Service List Response message containing at least one MBMS service ID for an MBMS service that the UE  502  has joined is received from the SGSN  506 , the RNC  504  determines in step  770  searches for an MBMS service context corresponding to an MBMS service ID extracted from the MBMS Service List Response message  
         [0137]    If it is determined in step  772  that there is a corresponding MBMS service context, the RNC  504  proceeds to step  774 . However, if the corresponding MBMS service context does not exist, the RNC  504  creates an MBMS service context corresponding to the MBMS service ID in step  778 . Further, the RNC  504  adds ID information of the UE  502  to the created MBMS service context in step  780 , and links the UE ID added to the MBMS service context with a corresponding UE context in step  782 .  
         [0138]    In step  774 , the RNC  504  determines whether an ID of the UE  502  is included in the MBMS service context. If it is determined in step  776  that an ID of the UE  502  is not included in the MBMS service context, the RNC  504  adds information on the UE  502  to the MBMS service context in step  780 . Thereafter, in step  782 , the RNC  504  links an ID of the UE  502  with a corresponding UE context. However, if it is determined in step  776  that an ID of the UE  502  is included in the MBMS service context, the RNC  504  ends the operation.  
         [0139]    [0139]FIG. 16 is a flowchart illustrating an operation of the SGSN  506  that manages an MBMS service context in association with the procedures illustrated in FIGS. 7 and 8. Referring to FIG. 16, in step  802 , the SGSN  506  receives from the RNC  504  an MBMS UE Validate Request message containing an MBMS service ID indicating an MBMS service that the UE  502  desires to receive. The MBMS UE Validate Request message additionally includes a UE ID of the UE  502  and an RNC ID of the RNC  504 . The SGSN  506  can optionally perform MBMS service authentication on the UE  502  in response to the MBMS UE Validate Request message. That is, in step  804 , the SGSN  506  determines whether the UE  502  has joined an MBMS service, thereby performing a service authentication operation.  
         [0140]    If the service authentication on the UE  502  is successful, the SGSN  506  proceeds to step  806  where it determines whether there is an MBMS service context corresponding to the MBMS service ID. However, if the service authentication on the UE  502  is unsuccessful, the SGSN  506  transmits an MBMS UE Validate Failure message to the RNC  504  in order to inform that the UE  502  has not joined the MBMS service via the SGSN  506  in step  822 .  
         [0141]    If it is determined in step  808  that the MBMS service context does exist, in step  810 , the SGSN  506  determines whether an ID of the UE  502  is included in the MBMS service context. However, if it is determined in step  808  that the MBMS service context does not exist, the SGSN  506  proceeds to step  822  where it sends an MBMS UE Validate Failure message to the RNC  504  to inform that the UE  502  has not joined the MBMS service via the SGSN  506 , and then ends the operation.  
         [0142]    If it is determined in step  812  that an ID of the UE  502  is not included in the MBMS service context, the SGSN  506  transmits in step  822  the MBMS UE Validate Failure message to the RNC  504  to inform that the UE  502  has not joined the MBMS service via the SGSN  506 . However, if it is determined in step  812  that an ID of the UE  502  is included in the MBMS service context, in step  814 , the SGSN  506  transmits an MBMS UE Validate Response message to the RNC  504  to inform that the UE  502  has joined the MBMS service via the SGSN  506 .  
         [0143]    In step  816 , the SGSN  506  searches for an RNC ID of the RNC  504  in the MBMS service context. If it is determined in step  818  that an RNC ID of the RNC  504  is not included in the MBMS service context, the SGSN  506  adds information on the RNC  504  to the MBMS service context in step  820 . However, if it is determined in step  818  that an RNC ID of the RNC  504  is already included in the MBMS service context, the SGSN  506  ends the operation.  
         [0144]    [0144]FIG. 17 is a flowchart illustrating an operation of the SGSN  506  that manages an MBMS service context in association with the procedure illustrated in FIG. 9. Referring to FIG. 17, in step  830 , the SGSN  506  receives from the RNC  504  an MBMS Service List Request message for requesting an MBMS service list including MBMS services that the UE  502  has joined.  
         [0145]    In step  832 , the SGSN  506  can optionally perform MBMS service authentication on the UE  502 . If the service authentication is unsuccessful, in step  852 , the SGSN  506  transmits an MBMS Service List Failure message to the RNC  504  to inform that the UE  502  has not joined any MBMS service via the SGSN  506 , and then ends the operation. However, if the service authentication is successful, the SGSN  506  searches a context of the UE  502  for MBMS service IDs for MBMS services that the UE  502  has joined via the SGSN  506 , in step  834 .  
         [0146]    If it is determined in step  836  that searching for the MBMS service IDs is unsuccessful, the SGSN  506  transmits in step  852  an MBMS Service List Failure message to the RNC  504  to inform that the UE  502  has not joined any MBMS service via the SGSN  506 , and then ends the operation. However, if it is determined in step  836  that searching for the MBMS service IDs is successful, in step  838 , the SGSN  506  searches for an MBMS service context corresponding to the MBMS service ID searched in the step  836 . If it is determined in step  840  that searching for the MBMS service context is unsuccessful, in step  852 , the SGSN  506  transmits an MBMS Service List Failure message to the RNC  504  to inform that the UE  502  has not joined any MBMS service via the SGSN  506 , and then ends the operation.  
         [0147]    However, if it is determined in step  840  that the MBMS service context exists, in step  842 , the SGSN  506  searches for an ID of the UE  502  in the MBMS service context. If it is determined in step  844  that an ID of the UE  502  is not included in the MBMS service context, in step  852 , the SGSN  506  transmits an MBMS Service List Failure message to the RNC  504  to inform that the UE  502  has not joined any MBMS service via the SGSN  506 , and then ends the operation.  
         [0148]    In an alternative embodiment, although an ID of the UE  502  is not included in the MBMS service context, if the UE  502  has normally joined the MBMS service, the SGSN  506  adds information on the UE  502  to the MBMS service context without transmitting the MBMS Service List Failure message.  
         [0149]    However, if it is determined in step  844  that an ID of the UE  502  is included in the MBMS service context, in step  846 , the SGSN  506  transmits an MBMS Service List Response message to the RNC  504  to inform that the UE  502  has joined the MBMS service via the SGSN  506 . The MBMS Service List Response message, as described in step  560  of FIG. 9, includes information on MBMS service(s) that the UE  502  corresponding to a UE ID included in the MBMS Service List Request message received in step  830  is currently joining, i.e., includes an MBMS service ID list.  
         [0150]    In step  848 , the SGSN  506  searches for an RNC ID of the RNC  504  in the MBMS service context. If it is determined in step  850  that an RNC ID of the RNC  504  is not included in the MBMS service context, the SGSN  506  adds information on the RNC  504  to the MBMS service context in step  854 . However, if it is determined in step  850  that an RNC ID of the RNC  504  is included in the MBMS service context, the SGSN  506  ends the operation.  
         [0151]    2. Management of a Service Context in an SGSN  
         [0152]    In a second embodiment of the present invention, in order to enable an SGSN to manage information on a UE that joined an MBMS service but is in a PMM-Idle/RRC-Connected mode, MBMS service-related information indicating that the UE is a terminal that successfully joined the MBMS service is transmitted to the SGSN via an RNC along with a predetermined message. The SGSN updates information on the UE in a corresponding MBMS service context requested by the UE among MBMS service contexts managed by the SGSN. Accordingly, the SGSN can manage a list of UEs that have set up RRC connection for a CS service together with its MBMS service context.  
         [0153]    The MBMS service-related information corresponds to an MBMS service ID indicating an MBMS service that the terminal joined, or an MBMS service activation indicator.  
         [0154]    FIGS.  18  to  21  are diagrams illustrating procedures for adding information on a UE to an MBMS service context of an SGSN associated with the UE that joined an MBMS service but is in a PMM-Idle mode. In FIGS.  18  to  21 , reference numeral  902  represents a UE receiving an MBMS service, reference numeral  904  represents an RNC for an MBMS service, associated with the UE  902 , and reference numeral  906  represents an SGSN of a CN for the MBMS service. In addition, an MBMS service context of the SGSN  906  will be referred to as a “first MBMS service context,” and an MBMS service context of the RNC  904  will be referred to as a “second MBMS service context.” The UE  902  is a UE that joined a desired MBMS service but is in a PMM-Idle mode where there is no PS service currently in operation via the SGSN  906 . In the PMM-Idle mode, because no SRNC exists for the UE  902  receiving an MBMS service, the SGSN  906  doest not transmit MBMS service-related information to the RNC  904  where the UE  902  is currently located.  
         [0155]    More specifically, FIGS. 18 and 19 are diagrams illustrating procedures for storing MBMS service-related information when the UE  902  requests the RNC  904  to set up RRC connection for a CS service. Referring to FIG. 18, in step  910 , the UE  902  sets up an RRC connection to the RNC  904  in order to receive a CS service. At this point, the UE  902  inserts a desired MBMS service ID into an RRC Connection Setup Request message or an RRC Connection Setup Complete message transmitted to the RNC  904 , in order to request the RNC  904  to add information on the UE  902  to an MBMS service context corresponding to the MBMS service ID. If the RRC connection is successfully set up between the UE  902  and the RNC  904 , the RNC  904  transmits in step  912  an MBMS UE Validate Request message to the SGSN  906  in order to request the SGSN  906  to determine whether the UE  902  has joined the MBMS service. The MBMS UE Validate Request message includes a UE ID of the UE  902 , the MBMS service ID, and an RNC ID of the RNC  904 .  
         [0156]    The SGSN  906  determines whether a second MBMS service context corresponding to the MBMS service ID included in the MBMS UE Validate Request message exists and whether the UE ID exists in the second MBMS service context. If the MBMS service ID included in the MBMS UE Validate Request message exists and the UE ID exists in the second MBMS service context, the SGSN  906  transmits in step  916  an MBMS UE Validate Response message to the RNC  904  in order to inform that the UE  902  is valid for the MBMS service. The MBMS UE Validate Response message can include a UE list of UEs valid for the MBMS service and information on the areas where the MBMS service is available.  
         [0157]    In an alternative embodiment, the SGSN  906  determines that the UE  902  is valid for the MBMS service, when an MM context corresponding to the UE ID included in the MBMS UE Validate Request message exists in the SGSN  906  and an MBMS service context corresponding to the MBMS service ID exists in the MM context.  
         [0158]    In step  914 , the SGSN  906  receiving the MBMS UE Validate Request message stores UE information indicating that the UE  902  is in an RRC-Connected, i.e., CMM-Connected mode for a CS service, in the second MBMS service context. In step  918 , the RNC  904  adds information on the UE  902  to a first MBMS service context thereof in response to the MBMS UE Validate Response message.  
         [0159]    Referring to FIG. 19, in step  920 , the UE  902  sets up an RRC connection to the RNC  904  in order to receive a CS service. Here, the UE  902  inserts an MBMS service activation indicator indicating that there is at least one MBMS service that the UE  902  has joined, into an RRC Connection Setup Request message or an RRC Connection Setup Complete message transmitted to the RNC  904 . The MBMS service activation indicator is set when the UE  902  has joined one or more MBMS services.  
         [0160]    If RRC connection is successfully established between the UE  902  and the RNC  904 , in step  922 , the RNC  904  transmits an MBMS Service List Request message to the SGSN  906  in order to request the SGSN  906  to determine whether the UE  902  has joined a certain MBMS service. The MBMS Service List Request message includes a UE ID of the UE  902  and an RNC ID of the RNC  904 .  
         [0161]    When an MM context corresponding to the UE ID included in the MBMS Service List Request message exists in the SGSN  906  and an MBMS service context exists in the MM context, in step  926  the SGSN  906  transmits an MBMS Service List Response message containing MBMS service IDs included in the MM context, to the RNC  904 . That is, the MBMS Service List Response message includes a list of MBMS service IDs for all MBMS services that the UE  902  has joined. In addition, the MBMS Service List Response message can include information on the areas where at least one MBMS service that the UE  902  has joined is available.  
         [0162]    In step  924 , in response to the MBMS Service List Request message, the SGSN  906  stores UE information indicating that the UE  902  is in an RRC-Connected, i.e., CMM-Connected mode for a CS service, in the MBMS service context. In step  928 , the RNC  904  adds UE information of the UE  902  to its own MBMS service context in response to the MBMS Service List Response message.  
         [0163]    Above, an embodiment where the UE uses an MBMS service ID and another embodiment where the UE uses an MBMS service activation indictor have been separately described. However, in a modified embodiment of the present invention, the UE can use both the MBMS service ID and the MBMS service activation indictor. That is, when the UE joins only one MBMS service, it transmits the MBMS service ID to an SGSN via an RNC, and when the UE joins two or more MBMS services, it transmits the MBMS service activation indicator to the SGSN via the RNC. As a result, the SGSN receives one of the two types of information through an MBMS UE Validate Request message or an MBMS Service List Request message from the RNC, adds information on the UE to its own MBMS service context through the above-described procedure, and transfers a response thereto to the RNC.  
         [0164]    [0164]FIG. 20 is a diagram illustrating a procedure in which the UE  902  receiving an MBMS service in a PMM-Idle state transitions to a PMM-Connected mode by requesting a PS network to set up connection while requesting the RNC  904  to set up RRC connection for a CS service, and stores MBMS service-related information in the RNC  904  and the SGSN  906 . Referring to FIG. 20, in step  930 , the UE  902  sets up an RRC connection to the RNC  904  in order to receive a CS service. In step  932 , the UE  902  determines to also request PMM-Signaling connection when requesting the RRC connection while it joins an MBMS service. That is, an RRC layer of the UE  902  requests an upper layer to transition to a PMM-Connected mode. Here, the “upper layer” refers to a packet mobility management (PMM) entity. If the PMM entity determines to connect PS signaling in response to a request from the RRC layer, in step  934 , the UE  902  transmits a Service Request message to the SGSN  906  through a NAS interface in order to request connection of PS signaling, and then transitions to a PMM-Connected mode in step  936 . The following operation between the SGSN  906  and the RNC  904  follows an MBMS UE Linking procedure for a UE in a PMM-Connected mode.  
         [0165]    The Service Request message includes either an MBMS service ID or an MBMS service activation indicator. The MBMS service activation indicator is added to the Service Request message as an information element (IE), or added to NAS messages as a Cause Value (e.g., Cause=“MBMS Service Activation”).  
         [0166]    In step  938 , the SGSN  906  changes state information of the UE  902  in an MM context of the UE  902  to PMM-Connected in response to the Service Request message. In step  940 , the SGSN  906  transfers an MBMS service ID list of the UE  902  to the RNC  904  through an MBMS UE Linking Request message. In step  942 , the RNC  904  adds information on the UE  902  to a corresponding MBMS service context in the RNC  904  by consulting the MBMS service ID list. In step  944 , the RNC  904  sends an MBMS UE Linking Response message to the SGSN  906  to inform that information on the UE  902  has been successfully added to its own MBMS service context.  
         [0167]    [0167]FIG. 21 is a diagram illustrating a procedure in which when requesting the RNC  904  to set up RRC connection for a CS service, the UE  902  receiving an MBMS service in a PMM-Idle state stores MBMS service-related information from the UE  902  to the RNC  904  through a Uu message and stores MBMS service-related information from the UE  902  to the SGSN  906  through a NAS message. In this procedure, MBMS service-related information transmitted to the SGSN  906  includes an MBMS service ID or an MBMS service activation indicator. In the following description, it will be assumed that the MBMS service ID is used as the MBMS service-related information.  
         [0168]    Referring to FIG. 21, in step  950 , the UE  902  sets up an RRC connection to the RNC  904  in order to receive a CS service. Here, at least one MBMS service ID indicating an MBMS service that the UE  902  has joined is included in an RRC connection message, i.e., an RRC Connection Setup Request message or an RRC Connection Setup Complete message, being transmitted from the UE  902  to the RNC  904  in order to set up RRC connection for a CS service. If the RRC connection between the UE  902  and the RNC  904  is successfully set up, in step  952 , the RNC  904  transmits an MBMS UE Validate Request message to the SGSN  906  in order to request the SGSN  906  to determine whether the UE  902  has joined the MBMS service. The MBMS UE Validate Request message includes a UE ID of the UE  902 , the MBMS service ID, and an RNC ID of the RNC  904 .  
         [0169]    When an MBMS service context corresponding to the MBMS service ID exists in the SGSN  906  and the UE ID exists in the MBMS service context, in step  954 , the SGSN  906  transmits an MBMS UE Validate Response message to the RNC  904  to inform that the UE  902  is valid for the MBMS service. The MBMS UE Validate Response message can also include information on the areas where the MBMS service is available.  
         [0170]    In addition, if an MM context corresponding to the UE ID exists in the SGSN  906  and an MBMS service context corresponding to the MBMS service ID exists in the MM context, the SGSN  906  receiving the MBMS UE Validate Request message determines that the UE  902  is valid for the MBMS service. In step  956 , the RNC  904  stores UE information indicating that the UE  902  is in a CMM-Connected mode, in the MBMS service context associated with the MBMS service.  
         [0171]    An RRC entity of the UE  902  reports completion of RRC connection to an upper layer of the UE  902  after setting up RRC connection in step  950 . Here, the “upper layer” refers to a PMM entity. If the PMM entity determines to connect PS signaling in response to a request from the RRC layer, in step  958  the UE  902  transmits a message informing the SGSN  906  that Linking information between the UE  902  and the MBMS service exists in the RNC  904  even though the UE  902  is in a CMM-Connected or PMM-Idle state, using a NAS interface. The above-described message is transmitted from the UE  902  to the SGSN  906 , and includes a parameter indicating that linking information between the UE  902  and the MBMS service exists in the RNC  904  even though the UE  902  is in a CMM-Connected or PMM-Idle state.  
         [0172]    In addition, the above-described message corresponds to a dedicated Service Request message for MBMS service request or a typical Service Request message to which a Cause Value having a value indicating MBMS service request is added. When the message is a dedicated Service Request message, the Service Request message includes a flag such as CMM-Connected. CMM-Connected=0 represents a CMM-Idle state, and CMM-Connected=1 represents a CMM-Connected state. When the message is a typical Service Request message to which a parameter is added, the Service Request message includes the MBMS service ID or a Cause Value having a new value indicating a CMM-Connected state.  
         [0173]    The Service Request message can become a dedicated message for MBMS service request or an existing Service Request message to which a Cause Value having a new value is added. When the Service Request message is defined as a dedicated message, the Service Request message includes a flag such as CMM-Connected. Likewise, CMM-Connected=0 indicates a CMM-Idle state, and CMM-Connected=1 indicates a CMM-Connected state.  
         [0174]    In step  960 , the SGSN  906  stores UE information indicating that the UE  902  is in a CMM-Connected state, in an MBMS service context corresponding to the MBMS service in response to the Service Request message. That is, the SGSN  906  stores the UE information in the MBMS service context corresponding to the MBMS service joined by the UE  902 . Here, if the Service Request message includes the MBMS service ID, the SGSN  906  searches the MBMS service context using the MBMS service ID. However, if the Service Request message does not include the MBMS service ID, the SGSN  906  searches an MM context using the UE ID, and then acquires the MBMS service context included in the MM context.  
         [0175]    After receiving the Service Request message in step  958  and updating its own MBMS service context, the SGSN  906  determines whether MBMS service-related information (such as an MBMS UE Validate Request message) for the UE  902  is received from the RNC  904 . If the MBMS service-related information is not received, the SGSN  906  transmits to the RNC  904  an MBMS UE Linking Request message containing at least one MBMS service ID for an MBMS service that the UE  902  has joined so that the RNC  904  can store information on the UE  902  in its own MBMS service context.  
         [0176]    Although not illustrated, in a modified embodiment of the present invention, in transmitting a Service Request message to the SGSN  906 , the UE  902  uses an MBMS service ID when it joins only one MBMS service, and uses an MBMS service activation indicator when it joins two or more MBMS services. The following operation in the modified embodiment is the same as the corresponding operation as described above.  
         [0177]    The reason for adding CMM-Connected information to the MBMS service context of an SGSN in this manner is to delete linking information for a UE in an RNC when the UE in a PMM-Idle/RRC-Connected state makes a service delete request. That is, through the procedures illustrated in FIGS.  18  to  21 , if the SGSN detects that the UE has RRC connection and the RNC stores the MBMS service-related information of the UE, then the SGSN uses the information in deleting linking between the UE and the MBMS service through delinking from the RNC when the UE makes an MBMS service leave request.  
         [0178]    [0178]FIGS. 22 and 23 are diagrams illustrating procedures for deleting MBMS service-related information of a UE from MBMS service contexts of an SGSN and an RNC. In FIGS. 22 and 23, reference numeral  1002  represents a UE receiving an MBMS service, reference numeral  1004  represents an RNC for a corresponding MBMS service, associated with the UE  102 , and reference numeral  1006  represents an SGSN of a CN for the MBMS service. Additionally, the UE  1002  is in a state where it has joined an MBMS service but has no other PS service in progress via the SGSN  1006 .  
         [0179]    More specifically, FIG. 22 is a diagram illustrating a procedure in which a UE receiving an MBMS service in a PMM-Idle state deletes MBMS service-related information in an RNC and deletes MBMS service-related information in an SGSN through an Iu message from the RNC to the SGSN, in releasing RRC connection set up for a CS service. Referring to FIG. 22, if a CS service of the UE  1002  is released (or suspended) in step  1010 , the RNC  1004  sends an RRC Connection Release message to the UE  1002  in step  1012 . The RRC Connection Release message transmitted from the UE  1002  to the RNC  1004  includes an MBMS service ID indicating an MBMS service in progress by the UE  1002 .  
         [0180]    In step  1014 , the RNC  1004  deletes information on the UE  1002  from its own MBMS service context. Thereafter, in step  1016 , the RNC  1004  informs the SGSN  1006  that because the UE  1002  released RRC connection, the linking between the UE  1002  and the MBMS service does not exist any longer in the RNC  1004 . In step  1016 , an MBMS UE Update Request message including the MBMS service ID and the UE ID is used. The MBMS UE Update Request message further includes a parameter Cause indicating that the UE  1002  has transitioned from the CMM-Connected mode to the CMM-Idle mode, in addition to the MBMS service ID and the UE ID.  
         [0181]    In step  1018 , the SGSN  1006  deletes UE information indicating that the UE  1002  is in a CMM-Connected mode, from an MBMS service context in the SGSN  1006  by consulting the MBMS UE Update Request message. In step  1020 , the SGSN  1006  responds to the RNC  1004  with an MBMS UE Update Response message.  
         [0182]    [0182]FIG. 23 is a diagram illustrating a procedure for deleting MBMS service-related information through an Iu message transmitted from an SGSN  1006  to an RNC  1004  when a UE  1002  receiving an MBMS service in a PMM-Idle state requests suspension of an MBMS service while managing RRC connection set up for a CS service. Referring to FIG. 23, the UE  1002  determines to suspend reception of at least one MBMS service in progress in step  1030 , and informs the SGSN  1006  of intended suspension of the MBMS service through a general MBMS Service Leave procedure in step  1032 . In step  1034 , the SGSN  1006  deletes UE information indicating that the UE  1002  is in a CMM-Connected mode, from an MBMS service context for the MBMS service, suspension of which was requested by the UE  1002 . Additionally in step  1034 , the SGSN  1006  first determines whether the UE information is stored in the MBMS service context, before deleting the UE information. If the UE information is stored in the MBMS service context, the SGSN  1006  transmits an MBMS UE Delinking Request message containing an MBMS service ID indicating an MBMS service that the UE  1002  desires to leave, to the RNC  1004  in step  1036 . The MBMS UE Delinking Request message includes the MBMS service ID. Here, because the MBMS UE Delinking Request message is transmitted through UE dedicated signaling based on an Iu interface, the RNC  1004  can distinguish the UE  1002  that transmitted the message.  
         [0183]    In step  1038 , the RNC  1004  determines whether the UE  1002  included in an MBMS service context of the RNC  1004  is the last UE. If the UE  1002  is the last UE linked to the MBMS service context of the RNC  1004 , the RNC  1004  deletes UE information of the UE  1002  from the MBMS service context, and in step  1040 , transmits an MBMS UE Delinking Response message to the SGSN  1006  in response to the MBMS UE Delinking Request message.  
         [0184]    [0184]FIG. 24 is a flowchart illustrating an operation of the SGSN  1006  according to the second embodiment of the present invention. Referring to FIG. 24, in step  1102 , an SGSN determines whether a message received from a UE via an RNC is an RRC connection message. If the received message is an RRC connection message, the SGSN proceeds to step  1104 , and if the received message is not an RRC connection message, the SGSN proceeds to step  1138 .  
         [0185]    In step  1104 , the SGSN determines whether an MBMS UE Validate Request message, i.e., a message for requesting the SGSN to check whether the UE is valid for a particular MBMS service, is received from the RNC. The MBMS UE Validate Request message includes a UE ID and an RNC ID, and may further include an MBMS service ID indicating the particular MBMS service. If the MBMS UE Validate Request message is received, the SGSN proceeds to step  1106 , and if the MBMS UE Validate Request message is not received, the SGSN proceeds to step  1128 .  
         [0186]    In step  1106 , the SGSN optionally performs MBMS service authentication on the UE, and if the service authentication is successful, the SGSN proceeds to step  1108 . However, if the service authentication is unsuccessful, the SGSN proceeds to step  1126   
         [0187]    In step  1108 , the SGSN determines whether there is an MBMS service context corresponding to the MBMS service ID. If it is determined in step  1108  that the MBMS service context exists, the SGSN proceeds to step  1110 . However, if the MBMS service context does not exist, the SGSN proceeds to step  1126 .  
         [0188]    In step  1110 , the SGSN determines whether the MBMS service ID is included in the MBMS service context. If it is determined in step  1110  that the MBMS service ID is included in the MBMS service context, the SGSN proceeds to step  1112 . However, if the MBMS service ID is not included in the MBMS service context, the SGSN proceeds to step  1126 .  
         [0189]    In step  1126 , the SGSN transmits an MBMS UE Validate Failure message to the RNC to inform that the UE has not joined the MBMS service via the SGSN, and then ends the operation.  
         [0190]    In step  1112 , the SGSN determines whether to store linking information. If the SGSN determines to store the linking information, it proceeds to step  1116 , and if the SGSN determines not to store the linking information, it proceeds to step  1118 . Here, the SGSN determines to store the linking information according to a predetermined operation mode when the UE directly stores MBMS service-related information of the UE in the RNC through a Uu message and the RNC transmits an Iu message to the SGSN to inform that RRC connection is set up.  
         [0191]    In step  1116 , the SGSN stores UE information indicating that the UE is in a CMM-Connected mode, in the MBMS service context, and then proceeds to step  1118 , in which the SGSN transmits to the RNC an MBMS UE Validate Response message indicating that the UE has joined the MBMS service via the SGSN, and then proceeds to step  1120 .  
         [0192]    In step  1120 , the SGSN determines whether the RNC ID is included in the MBMS service context. If it is determined that the RNC ID is not included in the MBMS service context, the SGSN proceeds to step  1124 , where the SGSN adds information on the RNC to the MBMS service context. However, if it is determined that the RNC ID is included in the MBMS service context in step  1120 , the SGSN ends the operation.  
         [0193]    In step  1128 , the SGSN determines whether an MBMS UE Update message is received from the RNC. If the MBMS UE Update message is received, the SGSN proceeds to step  1130 , but if the MBMS UE Update message is not received, the SGSN ends the operation.  
         [0194]    In step  1130 , the SGSN optionally performs MBMS service authentication on the UE, and if the service authentication is successful, the SGSN proceeds to step  1132  determining that the UE is valid for the MBMS service. However, if the service authentication is unsuccessful, the SGSN ends the operation. In step  1132 , the SGSN determines whether there is an MBMS service context corresponding to the MBMS service ID. If the MBMS service context exists in step  1132 , the SGSN proceeds to step  1134 , but if the MBMS service context does not exist in step  1132 , the SGSN ends the operation. In step  1134 , the SGSN deletes UE information indicating that the UE is in a CMM-Connected mode, from the MBMS service context. In step  1136 , the SGSN transmits a response message to the RNC.  
         [0195]    In step  1138 , the SGSN determines whether the message received from the UE is a Service Request message containing CMM-Connected mode information. If the received message is the Service Request message, the SGSN proceeds to step  1140 . The Service Request message includes an MBMS service ID. However, if the received message is not the Service Request message in step  1138 , the SGSN ends the operation.  
         [0196]    In step  1140 , the SGSN determines whether a cause of a Service Request message is CMM-Connected mode. If a cause of the message is CMM-Connected mode, the SGSN proceeds to step  1142 , but if a cause of the message is not CMM-Connected mode, the SGSN ends the operation.  
         [0197]    In step  1142 , the SGSN optionally performs MBMS service authentication on the UE. If the service authentication is unsuccessful, the SGSN ends the operation. However, if the service authentication is successful, the SGSN proceeds to step  1144  determining that the UE is valid for the MBMS service.  
         [0198]    In step  1144 , the SGSN determines whether there is an MBMS service context corresponding to the MBMS service ID. If the MBMS service context exists, the SGSN proceeds to step  1146 , but if the MBMS service context does not exist, the SGSN ends the operation. In step  1146 , the SGSN adds UE information indicating that the UE is in a CMM-Connected mode, to the MBMS service context.  
         [0199]    [0199]FIG. 25 is a flowchart illustrating an operation of a UE according to the second embodiment of the present invention. Referring to FIG. 25, in step  1202 , a UE transitions to a PMM-Idle mode after joining an MBMS service. In step  1204 , the UE determines whether it has RRC connection. Because the UE is in the PMM-Idle mode, if the UE has RRC connection, the RRC connection is for a CS service. If the UE has RRC connection, it proceeds to step  1210 , but otherwise, the UE proceeds to step  1206 .  
         [0200]    In step  1206 , the UE determines whether the MBMS service already joined by the UE is interrupted. If the MBMS service is not interrupted, the UE proceeds to step  1208 , but if the MBMS service is interrupted, the UE ends the operation.  
         [0201]    In step  1208 , the UE determines whether to perform an RRC connection setup procedure. If the UE determines to perform the RRC connection setup procedure, the UE determines in steps  1210 ,  1214  and  1220 , which case is present.  
         [0202]    If it is determined in step  1210  that the UE follows Case 1, the UE proceeds to step  1212 . Here, Case 1 represents an embodiment in which the UE directly stores MBMS service-related information in an RNC through a Uu message and the RNC transmits an Iu message to an SGSN to inform that the UE is performing an RRC connection setup procedure. In step  1212 , the UE transmits to the RNC an RRC Connection Setup Request message or an RRC Connection Setup Complete message containing an MBMS service ID or an MBMS service activation indicator, in order to request the RNC to add information on the UE to an MBMS service context corresponding to the MBMS service that the UE is joining.  
         [0203]    If it is determined in step  1210  that the UE does not follow Case 1, the UE determines in step  1214  whether it follows Case 2. If the UE follows Case 2, it proceeds to step  1216 . Here, Case 2 represents an embodiment in which when the UE sets up RRC connection for a CS service, it transitions to a PMM-Connected state and informs the SGSN that the UE is performing an RRC connection setup procedure through a NAS interface using the existing MBMS UE Linking procedure. In step  1216 , the UE transmits to the SGSN a Service Request message containing a parameter (for example, an MBMS service ID or an MBMS service activation indicator) indicating the MBMS service. In step  1218 , the UE transitions to a PMM-Connected mode, and then ends the operation.  
         [0204]    However, if it is determined in step  1214  that the UE does not follow Case 2, the UE determines in step  1220  whether it will follow Case 3. If the UE follows Case 3, it proceeds to step  1222 . In step  1222 , the UE transmits to the RNC an RRC Connection Setup Request message or an RRC Connection Setup Complete message containing an MBMS service ID or an MBMS service activation indicator, in order to request the RNC to add information on the UE to an MBMS service context corresponding to the MBMS service that the UE is joining. In step  1224 , the UE transmits a Service Request message and a parameter (for example, an MBMS service ID) indicating the MBMS service, including information indicating that the UE is a CMM-Connected mode, to the SGSN through a NAS interface.  
         [0205]    As can be appreciated from the foregoing description, when UEs having joined an MBMS service are in an RRC-Connected mode after setting up a call for a CS service or a PS service, the present invention prevents the UEs from failing to receive a notification for paging of the MBMS service in providing the MBMS service, thereby increasing success rate and reliability of MBMS paging. According to the present invention, when a UE is in a PMM-Idle/RRC-Connected mode, MBMS service linking information of the UE in an RNC and an SGSN is held in providing an MBMS service, making it possible to efficiently provide the MBMS service.  
         [0206]    While the present invention has been shown and described with reference to certain preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the appended claims.