Abstract:
The present disclosure relates to a pre-5 th -Generation (5G) or 5G communication system to be provided for supporting higher data rates Beyond 4 th -Generation (4G) communication system such as Long Term Evolution (LTE). An apparatus and method for managing a connection point with a data network in a wireless communication system is provided. A method of a terminal in a wireless communication system includes: receiving, from a network entity, a request for a relocation of an anchor gateway for connecting with a data network; and transmitting a message requesting the relocation of the anchor gateway to the network entity at a time which is determined based on a rule instructed by the request.

Description:
PRIORITY 
       [0001]    The present application claims priority under 35 U.S.C. §119 to an application filed in the Korean Intellectual Property Office on Jul. 29, 2014 and assigned Serial No. 10-2014-0096534, the contents of which are incorporated herein by reference. 
       BACKGROUND 
       [0002]    1. Technical Field 
         [0003]    Exemplary embodiments of the present disclosure relate to an apparatus and method for managing a connection point with a data network in a wireless communication system. 
         [0004]    2. Description of the Related Art 
         [0005]    To meet the demand for wireless data traffic having increased since deployment of 4th generation (4G) communication systems, efforts have been made to develop an improved 5th generation (5G) or pre-5G communication system. Therefore, the 5G or pre-5G communication system is also called a ‘Beyond 4G Network’ or a ‘Post LTE System’. 
         [0006]    The 5G communication system is considered to be implemented in higher frequency (mmWave) bands, e.g., 60 GHz bands, so as to accomplish higher data rates. To decrease propagation loss of the radio waves and increase the transmission distance, the beamforming, massive multiple-input multiple-output (MIMO), Full Dimensional MIMO (FD-MIMO), array antenna, an analog beam forming, large scale antenna techniques are discussed in 5G communication systems. 
         [0007]    In addition, in 5G communication systems, development for system network improvement is under way based on advanced small cells, cloud Radio Access Networks (RANs), ultra-dense networks, device-to-device (D2D) communication, wireless backhaul, moving network, cooperative communication, Coordinated Multi-Points (CoMP), reception-end interference cancellation and the like. 
         [0008]    In the 5G system, Hybrid FSK and QAM Modulation (FQAM) and sliding window superposition coding (SWSC) as an advanced coding modulation (ACM), and filter bank multi carrier (FBMC), non-orthogonal multiple access (NOMA), and sparse code multiple access (SCMA) as an advanced access technology have been developed. 
         [0009]    A mobile core network or an Access Service Network (ASN) includes a plurality of network entities performing given functions, in order to provide a wireless access to mobile terminals. For example, a Packet data network-Gateway (P-GW) connects the core network to an external Packet Data Network (PDN) such as Internet. 
         [0010]    The P-GW serves as an Internet Protocol (IP) anchor point for IP traffic which is forwarded via the P-GW. In recent years, technology for locally offloading some IP traffic without forwarding the IP traffic via a central P-GW has been suggested. An example of the technology for offloading traffic is a Selective IP Traffic Offload (SIPTO) mechanism. 
         [0011]    The traffic by the SIPTO is processed through a local P-GW. The local P-GW functions as a P-GW for the IP traffic passing through the local P-GW, and thus the local P-GW serves as an anchor of the IP traffic. When the SIPTO is employed in a mobile network, a plurality of local P-GWs may be distributed throughout the network. The IP traffic is anchored at the local P-GW. Therefore, when the user moves after IP session initialization, a User Equipment (UE) cannot relocate the local P-GW to which the UE is attached. If the local P-GW is relocated, ongoing IP traffic may be terminated, which causes service disruption to the user. However, since an enhanced local P-GW exists for users having high mobility, maintaining the initial local P-GW may not always be the optimum choice. 
       SUMMARY 
       [0012]    To address the above-discussed deficiencies, it is a primary object to provide an apparatus and method for managing a connection point with a data network in a wireless communication system. 
         [0013]    Another object of the present disclosure is to provide an apparatus and method for providing a service through an optimum anchor gateway in a wireless communication system. 
         [0014]    Another object of the present disclosure is to provide an apparatus and method for relocating an anchor gateway in a wireless communication system. 
         [0015]    Another object of the present disclosure is to provide an apparatus and method for relocating an anchor gateway without degrading user Quality of Experience (QoE) in a wireless communication system. 
         [0016]    Another object of the present disclosure is to provide an apparatus and method for relocating an anchor gateway by considering a flow state in a wireless communication system. 
         [0017]    Another object of the present disclosure is to provide an apparatus and method for providing information on a relocation of an anchor gateway in a wireless communication system. 
         [0018]    According to an aspect of the present disclosure, a method of a terminal in a wireless communication system includes: receiving, from a network entity, a request for a relocation of an anchor gateway for connecting with a data network; and transmitting a message requesting the relocation of the anchor gateway to the network entity at a time which is determined based on a rule instructed by the request. 
         [0019]    According to another aspect of the present disclosure, a method of a network entity in a wireless communication system includes: when a new anchor gateway for a terminal is determined, identifying information on session continuity of the terminal; and transmitting a message corresponding to the information on the session continuity. 
         [0020]    According to another aspect of the present disclosure, a method of a network entity in a wireless communication system includes: generating a message including information on session continuity; and transmitting the message. 
         [0021]    According to another aspect of the present disclosure, a terminal in a wireless communication system includes: a receiver configured to receive, from a network entity, a request for a relocation of an anchor gateway for connecting with a data network; and a transmitter configured to transmit a message requesting the relocation of the anchor gateway to the network entity at a time which is determined based on a rule instructed by the request. 
         [0022]    According to another aspect of the present disclosure, a network entity in a wireless communication system includes: a controller configured to, when a new anchor gateway for a terminal is determined, identify information on session continuity of the terminal; and a communication unit configured to transmit a message corresponding to the information on the session continuity. 
         [0023]    According to another aspect of the present disclosure, a network entity in a wireless communication system includes: a controller configured to generate a message including information on session continuity; and a communication unit configured to transmit the message. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]    For a more complete understanding of the present disclosure and its advantages, reference is now made to the following description taken in conjunction with the accompanying drawings, in which like reference numerals represent like parts: 
           [0025]      FIGS. 1A and 1B  illustrate views showing examples of a situation in which a gateway needs to be relocated in a wireless communication system according to an exemplary embodiment of the present disclosure; 
           [0026]      FIG. 2  illustrates a view showing a path for providing subscriber-based session continuity information in a wireless communication system according to an exemplary embodiment of the present disclosure; 
           [0027]      FIG. 3  illustrates a view showing a path for providing policy-based session continuity information in a wireless communication system according to an exemplary embodiment of the present disclosure; 
           [0028]      FIG. 4  illustrates a view showing exchange of signals for providing session continuity information through a bearer activation procedure in a wireless communication system according to an exemplary embodiment of the present disclosure; 
           [0029]      FIG. 5  illustrates a view showing exchange of signals for providing session continuity information through a bearer modification procedure in a wireless communication system according to an exemplary embodiment of the present disclosure; 
           [0030]      FIG. 6  illustrates a view showing exchange of signals for providing session continuity information through a bearer modification procedure, which is initiated by a Home Subscriber Server (HSS) in a wireless communication system according to an exemplary embodiment of the present disclosure; 
           [0031]      FIG. 7  illustrates a view showing a P-GW relocation procedure in a wireless communication system according to an exemplary embodiment of the present disclosure; 
           [0032]      FIG. 8  illustrates a view showing a Packet Data Network (PDN) reactivation procedure in a wireless communication system according to an exemplary embodiment of the present disclosure; 
           [0033]      FIG. 9  illustrates a view showing a P-GW relocation procedure in a wireless communication system according to another exemplary embodiment of the present disclosure; 
           [0034]      FIG. 10  illustrates a view showing a P-GW relocation procedure in a wireless communication system according to another exemplary embodiment of the present disclosure; 
           [0035]      FIG. 11  illustrates a view showing a PDN deactivation procedure in a wireless communication system according to an exemplary embodiment of the present disclosure; 
           [0036]      FIG. 12  illustrates a view showing an operation procedure of a terminal in a wireless communication system according to an exemplary embodiment of the present disclosure; 
           [0037]      FIG. 13  illustrates a view showing an operation procedure of a network entity which manages mobility in a wireless communication system according to an exemplary embodiment of the present disclosure; 
           [0038]      FIG. 14  illustrates a view showing an operation procedure of a network entity which provides session continuity information in a wireless communication system according to an exemplary embodiment of the present disclosure; 
           [0039]      FIG. 15  illustrates a block diagram of a terminal in a wireless communication system according to an exemplary embodiment of the present disclosure; and 
           [0040]      FIG. 16  illustrates a block diagram of a network entity in a wireless communication system according to an exemplary embodiment of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0041]    Hereinafter, techniques for controlling a data path in a wireless communication system will be explained. In particular, the present disclosure pertains to techniques for relocating an anchor gateway. 
         [0042]    The terms indicating network entities and the terms indicating connection states, which are used in the following description, are only for the convenience of explanation. Therefore, the present disclosure is not limited to the terms described below and other terms indicating objects having the same technical meanings may be used. For example, the term “terminal” used herein below may be replaced with “User Equipment (UE),” “Mobile Station (MS),” and “Mobile Terminal (MT).” 
         [0043]    There may exist a plurality of gateways for providing connection with an external Packet Data Network (PDN) such as Internet in order to offload traffic processing in a wireless access network or a mobile core network. Herein, the gateway may be referred to as a “Packet data network-Gateway (P-GW).” Therefore, a terminal may transmit and receive traffic via a different P-GW according to a location where initial access is achieved. The P-GW, which serves as a connection point with the external PDN for a specific terminal, may be referred to as an “anchor gateway” of the specific terminal. However, since the terminal is movable, it is not guaranteed that an initially selected P-GW is always an optimum P-GW. For example,  FIGS. 1A and 1B  illustrate examples of a situation in which the P-GW needs to be relocated. 
         [0044]      FIGS. 1A and 1B  illustrate views showing an example of a situation in which a gateway needs to be relocated in a wireless communication system according to an exemplary embodiment of the present disclosure. Referring to  FIGS. 1A and 1B , a core network includes a plurality of Serving-Gateways (S-GWs)  120 - 1  and  120 - 2 , and a plurality of P-GWs  130 - 1  and  130 - 2 . The S-GWs  120 - 1  and  120 - 2  are gateways for controlling routing and forwarding of packets transmitted to/received from a terminal  110 , and may be relocated according to movement of the terminal  110 . Although not shown in  FIG. 1 , the core network may further include a base station and network entities such as Mobile Management Entities (MMEs). The base station may be referred to as an “evolved NodeB (eNB).” 
         [0045]    Referring to view  FIG. 1A , the terminal  110  is connected with an external PDN via the first S-GW 1   120 - 1  and P-GW 1   130 - 1 . In this case, the P-GW 1   130 - 1  is an anchor gateway of the terminal  110 . Thereafter, when the terminal  110  moves as shown in view of  FIG. 1B , the gateway for processing the routing is relocated to the S-GW 2   120 - 2 . However, the anchor gate serving as a connection point with the PDN is maintained as the P-GW 1   130 - 1 . However, the P-GW 2   130 - 2  rather than the P-GW 1   130 - 1  may be the optimum anchor gateway for the terminal  110  and thus a procedure for relocating the anchor gateway of the terminal  110  to the P-GW 2   130 - 2  may be needed. 
         [0046]    As described above, the P-GW may need to be relocated. However, the relocation of the P-GW involves the change of an IP address. As such, when the P-GW is relocated by the network without recognizing an ongoing IP flow in the terminal, the relocation may cause degradation of User eXperience (UX) or user&#39;s QoE. Therefore, various exemplary embodiments of the present disclosure propose a P-GW relocation procedure considering the QoE of flows. 
         [0047]    When the P-GW is relocated based on the network, the interference by the ongoing flows in the terminal may badly affect the user QoE. However, considering that there are a variety of services, all applications may not always require session continuity. In other words, the necessity for the session continuity may depend on an application. In addition, the necessity for the session continuity may change with time. That is, a request for session continuity may be changed according to a kind of application or a state of an application. Therefore, there may be a situation where the IP session is broken without degrading the QoE. 
         [0048]    Hereinafter, various exemplary embodiments for relocating an anchor gateway by minimizing degradation of QoE will be explained. In the following explanation, “P-GW relocation” has the same meaning as “anchor gateway relocation.” 
         [0049]    Exemplary embodiments of the present disclosure include two kinds of methods for relocating a P-GW. The first method is time-independent P-GW relocation, and the second method is time-dependent P-GW relocation. 
         [0050]    In the case of the time-independent P-GW relocation, the P-GW is relocated based on partial flow information. When session continuity is needed according to the flow information, the P-GW is not relocated until a corresponding session is terminated. On the other hand, when the session continuity is not needed, the P-GW may be relocated as a more appropriate P-GW is found. In this case, the network determines whether the P-GW should be relocated or not according to a state change of a terminal. It may be determined whether the session continuity should be provided for a flow according to various criteria. 
         [0051]    For example, it may be determined whether the session continuity is needed or not based on at least one of a kind of application (e.g., a voice call, video streaming, a File Transfer Protocol (FTP) session, a chatting application, or the like), an application provider (e.g., an external service provider, a network operator), user subscription information (e.g., Gold, Silver, Bronze), and an operator policy (e.g., rules defined by an operator to determine session continuity, etc.). The criteria for determining to what kind of application, what application provider, or what subscriber rank the continuity will be provided may vary according to an exemplary embodiment and an intension of a person who embodies the present disclosure. 
         [0052]    In the case of the time-dependent P-GW relocation, the P-GW relocation may be triggered based on a current state of a flow. This is because all applications do not need session continuity. Therefore, the P-GW relocation is triggered when the session continuity is not critical to the flow. For example, the terminal may determine a time that the P-GW relocation does not badly affect the QoE of the flow, and trigger the P-GW relocation. 
         [0053]    Specifically, in the case of Hyper Text Transfer Protocol (HTTP)-based video streaming, when a video reproduction device has a sufficient video buffer, the P-GW relocation may not stall video reproduction. Therefore, when the P-GW relocation is triggered after a predetermined chunk of data has been downloaded, the application may not recognize the loss of continuity. 
         [0054]    In another example, in the case of online radio, when the P-GW relocation is achieved after a track has been downloaded, the user QoE may not be affected. The next track may be downloaded through a new P-GW after relocation. 
         [0055]    In another example, in the case of a chatting application/Social Network Service (SNS) application, when a current user does not interact with the application, the P-GW relocation may not badly affect the user QoE. The P-GW relocation may disconnect a keep-alive session, but the session may be re-established after the P-GW relocation. The user may not recognize the degradation of the QoE. 
         [0056]    In another example, in the case of a web application, when the P-GW relocation is triggered after an active component has been downloaded, the user QoE may not be degraded. In other words, the P-GW relocation may not stall or stop web page loading. 
         [0057]    The system according to an exemplary embodiment of the present disclosure may support the above-described two kinds of P-GW relocation methods. The time-independent P-GW relocation and the time-dependent P-GW relocation may be selectively performed according to circumstances. To select an appropriate P-GW relocation method, the system according to an exemplary embodiment of the present disclosure considers a plurality of levels of session continuity. For example, three levels of session continuity may be defined. Specifically, the levels of the session continuity may include “no session continuity” as a first level, “always session continuity” as a second level, and “on-demand session continuity” as a third level. The “no session continuity” means that the P-GW relocation is always accepted, the “always session continuity” means that the P-GW relocation is not accepted, and the “on-demand session continuity” means that the P-GW relocation is accepted when QoE is not degraded. Accordingly, the P-GW relocation is performed based on the level of session continuity support. 
         [0058]    The levels of the session continuity may be defined based on a subscriber or a flow. In other words, the levels of the session continuity may be assigned according to subscribers or flows. When the levels of the session continuity are assigned based on the subscribers, the levels of the session continuity may be provided through subscriber information or operator policy information. On the other hand, when the levels of the session continuity are assigned based on the flows, the levels of the session continuity may be provided through the operator policy information. 
         [0059]    When the levels of the session continuity are assigned according to the flows, the plurality of flows owned by a single terminal may have different levels. In this case, a single level of session continuity is applied to the terminal according to pre-defined priority. For example, the level of a high requirement for the session continuity may have high priority. Specifically, the “always session continuity” may have higher priority than the other levels, the “on-demand session continuity” may have higher priority than the “no session continuity.” and the “no session continuity” may have the lowest priority. 
         [0060]    According to an exemplary embodiment, the user subscription information may include session continuity for traffic. A network operator may assign the levels of session continuity for the traffic based on the user subscription information. To achieve this, traffic offload related-information may be added to the subscription information for each Access Point Name (APN) as shown in table 1 presented below: 
         [0000]    
       
         
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 items 
                 notes 
               
               
                   
               
             
             
               
                 traffic offload permission 
                 Indicates whether a SIPTO is allowed at 
               
               
                   
                 corresponding APN 
               
               
                 Levels for session continuity 
                 a. no session continuity 
               
               
                   
                 b. always session continuity 
               
               
                   
                 c. on-demand session continuity 
               
               
                   
               
             
          
         
       
     
         [0061]    According to an exemplary embodiment of the present disclosure, the traffic offload-related information may be provided via a path shown in  FIG. 2 .  FIG. 2  illustrates a view showing a path for providing subscriber-based session continuity information in a wireless communication system according to an exemplary embodiment of the present disclosure. 
         [0062]    As shown in  FIG. 2 , an Evolved Packet Network (EPC) includes an S-GW  220 , a P-GW  230 - 1 , a Policy and Charging Rules Function (PCRF)  240 , a Subscription Profile Repository (SPR)  250 , and an MME  260 . The S-GW  220 , which is a network entity for managing a user plane, controls routing of packets. The P-GW  230 - 1  is a connection point with an external PDN, and the PCRF  240  maintains and manages a network operator&#39;s policy. The SPR  250  stores users&#39; subscription information, and the MME  260 , which is a network entity for managing a control plane, manages mobility of a terminal. According to an exemplary embodiment, the SPR  250  retains a traffic offload-related context of each subscriber in addition to the information on the subscribers. For example, the traffic offload-related context may include information shown in table 1. 
         [0063]    In addition, an operator assisted application server  280 - 1  may be connected via the P-GW  230 - 1  via an Application Function (AF)  270 . The AP  270  is a network entity which provides information on an application to the PCRF  240 . In addition, a 3 rd  party application server  280 - 2  may be connected via the P-GW  230 - 1 . 
         [0064]    An interface between the SPR  250  and the PCRF  240  may be referred as “Sp,” an interface between the PCRF  240  and a Policy and Charging Enforcement Function (PCEF) of the P-GW  230 - 1  may be referred to as ‘Gx,’ and an interface between the PCRF  240  and a Traffic Detection Function (TDF) of the P-GW  230 - 1  may be referred to as “Sd.” An interface between the AP  270  and the PCRF  240  may be referred to as “Rx.” 
         [0065]    A terminal  210  may wirelessly access via a first base station  210 - 1  and access the external PDN (e.g., Internet) via a local (L)-PGW 1   230 - 2 . After the terminal  210  accesses the network, the traffic offload-related context may be fetched from the SPR  250  and stored in the MME  260 . In other words, the MME  260  receives the traffic offload-related context on the user of the terminal  210  from the SPR  250  and stores the traffic offload-related context. Thereafter, the terminal  210  is handed over to a base station  2   290 - 2  by movement. In this case, an L-PGW 2   230 - 3  is selected as an optimum anchor gateway. Therefore, it is determined whether the P-GW is relocated or not according to a level of session continuity applied to the terminal  210 . In the case of  FIG. 2 , the level of the session continuity of the terminal  210  is “on-demand session continuity.” Accordingly, when it is determined that QoE is not degraded, the terminal  210  or the network triggers the P-GW relocation. When the P-GW relocation is triggered by the network, the MME  260  may trigger the P-GW relocation. 
         [0066]    According to another exemplary embodiment of the present disclosure, the network operator may define the level of the session continuity and the level of the session continuity may be provided for each flow level or a user level. In the case of session continuity which varies according to the flow, the terminal may have different levels of session continuity for different applications. In this case, the PCRF may provide authorization of the session continuity for each flow based on the operator policy. In this case, tighter control may be performed for the session continuity. For example, the levels of the session continuity by the policy may be determined based on a flow type (e.g., a web, audio streaming, video streaming, adaptive streaming, gaming, etc.), user subscription information (e.g., gold/silver/bronze), an application provider (e.g., who provides a service), and the like. In this case, information on the session continuity may be provided as shown in  FIG. 3 .  FIG. 3  illustrates a view showing a path for providing policy-based session continuity information in a wireless communication system according to an exemplary embodiment of the present disclosure. 
         [0067]    As shown in  FIG. 3 , an EPC includes an S-GW  320 , a P-GW  330 - 1 , a PCRF  340 , an SPR  350 , and MME  360 . The S-GW  320 , which is a network entity for managing a user plane, controls routing of packets. The P-GW  330 - 1  is a connection point with an external PDN, and the PCRF  340  maintains and manages a network operator&#39;s policy. The SPR  350  stores users&#39; subscription information, and the MME  360 , which is a network entity for managing a control plane, manages mobility of a terminal. In addition, an operator assisted application server  380 - 1  may be connected via the P-GW  330 - 1  via an AF  370 . The AP  370  is a network entity which provides information on an application to the PCRF  340 . In addition, a 3 rd  party application server  380 - 2  may be connected via the P-GW  330 - 1 . An interface between the SPR  350  and the PCRF  340  may be referred to as “Sp,” an interface between the PCRF  340  and a PCEF of the P-GW  330 - 1  may be referred to as “Gx,” and an interface between the PCRF  340  and a TDF of the P-GW  330 - 1  may be referred to as “Sd.” An interface between the AP  370  and the PCRF  340  may be referred to as “Rx.” 
         [0068]    A terminal  310  may wirelessly access via a first base station  310 - 1  and access the external PDN (e.g., Internet) via an L-PGW 1   330 - 2 . After the terminal  310  accesses the network, the PCRF  340  determines a level of session continuity for a corresponding flow in a flow setup process. In other words, the PCRF  340  determines the level of the session continuity based on an operator policy which is determined based on various factors. For example, the PCRF  340  authenticates the level of the session continuity of the terminal  310  during a bearer setup procedure, and provides information on the determined level of the session continuity to the MME  360 . That is, the MME  360  acquires the information on the level of the session continuity from the PCRF  340  during the flow setup. Thereafter, the terminal  310  is handed over to a base station  2   390 - 2  by movement. In this case, an L-PGW 2   330 - 3  is selected as an optimum anchor gateway. Therefore, it is determined whether the P-GW is relocated or not according to a level of session continuity applied to the terminal  310 . In the case of  FIG. 3 , the level of the session continuity of the terminal  310  is “on-demand session continuity.” Accordingly, when it is determined that QoE is not degraded, the terminal  310  or the network triggers the P-GW relocation. When the P-GW relocation is triggered by the network, the MME  360  may trigger the P-GW relocation. 
         [0069]    In the P-GW relocation procedure described with reference to  FIG. 3 , the MME acquires session continuity information from the PCRF. The session continuity information may be provided to the MME through signaling of various methods. For example, the session continuity information may be forwarded through one of a bearer activation procedure and a bearer modification procedure. In other words, the session continuity information may be included in at least one message for the bearer activation procedure or the bearer modification procedure. Specifically, the session continuity information may be forwarded as shown in  FIGS. 4 ,  5 , and  6 . 
         [0070]      FIG. 4  illustrates a view showing exchange of signals for providing session continuity information through a bearer activation procedure in a wireless communication system according to an exemplary embodiment of the present disclosure. 
         [0071]    Referring to  FIG. 4 , in step  401 , an AF  470  transmits a service notification to a PCRF  440 . The service notification includes information on a service to be provided to a terminal  410 . According to an exemplary embodiment of the present disclosure, step  401  may be omitted in the bearer activation procedure. 
         [0072]    In step  403 , the PCRF  440  and a P-GW  430  perform an IP-Connectivity Access Network (CAN) session modification procedure. In this case, dynamic Policy and Charging Control (PCC) may be applied. When a local policy other than the dynamic PCC is applied, step  403  may be omitted. 
         [0073]    In step  405 , the PCRF  440  transmits policy and charging rule provisioning information to the P-GW  430 . The session continuity information on the terminal  410  may be transmitted along with the policy and charging rule. The session continuity information may be included in the policy and charging rule. According to an exemplary embodiment, step  405  may be included in step  403 . 
         [0074]    In step  407 , the P-GW  430  transmits a create bearer request message to an S-GW  420 . The create bearer request message instructs to create a bearer and includes information on the bearer (e.g., a context, identification information, and service quality information of a bearer). In particular, according to an exemplary embodiment of the present disclosure, the create bearer request message may include the session continuity information. 
         [0075]    In step  409 , the S-GW  420  transmits the create bearer request message to an MME  460 . The create bearer request message instructs to create a bearer and includes information on the bearer (e.g., a context, identification information, and service quality information of a bearer). In particular, according to an exemplary embodiment of the present disclosure, the create bearer request message may include the session continuity information. 
         [0076]    In step  411 , the MME  460  stores the session continuity information. The MME  460  stores and maintains the context on the bearer, and stores the session continuity information in the context on the bearer. According to another exemplary embodiment of the present disclosure, the session continuity information may be stored separately from the context. Accordingly, the MME  460  guarantees the session continuity information on the terminal  410 . 
         [0077]    In step  413 , the MME  460  transmits a bearer setup request/session management request message to a base station  490 . The bearer setup request/session management request message includes a QoS parameter of a bearer, QoS class identification information (QoS class identifier (QCI)), bandwidth restriction information (e.g., Aggregated Maximum Bit Rate (AMBR)), and the like. 
         [0078]    In step  415 , the base station  490  transmits a Radio Resource Control (RRC) connection reconfiguration message to the terminal  410 . The RRC connection reconfiguration message instructs the terminal  410  to change or create RRC connection. For example, the RRC connection reconfiguration message includes information necessary for creating or changing RRC connection, such as wireless bearer identification information or the like. The RRC connection reconfiguration message may include an attach accept message. 
         [0079]    In step  417 , the terminal  410  transmits an RRC connection reconfiguration complete message to the base station  490 . That is, the terminal  410  transmits a response to the RRC connection reconfiguration message received in step  415 . That is, the RRC connection reconfiguration complete message informs that the creation of the RRC connection is completed. In step  419 , the base station  490  transmits a bearer setup response to the MME  460 . That is, the base station  490  transmits a response to the bearer setup request message received in step  413 . 
         [0080]    In step  421 , the terminal  410  transmits a direct transfer message to the base station  490 . The direct transfer message may include an attach complete message. The attach complete message may include bearer identification information, a session management response, or the like. In step  423 , the base station  423  transmits a session management response message to the MME  460 . That is, the base station  423  transmits a response to the session management request message received in step  413 . In step  425 , the MME  460  transmits a create bearer response message to the S-GW  420 . That is, the MME  460  transmits a response to the create bearer request message received in step  409 . The create bearer response message may include a context on the bearer or the like. 
         [0081]    In step  427 , the S-GW  420  transmits the create bearer response message to the P-GW  430 . That is, the S-GW  420  transmits a response to the create bearer request message received in step  407 . The create bearer response message may include a context on the bearer or the like. In step  429 , the P-GW  430  and the PCRF  440  perform an IP-CAN session modification procedure. 
         [0082]      FIG. 5  illustrates a view showing exchange of signals for providing session continuity information through a bearer modification procedure in a wireless communication system according to an exemplary embodiment of the present disclosure. 
         [0083]    Referring to  FIG. 5 , in step  501 , an AF  570  transmits a service notification to a PCRF  540 . The service notification includes information on a service to be provided to a terminal  510 . In some cases, step  501  may be omitted in the bearer activation procedure. 
         [0084]    In step  503 , the PCRF  540  performs an IP-CAN session modification procedure with respect to a P-GW  530 . In this case, dynamic PCC may be applied. When a local policy other than the dynamic PCC is applied, step  503  may be omitted. 
         [0085]    In step  505 , the PCRF  540  transmits policy and charging rule provisioning information to the P-GW  530 . Herein, session continuity information on the terminal  510  may be transmitted along with the policy and charging rule. The session continuity information may be included in the policy and charging rule. According to another exemplary embodiment, step  505  may be included in step  503 . 
         [0086]    In step  507 , the P-GW  530  transmits an update bearer request message to an S-GW  520 . The update bearer request message instructs to change a bearer and includes information on the bearer (e.g., a context, identification information, and service quality information of a bearer). In particular, according to an exemplary embodiment of the present disclosure, the update bearer request message may include the session continuity information. 
         [0087]    In step  509 , the S-GW  520  transmits the update bearer request message to the MME  560 . The update bearer request message instructs to change a bearer and includes information on the bearer (e.g., a context, identification information, and service quality information of a bearer). In particular, according to an exemplary embodiment of the present disclosure, the update bearer request message may include the session continuity information. 
         [0088]    In step  511 , the MME  560  stores the session continuity information. The MME  560  stores and maintains the context on the bearer, and stores the session continuity information by updating the context of the bearer. According to another exemplary embodiment of the present disclosure, the session continuity information may be stored separately from the context. Accordingly, the MME  560  guarantees the session continuity information on the terminal  510 . 
         [0089]    In step  513 , the MME  560  transmits a bearer modify request/session management request message to a base station  590 . The bearer modify request/session management request message may include a QoS parameter of a bearer, QoS class identification information, bandwidth restriction information (e.g., AMBR), and the like. 
         [0090]    In step  515 , the base station  590  transmits an RRC connection reconfiguration message to the terminal  510 . The RRC connection reconfiguration message instructs the terminal  510  to change or create RRC connection. For example, the RRC connection reconfiguration message includes information necessary for creating or changing RRC connection, such as wireless bearer identification information or the like. 
         [0091]    In step  517 , the terminal  510  transmits an RRC connection reconfiguration complete message to the base station  590 . That is, the terminal  510  transmits a response to the RRC connection reconfiguration message received in step  515 . That is, the RRC connection reconfiguration complete message informs that the change of the RRC connection is completed. In step  519 , the base station  590  transmits a bearer modify response message to the MME  560 . That is, the base station  590  transmits a response to the bearer modify request message received in step  513 . 
         [0092]    In step  521 , the terminal  510  transmits a direct transfer message to the base station  590 . In step  523 , the base station  523  transmits a session management response message to the MME  560 . That is, the base station  523  transmits a response to the session management request message received in step  513 . In step  525 , the MME  560  transmits an update bearer response message to the S-GW  520 . That is, the MME  560  transmits a response to the update bearer request message received in step  509 . The update bearer response message may include the context on the bearer or the like. 
         [0093]    In step  527 , the S-GW  520  transmits the update bearer response message to the P-GW  530 . That is, the S-GW  520  transmits a response to the update bearer request message received in step  507 . The update bearer response message may include the context on the bearer or the like. In step  529 , the P-GW  530  and the PCRF  540  perform an IP-CAN session modification procedure. 
         [0094]      FIG. 6  illustrates a view showing exchange of signals for providing session continuity information through a bearer modification procedure which is initiated by a Home Subscriber Server (HSS) in a wireless communication system according to an exemplary embodiment of the present disclosure. 
         [0095]    Referring to  FIG. 6 , in step  601 , an HSS  698  instructs an MME  660  to add data of a subscriber. In step  603 , the MME  660  transmits, to the HSS  698 , an acknowledgement (ACK) identifying that a request for addition of subscriber data has been received. In step  605 , the MME  660  updates a context of the subscriber. In this case, when the data of the subscriber transmitted in step  601  includes session continuity information, the context includes the session continuity information. In step  607 , the MME  660  transmits a modify bearer command message to an S-GW  620 . The modify bearer command message, which is a message used in the bearer modification procedure initiated by the HSS, may include information necessary for modifying a bearer, such as bearer identification information, a bearer context, or the like. In step  609 , the S-GW  620  transmits the modify bearer command message to a P-GW  630 . 
         [0096]    In step  611 , the P-GW  630  and a PCRF  640  perform a PCEF initiation IP-CAN session modification procedure. In step  613 , the PCRF  640  transmits policy and charging rule provisioning information to the P-GW  630 . In this case, the session continuity information on the terminal  610  may be transmitted along with the policy and charging rule. The session continuity information may be included in the policy and charging rule. 
         [0097]    In step  615 , the P-GW  630  transmits an update bearer request message to an S-GW  620 . The update bearer request message instructs to change a bearer and includes information on the bearer (e.g., a context, identification information, service quality information of a bearer, or the like). In particular, according to an exemplary embodiment of the present disclosure, the update bearer request message may include the session continuity information. 
         [0098]    In step  617 , the S-GW  620  transmits the update bearer request message to an MME  660 . The update bearer request message instructs to change a bearer and includes information on the bearer (e.g., a context, identification information, and service quality information of a bearer). In particular, according to an exemplary embodiment of the present disclosure, the update bearer request message may include the session continuity information. 
         [0099]    In step  619 , the MME  660  stores the session continuity information. The MME  660  stores and maintains the context on the bearer, and stores the session continuity information by updating the context of the bearer. According to another exemplary embodiment of the present disclosure, the session continuity information may be stored separately from the context. Accordingly, the MME  660  guarantees the session continuity information on the terminal  610 . 
         [0100]    In step  621 , the MME  660  transmits a bearer modify request/session management request message to a base station  690 . The bearer modify request/session management request message may include a QoS parameter of a bearer, QoS class identification information, bandwidth restriction information (e.g., AMBR), and the like. 
         [0101]    In step  623 , the base station  690  transmits an RRC connection reconfiguration message to the terminal  610 . The RRC connection reconfiguration message instructs the terminal  610  to change or create RRC connection. For example, the RRC connection reconfiguration message includes information necessary for creating or changing RRC connection, such as wireless bearer identification information or the like. 
         [0102]    In step  625 , the terminal  610  transmits an RRC connection reconfiguration complete message to the base station  690 . That is, the terminal  610  transmits a response to the RRC connection reconfiguration message received in step  615 . That is, the RRC connection reconfiguration complete message informs that the change of the RRC connection is completed. In step  627 , the base station  690  transmits a bearer modify response message to the MME  660 . That is, the base station  690  transmits a response to the bearer modify request message received in step  613 . 
         [0103]    In step  629 , the terminal  610  transmits a direct transfer message to the base station  690 . In step  631 , the base station  623  transmits a session management response message to the MME  660 . That is, the base station  623  transmits a response to the session management request message received in step  613 . In step  633 , the MME  660  transmits an update bearer response message to the S-GW  620 . That is, the MME  660  transmits a response to the update bearer request message received in step  609 . The update bearer response message may include the context on the bearer or the like. 
         [0104]    In the exemplary embodiment illustrated in  FIG. 6 , when sufficient session continuity information is provided to the MME  660  through step  601 , subsequent steps  607  to  637  may be omitted. 
         [0105]    The P-GW relocation procedure according to an exemplary embodiment of the present disclosure depends on a level of session continuity. According to an exemplary embodiment of the present disclosure, when subscription information based on the session continuity is considered, the P-GW relocation may be performed for each user. According to another exemplary embodiment of the present disclosure, when a policy based on the session continuity is applied, the P-GW relocation may be performed for each flow or each user. When the MME finds a more appropriate P-GW for the terminal, the P-GW relocation activation may be initiated by the MME. Prior to activating the P-GW relocation, the MME identifies the level of the session continuity from the context of the terminal or the context of the bearer. A detailed procedure may vary according to the level of the session continuity. 
         [0106]    When the level of the session continuity is “no session continuity,” the MME may determine the P-GW relocation. When the MME finds a more appropriate P-GW and the level of the session continuity for the terminal is “no session continuity,” the MME deactivates the PDN and controls to reactivate the PDN in a new P-GW. Specifically, the P-GW relocation may be performed as shown in  FIG. 7 .  FIG. 7  illustrates a view showing a P-GW relocation procedure in a wireless communication system according to an exemplary embodiment of the present disclosure. 
         [0107]    Referring to  FIG. 7 , in step  701 , an MME  760  determines a new P-GW. Herein, the new P-GW may be determined by movement of a terminal  710 . For example, the new P-GW may be found during a Tracking Area Update (TAU) procedure. For example, the MME  760  may determine the new P-GW based on a distance to the terminal  710 . Herein, the distance may include at least one of a physical distance or a logical distance. The logical distance includes a data transfer delay time. In another example, the MME  760  may determine the new P-GW based on a traffic load of a plurality of P-GWs. In another example, both the traffic load and the distance may be considered. In the exemplary embodiment of  FIG. 7 , an L-GW 1   730 - 1  is a current P-GW of the terminal  710  and an L-GW 2   730 - 2  is selected as a new P-GW. 
         [0108]    In step  703 , the MME  760  identifies session continuity information of the terminal  710 . In the exemplary embodiment of  FIG. 7 , the MME  760  identifies that the level of the session continuity is “no session continuity.” The session continuity information may be managed as a part of a context of the terminal  710  or a context of a bearer owned by the terminal  710 . 
         [0109]    In step  705 , the MME  760  transmits a PDN reactivation request to the terminal  710 . The PDN reactivation request is forwarded to a base station  790  and forwarded from the base station  790  to the terminal  710  via a radio channel. That is, since the level of the session continuity is “no session continuity,” the MME  760  triggers P-GW relocation without considering a state of a flow of the terminal  710 . 
         [0110]    In step  707 , the terminal  710 , the base station  790 , the L-GW 1   730 - 1 , and the MME  760  perform a PDN disconnection procedure. In other words, the terminal  710  disconnects IP layers connected through the L-GW 1   730 - 1  which is the current P-GW. In this case, the PDN disconnection may be requested by the terminal  710  or the MME  760 . For example, the PDN disconnection procedure may be performed as shown in  FIG. 8  presented below. 
         [0111]    In step  709 , the terminal  710 , the base station  790 , the L-GW 2   730 - 2 , and the MME  760  perform a PDN connection setup procedure. In other words, the terminal  710  sets up connection of IP layers through the L-GW 1   730 - 1  which is the new P-GW. To this end, the P-GW of the terminal  710  is relocated. That is, the P-GW may be relocated by setting up connection with the data network again after disconnecting from the data network. In this case, when the connection with the data network is set up again, the MME  760  proceeds with the connection setup procedure through the new P-GW, such that an anchor gateway for the terminal  710  is relocated. However, according to another exemplary embodiment of the present disclosure, a single procedure defined to relocate the anchor gateway may be performed instead of the procedure of two phases including the disconnection and the connection setup. 
         [0112]      FIG. 8  illustrates a view showing a PDN reactivation procedure in a wireless communication system according to an exemplary embodiment of the present disclosure. 
         [0113]    Referring to  FIG. 8 , in step  801 , an MME  860  determines P-GW relocation. Step  801  may be performed similarly to steps  701  and  703  of  FIG. 7 . For example, the MME  860  determines a new P-GW and identifies session continuity information of a terminal  810 . In the exemplary embodiment of  FIG. 8 , the level of the session continuity of the terminal  810  is “no session continuity.” Although not shown in  FIG. 8 , the MME  860  may transmit a P-GW reactivation request to the terminal  810 . 
         [0114]    In step  803 , the terminal  810  transmits a PDN disconnection request message to the MME  860 . The PDN disconnection request message informs that disconnection of IP layers connected through a P-GW  830  is requested. In step  805 , the MME  860  triggers PDN disconnection. In the exemplary embodiment of  FIG. 8 , the level of the session continuity of the terminal  801  is “no session continuity.” Therefore, since the state of a flow of the terminal  801  is not considered, a procedure for the PDN disconnection may be performed without involvement of the terminal  810  according to another exemplary embodiment of the present disclosure. For example, steps  803  and  805  may be omitted. When steps  803  and  805  are omitted, the procedure shown in  FIG. 8  may be referred to as an MME-initiated PDN reactivation procedure. On the other hand, when steps  803  and  805  are performed, the procedure shown in  FIG. 8  may be referred to as a terminal-initiated PDN reactivation procedure. 
         [0115]    In step  807 , the MME  860  transmits a delete session request message to an S-GW  820 . In step  809 , the S-GW  820  transmits the delete session request message to the P-GW  830 . The delete session request message informs that disconnection from the PDN is requested. For example, the delete session request message may include a cause of disconnection, user location information, etc. In step  811 , the P-GW  830  transmits a delete session response message to the S-GW  820 . That is, the P-GW  830  transmits a response to the delete session request message received in step  809 . 
         [0116]    In step  813 , the P-GW  830  and a PCRF  840  perform an IP-CAN session termination procedure. That is, the P-GW  830  and the PCRF  840  perform signaling for removing an IP-CAN session. For example, the P-GW  830  transmits an indication for the IP-CAN session termination to the PCRF  840 , and the PCRF  840  processes information on a policy and charging rule and then transmits an ACK to the P-GW  830 . According to another exemplary embodiment of the present disclosure, step  813  may be omitted. 
         [0117]    In step  815 , the S-GW  820  transmits the delete session response message to the MME  860 . That is, the S-GW  820  transmits a response to the delete session request message received in step  807 . In step  817 , the MME  860  transmits a deactivate bearer request message to a base station  890 . The deactivate bearer request message informs that deletion of a bearer owned by the terminal  810  is requested. In step  819 , the base station  890  transmits an RRC connection reconfiguration message to the terminal  810 . The RRC connection reconfiguration message instructs the terminal  810  to delete RRC connection. For example, the RRC connection reconfiguration message includes information necessary for deleting RRC connection, such as wireless bearer identification information or the like. 
         [0118]    In step  821 , the terminal  810  transmits an RRC connection reconfiguration complete message to the base station  890 . That is, the terminal  810  transmits a response to the RRC connection reconfiguration message received in step  819 . That is, the RRC connection reconfiguration complete message informs that the deletion of the RRC connection is completed. In step  823 , the base station  890  transmits a deactivate bearer response message to the MME  860 . That is, the base station  890  transmits a response to the deactivate bearer request message received in step  817 . In step  825 , the terminal  810  transmits a direct transfer message to the base station  890 . In step  827 , the base station  823  transmits an evolved packet system (EPS) bearer context deactivate accept message to the MME  860 . 
         [0119]    When the level of the session continuity is “always session continuity,” the session continuity should be always guaranteed for activated flows. Therefore, P-GW relocation may not be performed. In order to provide the session continuity for the activated flows, the MME may provide IP mobility between a previous P-GW and a new P-GW. The IP mobility is to guarantee continuity of a service by maintaining a session in spite of changing an end point of IP. Specifically, the IP mobility may be provided by technology such as Mobile IP (MIP) and Proxy Mobile IP (PMIP). For example, a procedure shown in  FIG. 9  may be performed.  FIG. 9  illustrates a view showing a P-GW relocation procedure in a wireless communication system according to another exemplary embodiment of the present disclosure. 
         [0120]    Referring to  FIG. 9 , in step  901 , an MME  960  determines a new P-GW. Herein, the new P-GW may be determined by movement of a terminal  910 . For example, the new P-GW may be found during a TAU procedure. For example, the MME  960  may determine the new P-GW based on a distance to the terminal  910 . Herein, the distance may include at least one of a physical distance or a logical distance. The logical distance includes a data transfer delay time. In another example, the MME  960  may determine the new P-GW based on a traffic load of a plurality of P-GWs. In another example, both the traffic load and the distance may be considered. In the exemplary embodiment of  FIG. 9 , an L-GW 1   930 - 1  is a current P-GW of the terminal  910  and an L-GW 2   930 - 2  is selected as a new P-GW. 
         [0121]    In step  903 , the MME  960  identifies session continuity information of the terminal  910 . In the exemplary embodiment of  FIG. 9 , the MME  960  identifies that the level of the session continuity is “always session continuity.” The session continuity information may be managed as a part of a context of the terminal  910  or a context of a bearer owned by the terminal  910 . 
         [0122]    In step  905 , the MME  960  transmits a P-GW relocation request message to the L-GW 1   930 - 1 , which is the current P-GW. The P-GW relocation request message induces IP mobility to be provided via the new P-GW. For example, the P-GW relocation request message informs that the new P-GW has been determined, and also, informs that the PDN cannot be reactivated. For example, the P-GW relocation request message may include at least one of information for indicating the L-GW 2   930 - 2  as a new P-GW, information for requesting to provide IP mobility via the L-GW 2   930 - 2 , and information for indicating that the level of the session continuity of the terminal  910  is “always session continuity.” 
         [0123]    In step  907 , the L-GW 1   930 - 1  performs an IP flow forwarding procedure. In other words, the L-GW 1   930 - 1  performs a procedure for providing IP mobility via the L-GW 2   930 - 2 . Specifically, the L-GW 1   930 - 1  may generate a tunnel with the L-GW 2   930 - 2  and sets up a routing path for forwarding traffic transmitted to the terminal  910  to the L-GW 2   930 - 2  via the tunnel. 
         [0124]    In step  909 , the L-GW 1   930 - 1  transmits a P-GW relocation ACK to the MME  960 . That is, the L-GW 1   930 - 1  transmits a response to the P-GW relocation request message received in step  905 . Accordingly, the MME  960  may identify that the procedure for forwarding the IP flow is completed. 
         [0125]    When the level of the session continuity is “on-demand session continuity,” the MME provides IP mobility between the previous P-GW and the new P-GW first, and controls to trigger the P-GW relocation based on the state of the flow. In other words, the MME requests the terminal to initiate the P-GW relocation when the MME wishes to trigger the P-GW relocation. For example, a procedure shown in  FIG. 10  may be performed.  FIG. 10  illustrates a view showing a P-GW relocation procedure in a wireless communication system according to another exemplary embodiment of the present disclosure. 
         [0126]    Referring to  FIG. 10 , in step  1001 , an MME  1060  determines a new P-GW. Herein, the new P-GW may be determined by movement of a terminal  1010 . For example, the new P-GW may be found during a TAU procedure. For example, the MME  1060  may determine the new P-GW based on a distance to the terminal  1010 . Herein, the distance may include at least one of a physical distance or a logical distance. The logical distance includes a data transfer delay time. In another example, the MME  1060  may determine the new P-GW based on a traffic load of a plurality of P-GWs. In another example, both the traffic load and the distance may be considered. In the exemplary embodiment of  FIG. 10 , an L-GW 1   1030 - 1  is a current P-GW of the terminal  1010  and an L-GW 2   1030 - 2  is selected as a new P-GW. 
         [0127]    In step  1003 , the MME  1060  identifies session continuity information of the terminal  1010 . In the exemplary embodiment of  FIG. 10 , the MME  1060  identifies that the level of the session continuity is “on-demand session continuity.” The session continuity information may be managed as a part of a context of the terminal  1010  or a context of a bearer owned by the terminal  1010 . 
         [0128]    In step  1005 , the MME  1060  transmits an on-demand PDN deactivation request to the terminal  1010 . The PDN deactivation request is forwarded to a base station  1090  and forwarded from the base station  1090  to the terminal  1010  via a radio channel. That is, since the level of the session continuity is “on-demand session continuity”, the MME  1060  requests to trigger P-GW relocation based on the state of the flow of the terminal  1010 . 
         [0129]    In step  1007 , the terminal  1010  transmits an on-demand PDN deactivation ACK to the MME  1060 . That is, the terminal  1010  transmits a response to the on-demand PDN deactivation request message received in step  1005 . Accordingly, the MME  1060  identifies that the P-GW relocation will be triggered at a specific time afterward based on the state of the flow of the terminal  1010 . 
         [0130]    In step  1009 , the MME  1060  transmits a P-GW relocation request message to the L-GW 1   1030 - 1 , which is the current P-GW. The P-GW relocation request message induces IP mobility to be provided via the new P-GW. For example, the P-GW relocation request message informs that the new P-GW has been determined, and also, informs that the PDN cannot be reactivated. For example, the P-GW relocation request message may include at least one of information for indicating the L-GW 2   1030 - 2  as a new P-GW, and information for requesting to provide IP mobility via the L-GW 2   1030 - 2 . 
         [0131]    In step  1011 , the L-GW 1   1030 - 1  performs an IP flow forwarding procedure. In other words, the L-GW 1   1030 - 1  performs a procedure for providing IP mobility via the L-GW 2   1030 - 2 . Specifically, the L-GW 1   1030 - 1  may generate a tunnel with the L-GW 2   1030 - 2  and sets up a routing path for forwarding traffic transmitted to the terminal  1010  to the L-GW 2   1030 - 2  via the tunnel. 
         [0132]    In step  1013 , the L-GW 1   1030 - 2  transmits a P-GW relocation ACK to the MME  1060 . That is, the L-GW 1   1030 - 1  transmits a response to the P-GW relocation request message received in step  1009 . Accordingly, the MME  1060  may identify that the procedure for forwarding the IP flow is completed. 
         [0133]    In step  1015 , the terminal  1010  determines that it is possible to relocate the P-GW. It may be determined whether it is possible to relocate the P-GW based on the state of the flow owned by the terminal  1010 . That is, the terminal  1010  determines a time that the P-GW relocation does not badly affect the QoE of the flow. For example, when a sufficient video buffer is guaranteed in a video streaming service, when downloading of a specific track in an online radio service is completed, when a current user does not interact with an application in a chatting application/SNS application, or when downloading of an active component in a web application is completed, the terminal may determine that it is possible to relocate the P-GW. 
         [0134]    In step  1017 , the terminal  1010 , the base station  1090 , the L-GW  1030 - 1 , and the MME  1060  performs a PDN disconnection procedure. For example, the terminal  1010  may request the MME  1060  to disconnect from the PDN via the L-GW 1   1030 - 1 . In another example, the terminal  1010  notifies the MME  1060  that the time to relocate the P-GW arrives, and the MME  1060  may trigger disconnection from the PDN connected via the L-GW 1   1030 - 1 . Thereafter, although not shown in  FIG. 10 , the terminal  1010 , the base station  1090 , the L-GW 2   1030 - 2 , and the MME  1060  may perform a PDN connection setup procedure. In other words, the terminal  1010  may set up connection of IP layers via the L-GW 2   1030 - 2  which is the new P-GW. Accordingly, the P-GW of the terminal  1010  may be relocated. For example, the PDN disconnection procedure may be performed as shown in  FIG. 11 . 
         [0135]    In step  1019 , the terminal  1010 , the base station  1090 , the L-GW 2   1030 - 2 , and the MME  1060  perform a PDN connection setup procedure. In other words, the terminal  1010  sets up connection of IP layers through the L-GW 1   1030 - 1  which is the new P-GW. To achieve this, the MME  1060  may transmit a message requesting to connect with the data network via the L-GW 2   1030 - 2  to another network entity (e.g., an S-GW). Thus, the P-GW of the terminal  1010  may be relocated. That is, the P-GW may be relocated by setting up connection with the data network again after disconnecting from the data network. In this case, when the connection with the data network is set up again, the MME  1060  proceeds with the connection setup procedure through the new P-GW, such that an anchor gateway for the terminal  1010  is relocated. However, according to another exemplary embodiment of the present disclosure, a single procedure defined to relocate the anchor gateway may be performed instead of the procedure of two phases including the disconnection and the connection setup. 
         [0136]    According to the exemplary embodiment of  FIG. 10 , the new P-GW of the terminal  1010  is determined, and then, the P-GW relocation is performed after a predetermined time elapses. Therefore, the optimum P-GW may be relocated again before the predetermined time elapses. In this case, the P-GW which is set up for connection as an anchor gateway in step  1019  may be different from the P-GW which is determined in step  1001 . 
         [0137]      FIG. 11  illustrates a view showing a PDN deactivation procedure in a wireless communication system according to an exemplary embodiment of the present disclosure. 
         [0138]    Referring to  FIG. 11 , in step  1101 , an MME  1160  requests a terminal  1110  to trigger PDN disconnection based on a flow state. Step  1101  may be performed similarly to steps  1001  and  1005  of  FIG. 10 . For example, the MME  1160  determines a new P-GW and identifies session continuity information of the terminal  1110 . In the exemplary embodiment of  FIG. 11 , the level of the session continuity of the terminal  1110  is “on-demand session continuity.” Although not shown in  FIG. 11 , the MME  1160  may transmit a P-GW deactivation request to the terminal  1110 . 
         [0139]    In step  1103 , the terminal  1110  transmits a PDN disconnection request message to the MME  1160 . That is, the terminal  1110  determines that it is possible to disconnect from the PDN based on the flow state and requests to disconnect from the PDN connected via the P-GW  1130  which is the current P-GW. The PDN disconnection request message informs that disconnection of IP layers connected through the P-GW  1130  is requested. In step  1105 , the MME  1160  triggers PDN disconnection. According to another exemplary embodiment of the present disclosure, steps  1103  and  1105  may be omitted. When steps  1103  and  1105  are omitted, the procedure shown in  FIG. 11  may be referred to as an MME-initiated PDN deactivation procedure. In this case, the terminal  1110  may provide information on the state of the flow to the MME  1160  such that the MME  1160  determines the time to relocate the P-GW. In addition, the terminal  1110  may notify the MME  1160  that the time to accept the P-GW relocation arrives. On the other hand, when steps  1103  and  1105  are performed, the procedure shown in  FIG. 11  may be referred to as a terminal-initiated PDN deactivation procedure. 
         [0140]    In step  1107 , the MME  1160  transmits a delete session request message to an S-GW  1120 . In step  1109 , the S-GW  1120  transmits the delete session request message to the P-GW  1130 . The delete session request message informs that disconnection from the PDN is requested. For example, the delete session request message may include a cause of disconnection, user location information, etc. In step  1111 , the P-GW  1130  transmits a delete session response message to the S-GW  1120 . That is, the P-GW  1130  transmits a response to the delete session request message received in step  1109 . 
         [0141]    In step  1113 , the P-GW  1130  and a PCRF  1140  perform an IP-CAN session termination procedure. That is, the P-GW  1130  and the PCRF  1140  perform signaling for removing an IP-CAN session. For example, the P-GW  1130  transmits an indication for the IP-CAN session termination to the PCRF  1140 , and the PCRF  1140  processes information on a policy and charging rule and then transmits an ACK to the P-GW  1130 . According to another exemplary embodiment of the present disclosure, step  1113  may be omitted. 
         [0142]    In step  1115 , the S-GW  1120  transmits a delete session response message to the MME  1160 . That is, the S-GW  1120  transmits a response to the delete session request message received in step  1107 . In step  1117 , the MME  1160  transmits a deactivate bearer request message to a base station  1190 . The deactivate bearer request message informs that deletion of a bearer owned by the terminal  1110  is requested. In step  1119 , the base station  1190  transmits an RRC connection reconfiguration message to the terminal  1110 . The RRC connection reconfiguration message instructs the terminal  1110  to delete RRC connection. For example, the RRC connection reconfiguration message includes information necessary for deleting RRC connection such as wireless bearer identification information or the like. 
         [0143]    In step  1121 , the terminal  1110  transmits an RRC connection reconfiguration complete message to the base station  1190 . That is, the terminal  1110  transmits a response to the RRC connection reconfiguration message received in step  1119 . That is, the RRC connection reconfiguration complete message informs that the deletion of the RRC connection is completed. In step  1123 , the base station  1190  transmits a deactivate bearer response message to the MME  1160 . That is, the base station  1190  transmits a response to the deactivate bearer request message received in step  1117 . In step  1125 , the terminal  1110  transmits a direct transfer message to the base station  1190 . In step  1127 , the base station  1190  transmits an EPS bearer context deactivate accept message to the MME  1160 . 
         [0144]    According to various exemplary embodiments of the present disclosure as described above, more control methods for the P-GW relocation may be provided to the operator. The operator may define policies for the levels of the session continuity provided for each flow or each user. In addition, various exemplary embodiments of the present disclosure can enhance network efficiency without badly affecting user QoE. In particular, the P-GW relocation based on “on-demand session continuity” may be triggered based on the current state of the flow. 
         [0145]    In the 3GPP, there exists a research called “CSIPTO” for co-ordination of SIPTO traffic between multi-P-GWs. As mobile networks are growing up and dense arrangements are considered, the SIPTO is an effective solution to the off-loading of traffic via a local P-GW. In this case, the P-GW relocation may be factored in considering session continuity. The proposed mechanism allows the operator to define levels of session continuity of users to use network resources effectively. The on-demand session continuity allows the P-GW relocation in the middle of a session when QoE is not much degraded. Such a mechanism may be applied when the flows do not always require the session continuity, such as Dynamic Adaptive Streaming over HTTP (DASH) or a push service. 
         [0146]      FIG. 12  illustrates a view showing an operation procedure of a terminal in a wireless communication system according to an exemplary embodiment of the present disclosure. 
         [0147]    Referring to  FIG. 12 , the terminal receives a request for disconnection from a data network from one of the network entities in a core network in step  1201 . For example, the request may be received from a network entity which manages mobility, that is, an MME. According to an exemplary embodiment of the present disclosure, the request may instruct prompt network disconnection, that is, unconditional network disconnection. According to another exemplary embodiment of the present disclosure, the request may instruct network disconnection at a time which is determined according to a pre-defined rule. 
         [0148]    Thereafter, the terminal proceeds to step  1203  to transmit a message for requesting disconnection from the data network. The message may trigger the disconnection or may request one of the network entities of the core network to trigger the disconnection. According to an exemplary embodiment of the present disclosure, the terminal may transmit the message according to the request received in step  1201 , without considering the state of at least one flow. According to another exemplary embodiment of the present disclosure, the terminal determines whether the disconnection from the data network is acceptable or not according to a pre-defined rule, and then, when the disconnection from the data network is acceptable, the terminal may transmit the message. For example, the pre-defined rule may be defined based on the state of the at least one flow owned by the terminal. For example, the terminal may transmit the message when a disorder is not created in the continuity of a service by the disconnection from the data network. Specifically, if a service performing continuous data consumption (e.g., video streaming, and online radio) is executed, the terminal may transmit the message when more than a predetermined amount data is buffered. Alternatively, if a service requiring discontinuous data transmission (e.g., chatting, an SNS, webpage searching) is executed, the terminal may transmit the message when there is no data currently being downloaded or no data to be transmitted. 
         [0149]    Although not shown in  FIG. 12 , after transmitting the message requesting the disconnection from the data network, the terminal may perform a procedure for disconnecting from the data network. For example, the procedure for disconnecting from the data network may be performed as shown in  FIG. 8  or  11 . Thereafter, the terminal may perform a procedure for setting up connection with the data network again. Accordingly, an anchor gateway which serves as a connection point with the data network for the terminal is relocated. 
         [0150]    According to another exemplary embodiment of the present disclosure, step  1203  may be omitted. In this case, the procedure for disconnecting from the data network may be initiated by the network. To achieve this, when the disconnection is performed according to the pre-defined rule, the terminal may provide information necessary for determining the time to accept the disconnection to the core network. For example, the information necessary for determining the time to accept the disconnection may include at least one of information for notifying that the disconnection is accepted and information for indicating the state of the flow. 
         [0151]      FIG. 13  illustrates a view showing an operation procedure of a network entity which manages mobility in a wireless communication system according to an exemplary embodiment of the present disclosure. 
         [0152]    Referring to  FIG. 13 , in step  1301 , the network entity determines a new anchor gateway for a terminal. For example, the network entity may determine the new anchor gateway based on at least one of a distance to the terminal and a traffic load. Herein, the distance includes at least one of a physical distance or a logical distance and the logical distance includes a data transfer delay time. The new anchor gateway may be determined when a Tracking Area (TA) of the terminal is updated. 
         [0153]    After determining the new anchor gateway, the network entity proceeds to step  1303  to identify a level of session continuity of the terminal. According to an exemplary embodiment of the present disclosure, the level of the session continuity is divided into a first level, a second level, and a third level. The network entity retains session continuity information for each terminal or each flow of the terminal. When the terminal retains a plurality of flows and each flow has a different level of session continuity, a single level is selected according to pre-defined priority. The session continuity information may be provided to the network entity through at least one of a procedure in which the terminal initially accesses, a procedure in which a bearer is activated, and a procedure in which a bearer is modified. For example, the session continuity information may be provided through the procedure as shown in  FIG. 4 ,  5 , or  6 . In this case, the network entity may be an MME. 
         [0154]    When the level of the session continuity is the first level, the network entity proceeds to step  1305  to control the current anchor gateway to forward traffic to a P-GW which is selected as the new anchor gateway. That is, the first level refers to “always session continuity,” and, in this case, the anchor gateway is not relocated. However, to provide IP mobility, the traffic destined for the terminal is transmitted to the terminal via the P-GW which is selected as the new anchor gateway. To achieve this, the current anchor gateway routes the data destined for the terminal to the P-GW which is selected as the new anchor gateway. To achieve this, the network entity transmits a message instructing to forward the traffic to the current anchor gateway. Herein, the message may include at least one of identification information of the P-GW selected as the new anchor gateway, information for requesting to provide the IP mobility via the P-GW, and information for indicating that the level of the session continuity of the terminal is “always session continuity.” 
         [0155]    When the level of the session continuity is the second level, the network entity proceeds to step  1307  to control to relocate the anchor gateway regardless of a flow state. That is, the second level refers to “no session continuity.” To achieve this, the network entity transmits a request for data network reactivation to the terminal. In addition, after performing a procedure for the terminal to disconnect from the data network, the network entity performs a procedure for the terminal to set up connection with the data network. In this case, the network entity sets up connection with the data network via the P-GW which is selected as the new anchor gateway. To this end, the anchor gateway for the terminal is relocated. For example, the network entity performs the procedure as shown in  FIG. 7 . 
         [0156]    When the level of the session continuity is the third level, the network entity proceeds to step  1309  to control to relocate the anchor gateway at a time which is determined according to the flow state. That is, the third level refers to “on-demand session continuity.” To achieve this, the network entity transmits a request for data network deactivation to the terminal. The request instructs the terminal to relocate the anchor gateway, that is, instructs to determine the time to accept disconnection from the data network. Thereafter, the network entity controls to forward the traffic to the new anchor gateway, and then, performs a procedure for relocating the anchor gateway according to a request or notification from the terminal. For example, the network entity may perform the procedure as shown in  FIG. 10 . 
         [0157]      FIG. 14  illustrates a view showing an operation procedure of a network entity which provides session continuity information in a wireless communication system according to an exemplary embodiment of the present disclosure. 
         [0158]    Referring to  FIG. 14 , the network entity generates a message including session continuity information in step  1401 . The session continuity information may be provided by another network entity, inputted by a network operator, or generated according to a pre-defined rule. The pre-defined rule may be defined to classify the level of the session continuity based on one of a kind of application, an application provider, user subscription information, and an operator policy. 
         [0159]    Thereafter, the network entity proceeds to step  1403  to transmit the message including the session continuity information. For example, step  1403  may be one of steps  405 ,  407 , and  409  of  FIG. 4 , steps  505 ,  507 , and  509  of  FIG. 5 , and steps  601 ,  613 ,  615 , and  617  of  FIG. 6 . In addition, the network entity may be one of an HSS server, a PCRF server, a P-GW, and an S-GW. 
         [0160]      FIG. 15  illustrates a block diagram of a terminal in a wireless communication system according to an exemplary embodiment of the present disclosure. 
         [0161]    Referring to  FIG. 15 , the terminal includes a Radio Frequency (RF) processing unit  1510 , a baseband processing unit  1520 , a storage unit  1530 , and a control unit  1540 . 
         [0162]    The RF processing unit  1510  performs a function for transmitting and receiving signals via a radio channel, such as signal band conversion, amplification, and the like. That is, the RF processing unit  1510  up-converts a baseband signal provided from the baseband processing unit  1520  into an RF band signal, transmits the RF band signal via an antenna, and down-converts an RF band signal received via the antenna into a baseband signal. For example, the RF processing unit  1510  may include a transmission filter, a reception filter, an amplifier, a mixer, an oscillator, a Digital-to-Analogue Converter (DAC), an Analogue to Digital Converter (ADC), and the like. In  FIG. 15 , only a single antenna is illustrated, but the terminal may include a plurality of antennas. 
         [0163]    The baseband processing unit  1520  may convert between a baseband signal and a bit string according to a physical layer standard of a system. For example, when transmitting data, the baseband processing unit  1520  generates complex symbols by encoding and modulating transmission bit strings. In addition, when receiving data, the baseband processing unit  1520  may restore reception bit strings by demodulating and decoding baseband signals provided from the RF processing unit  1510 . For example, according to the Orthogonal Frequency Division Multiplexing (OFDM) method, when transmitting data, the baseband processing unit  1520  generates the complex symbols by encoding and modulating the transmission bit strings, maps the complex symbols onto sub carriers, and configures OFDM symbols by performing an Inverse Fast Fourier Transform (IFFT) operation and inserting a Cyclic Prefix (CP). In addition, when receiving data, the baseband processing unit  1520  divides the baseband signal provided from the RF processing unit  1510  on an OFDM symbol basis, restores the signals which have been mapped onto sub carriers through the Fast Fourier Transform (FFT) operation, and then restores reception bit strings by demodulating and decoding. The baseband processing unit  1520  and the RF processing unit  1510  may transmit and receive the signals as described above. Accordingly, the baseband processing unit  1520  and the RF processing unit  1510  may be referred to as a transmitting unit, a receiving unit, a transmitting and receiving unit, or a communication unit. 
         [0164]    The storage unit  1530  stores data such as basic programs, application programs, setting information, and temporary information for operations of the terminal. For example, the storage unit  1530  may provide stored data according to a request of the control unit  1540 . 
         [0165]    The control unit  1540  controls the overall operations of the terminal. For example, the control unit  1540  may transmit and receive signals through the baseband processing unit  1520  and the RF processing unit  1510 . In addition, the control unit  1540  records and reads out data on and from the storage unit  1550 . To achieve this, the control unit  1540  may include at least one processor. For example, the control unit  1540  may include a Communication Processor (CP) to control communication and an Application Processor (AP) to control upper layers such as application programs and the like. According to an exemplary embodiment of the present disclosure, the control unit  1540  may include a connection management unit  1542  to determine the time to accept disconnection from a data network. For example, the control unit  1540  may control the terminal to perform the procedures shown in  FIG. 2  to  FIG. 12 . The operations of the control unit  1540  according to an exemplary embodiment of the present disclosure are as follows. 
         [0166]    The control unit  1540  receives a request for disconnection from a data network from one of the network entities in a core network via the RF processing unit  1510  and the baseband processing unit  1520 . The request may instruct prompt disconnection from the network or disconnection from the network at a time which is determined according to a pre-defined rule. Thereafter, the control unit  1540  proceeds to transmit a message requesting disconnection from the data network. Herein, the message may trigger the disconnection or may request one of the network entities of the core network to trigger the disconnection. According to an exemplary embodiment of the present disclosure, the control unit  1540  may transmit the message without considering the state of at least one flow. According to another exemplary embodiment of the present disclosure, the control unit  1540  determines whether disconnection from the data network is acceptable or not according to the pre-defined rule, and then, when the disconnection from the data network is acceptable, transmits the message. For example, the pre-defined rule may be defined based on the state of at least one flow owned by the terminal. Thereafter, the controller unit  1540  may perform a procedure for disconnecting from the data network. For example, the procedure for disconnecting from the data network may be performed as shown in  FIG. 8  or  FIG. 11 . Thereafter, the control unit  1540  may perform a procedure for setting up connection with the data network again. Accordingly, an anchor gateway which serves as a connection point with the data network for the terminal is relocated. 
         [0167]    According to another exemplary embodiment of the present disclosure, the control unit  1540  may not transmit the message requesting the disconnection from the data network. In this case, the procedure for disconnecting from the data network is initiated by the network. To achieve this, when the disconnection is performed according to the pre-defined rule, the control unit  1540  may provide information necessary for determining the time to accept the disconnection to the core network. 
         [0168]      FIG. 16  illustrates a block diagram of a network entity in a wireless communication system according to an exemplary embodiment of the present disclosure. 
         [0169]    As shown in  FIG. 16 , the network entity includes a communication unit  1610 , a storage unit  1620 , and a control unit  1630 . 
         [0170]    The communication unit  1610  provides an interface for communicating with other entities in the network. That is, the communication unit  1610  converts bit strings transmitted from the network entity to another entity into physical signals, and converts physical signals received from another entity into bit strings. 
         [0171]    The storage unit  1620  stores data such as basic programs, application programs, setting information, or the like for operations of the network entity. According to an exemplary embodiment of the present disclosure, the storage  1620  stores and manages session continuity information of the terminal. The session continuity information includes a level of session continuity. The level of the session continuity is divided into “always session continuity,” “no session continuity,” and “on-demand session continuity.” In addition, the storage  1620  provides stored data according to a request of the control unit  1630 . 
         [0172]    The control unit  1630  controls the overall operations of the network entity. For example, the control unit  1630  may transmit and receive signals through the communication unit  1610 . In addition, the control unit  1630  records and reads out data on and from the storage unit  1620 . According to an exemplary embodiment of the present disclosure, the control unit  1630  may control a procedure for relocating an anchor gateway of the terminal. In addition, the control unit  1630  may be provided with the session continuity information stored in the storage  1620  from another entity or may provide the session continuity information to another entity. For example, the control unit  1630  controls the network entity to perform the procedures shown in  FIGS. 2 to 11 ,  13 , and  14 . The operations of the control unit  1630  according to an exemplary embodiment of the present disclosure are as follows. 
         [0173]    According to an exemplary embodiment of the present disclosure, the control unit  1630  determines a new anchor gateway for the terminal. For example, the control unit  1630  may determine the new anchor gateway based on at least one of a physical distance or a logical distance to the terminal, a data transfer delay time, and a traffic load. Thereafter, when the level of the session continuity is a first level, the control unit  1630  controls a current anchor gateway to forward traffic to a P-GW which is selected as the new anchor gateway. Specifically, the control unit  1630  may transmit a message instructing to forward the traffic to the current anchor gateway via the communication unit  1610 . When the level of the session continuity is a second level, the control unit  1630  controls to relocate the anchor gateway regardless of a flow state. To achieve this, the control unit  1630  transmits a request for data network reactivation to the terminal via the communication unit  1610 , and, after performing a procedure for the terminal to disconnect from the data network, performs a connection setup procedure for the terminal with the data network. When the level of the session continuity is a third level, the control unit  1630  controls to relocate the anchor gateway at a time which is determined according to a flow state. To achieve this, the control unit  1630  transmits a request for data network deactivation to the terminal via the communication unit  1610 , and, after controlling to forward the traffic to the new anchor gateway, may perform a procedure for relocating the anchor gateway according to a request or notification from the terminal. 
         [0174]    According to another exemplary embodiment of the present disclosure, the control unit  1630  generates a message including session continuity information and transmits the message including the session continuity information. That is, the network entity may be one of an HSS server, a PCRF server, a P-GW, and an S-GW. In this case, the session continuity information may be provided by another network entity, inputted by a network operator, or generated according to a pre-defined rule. The pre-defined rule may be defined to classify the level of the session continuity based on one of a kind of application, an application provider, user subscription information, and an operator policy. 
         [0175]    A connection point with a data network is managed based on information on session continuity for each user or each flow and a state of a flow in a wireless communication system, so that network efficiency can be enhanced without badly affecting user QoE. 
         [0176]    Embodiments of the present invention according to the claims and description in the specification can be realized in the form of hardware, software or a combination of hardware and software. 
         [0177]    Such software may be stored in a computer readable storage medium. The computer readable storage medium stores one or more programs (software modules), the one or more programs comprising instructions, which when executed by one or more processors in an electronic device, cause the electronic device to perform methods of the present invention. 
         [0178]    Such software may be stored in the form of volatile or non-volatile storage such as, for example, a storage device like a Read Only Memory (ROM), whether erasable or rewritable or not, or in the form of memory such as, for example, Random Access Memory (RAM), memory chips, device or integrated circuits or on an optically or magnetically readable medium such as, for example, a Compact Disc (CD), Digital Video Disc (DVD), magnetic disk or magnetic tape or the like. It will be appreciated that the storage devices and storage media are embodiments of machine-readable storage that are suitable for storing a program or programs comprising instructions that, when executed, implement embodiments of the present invention. Embodiments provide a program comprising code for implementing apparatus or a method as claimed in any one of the claims of this specification and a machine-readable storage storing such a program. Still further, such programs may be conveyed electronically via any medium such as a communication signal carried over a wired or wireless connection and embodiments suitably encompass the same. 
         [0179]    In the above-described exemplary embodiments, the elements included in the present disclosure are expressed in a singular form or a plural form according to an exemplary embodiment. However, the singular form or plural form is only selected to correspond to a situation suggested for convenience of explanation and the present disclosure is not limited to a single element or a plurality of elements, and the elements expressed in the plural form may be configured as a single element or the element expressed in the singular form may be configured as plural elements.