Abstract:
A method for managing congestion in a base station in a mobile communication system according to one embodiment of the present invention comprises the steps of: requesting user subscription information to a mobility management entity (MME); receiving the user subscription information from the MME; and performing a congestion control in a communication between terminals on the basis of the received user subscription information. According to the embodiment, action may be taken in consideration of the user information and a current congestion state when controlling the congestion in a wireless communication system, and thus side effects resulting from the congestion control may be reduced. Further, the present invention provides a method and device for not charging for dropped packets when performing a packet drop, and thus the congestion control may be performed more easily. Also, the present invention has an advantage of performing the congestion control, according to the type of packets to which congestion control is applied or the type of application or service which has generated packets, at the time of controlling the congestion, thereby minimizing user&#39;s inconvenience due to the congestion control.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
       [0001]    This application claims the benefit under 35. U.S.C. §371 of an International application filed on Jan. 20, 2014 and assigned application number PCT/KR2014/000558, which claims the benefit of a Korean patent application filed on Jan. 18, 2013 in the Korean Intellectual Property Office and assigned the serial number 10-2013-0006081, a Korean patent application filed on Mar. 22, 2013 in the Korean Intellectual Property Office and assigned the serial number 10-2013-0030770, and a Korean patent application filed on Oct. 31, 2013 in the Korean Intellectual Property Office and assigned the serial number 10-2013-0131691, the entire disclosure of which is hereby incorporated by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to a method and apparatus for adjusting a service level in a congestion state in a wireless communication system, and more particularly, to a method for solving congestion when congestion occurs and a method and apparatus for reducing adverse effects caused by solving the congestion. 
       BACKGROUND 
       [0003]      FIG. 1  illustrates a structure of an LTE mobile communication system. 
         [0004]    Referring to  FIG. 1 , a wireless access network of the LTE mobile communication system includes a next-generation base station (Evolved Node B, EUTRAN, hereinafter, referred to as “eNB” or “NodeB”)  110 , an MME (Mobility Management Entity)  120 , and an S-GW (Serving-Gateway)  130 . A user equipment (hereinafter, referred to as “terminal” or “UE”)  100  is connected to an external network via the eNB  110 , the S-GW  130 , and a P-GW (Packet Data Network-Gateway)  160 . An AP (Application Function) is a device that exchanges application-related information with a user in the application level. A PCRF (Policy and Charging Rules Function)  150  is a device that controls a policy related to the Quality of Service (QoS) of a user, and a PCC (Policy and Charging Control) rule corresponding to the policy is transferred and applied to the P-GW  160 . 
         [0005]    The eNB  110  is an RAN (Radio Access Network) node, and corresponds to an RNC (Radio Network Controller) of a UTRAN system and a BSC (Base Station Controller) of a GERAN system. The eNB  110  is connected to the UE  100  via a wireless channel, and performs a similar role to the existing RNC/BSC. 
         [0006]    In the LTE system, since all user traffic including a real-time service such as VoIP (Voice over IP) through an Internet protocol (IP) are serviced through a shared channel, a device for collecting and scheduling status information of UEs  100  is needed, and the eNB  110  serves as this device. 
         [0007]    The S-GW  130  is an entity to provide data bearers and establishes and releases data bearers under the control of the MME  150 . The MME  150  is responsible for various control functions and is connected to a plurality of eNBs. 
         [0008]    The PCRF  150  is an entity that generally controls QoS and charging for traffic. 
         [0009]    In general, a User Plane (UP) refers to a path connecting the UE  100  to the RAN node, the RAN node to the S-GW  130 , and the S-GW  130  to the P-GW  160 , through which user data is transmitted and/or received. Of this path, a section that uses a wireless channel with seriously limited resources is a path between the UE  100  and the RAN node. 
         [0010]    In a wireless communication system such as LTE, QoS may be applied in units of EPS bearers. One EPS bearer is used to transport IP flows having the same QoS requirements. In the EPS bearers, QoS-related parameters may be designated and include QoS Class Identifier (QCI) and Allocation and Retention Priority (ARP). The EPS bearer corresponds to a PDP context of the GPRS system. 
         [0011]    Therefore, there is a need for a method for reducing congestion that may occur due to limitations of resources in a wireless communication system. 
       SUMMARY 
     Technical Problem 
       [0012]    Therefore, the present invention has been made in view of the above-mentioned problems, and an aspect of the present invention is to provide a method and apparatus in which an Evolved Node B (eNB) may control congestion in consideration of user characteristics or service application, in order to respond to a congestion state while preventing a user quality of experience for service from deteriorating in a Radio Access Network (RAN) congestion state (hereinafter, equally used with a User Plane (UP) congestion state). 
         [0013]    Another aspect of the present invention is to provide a method and apparatus in which an eNB may enable a communication network operator for packet to readily impose a charge for a packet to which the congestion control is applied. 
         [0014]    Still another aspect of the present invention is to provide a method and apparatus in which a User Equipment (UE) may efficiently perform congestion control through congestion control information in an eNB to which the UE is moved when handover occurs between eNBs. 
         [0015]    Yet another aspect of the present invention is to provide a method and apparatus in which an eNB may perform congestion control in accordance with a character of a packet to which the congestion control is applied, when performing the congestion control. 
       Solution to Problem 
       [0016]    In accordance with an aspect of the present invention, there is provided a method for controlling congestion of an Evolved Node B (eNB) in a mobile communication system including: requesting user subscription information from a Mobility Management Entity (MME); receiving the user subscription information from the MME; and performing congestion control in communication with a User Equipment (UE) based on the received user subscription information. 
         [0017]    In accordance with another aspect of the present invention, there is provided a method for controlling congestion in an MME of a mobile communication system including: receiving a request for user subscription information from an eNB; and transmitting user subscription information to the eNB based on the request. Here, the eNB may perform congestion control in communication with a UE based on the received user subscription information. 
         [0018]    In accordance with still another aspect of the present invention, there is provided an eNB in a mobile communication system including: a transmission/reception unit that requests user subscription information from an MME, and receives the user subscription information from the MME; and a control unit that performs congestion control in communication with a UE based on the received user subscription information. 
         [0019]    In accordance with yet another aspect of the present invention, there is provided an MME of a mobile communication system including: a transmission/reception unit that receives a request for user subscription information from an eNB; and a control unit that controls the transmission/reception unit to transmit user subscription information to the eNB based on the request. Here, the eNB may perform congestion control in communication with a UE based on the received user subscription information. 
         [0020]    In accordance with further aspect of the present invention, there is provided a method for managing congestion in a UE of a mobile communication system, including: transmitting a policy request message to a User Plane Congestion (UPCON) policy server; receiving, from the UPCON policy server, a policy response message including whether one or more applications corresponding to the policy request message are attended/unattended; generating, by an application executed by the UE, data; and transmitting, to the eNB, the generated data and a signal including whether the generated data is attended/unattended based on the policy response message. 
         [0021]    In accordance with further aspect of the present invention, there is provided a method for managing congestion in an eNB of a mobile communication system, including: receiving, from a UE, data generated by an application executed in the UE and a first signal including whether the generated data is attended/unattended; storing information including whether the data generated by the application is attended/unattended based on the received signal; transmitting the data generated by the application to a gateway; receiving, from the gateway, a second signal including data generated by a destination server to correspond to the data generated by the application; and performing congestion control based on the stored information when transmitting the data generated by the server in a case in which a UP is in a congestion state. 
         [0022]    In accordance with further aspect of the present invention, there is provided a method for transmitting and receiving data in an eNB of a mobile communication system, including: receiving a data packet from a core network; transmitting the received data packet to a UE; detecting that connection to the UE is unavailable; and transmitting the detection result to the core network. Here, the core network that has received the detection result may change information related to the data packet transmitted to the UE. 
         [0023]    In accordance with further aspect of the present invention, there is provided a method for transmitting and receiving data in a core network node of a mobile communication system, including: transmitting a data packet to an eNB; receiving, from the eNB, a message including information about a connection state between the eNB and a UE; and changing information about the transmitted data packet when the connection state is unavailable. 
       Advantageous Effects 
       [0024]    According to embodiments, it is possible to take a measure in consideration of UE context and a current congestion state when performing congestion control in a wireless communication system, thereby reducing side effects due to congestion control. 
         [0025]    Also, it is possible to prevent charge imposition for a dropped packet when performing packet drop, thereby more readily performing congestion control. 
         [0026]    Also, by performing congestion control in accordance with a type of a packet to which congestion control is applied at the time of congestion control, it is possible to minimize the user&#39;s inconvenience due to congestion control. 
         [0027]    Also, by receiving attended/unattended information of an application from a policy server, it is possible to perform congestion control in accordance with a character of a packet caused by the application at the time of congestion control. 
         [0028]    Also, when a UE fails to receive a data packet, a core network may adjust a transmitted packet or change charging information, by which it is possible to prevent a packet from being dropped in an eNB or the core network and prevent the occurrence of improper charge imposition on a UE. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0029]      FIG. 1  illustrates a structure of a wireless communication system according to the related art; 
           [0030]      FIG. 2  is a signal flowchart illustrating a congestion state according to an embodiment of the present invention; 
           [0031]      FIG. 3  illustrates a signal flow for performing congestion control according to an embodiment of the present invention; 
           [0032]      FIG. 4  illustrates a signal flow for performing congestion control according to an embodiment of the present invention; 
           [0033]      FIG. 5  illustrates data transmission and reception for performing congestion control according to an embodiment of the present invention; 
           [0034]      FIG. 6  illustrates a signal flow for congestion control at the time of handover of a UE according to an embodiment of the present invention; 
           [0035]      FIG. 7  illustrates a signal flow for congestion control at the time of handover of a UE according to another embodiment of the present invention; 
           [0036]      FIG. 8  illustrates a signal flow for congestion control at the time of handover according to still another embodiment of the present invention; 
           [0037]      FIG. 9  illustrates a signal flow for congestion control based on a character of a packet according to an embodiment of the present invention; 
           [0038]      FIG. 10  illustrates a signal flow for congestion control based on a character of a packet according to another embodiment of the present invention; 
           [0039]      FIG. 11  illustrates a signal flow for congestion control based on a character of a packet according to still another embodiment of the present invention; 
           [0040]      FIG. 12  illustrates a signal flow for congestion control based on a character of a packet according to yet another embodiment of the present invention; 
           [0041]      FIG. 13  illustrates a structure when congestion control is performed based on a character of an application in a communication system according to an embodiment of the present invention; 
           [0042]      FIG. 14  illustrates a signal flow and data processing for congestion control based on a character of an application according to still another embodiment of the present invention; 
           [0043]      FIG. 15  illustrates a connection loss state between an eNB and a UE according to an embodiment of the present invention; 
           [0044]      FIG. 16  illustrates a method of transmitting and receiving signals at the time of connection loss according to an embodiment of the present invention; and 
           [0045]      FIG. 17  is a flowchart illustrating operations of a core network node according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0046]    Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. 
         [0047]    In describing the exemplary embodiments of the present invention, descriptions related to technical contents which are well-known in the art to which the present invention pertains, and are not directly associated with the present invention, will be omitted. Such an omission of unnecessary descriptions is intended to prevent obscuring of the main idea of the present invention and more clearly transfer the main idea. 
         [0048]    For the same reason, in the accompanying drawings, some elements may be exaggerated, omitted, or schematically illustrated. Further, the size of each element does not entirely reflect the actual size. In the drawings, identical or corresponding elements are provided with identical reference numerals. 
         [0049]    In the following description of embodiments of the present invention, a detailed description of known functions or configurations incorporated herein will be omitted when it is determined that the detailed description thereof may unnecessarily obscure the subject matter of the present invention. 
         [0050]    In addition, in the specific description of the embodiments of the present invention, a basic 3GPP (Third Generation Partnership Project) LTE system is described as a main target, but embodiments of the present invention may also be applicable with some modifications in other communication/computer systems having a similar technical background and system type to the extent not departing significantly from the scope of the present invention, which will be determined by skilled persons with technical knowledge in the art. For example, the present technique using the LTE system as the main target may be applicable even in UTRAN/GERAN systems having a similar system structure. In this case, an ENB (RAN node) may be replaced by RNC/BSC, an S-GW (Serving-Gateway) may be omitted or included in an SGSN (Serving GPRS Support Node), and a P-GW (Packet Data Network-Gateway) may correspond to a GGSN (Gateway GPRS Support Node). In addition, a concept of a bearer of the LTE system may correspond to the PDP context of the UTRAN/GERAN system. 
         [0051]    In addition, according to an embodiment, an RAN (Radio Access Network) should transmit and receive data with a user within limited frequencies. When the number of users is increased within a cell controlled by the RAN node, or when an amount of traffic transmitted and received by users is increased, a congestion state may be generated in the RAN. In order to respond to the congestion state without deteriorating a user quality of experience for service in such RAN congestion state (hereinafter, equally used with a User Plane (UP) congestion state), congestion control considering user characteristics or service applications is required. A system component that can autonomously perform an operation corresponding to the congestion state may be a configuration of at least one of a UE (User Equipment), a communication network, and a component that transmits traffic. 
         [0052]    When a subject that manages traffic with respect to the congestion state is an RAN (E-UTRAN or eNodeB in the case of the LTE network) within a network, the RAN may perform differential transmission of data packets that satisfy specific conditions or perform an operation of extremely dropping the data packet rather than transmitting the data packet when the congestion state is severe. In this instance, there may occur a case in which, even though an entity (generally P-GW in the case of the LTE network) for collecting transmission information (the number or volume of transmitted packets) of the packet with respect to the UE for the purpose of charge imposition has already generated charging information about the packet, the corresponding packet cannot be transmitted to the RAN due to the congestion state, or service cannot be properly received compared to the charge imposition. 
         [0053]      FIG. 2  is a signal flowchart illustrating a congestion state according to an embodiment of the present invention. 
         [0054]    Referring to  FIG. 2 , in step  215 , it may be assumed that a User Equipment (UE)  202  receives a service in a congested RAN  215 . 
         [0055]    In step  210 , a downlink packet may reach a GW node  206  (S-GW or P-GW, but preferably, P-GW). 
         [0056]    In step  220 , the GW node  206  (generally, P-GW) that collects charging-related information may generate charging information related to the corresponding packet. 
         [0057]    In step  225 , the GW node  206  may transmit the packet that has generated the charging information to the RAN node  204 . 
         [0058]    In step  230 , there may occur a case in which the RAN node  204  drops the packet that should be transmitted to the UE  202  whiling failing to transmit the packet to the UE  202  due to congestion, due to a congestion state. 
         [0059]    When the packet for which a charge has been already imposed in step  230  is dropped, there may occur a case in which a charge is imposed for the dropped packet although even an attempt to transmit the corresponding packet to the UE  202  has not been made such as in step  235 . 
         [0060]    In order to address the foregoing problem, the RAN node  204  may apply control such as dropping the packet so long as a problem of the charge imposition on the UE  202  does not occur even though the RAN node  204  applies congestion control. 
         [0061]      FIG. 3  illustrates a signal flow for performing congestion control according to an embodiment of the present invention. 
         [0062]    Referring to  FIG. 3 , a user subscription information database (HSS)  306  stores information about a charging type to be applied to a UE, and then also transmits the stored information about the charging type when transmitting user subscription information to a core network node (e.g., MME (Mobility Management Entity)  304 ). The core network node may enable the corresponding charging type-related information to be included as a part of the UE context transmitted to the RAN node  302 , as necessary. The RAN node  302  that has received the UE context may apply a gating operation (dropping the packet rather than transmitting the packet) or differential transmission with respect to the corresponding packet, when no problem occurs even though the corresponding packet is not transmitted but dropped according to the charging type of the UE in a congestion state (e.g., a case of flat charging or flat rate plan, a case of an unlimited charging plan, or a case in which a packet is allowed to be dropped according to setting of a network operator or a user). The foregoing operation may be simply changed to perform an operation of dropping the corresponding packet only when the user subscription information includes information about whether the data packet is allowed to be dropped rather than transmitted from the network to the UE and this information is transmitted to the RAN node  302  and allowed. The charging type and whether the packet is allowed to be dropped may be distinguished per UE or per service. As an example of being distinguished per service, a case in which the charging type and whether the packet is allowed to be dropped is distinguished by at least one of per PDN (Packet Data Network) connection (per APN) and per bearer (per EPS bearer) may be given. For example, when packet drop is allowed only with respect to one EPS bearer according to subscription information transmitted from a subscription information server to the RAN node  302  even though the UE generates two EPS bearers, or when there is no problem in the charging type due to packet drop, the RAN node  302  may apply gating (packet drop) only to the corresponding EPS bearer. 
         [0063]    Referring to  FIG. 3 , in step  310 , when transmitting the user subscription information to the MME  304  (updating location ack (acknowledge) or inserting subscription information message), the HSS  306  may enable the charging type and information indicating whether packet drop is allowed to be included in the subscription information, and transmit the user subscription information. According to an embodiment, the charging type may include a charging type applied to the UE. The charging type may include an identifier for identifying flat charging, online charging, offline charging, unlimited data plan, volume-based charging, and the like. The MME  304  may store the received identifier. 
         [0064]    The MME  304  may transmit the stored UE context to the RAN node  302 , as necessary. Such transmission of the UE context to the RAN node  302  may include a case in which information indicating occurrence of congestion is received from the RAN node  302 . 
         [0065]    In step  315 , the RAN node  302  may notify the MME  304  of the information indicating occurrence of congestion. 
         [0066]    In step  320 , the MME  304  may determine whether to notify the RAN node  302  of the stored UE context and the information indicating whether packet drop is allowed, based on the message received in step  315 . The determination may be performed by a user identifier set in advance or by setting of a network operator. 
         [0067]    In step  325 , the MME  304  that has determined that the stored UE context and the information indicating that packet drop is allowed can be transmitted may transmit, to the RAN node  302 , the stored UE context and the information indicating that packet drop is allowed. According to an embodiment, the MME  304  may enable the stored UE context and the information indicating that packet drop is allowed to be included in the UE context (included in a S1-AP initial context setup request message), and transmit the UE context to the RAN node  302 . The RAN node  302  may store the received message. 
         [0068]    In step  330 , the RAN node  302  may have the charging type (flat charging, unlimited charging plan, or the like) in which there is no problem even though the data packet is dropped in the congestion state, or apply an operation of dropping the corresponding packet only with respect to a UE in which packet drop is allowed according to the user subscription information. 
         [0069]    According to an embodiment, when the foregoing operation is applied for per PDN connection (per APN) or per bearer (per EPS bearer), the information about charging type or the information indicating that packet drop is allowed may be separately transmitted per PDN connection or per bearer. 
         [0070]    In addition, according to another embodiment, the UE context may be transmitted to the P-GW. According to an embodiment, an SPR may transmit the UE context to the P-GW. When the HSS or the SPR is not directly connected to the P-GW, the corresponding user subscription information may be transmitted to a PCRF (Policy and Charging Rules Function) by the HSS or the SPR, and transmitted as a part of PCC (Policy and Charging Control) rule or ADC rule which is transmitted by the PCRF in order to control the P-GW. 
         [0071]    The UE context may include information that can be used as a determination factor in dropping the corresponding packet. The UE context may include the information that has been used to describe the embodiment of  FIG. 3 . 
         [0072]    The P-GW that has received the UE context may store the UE context, enable information that can be determined when congestion is controlled by the RAN node  302  based on the UE context to be included in the packet, and transmit the packet. According to an embodiment, the information that can be determined when congestion is controlled may include an indicator indicating a case in which it is possible to drop the corresponding packet or an identifier indicating a transmission priority, and the indicator information may be included in a GTP-U header of the transmitted data packet, and transmitted. When the S-GW should transmit, to an eNB, the packet received from the P-GW, the S-GW may perform a process in which the information included in the GTP-U header is inserted again in the GTP-U header of the packet transmitted to the eNB and transmitted. 
         [0073]    When dropping the packet so as to control congestion, the eNB may inspect the packet to be dropped, and drop the packet when the indicator indicates that it is possible to drop the packet. In addition, the indicator may include a priority that can be determined when the packet is dropped.  FIG. 4  illustrates a signal flow for performing congestion control according to an embodiment of the present invention. 
         [0074]    Referring to  FIG. 4 , according to another embodiment, a method of determining whether a charge is imposed for the transmitted packet based on transmission success or transmission failure of the transmitted packet may be proposed. 
         [0075]    GW nodes  406  and  408  that transmit a downlink packet up to an RAN node  402  in a core network may transmit the packet by attaching a sequence number to the packet when transmitting the packet. The RAN node  402  may notify again the GW nodes  406  and  408  of information indicating whether to transmit the corresponding packet. When the packets are transmitted up to the RAN node  402  via several nodes, intermediate hop nodes store SN mapping information of the received packet and the transmitted packet, and then change, when transmitting the information indicating whether to transmit the corresponding packet, the SN mapping information to SNs for the corresponding packets and transmit the SNs. When this information is transmitted up to a node that generates charging information, the charging information may be generated or corrected according to whether the corresponding packet is actually transmitted. According to an embodiment, this operation may be applied only to specific PDN connection or an EPS bearer. 
         [0076]    In step  410 , the RAN node  402  may transmit, to an MME  404 , a message requesting to transmit the data packets by attaching SNs to the data packets transmitted to the RAN node  402  itself, as necessary (for example, a case of starting congestion control). In this instance, the RAN node  402  may request the transmission of the data packets from a specific bearer or regardless of the bearer. 
         [0077]    In step  415 , the MME  404  may transmit, to the S-GW  406 , the message requesting to transmit the data packets by attaching SNs to the data packets, based on the reception of the foregoing request. According to an embodiment, the message requesting to transmit the data packets by attaching SNs to the data packets may include information requesting, from a modify bearer request message, that the corresponding SN should be necessarily written on the corresponding header in a case of the GTP-U packet to be transmitted in the future. This request may be performed per bearer as described above. In addition, the S-GW  406  may store an SN mapping table of a packet to be transmitted based on the request. Thus, the S-GW  406  may map the SN of the packet received from the P-GW  408  and the SN of the packet transmitted to the eNB  402 . 
         [0078]    In step  420 , the S-GW  406  may transmit, to the P-GW  408 , the message requesting to transmit the data packets by attaching SNs to the data packets. According to an embodiment, the message requesting to transmit the data packets by attaching SNs to the data packets may include information requesting, from a transmitted modify bearer request message, that the corresponding SN should be necessarily written on the corresponding header in a case of the GTP-U packet to be transmitted in the future. This request may be performed per bearer as described above. 
         [0079]    In step  425 , the P-GW  408  that has received this may store information indicating that the SN of the transmitted packet should be used (which bearer should be applied when the request is performed per bearer), and transmit the corresponding response to the S-GW  406 . Thereafter, the respective nodes write the SN on the GTP-U header and transmit the corresponding packet, in a case of a data packet for a user (or a user&#39;s bearer) in which the SN is set to be used. In addition, in step  430 , the S-GW  406  may transmit the transmitted response to the MME  404 . 
         [0080]      FIG. 5  illustrates data transmission and reception for performing congestion control according to an embodiment of the present invention. 
         [0081]    Referring to  FIG. 5 , transmission of the data packet and charging control may be performed in a method shown in  FIG. 5 . In addition, according to an embodiment, an SN capable of identifying a packet transmitted according to setting in  FIG. 4  may be used in the packet. In addition, an S-GW  506  may store a mapping table of the transmitted SN. 
         [0082]    In step  510 , a P-GW  506  may record SN information with respect to a downlink packet by information set in advance or according to the embodiment. According to an embodiment, the SN information may be recorded in the transmitted packet using a SN field of the GTP-U header. 
         [0083]    In step  515 , when transmitting the received packet to an RAN node  502 , the S-GW  504  may write the SN of the transmitted packet on a GTP-U header, and transmit the corresponding packet. Preferably, the S-GW  504  may write an SN field on a newly attached GTP-U header and transmit the corresponding packet. In addition, the S-GW  504  may store mapping information about the SN of the GTP-U packet which the S-GW  504  itself receives from the P-GW  506  and mapping information about the SN of the GTP-U packet that is used when the S-GW  504  transmits, to the RAN node  502 , the SN of the GTP-U packet which the S-GW  504  itself receives from the P-GW  506 . 
         [0084]    In step  520 , the RAN node  502  may transmit or drop the received packet according to its congestion state. According to an embodiment, the RAN node  502  may adjust the order of the transmission of the packet so as to control the congestion state. 
         [0085]    In step  525 , the RAN node  502  transmits the SN of the corresponding packet and information about a state of the corresponding packet to the S-GW  504 . The state of the packet may include at least one of transmission success of the packet, transmission failure of the packet, whether the packet is dropped, and a time during which the packet stays in a buffer. 
         [0086]    In step  530 , the S-GW  504  may determine the SN of the GTP-U packet received from the P-GW  506  using the SN included in the information received in step  520  and mapping information stored in advance, based on the information received in step  520 . 
         [0087]    In step  535 , the S-GW  504  may transmit the transmission state of the packet to the P-GW  506  based on the SN determined in step  530 . According to an embodiment, the S-GW  504  transmits, to the P-GW  506 , information including SNs of packets S5/S8 (interface between the S-GW  504  and the P-GW  506 ) and the state of the corresponding packet. 
         [0088]    In step  540 , when receiving the information, the P-GW  506  may generate charging information or utilize the received information when correcting the already generated charging information. Such packet transmission information transmitted from the RAN node  502  up to the P-GW  506  may be sent using a separate GTP-C message, or transmitted in the form of a next extension header of a GTP-U header of an uplink packet. In addition, the transmission information may be sent in a short period (for example, whenever receiving each packet) for the purpose of real-time charging, or the information collected at prescribed time intervals may be transmitted at the same time so as to reduce the signaling load. 
         [0089]      FIG. 6  illustrates a signal flow for congestion control at the time of handover of a UE according to an embodiment of the present invention. 
         [0090]    Referring to  FIG. 6 , when a UE  602  is connected to a first eNB  604  which applies congestion control due to the occurrence of congestion, receives services from the first eNB  604 , and then is moved to a second eNB  606 , the second eNB  606  is incapable of knowing states of data packets of the UE  602  transmitted and received in the first eNB  604 , and therefore a problem in which the service qualities of other UEs are degraded due to a case in which the UE  602  is incapable of continuously receiving the service or due to the moved UE  602  may occur. In order to address the problem, when handover occurs, the first eNB  604  may notify the second eNB  606  of information indicating that the packets of the UE  602  have been subjected to congestion control, and the second eNB  606  may perform packet transmission control based on the notified information. 
         [0091]    According to an embodiment, when the UE  602  performs handover from the congested first eNB  604  to the uncongested second eNB  606 , the packet transmission control may be to transmit the corresponding packet prior to the traffic of other UEs having the same transmission priority in order to alleviate the starvation of the UE  602 . 
         [0092]    According to another embodiment, when the UE  602  performs handover from the congested first eNB  604  to the congested second eNB  606 , the packet transmission control may be to prevent the service qualities of other UEs from being degraded by consecutively lowering the transmission priority of the UE  602  that has been already subjected to congestion control. 
         [0093]    In step  610 , the UE  602  may transmit, to the first eNB  604 , measurement report information obtained by measuring a communication state. The measurement report information may include information through which whether to perform handover can be determined. 
         [0094]    In step  615 , the first eNB  604  determines whether to perform handover based on the transmitted measurement report information. According to an embodiment, the first eNB  604  may determine handover to the second eNB  606 . When handover occurs, a handover request message transmitted to the second eNB  606  by the first eNB  604  may include at least one of information indicating whether the UE has been subjected to congestion control, information indicating which kind of scheduling policy is applied, information indicating whether the corresponding user is a de-prioritized user, subscription levels of the corresponding UEs (e.g., gold/silver/bronze membership users, etc.), and charging methods (e.g., unlimited charging plan, flat rate plan, an object to which number/volume-based charging is applied, etc.). When performing congestion control in the subsequent steps, the second eNB  606  may perform congestion control based on the received information included in the handover request message. In addition, according to an embodiment, the second eNB  606  that has received the information included in the handover request message stores and uses this information. In particular, information (e.g., whether to apply congestion control, congestion control application level, etc.) related to congestion control performed with respect to the UE  602  may be used when determining whether to raise or lower the transmission priority in a case of transmitting data traffic forwarded from the first eNB  604  during a handover process. Alternatively, the information related to congestion control performed with respect to the UE  602  may be used to apply congestion control when RAN congestion occurs in the second eNB. According to an embodiment, the de-prioritized user may include a user of a UE that is subjected to congestion control by a network. 
         [0095]    In step  620 , a handover process between the first eNB  604  and the second eNB  606  is performed, and in step  625 , the first eNB  604  may transmit information required for the handover process to the second eNB  606 . 
         [0096]    In step  630 , the second eNB  606  may perform congestion control by determining the transmission priority based on the information received from the first eNB  625 . 
         [0097]    In step  635 , the second eNB  606  may transmit data to the UE  602 . According to an embodiment, in step  630 , congestion control may be performed based on the transmission priority determined in step  630  in a congestion state. 
         [0098]      FIG. 7  illustrates a signal flow for congestion control at the time of handover of a UE according to another embodiment of the present invention. 
         [0099]    Referring to  FIG. 7 , in step  710 , a UE  702  may transmit, to a first eNB  704 , measurement report information obtained by measuring a communication state. The measurement report information may include information through which whether to perform handover can be determined. 
         [0100]    In step  715 , the first eNB  704  determines whether to perform handover based on the transmitted measurement report information. According to an embodiment, the first eNB  704  may determine handover to the second eNB  706 . The first eNB  704  may perform handover to the second eNB  706 . 
         [0101]    In step  720 , the first eNB  704  may transmit, to the second eNB  706 , a message including information related to congestion control of the UE  702 . According to an embodiment, the first eNB  704  may enable information about whether to apply differential transmission per data packet, information about a time during which the corresponding packet stays in a buffer of the corresponding eNB, and the like to be included in an SN status transfer transmitted to the second eNB  706 , and transmit the SN status transfer. The first eNB  704  may enable congestion control information to be included in a control message, and transmit the control message to the second eNB  706 . 
         [0102]    In step  725 , the first eNB  704  may transmit data including information required for handover to the second eNB  706 . 
         [0103]    In step  730 , the second eNB  706  may store the information received from the first eNB  704  and use the stored information to perform congestion control based on the stored information. According to an embodiment, the stored information may be used when determining whether to raise or lower the transmission priority in a case of transmitting data traffic forwarded from the first eNB  704  during a handover process. According to another embodiment, the second eNB  706  may apply a method such as preferentially transmitting a packet in which a time during which the packet stays in the buffer is 100 ms or more. 
         [0104]      FIG. 8  illustrates a signal flow for congestion control at the time of handover according to still another embodiment of the present invention. 
         [0105]    In  FIG. 8 , procedures of steps  810  and  815  may respectively correspond to procedures of steps  710  and  715  of  FIG. 7 . 
         [0106]    Referring to  FIG. 8 , in step  820 , when handover occurs, a first eNB  804  may transmit, to a second eNB  806 , information about whether to apply differential transmission of each packet or information about a time during which the corresponding packet stays in a buffer of the corresponding eNB, using new fields of PDCP headers of forwarded data packets. 
         [0107]    In step  825 , the second eNB  806  that has received the foregoing information may store the foregoing information. Thereafter, the stored information may be used when determining whether to raise or lower the transmission priority in a case of transmitting, to a UE  802 , data traffic forwarded from the first eNB  804  during a handover process. For example, a method such as preferentially transmitting a packet in which a time during which the packet stays in the buffer is 100 ms or more may be applied. 
         [0108]    In  FIGS. 6 to 8 , the congestion control-related information transmitted between the respective eNBs may be associated with each other, and it should be noted that the related information of the different embodiments may be borrowed and used in each embodiment. 
         [0109]      FIG. 9  illustrates a signal flow for congestion control based on a character of a packet according to an embodiment of the present invention. 
         [0110]    Referring to  FIG. 9 , most of the traffic currently used by a UE  902  is generated without direct interaction with a user. For example, traffic may be generated due to data transmitted and received in the background by applications currently executed in the UE  902  even though a user prevents the UE  902  from being directly used by turning on a screen of the UE  902 . Such background traffic is transmitted and received regardless of the user&#39;s intention, and therefore it is unnecessary to preferentially transmit the background traffic in a congestion state. According to an embodiment, data having direct interaction with a user may be referred to as attended data, and data not having direct interaction with a user may be referred to as unattended data. 
         [0111]    Thus, in the case of the data not having direct interaction with the user, the user of the UE  902  cannot directly recognize inconvenience even though the data is not preferentially transmitted, and the data may be transmitted again by the subsequent re-transmission process, and therefore it is possible to lower the transmission priority in the congestion state. 
         [0112]    In step  910 , the UE  902  may transmit an RRC connection request message to an eNB  904 . In step  915 , the eNB  904  may transmit an RRC connection setup request to the UE  902  based on the message transmitted in step  910 . The RRC connection setup request message may include a message notifying that the eNB  904  is in a congestion state. 
         [0113]    In step  920 , the UE  902  may transmit an RRC connection complete message to the eNB  904 . The RRC connection complete message may include at least one of an attach request/service request message and an NAS message. In addition, in step  915 , the UE  902  that has received the message notifying the congestion from the eNB  904  may enable information including whether data whose transmission is requested is attended/unattended to be included in the RRC connection complete message, and transmit the RRC connection complete message. 
         [0114]    In step  925 , the eNB  904  may store information indicating that the data whose transmission is requested is unattended. When the data whose transmission is requested is attended, the corresponding operation may be performed in a similar manner to that of an existing operation. 
         [0115]    In step  930 , the UE  902  may store information indicating that the eNB  904  is in the congestion state. In the transmission according to this, when detecting whether to display data or when the data transmitted by the UE is changed to be attended in the subsequent step, the corresponding message may be transmitted to the eNB  904 . 
         [0116]    In step  935 , the entire process of attach/service request among the UE  902 , the eNB  904 , and an S-GW/P-GW  906  may be completed. 
         [0117]    In step  940 , downlink data may be transmitted to the S-GW/P-GW  906 , the eNB  904 , and the UE  902 . 
         [0118]    In step  945 , the eNB  904  may lower the transmission priority of the traffic belonging to a non-GBR bearer out of the traffic for the corresponding UE. 
         [0119]    Steps  950  and  960  correspond to a case in which there is a change in the data transmitted by the UE  902 , and steps  965  to  975  correspond to a case in which the congestion state of the eNB  904  is released. 
         [0120]    In step  950 , the UE  902  may detect the attendance change of the transmitted data. According to an embodiment, the attendance change may include at least one of a case in which data to be transmitted and received is generated by a user&#39;s input and a case in which a display unit of the UE  902  is turned on. 
         [0121]    In step  955 , the UE  902  may transmit, to the eNB  904 , a message indicating that the state of the data transmitted by the UE is changed. This message may be transmitted only when the UE  902  is notified of the congestion state of the eNB  904 . According to an embodiment, the UE  902  may transmit, to the eNB  904 , information indicating that the state of the data transmitted through an RRC UE status message becomes attended. 
         [0122]    In step  960 , the eNB  904  may change an unattended state to an attended state based on the message received in step  955 . In addition, according to an embodiment, the eNB  904  that has received the message no longer lowers the transmission priority of non-GBR traffic. 
         [0123]    In step  965 , the congestion state of the eNB may be released. In this case, the eNB  904  may stop scheduling for lowering the priority of non-GBR bearer transmission. 
         [0124]    In step  970 , the eNB  904  may transmit, to the UE  902 , a message indicating that the congestion state of the eNB  904  is released. According to an embodiment, the message may be included in an RRC eNB status message and transmitted. 
         [0125]    In step  975 , the UE  902  may store information indicating that the congestion state of the eNB  904  is released. 
         [0126]    According to an embodiment, the UE  902  may notify the change in the attended (intended by a user)/unattended (unintended by a user) state only in an RAN congestion state. Whether the UE is attended/unattended may be determined when a program other than a program set by an operator is executed or when data is generated even though the screen of the UE is turned off. The UE  902  recognizes that congestion occurs in an RAN from the eNB  904  through the RRC connection setup request message, enables the attended/unattended state of the UE  902  to be included in the RRC connection complete message, and transmits the RRC connection complete message. 
         [0127]    In this process, the UE  902  stores information about whether the eNB  904  is congested, and the eNB  904  stores information about whether the corresponding user is in the unattended state. When downlink data reaches the P-GW in the case of notifying that the UE  902  is unattended, the eNB  904  may lower the transmission priority of the traffic belonging to the non-GBR bearer out of the traffic for the corresponding UE. When the eNB  904  is still congested even though the UE is changed to the attended state, the UE  902  transmits the state change through the RRC UE status message. The eNB that has received this no longer lowers the transmission priority of the non-GBR traffic. Meanwhile, when the congestion of the eNB  904  is released, the transmission priority of the non-GBR traffic may not be lowered despite notifying that the UE  902  is in the unattended state, and information indicating that the eNB  904  is no longer congested may be notified to the UE  902  through the RRC eNB status message. The UE  902  may store the state of the eNB  904 . 
         [0128]    According to the above-described embodiment, there is an advantage in that the UE  902  is capable of dynamically transmitting traffic in a differential manner in a state of being active, but there is a disadvantage in that signaling may frequently occur or overflow of the data buffer of the eNB may occur. 
         [0129]      FIG. 10  illustrates a signal flow for congestion control based on a character of a packet according to another embodiment of the present invention. 
         [0130]    Referring to  FIG. 10 , according to another embodiment of the present invention, a method of notifying information about whether an UE  1002  is attended using a packet (preferably, GTP-U header) transmitted up to a P-GW  1006  in a congestion state may be proposed. For this, when there is uplink data, the header of the uplink data is used, and otherwise, a dummy packet is made and transmitted. In this case, the GTP-U header may include information about whether the corresponding UE is attended together with information notifying that the corresponding packet is a dummy. 
         [0131]    Steps  1010  and  1015  may be performed in a similar manner to that of steps  910  and  915  of  FIG. 9  so as to correspond to steps  910  and  915  of  FIG. 9 . 
         [0132]    In step  1015 , the UE  1002  may recognize that congestion occurs in an RAN from an eNB  1004  through an RRC connection setup request message, and in step  1020 , the UE  1002  may verify attendance. 
         [0133]    Step  1025  may be performed in a similar manner to that of step  920  of  FIG. 9  so as to correspond to step  920  of  FIG. 9 . The UE  1002  may enable its attended/unattended state to be included in an RRC connection complete message and transmit the RRC connection complete message. 
         [0134]    In step  1035 , the eNB  1004  may store the attendance state of the UE. According to an embodiment, the eNB  1004  may store information indicating that the UE transmits and receives data while being in the unattended state. 
         [0135]    In step  1035 , the UE  1002  may store information indicating that the eNB  1004  is in the congestion state. 
         [0136]    In step  1040 , the UE  1002 , the eNB  1004 , and an S-GW/P-GW  1006  may perform the entire process of attach/service request. 
         [0137]    In step  1045 , when there is a non-GBR uplink packet transmitted from the UE  1002 , the eNB  1004  may use the non-GBR uplink packet, and otherwise, the eNB  1004  may display whether the UE  1002  is attended/unattended by generating a dummy packet. According to an embodiment, preferably, the eNB  1004  may display, in the GTP-U header, whether the UE  1002  is attended/unattended. 
         [0138]    In step  1050 , information displaying whether the UE  1002  is attended/unattended may be transmitted up to the S-GW/P-GW  1006  in the same manner. 
         [0139]    In step  1055 , when the S-GW/P-GW  1006  is in the unattended state, the priority of traffic transmitted to the corresponding UE  1002  may be lowered. According to an embodiment, the S-GW/P-GW  1006  may lower the transmission priority of the non-GBR traffic with respect to the UE  1002  when the corresponding UE  1002  is in the unattended state. 
         [0140]    Steps  1065  to  1080  correspond to an example of transmitting, when a change in the attendance of the UE  1002  is detected, the detected change to the eNB  1004  and the S-GW/P-GW  1006 . 
         [0141]    When the eNB  1004  is still congested even though the UE  1002  is changed to the attended state in step  1065 , the UE  1002  may transmit the state change to the eNB  1004  through an RRC UE status message in step  1070 . In step  1080 , the eNB  1004  that has received this may notify the S-GW/P-GW  1006  that the UE  1002  is changed to be attended using the GTP-U header in the same manner as that in the foregoing description. As the message transmitting each piece of information, other messages may be used according to embodiments. 
         [0142]    Steps  1085  to  1095  correspond to a method in which the eNB  1004  transmits information to each component when the congestion of the eNB  1004  is released. 
         [0143]    In step  1085 , the eNB  1004  may determine whether the congestion state is released. In addition, according to an embodiment, the eNB  1004  may transmit, only to UEs which become unattended, information indicating that the congestion state of the eNB  1004  is released. However, in a different embodiment, the eNB  1004  may transmit, to all UEs  1002 , the information indicating that the congestion state of the eNB  1004  is released. 
         [0144]    In step  1090 , the eNB  1004  may transmit, to the S-GW/P-GW  1006 , the information indicating that the congestion state of the eNB  1002  is released. The eNB  1002  may enable this information to be included in the header of dummy data, and transmit the dummy data. 
         [0145]    In step  1092 , the eNB  1004  may transmit, to the UE  1002 , the information indicating that the congestion state of the eNB  1004  is released. According to an embodiment, the eNB  1004  may notify the UE  1002  of this information through an RRC eNB status message. In addition, according to an embodiment, the UE  1002  notifies that a user is in an attended state using the GTP-U header regardless of the unattended state of the UE. The GW nodes  1006  that have received this may not lower the transmission priority of the non-GBR traffic. 
         [0146]    According to the above-described embodiment, there is an advantage in that differential transmission may be dynamically applied to the UE  1002  which is simple and active, but there is a disadvantage in that signaling may frequently occur. 
         [0147]      FIG. 11  illustrates a signal flow for congestion control based on a character of a packet according to still another embodiment of the present invention. 
         [0148]    Referring to  FIG. 11 , according to an embodiment, a method of broadcasting a congestion state of an eNB  1104  and determining whether a UE  1102  notifies a change in the attended state based on received broadcast information is proposed. 
         [0149]    In step  1110 , the UE  1102  may set a type of an application or a QCI of an EPS bearer to which the attended/unattended states of the UE  1102  should be reported in a congestion state, using a method of using an OMA-DM server  1108 . 
         [0150]    In step  1115 , attach request/service request may be processed among the UE  1102 , the eNB  1104 , and the S-GW/P-GW  1106 . 
         [0151]    When traffic is generated from the application to which the attended/unattended states should be reported or the UE  1102  has the QCI to which the attended/unattended states should be reported in step  1120 , the UE  1102  may periodically receive an SIBn for broadcasting congestion information in step  1125 . The UE  1002  may transmit an attendance state of the UE based on the received SIBn. When the SIBn notifies that the eNB  1104  is currently congested, the UE  1102  may determine whether the UE  1102  is attended or unattended in step  1130 , and when the attendance state of the UE  1102  is changed, the UE  1102  may notify the eNB  1104  of the changed attendance state in step  1150 . According to an embodiment, the UE  1102  may notify the eNB  1104  of the change in the attendance state using an RRC UE status message. 
         [0152]    The subsequent operation may be the same as that of  FIG. 9 , and when the GW node performs traffic control as described in  FIG. 10 , steps  1115  to  1140  of  FIG. 11  may be replaced by steps  1010  to  1050  of  FIG. 10 . However, according to an embodiment, when releasing the congestion state of the eNB  1104 , whether the congestion state is released may be notified to the UE  1102  through the SIBn in step  1165 . 
         [0153]    Meanwhile, congestion information of the broadcasted RAN may be used even to reduce an amount of data actively generated in the UE  1102 . For this, the eNB  1104  may transmit either information indicating a degree of the current congestion state or information indicating an amount of data that should be reduced compared to the current amount of data. For example, when an amount of data that is generated is requested to be reduced by 20% compared to the current amount of data through the congestion information broadcasted by the SIBn, the UEs  1102  that have received the request may perform an operation of reducing the amount of data that is generated by the UEs  1002  or data to be generated by requests of the UEs  1002  by 20%. 
         [0154]    The method according to the embodiment may reduce the effect of signaling using an SIB, but a part of the broadcasting resources may be consumed. 
         [0155]      FIG. 12  illustrates a signal flow for congestion control based on a character of a packet according to yet another embodiment of the present invention. 
         [0156]    Referring to  FIG. 12 , a method that can be used to perform congestion control in a congestion state without the intervention of a UE  1202  is proposed. 
         [0157]    According to an embodiment, a P-GW  1206  may drop a DL packet or adjust a scheduling speed according to congestion state information and gating state information. 
         [0158]    In step  1210 , among a UE  1202 , an eNB  1204 , and the S-GW/P-GW  1206 , attach request/service request may be processed. 
         [0159]    In step  1215 , when congestion occurs, the eNB  1204  may transmit a message notifying the corresponding congestion state to the S-GW/P-GW  1206 . According to an embodiment, in step  1220 , the eNB  1204  may transmit the congestion state to the S-GW/P-GW  1206  using a GTP-U header. This may be performed in a similar manner to a method in which the eNB transmits the congestion state to the GW node in the above-described embodiment. In addition, the S-GW may relay the related header to the P-GW. According to an embodiment, the eNB may transmit information about whether the eNB is congested to the S-GW/P-GW  1206  using a header of dummy data. 
         [0160]    In step  1225 , when congestion control is performed in units of cells, the P-GW  1206  performs DPI with respect to all active non-GBR bearers which receive services in a congested cell (ECGI), thereby selecting target flows. When applying the corresponding operation only to the specific UE  1202 , the P-GW  1206  performs DPI with respect to all active non-GBR bearers of the corresponding UE  1202 , thereby selecting target flows. In step  1230 , the P-GW  1206  selects a minimum bit rate of the target flow based on the DPI result, and transmits the selected minimum bit rate to the eNB  1204  when transmitting DL data to the GTP-U header. 
         [0161]    In steps  1235  and  1240 , the eNB  1204  may perform scheduling so as to satisfy the minimum bit rate on the basis of the minimum bit rate included in the GTP-U header. 
         [0162]    According to an embodiment, in step  1245 , when it cannot satisfy the requested minimum bit rate due to the severe congestion of the eNB  1204 , the eNB  1204  may request gating close for the corresponding flow from the P-GW  1206 . The S-GW/P-GW  1206  that has received the request of step  1245  may store the request for gating close, and then all drop packets of the related flows. 
         [0163]    In addition, in step  1235 , when it cannot satisfy the minimum bit rate, the eNB  1204  may all drop the corresponding packets. 
         [0164]    In step  1255 , when releasing congestion of the eNB  1204 , the eNB  1204  may transmit a message indicating that the congestion has been released to the S-GW/P-GW  1206 . According to an embodiment, a congestion stop state may be transmitted to the S-GW/P-GW  1206  using the GTP-U header through the transmitted message. When such control (S-GW relays the related header to P-GW) is performed in units of cells, the P-GW  1206  that has received this may delete congestion state information and state information per flow being currently subjected to gating close, and when such control is performed in units of UEs  1202 , the P-GW  1206  may delete congestion state information and gating close state information of flows of the corresponding UE in step  1265 . 
         [0165]      FIG. 13  illustrates a network configuration when congestion control is performed based on a character of an application in a communication system according to an embodiment of the present invention. 
         [0166]    Referring to  FIG. 13 , an operator IP service network may include a User Plane Congestion (UPCON) policy server  1390 . The UPCON policy server  1390  may be a server that determines a policy for user plane-related congestion control, and may be located in the operator IP service network or located in at least one of a PCRF  1350  and an HSS. In addition, according to an embodiment, the UPCON policy server  1390  may be access network discovery and selection function (ANDSF). According to an embodiment, the UPCON policy server  1390  may transmit information for congestion control to other communication entities. 
         [0167]      FIG. 14  illustrates a signal flow and data processing for congestion control based on a character of an application according to still another embodiment of the present invention. 
         [0168]    Referring to  FIG. 14 , a signal flow when the UPCON policy server  1390  exists within the operator IP service network in the same manner as that in  FIG. 13  and congestion control is performed in a mobile communication network based on a character of the corresponding application is illustrated. 
         [0169]    According to an embodiment, the UPCON policy server  1403  is a server that stores setting concerning attended/unattended per application set by the operator, and as in the description of the structure of  FIG. 13 , and may be an entity that is located within the operator IP service network so as to be connected to the corresponding UE via a data network. However, the location of the UPCON policy server  1403  is not limited to the operator IP service network. 
         [0170]    According to an embodiment, a UE  1400  may acquire an address of the UPCON policy server  1403  by sending a DNS query using information of the UPCON policy server  1403  stored in the UE  1400  or requesting information from a DHCP (Dynamic Host Configuration Protocol) server. The information of the UPCON policy server  1403  may include an FQDN (fully qualified domain name). 
         [0171]    In step  1410 , the UE  1400  transmits, to the UPCON policy server  1403 , a request message for requesting a policy using the address of the UPCON policy server  1403 . The request message includes an ID for identifying the UE  1410 . In addition, according to an embodiment, the policy may include a factor for determining a congestion control-related policy. In addition, according to an embodiment, the request message may additionally include an ID for identifying one or more applications executed in the UE  1410 . 
         [0172]    In step  1411 , the UPCON policy server  1403  that has received the request message of step  1410  verifies the ID of the UE  1400 . In addition, the UPCON policy server  1403  may store attended/unattended setting per ID of the application set by the operator, and transmit a response message to the UE  1400  in response to the request of step  1410 . In addition, according to an embodiment, the UPCON policy server  1403  may determine whether the UE  1400  is a roaming UE based on the ID of the UE  1400 , and apply an attended/unattended setting value per ID of another application depending on the operator that operates roaming, thereby configuring the corresponding response. In addition, the UPCON policy server  1403  may apply the attended/unattended setting based on the received one or more application IDs, thereby configuring the corresponding response. The setting may be also configured differently depending on a network operator that provides services to the UE. 
         [0173]    According to an embodiment, the UPCON policy server  1403  may store attended/unattended setting per application based on at least one of a user&#39;s usage pattern and the application&#39;s character, and when there is the request of the UE  1400  such as in step  1410 , the UPCON policy server  1403  may transmit an attended/unattended setting list corresponding to the application ID to the UE  1400 . 
         [0174]    In step  1412 , the UE  1400  that has received the response message of the UPCON policy server  1403  stores information included in the received message. The information included in the received message may include an application ID list and information about whether each application is attended or unattended. 
         [0175]    According to an embodiment, after step  1412 , when the application executed in the UE  1400  generates data, the UE  1400  may determine whether the application that causes the generation of the data is set to be attended or unattended based on the information stored in step  1412 . 
         [0176]    In step  1413 , the UE  1400  may enable the information about whether the application causing the generation of the data is attended or unattended to be included in data to be transmitted according to the determination result, and transmit the data to be transmitted to the eNB  1401 . According to an embodiment, the information about whether the application is attended or unattended may be included in at least one of the headers of the data to be transmitted, and preferably, an attended/unattended display extension field vale may be set in at least one of an extension field of an IP header and an extension field of a PDCP header, and transmitted to the eNB  1401 . 
         [0177]    In step  1414 , the UE  1400  may transmit the data that has been processed in step  1413  to the eNB  1401 . 
         [0178]    In step  1414 , the UE  1400  may transmit the data that has been processed in step  1413  to the eNB  1401 . 
         [0179]    In step  1415 , the eNB  1401  that has received the data transmitted in step  1414  may verify the value set by the UE  1400  in step  1413 . In addition, according to an embodiment, the eNB  1401  may perform a process of storing at least one of an address of the received data, port information, and attended/unattended setting, and then deleting attended/unattended-related information. 
         [0180]    According to an embodiment, the address of the received data may be included in the IP header, and may include at least one of a source address of the received data and a destination address of the received data. 
         [0181]    In step  1216 , the eNB  1401  may transmit the data having been processed in step  1205  to an S-GW/P-GW  1402 , and the S-GW/P-GW  1402  may transmit the transmitted data to the outside of the operator network. 
         [0182]    When receiving the data transmitted to the UE  1400  in step  1417   a , the S-GW/P-GW  1402  may transmit the received data to the eNB  1401  in step  1417   b.    
         [0183]    In step  1418 , the eNB  1401  that has received the data inspects an IP header of the data received in step  1417   b  when the eNB  1401  is currently in a congestion state. According to an embodiment, the congestion state may be determined based on the information included in the received data or an amount of transmitted and received data of the eNB  1401 . According to an embodiment, when inspecting the IP header of the received data, the eNB  1401  compares a destination address stored in step  1415  and a source address of the data received in step  1417   b , and compares a source address stored in step  1415  and a destination address of the data received in step  1417   b . In addition, in the same manner even in the case of a port number, the eNB  1401  compares a destination port stored in step  1415  and a source port received in step  1417   b , and compares a source port stored in step  1415  and a destination port received in step  1417   b . In the foregoing comparison process, one or more values may be compared according to embodiments, and when the values coincide with each other based on the comparison result, whether the corresponding data traffic is stored to be attended or unattended is determined in step  1415 . The foregoing determination process may include a process of comparing an application ID that causes generation of the data traffic. When the application is set to be attended based on the determination result, the eNB  1401  transmits the corresponding data traffic to the UE  1400  without adjustment of the priority of the corresponding data traffic. When the application is set to be unattended based on the determination result, the eNB  1401  may perform scheduling by lowering the priority of the corresponding data traffic. The process of lowering the priority of the corresponding data traffic may include a process of delaying the transmission of a packet included in the data traffic or a process of dropping the packet included in the data traffic. 
         [0184]    In step  1419 , the eNB  1401  may transmit data including the data received in step  1417   b  to the UE  1400  based on the result of step  1418 . 
         [0185]    In addition, according to another embodiment, in step  1416 , the eNB  1401  may transmit a packet including an indicator indicating attended/unattended states to the outside of the operator network. According to an embodiment, the indicator may be included in the IP header, and an application server that has received the foregoing packet may determine a data transmission method based on the attended/unattended states. 
         [0186]    Meanwhile, the embodiment of the present invention may be used to mitigate or prevent the occurrence of improper charge imposition on the UE in the operator network. 
         [0187]    More specifically, inaccurate charge imposition for data of the UE may occur even a case in which the UE is unable to communicate with the system temporarily. By way of example, when a UE is temporarily moved to 2G/3G networks to use CS services due to generation of a voice call in an area in which VoLTE or CSFB is not supported in a case in which the UE is located in the shadow area, the UE is unable to receive the data packet from the network. 
         [0188]    In this case, a service disabled state in which the UE is unable to receive data packet from the network is detected and it may take time to transmit the service disabled state to the core network. In this manner, when the packets are continuously introduced to the eNB or the core network node while the service disabled state is transmitted to the core network, a case in which the packet is lost in the eNB or the core network node and thereby cannot be transmitted to the UE even though charging information is generated may occur. 
         [0189]      FIG. 15  illustrates a connection loss state between an eNB and a UE according to an embodiment of the present invention. 
         [0190]    Referring to  FIG. 15 , according to an embodiment, a UE  1502 , an eNB  1504 , an MME  1506 , an S-GW  1508 , and a P-GW  1510  may transmit and receive signals to and from other entities. 
         [0191]    According to an embodiment, the UE  1502  may receive a data packet from the eNB  1504  when a connection state between the UE  1502  and the eNB  1504  is achieved in step  1515 . 
         [0192]    In this instance, a downlink data packet is generated from a PDN (Packet Data Network) and transmitted to the P-GW  1510 . In step  1512 , the P-GW  1510  generates charging information about the received data packet, and then transmits the data packet to the S-GW  1508 . 
         [0193]    In at least one of steps  1520  and  1525 , the S-GW  1508  that has received the data packets transmits the data packets to the connected eNB  1504  when the UE is in a connection mode. According to an embodiment, the data packet may be transmitted to the eNB through the MME  1506 . 
         [0194]    However, in step  1530 , the UE  1502  may be moved either to the shadow area out of the connection mode, or to 2G/3G systems for voice services due to the fact that functions such as VoLTE, CSFB, and the like of the operator network are not supported. In this case, connection loss may occur between the UE  1502  and the eNB  1504  such as in step  1535 . 
         [0195]    In this instance, it may take time to detect the fact that the UE  1502  no longer transmits and receives data to and from the eNB  1504 , and therefore the data packets may be continuously transmitted from the P-GW  1510  to the S-GW  1508  and the eNB  1502 . When, due to this, buffer overflow or packet loss occurs in the S-GW  1508  or the eNB  1504  (step  1540  or step  1545 ), a case in which a user of the UE  1502  has to pay a fee for the packet which the UE  1502  fails to receive may occur. 
         [0196]    In an embodiment of the present invention proposed to address the foregoing problem, when the UE  1502  no longer receives the data packet as in the above-described embodiment (when the UE  1502  detects an idle mode caused by a radio link failure or the like), it is possible to prevent charging information from being further generated and prevent the data packet which the UE  1502  fails to receive from being transmitted to the S-GW  1508  or the eNB  1504 , by notifying even the core network including the S-GW  1508  and P-GW  1510  of this information indicating that the UE  1502  no longer receives the data packet. 
         [0197]      FIG. 16  illustrates a method of transmitting and receiving signals at the time of connection loss according to an embodiment of the present invention. 
         [0198]    Referring to  FIG. 16 , according to an embodiment, a UE  1602 , an eNB  1604 , an MME  1606 , an S-GW  1608 , and a P-GW  1610  may transmit and receive signals to and from other entities. 
         [0199]    In step  1615 , when a connection state between the UE  1602  and the eNB  1604  is achieved, the UE  1602  may receive a data packet from the eNB  1604 . 
         [0200]    In this instance, a downlink data packet is generated from a PDN and transmitted to the P-GW  1610 . In step  1612 , the P-GW  1610  generates charging information about the received data packet and then transmits the generated data packet in at least one of steps  1620  and  1625  to the S-GW  1608 , and the S-GW  1608  that has received the transmitted data packet transmits the data packets to the connected eNB  1604  when the UE is in a connection mode. According to an embodiment, the data packets may be transmitted to the eNB  1604  through the MME  1606 . 
         [0201]    However, in step  1630 , the UE  1602  may be moved either to the shadow area out of the connection mode, or to 2G/3G systems for voice services due to a fact that functions such as VoLTE, CSFB, and the like of the operator network are not supported. In this case, connection loss may occur between the UE  1602  and the eNB  1604  such as in step  1635 . 
         [0202]    In this instance, it may take time to detect a fact that the UE  1602  no longer transmits and receives data to and from the eNB  1604 , and therefore the data packets may be continuously transmitted from the P-GW  1610  to the S-GW  1608  and the eNB  1604 . 
         [0203]    In this case, such as in step  1640  or step  1645 , buffer overflow or packet loss occurs in at least one of the S-GW  1608  or the eNB  1604 . 
         [0204]    In step  1650 , the eNB  1604  may detect a fact that the connection to the UE  1602  is no longer available (in this instance, it can be seen through a case in which a reception response for a downlink packet transmitted by the eNB is not received from the UE within a predetermined time, or a case in which the foregoing case is repeated more than several times). 
         [0205]    In this case, the eNB  1604  may transmit, to the MME  1606 , at least one of information indicating that the UE  1602  is no longer in the connection mode and information indicating that charge imposition for the downlink on the UE  1602  should be prevented. According to an embodiment, the foregoing information may be transmitted to the MME  1606  through an S1 release request message. 
         [0206]    In step  1660 , when receiving the foregoing information from the eNB, the MME  1606  may transmit, to the S-GW  1608 , a message including the information received in step  1655 , and in this instance, a modify bearer request message may be used. 
         [0207]    Meanwhile, in step  1665 , when receiving the foregoing message, the S-GW  1608  may no longer transmit the data packet until receiving information indicating that the connection to the UE  1602  is available again, and transmit a message including the foregoing information to the P-GW  1610  per PDN connection or EPS bearer. According to an embodiment, the transmitted message may be transmitted up to the P-GW  1610  through the message such as the modify bearer request message. In this instance, the S-GW  1608  may transmit the foregoing information to all P-GWs  1610  in which the UE has the PDN connection. 
         [0208]    In step  1670 , when receiving the foregoing information, the P-GW  1610  may change a state concerning the downlink data packet of the UE  1602  to pause, and stop charge imposition. In addition, in order to prevent additional data packet loss, the P-GW  1610  may stop the data packet transmission before receiving a separate request from the S-GW  1608 . 
         [0209]    According to the above-described embodiment, when the connection to the UE  1602  becomes unavailable, the unavailable connection to the UE  1602  may be detected and notified to the core network, through which it is possible to prevent the occurrence of an additional charging error or the occurrence of data packet loss. According to an embodiment of the present invention, a technique that corrects, when an error (namely, a case in which a charge even for a packet that is not attempted to be transmitted is imposed on a user) occurs in the charging information due to the occurrence of the data packet loss, the error so that the charging information error may be minimize is proposed. 
         [0210]    According to an embodiment, a node that generates the charging information (e.g., P-GW) may inspect a downlink packet transmitted to a user and thereby store information indicating that packets having what kind of packet ID (e.g., TCP sequence number) are transmitted to the UE, and inspect an acknowledgement transmitted by the UE and thereby determine what kind of packet is successfully transmitted to the UE. When the acknowledgement is not transmitted within a predetermined time even though the data packet has been transmitted to the UE, or when information indicating that the connection to the UE is no longer available or information indicating that charge imposition should be stopped is received, the P-GW may determine the occurrence of the data packet loss, and correct the charging information (namely, such as stopping charge imposition for the packet in which the acknowledgement is not detected). 
         [0211]      FIG. 17  is a flowchart illustrating operations of a core network node according to an embodiment of the present invention. More specifically, in  FIG. 17 , the operations of the core network node (e.g., P-GW) that manages charging information is illustrated. 
         [0212]    Referring to  FIG. 17 , in step  1705 , the P-GW may receive a data packet from a PDN. 
         [0213]    In step  1715 , the P-GW may determine to which TCP session or IP flow the corresponding data packet belongs using packet inspection. In this instance, whether to apply this process may be determined either based on a PCC rule received through a PCRF, or based on user bearer information received from the S-GW. The P-GW determines the TCP session/IP flow to which the packet belongs and a sequence number of TCP through the foregoing process, generates charging information, and starts a timer. The value of the timer may be determined by a value set in advance or variable setting. 
         [0214]    In step  1720 , the P-GW may determine whether an acknowledgement for the TCP transmitted by the UE has been transmitted within the value of the timer. According to an embodiment, when receiving the packet from the UE in a direction of the uplink, the P-GW may apply the packet detection in the same manner as the above description, and when matching occurs, for which downlink TCP packet the acknowledgement is completely received may be determined. For example, when the sequence number of the TCP packet detected by the P-GW is 1000 and the sequence number of a TCP ack packet transmitted to the same TCP session by the UE is 1001, this refers to the instance that the TCP packet having the sequence number up to 1000 has been successfully received. Whether the data packets of uplink/downlink belong to the same IP flow or TCP session may be determined using an IP transmission and reception address, a port number, or the like. 
         [0215]    When it fails to recognize that the transmission of the downlink TCP packet is successfully performed within the time set in advance, the P-GW may determine that packet loss occurs in step  1730 , and correct or delete charging information about the packet so that charge imposition for the packet that cannot be transmitted may be prevented. 
         [0216]    According to an embodiment, when the transmission of the TCP packet is successfully performed, the P-GW may determine that the charging information is available and maintain the applied charging information in step  1725 . 
         [0217]    When information about whether the connection to the UE is available or charging stop information is applied as described in the above-described embodiment of the prevent invention, the P-GW transmits the data packet to the downlink and starts the timer. However, when failing to determine whether the packet transmission is successfully performed through uplink packet inspection, and when receiving information indicating that the connection to the UE is lost or information indicating that charge imposition should be stopped from the S-GW even before the timer is not completed yet, the P-GW may determine that packet loss occurs in the same manner as that in the above description, and correct and delete the charging information about the packet so that charge imposition for the packet that cannot be transmitted may be prevented. 
         [0218]    In the foregoing embodiment, for convenience of description, a case in which the TCP is used has been used, but the embodiment of the present invention may be also applied to cases in which different kinds of protocols (e.g., UDP, RTP, etc.) are used. 
         [0219]    In the above-described embodiments, each component may include a transmission/reception unit that transmits and receives data to and from the other components and a control unit that controls the transmission/reception unit and performs determination based on the data transmitted and received through the transmission/reception unit. 
         [0220]    Those skilled in the art can appreciate that it is possible to implement the present invention in another specific form without changing the technical idea or the indispensable characteristics of the present invention. Accordingly, it should be understood that the embodiments described above are merely exemplary and are not limited. The scope of the present invention is defined by the appended claims to be described later, rather than the detailed description. Accordingly, it should be appreciated that all modifications or variations derived from the meaning and scope of the appended claims and their equivalents are included in the range of the present invention. 
         [0221]    Although exemplary embodiments of the present invention have been shown and described in this specification and the drawings, they are used in general sense in order to easily explain technical contents of the present invention, and to help comprehension of the present invention, and are not intended to limit the scope of the present invention. It is obvious to those skilled in the art to which the present invention pertains that other modified embodiments on the basis of the spirits of the present invention besides the embodiments disclosed herein can be carried out.