Abstract:
A method and an apparatus for transmitting data in a wireless communication network are provided. A base station having information of an idle mode user equipment transmits a connecting operation mode to the user equipment when the idle mode user equipment is connected to the base station. The user equipment transmits a small amount of data together with a connection request completion message to the base station. The base station transmits, over a network, the data received from the user equipment, without being interlinked with a mobility management entity, and the user equipment returns back to an idle operation mode after data transmission. Thus, the overhead required to support signaling of the base station for acquiring context information of the user equipment can be reduced in order to provide the user equipment with an efficient data transmission environment.

Description:
PRIORITY 
     This application is a National Stage application under 35 U.S.C. §371 of an International application filed on Nov. 4, 2010 and assigned application No. PCT/KR2010/007758, and claims the benefit under 35 U.S.C. §119(a) of Korean patent applications filed in the Korean Industrial Property Office on Nov. 4, 2009 and Feb. 18, 2010 and respectively assigned Serial Nos. 10-2009-0105866 and 10-2010-0014703, the entire disclosure of each of which is hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method and apparatus for transmitting data in a radio communication network. More particularly, the present invention relates to a method and apparatus for a User Equipment (UE) to transmit data when the UE that is in an idle mode accesses an evolved-Node B (eNB) for transmission of a small amount of data. 
     2. Description of the Related Art 
     In general, Universal Mobile Telecommunications System (UMTS) is a 3 rd  Generation (3G) communication system that is based on Global System for Mobile communications (GSM) and General Packet Radio Services (GPRS), and that uses Wideband Code Division Multiple Access (WCDMA). The 3 rd  Generation Partnership Project (3GPP), which works for standardization of UMTS, has proposed Evolved Packet System (EPS) that corresponds to a next generation communication system of UMTS such as a Long Term Evolution (LTE) system, for embodying a high-speed packet-based communication. 
       FIG. 1  illustrates a configuration of an LTE radio communication network according to the related art. 
     As shown in  FIG. 1 , the radio communication network may include an eNB  102 , a Mobility Management Entity (MME)  104 , a Serving GateWay (S-GW)  106 , a Packet Data Network GateWay (PDN-GW)  108 , and a UE  100 . 
     The eNB  102  may be an eNB that manages a macrocell. Here, for ease of description, the terms “macrocell” and “eNB” may be used interchangeably, although the macrocell is a cell in a general cellular system and the eNB  102  is an eNB that manages and controls the macrocell. 
     The eNB  102  may be connected to the UE  100  through a radio channel, and may control a radio resource. For example, the eNB  102  may generate control information required in the macrocell as system information and broadcast the system information, or may allocate radio resources so as to perform, with the UE  100 , transmission and reception of data or control information. In addition, the eNB  102  may collect information of channel measurement results of a current cell and adjacent cells from the UE  100  so as to determine a handover, and may command the UE  100  to perform the handover. Accordingly, the eNB  102  may include a control protocol, such as a radio resource protocol associated with radio resource management and the like. 
     The MME  104  may manage a mobility of the UE  100  that is in an idle mode, and may select the PDN-GW  108  and the S-GW  106  for data transmission of the UE  100 . In addition, the MME  104  may perform functions associated with roaming and authentication of the UE  100 . The MME  104  may process a bearer signal occurring from the UE  100 . 
     The S-GW  106  may function as a mobile anchor when a handover occurs between eNBs or movement occurs between 3GPP radio networks. The PDN-GW  108  may allocate an Internet Protocol (IP) address of the UE  100 , may perform connecting of a core network and a packet data network, and may function as a mobile anchor when movement occurs between a 3GPP radio network and a non-3GPP radio network. Also, the PDN-GW  108  may determine a bearer band to be provided to a subscriber, and may perform forwarding and routing of packet data. 
     When the UE  100  accesses the eNB  102 , the UE  100  may access an Internet network  110  through use of a data transmission path  110  that goes through the eNB  102 , the S-GW  106 , and the PDN-GW  108 . To implement the above, a related signaling may be transferred via a path that goes through the UE  100 , the eNB  102 , the MME  104 , the S-GW  106 , and the PDN-GW  108 . 
       FIG. 2  illustrates a process where a UE that is in an idle mode transmits data in an LTE radio communication network according to the related art. 
     Referring to  FIG. 2 , a UE  200  that is in an idle mode may transmit a Radio Resource Control (RRC) connection request message to an eNB  202  in operation  210 . The RRC connection request message may include an Identifier (ID) of the UE  200 , that is, a System Architecture Evolution (SAE) Temporary Mobile Subscriber Identifier (S-TMSI). The eNB  202  may transmit an RRC connection setup message to the UE  200  in operation  212 , and the UE  200  may transfer an RRC connection setup complete message to the eNB  202  in operation  214 . The RRC connection setup complete message may include a Non-Access Stratum (NAS) message that the UE  200  transmits to an MME  204 . The NAS message may be a message to request a service from an NAS layer that connects the UE  200  and the MME  204  so as to switch the UE  200  from an idle mode to an active mode. 
     The eNB  202  may notify of the connection of the UE  200  to the MME  204  through INITIAL UE MESSAGE in operation  216 , and may transmit the NAS message received in operation  214  to the MME  204 . 
     In operation  218 , the MME  204  may transmit, to the eNB  202 , security information of the UE  200 , information associated with a data bearer of the UE  200 , information associated with an S-GW  206  to which the eNB  202  is to transmit data received from the UE  200 , that is, S1-U UL information (uplink bearer GPRS Tunneling Protocol (GTP) Tunnel ID (TEID)), an IP address of the S-GW  206 , and context information of the UE  200  such as mobility management information of the UE  200 , through use of an INITIAL CONTEXT SETUP REQUEST message. 
     In operations  220  and  222 , the eNB  202  may set an Access Stratum (AS) security and a data bearer between the UE  200  and the eNB  202  in conjunction with the UE  200  based on the context information of the UE  200  received in operation  218 , through use of an RRC connection reconfiguration message and an RRC connection reconfiguration complete message. 
     In operation  224 , the eNB  202  may inform the MME  204  that the context of the UE  200  and the data bearer are successfully set, through use of an INITIAL CONTEXT SETUP RESPONSE message, and may also transmit information associated with the eNB  202  required for transmitting data from the S-GW  206  to the UE  200 , that is, S1-U DL information of the UE  200  (downlink bearer GTP TEID and an IP address of the eNB  202 ). That is, the MME  204  may transmit, to the S-GW  206 , the downlink bearer GTP TEID of the UE  200  and the IP address of the eNB  202  received from the eNB  202  in operation  224 , through use of an Update Bearer Request message in operation  226 , and may receive a response message from the S-GW  206  through use of an Update Bearer Response message in operation  228 . 
     Through the processes as described in the foregoing, the UE  200  may transmit data after operation  222 , and the data transmitted from the UE  200  may be transmitted to an Internet network via the eNB  202 , the S-GW  206 , and the PDN-GW  208  in operation  230 . 
     As shown in  FIG. 2 , to transmit data, the UE  200  that is in an idle mode may require ten signalings that are transmitted and received in operations  210  through  228 . This condition is equivalently applied even when a significantly small amount of data is transmitted, such as an alarm message, a power consumption measurement results reporting message, and the like. Also, when the amount of data is significantly small, the signaling overhead necessary for support of the transmitted and received data may be even greater than the amount of data to be transmitted. Accordingly, there is a need for a method to overcome these drawbacks. 
     SUMMARY OF THE INVENTION 
     Aspects of the present invention are to address at least the above-mentioned problems and/or disadvantages and to provide at least the advantages described below. Accordingly, an aspect of the present invention is to provide a radio communication network structure and a method thereof, which decreases signaling overhead of data transmission through use of context information of an idle mode User Equipment (UE) that an evolved Node B (eNB) stores in advance, when the idle mode UE accesses the eNB, and thus may provide an effective data transmission environment to the UE. 
     In accordance with an aspect of the present invention, a method of transmitting data in a radio communication network is provided. The method includes transmitting, by an eNB, a radio resource connection setup message to a UE when the UE that is in an idle mode accesses the eNB, receiving data and a radio connection setup complete message from the UE in response to the radio resource connection setup message, transmitting, by the eNB, the data received from the UE to a Mobility Management Entity (MME), receiving, by the eNB, a UE context release message from the MME, and releasing Radio Resource Control (RRC) connection with the UE. 
     In accordance with another aspect of the present invention, a method of transmitting data in a radio communication network is provided. The method includes receiving, by an MME, a connection notification message associated with a UE from an eNB when the UE that is in an idle mode accesses the eNB, transmitting, by the MME, data to a Serving GateWay (S-GW) when the data transmitted from the UE is received with the connection notification message, and transmitting, by the MME, a UE context release message to the eNB. 
     In accordance with another aspect of the present invention, a radio communication system that transmits and receives data in a radio communication network is provided. The system includes an eNB to receive a radio connection setup complete message including data from a UE when an RRC connection is set up with the UE in response to a request from the UE that is in an idle mode, to transmit the data received from the UE to an MME, to receive a UE context release message from the MME, and to release the RRC connection with the UE, and the MME to receive, from the eNB, a connection notification message associated with the UE, to transmit data to an S-GW when the data transmitted from the UE is received with the connection notification message, and to transmit the UE context release message. 
     In accordance with another aspect of the present invention, a method of transmitting data in a radio communication network is provided. The method includes transmitting, by an MME to an S-GW, a bearer create session request message including a data transport indicator that indicates that the MME is capable of directly transmitting data to the UE, in response to a connection request from the UE, receiving, by the MME, a bearer create session response message from the S-GW, and transmitting context information of the UE to an eNB, and receiving, by the MME, data to be transmitted to the UE from the S-GW when a bearer is released since the UE is switched into an idle mode, and transmitting the data to the UE. 
     In accordance with another aspect of the present invention, a method of transmitting data in a radio communication network is provided. The method includes receiving, by an S-GW from an MME, a bearer create session request message including a data transport indicator indicating that the MME is capable of directly transmitting data to a UE, in response to a connection request from the UE, and registering, by the S-GW, whether the MME is capable of providing data transport support with respect to a bearer of the data, transmitting, by the S-GW, the bearer create session request message to a Packet Data Network GateWay (PDN-GW), receiving a bearer create session response message, transmitting the bearer create session response message to the MME, receiving, by the S-GW from the PDN-GW, data to be transmitted to the UE after the UE is switched into an idle mode and a bearer is released, and determining, by the S-GW, that the MME is capable of directly transmitting the data to the UE, based on the data transport indicator, and transmitting the data to the MME. 
     In accordance with another aspect of the present invention, a radio communication system that transmits and receives data in a radio communication network is provided. The system includes an MME to transmit a bearer create session request message including a data transport indicator that indicates that the MME is capable of directly transmitting data to a UE, in response to a connection request from the UE, to receive a bearer create session response message, to transmit context information of the UE to an eNB, and to transmit data to the UE when the data to be transmitted to the UE is received after the UE is switched into an idle mode and a bearer is released, and an S-GW to receive the bearer create session request message from the MME, to register whether the MME is capable of providing data transport support with respect to the bearer of the data, to transmit the bearer create session request message to a PDN-GW, to receive a bearer create session response message, to determine that the MME is capable of directly transmitting data to the UE based on the data transport indicator when the data to be transmitted to the UE is received from the PDN-GW after the UE is switched into an idle mode and the bearer is released, and to transmit the data to the MME. 
     In accordance with another aspect of the present invention, a method of transmitting data in a radio communication network is provided. The method includes receiving, by a UE from an eNB, information required for generating Access Stratum (AS) security information when the UE that is in an idle mode accesses the eNB, generating, by the UE, a new AS security context based on the AS security information received from the eNB, transmitting, by the UE, a connection request complete message and data based on the generated AS security context, and switching, by the UE, a mode into an idle mode. 
     In accordance with another aspect of the present invention, a method of transmitting data in a radio communication network is provided. The method includes transmitting, by an eNB, information required for generating AS security information for AS security with the UE when a UE that is in an idle mode accesses the eNB, receiving, by the eNB from the UE, a connection request complete message and data based on a new AS security context generated by the UE through use of AS security information received from the eNB, and transmitting, by the eNB to a network, the data received from the UE based on uplink information stored in advance. 
     In accordance with another aspect of the present invention, a radio communication system that transmits and receives data in a radio communication network is provided. The system includes a UE to transmit a radio resource connection request message in an idle mode, to receive information required for generating AS security information so as to generate a new AS security context, to transmit an access request complete message and data based on the generated AS security context, and to switch a mode into an idle mode, and an eNB to transmit the information required for generating the AS security information for AS security with the UE when the UE that is in an idle mode accesses the eNB, to receive the access request complete message and the data from the UE based on the new AS security context generated by the UE, and to transmit the data received from the UE to a network based on uplink information stored in advance. 
     In accordance with another aspect of the present invention, a method of transmitting data in a radio communication network is provided. The method includes receiving, by a UE from an eNB, an indicator indicating that AS security information that is previously used for communication with the UE is to be reused, when the UE that is in an idle mode accesses the eNB, transmitting, by the UE, a connection request complete message and data through use of a previously used AS security context based on the indicator received from the eNB, and switching, by the UE, a mode into the idle mode. 
     In accordance with another aspect of the present invention, a radio communication system that transmits and receives data in a radio communication network is provided. The system includes a UE to transmit a radio resource connection request message in an idle mode, to receive an indicator indicating that previously used AS security information is to be reused, to transmit a connection request complete message and data based on a previously used AS security context, and to switch a mode into an idle mode, and an eNB to transmit the indicator indicating that the AS security information set for previous communication with the UE when the UE that is in an idle mode accesses the eNB, to receive the connection request complete message and data from the UE based on the previously used AS security context, and to transmit the data received from the UE to a network based on uplink information stored in advance. 
     In accordance with another aspect of the present invention, a method of transmitting data in a radio communication network is provided. The method includes receiving, by a UE from an eNB, a radio resource connection setup message when the UE that is in an idle mode accesses the eNB, transmitting, by the UE to the eNB, a radio connection setup complete message including data, and receiving, by the UE, a context release message from the eNB that transmits the data to a network, and switching a mode into an idle mode. 
     Other aspects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses exemplary embodiments of the invention. 
     According to exemplary embodiments of the present invention, when a UE that is in an idle mode accesses an eNB for data transmission, the eNB decreases signaling for obtaining context information of the UE and thus, may provide the UE with an efficient data transmission environment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, features, and advantages of certain exemplary embodiments of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a diagram illustrating a configuration of a radio communication network according to the related art; 
         FIG. 2  is a diagram illustrating a method where a User Equipment (UE) that is in an idle mode transmits data in a radio communication network according to the related art; 
         FIG. 3  is a diagram illustrating a method where a UE that is in an idle mode accesses an evolved Node B (eNB), updates Access Stratum (AS) security information, and transmits data according to a first exemplary embodiment of the present invention; 
         FIG. 4  is a diagram illustrating a method where a UE that is in an idle mode accesses an eNB, reuses AS security information, and transmits data according to a second exemplary embodiment of the present invention; 
         FIG. 5  is a diagram illustrating a method where a UE that is in an idle mode accesses an eNB and transmits data to a Mobility Management Entity (MME), and the MME transfers the data to a Serving GateWay (S-GW), according to a third exemplary embodiment of the present invention; 
         FIG. 6  illustrates an operation of a UE according to the first exemplary embodiment of the present invention; 
         FIG. 7  illustrates an operation of a UE according to the second exemplary embodiment of the present invention; 
         FIG. 8A  illustrates an operation of an eNB according to the third exemplary embodiment of the present invention; 
         FIG. 8B  illustrates an operation of an MME according to the third exemplary embodiment of the present invention; 
         FIG. 9  is a diagram illustrating a method where an S-GW transmits received data to an MME, and the MME transfers the data to a UE, according to a fourth exemplary embodiment of the present invention; and 
         FIGS. 10A and 10B  illustrate an operation of an S-GW according to the fourth exemplary embodiment of the present invention. 
     
    
    
     Throughout the drawings, it should be noted that like reference numbers are used to depict the same or similar elements, features, and structures. 
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of exemplary embodiments of the invention as defined by the claims and their equivalents. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope and spirit of the invention. In addition, descriptions of well-known functions and constructions may be omitted for clarity and conciseness. 
     The terms and words used in the following description and claims are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the invention. Accordingly, it should be apparent to those skilled in the art that the following description of exemplary embodiments of the present invention is provided for illustration purpose only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents. 
     It is to be understood that the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a component surface” includes reference to one or more of such surfaces. 
     Although terms used in the following description of exemplary embodiments of the present invention are based on the 3 rd  Generation Partnership Project Long Term Evolution (3GPP LTE) system standards, it is to be understood that the terms are not intended to limit application of the present invention to any particular standard. Also, in exemplary embodiments of the present invention, a cell and an evolved-Node B (eNB) may be directed to the same meaning. Accordingly, a macrocell and the eNB may be directed to the same meaning. 
     Exemplary embodiments of the present invention are to simplify a data transmission procedure of a User Equipment (UE) when the UE transmits a small amount of data. For example, when a UE is installed as an intrusion detecting device, such as in a home, and is equipped with an LTE module, the UE may not need to perform transmission and reception of data with a network at normal times, but may only need to transmit an alarm message to the network when an intrusion is detected. Also, the UE may be returned to an idle mode immediately after transmitting the alarm message. Similarly, when a device that measures an amount of consumed power is equipped with an LTE module, the UE may only be required to transmit a measurement value of the amount of consumed power to the network at regular intervals, and may not need to perform transmission and reception of data with the network. Also, the UE may be stationary or may not be outside of a predetermined range and thus, may always communicate with the same eNB. Accordingly, when exemplary embodiments of the present invention are applied to a case where the stationary UE transmits a small amount of data, signaling may be decreased and an effective data transmission environment may be provided to the UE. 
       FIG. 3  illustrates a method where a UE that is in an idle mode accesses an eNB, updates Access Stratum (AS) security information, and transmits data according to a first exemplary embodiment of the present invention. 
     Referring to  FIG. 3 , an eNB  302  stores a System Architecture Evolution (SAE) Temporary Mobile Subscriber Identifier (S-TMSI) corresponding to information associated with a UE  300  that is in an idle mode, AS security information associated with security information between the UE  300  and the eNB  302 , and S1-U UL (User Plane Uplink) information to be used for transmitting data from the eNB  302  to a Serving GateWay (S-GW)  306 , in advance. Although the UE  300  that receives a service from the eNB  302  is switched into an idle mode, the eNB  302  may not remove information used during a previous access, and may store the information in operation  310 . In operation  312 , the UE  300  that is in an idle mode may transmit, to the eNB  302 , a Radio Resource Control (RRC) connection request message along with the S-TMSI information associated with the UE  300 , for data transmission. As circumstances demand, the UE  300  may transmit a short data indicator indicating that a small amount of data is to be transmitted to the eNB  302 . In operation  314 , based on the S-TMSI information of the UE  300 , the eNB  302  may determine whether it includes information associated with the UE  300 . When the eNB  302  stores the information associated with the UE  300  of the corresponding ID, the eNB  302  may transmit an RRC connection setup message to the UE  300  in operation  316 , in response to the RRC connection request message received in operation  312 , along with information associated with an AS security algorithm and a Next-hop Chaining Count (NCC) value required for generating new AS security information. In operation  318 , the UE  300  may generate and set a new AS security context with the eNB  302 . In operation  320 , the UE  300  may transfer an RRC connection setup complete message to the eNB  302 , and may transmit the desired data, as opposed to a Non-Access Stratum (NAS) message. The data may be secured based on the AS security information newly generated in operation  318 . In this example, as circumstances demand, an indicator, that is, an Internet Protocol (IP) data indicator, may be transmitted so as to indicate that the data, as opposed to the NAS message, is transmitted. When the eNB  302  recognizes that the message received from the UE  300  is the data, as opposed to the NAS message, the eNB  302  may transfer the data to the S-GW  306  based on the S1-U UL information from among UE information stored in the eNB  302 , and the S-GW  306  may transfer the data received from the eNB  302  to a Packet Data Network-GateWay (PDN-GW)  308  in operations  324  and  326 . The UE  300  that transmits the data to the eNB  302  in operation  320  may be switched into an idle mode again in operation  322 . In this exemplary implementation, the eNB  302  does not exchange messages with a Mobility Management Entity (MME)  304 , thus reducing signaling overhead. 
       FIG. 4  illustrates a method where a UE that is in an idle mode accesses an eNB, reuses AS security information, and transmits data according to a second exemplary embodiment of the present invention 
     Referring to  FIG. 4 , an eNB  402  may store S-TMSI information corresponding to information associated with a UE  400  that is in an idle mode, AS security information corresponding to security information between the UE  400  and the eNB  402 , and S1-U UL information to be used for transmitting data from the eNB  402  to an S-GW  406 , in advance. Although the UE  400  that receives a service from the eNB  402  is switched into an idle mode, the eNB  402  may not remove information used during a previous access, and may store the information in operation  410 . In operation  412 , the UE  400  that is in an idle mode may transmit, to the eNB  402 , an RRC connection request message for data transmission, along with the S-TMSI information of the UE  400 . As circumstances demand, the UE  400  may also transfer a short data indicator indicating that a small amount of data is to be transmitted to the eNB  402 . In operation  414 , based on the S-TMSI information, the eNB  402  may determine whether it stores information associated with the UE  400 . When the eNB  402  stores the information associated with the UE  400 , the eNB  402  may transmit an RRC connection setup message to the UE  400  in operation  416 , in response to the RRC connection request message received in operation  412 , along with a Reuse AS security indicator corresponding to an indicator that instructs to reuse the AS security information used when the UE  400  has previously accessed the eNB  402 . In operation  418 , the UE  400  may reset an existing AS security context with the eNB  402 . In operation  420 , the UE  400  may transfer an RRC connection setup complete message to the eNB  402 . In this example, the UE  400  may transmit the desired data, as opposed to an NAS message. The data may be secured based on the AS security information. As circumstances demand, an IP data indicator may also be transmitted to the eNB  402  so as to indicate that the data, as opposed to the NAS message, is transmitted. When the eNB  402  recognizes that the message received from the UE  400  is the data, as opposed to the NAS message, the eNB  402  may transfer the data to the S-GW  406  based on the S1-U UL information from among UE information stored in the eNB  402 , and the S-GW  406  may transfer the data received from the eNB  402  to a PDN-GW  408  in operations  424  and  426 . The UE  400  that transmits the data to the eNB  402  in operation  420  may be switched into an idle mode again in operation  422 . In this exemplary implementation, the eNB  402  does not exchange messages with an MME  404 , thus saving resources otherwise used for signaling. 
       FIG. 5  illustrates a method where a UE that is in an idle mode accesses an eNB and transmits data to an MME, and the MME transfers the data to an S-GW, according to a third exemplary embodiment of the present invention. 
     Referring to  FIG. 5 , a UE  500  that is in an idle mode may transmit an RRC connection request message to an eNB  502  for data transmission in operation  510 . In operation  512 , the eNB  502  may transmit an RRC connection setup message to the UE  500  in response to the RRC connection request message received in operation  510 . Accordingly, the UE  500  may transmit an RRC connection setup complete message including an NAS message, to the eNB  502  in operation  514 . In this example, the NAS message may be transmitted by including IP data in the NAS message, or the NAS message may be transmitted along with the IP data. In operation  516 , the eNB  502  may transfer, to an MME  504 , the NAS message including the IP data transferred from the UE  500  or the NAS message and the IP data. In this example, an NAS message provided in a new form may be added to transfer the IP data, or an indicator indicating that the IP data is included in the existing NAS message may be added. 
     The MME  504  that receives the NAS message from the eNB  502  may determine whether the IP data is included in the NAS message when a form of the NAS message is for data transmission or when the indicator indicating that an NAS message includes an IP data exists. When the IP data is determined to be included in the NAS message received from the eNB  502 , the MME  504  may transfer the data transferred from the eNB  502  to an S-GW  506  through use of a DATA TRANSPORT message in operation  518 , or may transfer the data to the S-GW  506  through use of S1-U UL information in operation  520 . In operation  524 , the S-GW  506  may transfer the data transferred from the MME  504  to a PDN-GW  508 . The MME  504  that transmits the data in operation  518  or operation  520 , may transmit a UE context release message to the eNB  502  in operation  522 , so as to switch the UE  500  into an idle mode. The eNB  502  that receives the UE context release message may transfer an RRC connection release message to the UE  500  in operation  526 , so as to disconnect an RRC connection with the UE  500 , and may be switched into an idle mode again in operation  528 . When an indicator that requests additional data transmission is included in the NAS message of the UE  500  in operation  516 , the MME  504  may not transfer the UE context release message in operation  522 , and may transmit an INITIAL CONTEXT SETUP REQUEST message to the eNB  502  as described above in operation  218  so that operations  218  through  230  may be performed. 
       FIG. 6  illustrates an operation of a UE according to the first exemplary embodiment of the present invention. 
     Referring to  FIG. 6 , a UE that is in an idle mode may continuously store AS security information that is used for a previous connection, in operation  602 , and may transmit an RRC connection request message to an eNB in operation  604  when data needs to be transmitted. In operation  606 , the UE may receive an RRC connection setup message from the eNB in response to the RRC connection request message received in operation  604 . When a message received in operation  606  includes an NCC value and an AS security algorithm or other security information generating indicators are included in operation  608 , the UE may generate information associated with AS security in operation  610 . In operation  612 , the UE may transfer, to the eNB, data encrypted through use of updated information associated with AS security along with an RRC connection setup complete message or may transfer the encrypted data by including the encrypted data in the RRC connection setup complete message. 
     When a security information update indicator is not included in the RRC connection setup message in operation  608 , the UE may remove the stored AS security information in operation  616 , and may include an NAS message in the RRC connection setup complete message and may transmit the RRC connection setup complete message in operation  618 . The UE may set a new AS security based on a command from the eNB in operation  620 , and may transmit the encrypted data in operation  622 . 
       FIG. 7  illustrates an operation of a UE according to the second exemplary embodiment of the present invention. 
     Referring to  FIG. 7 , a UE that is in an idle mode may continuously store AS security information that is used for a previous connection, in operation  702 , and may transmit an RRC connection request message to an eNB in operation  704  when data needs to be transmitted. In operation  706 , the UE may receive an RRC connection setup message from the eNB in response to the RRC connection request message transmitted in operation  704 . When it is determined in step  708  that the message received in operation  706  includes a “Reuse AS security indicator” that instructs to reuse previously used AS security information, or another security information reuse indicator, the UE may reuse AS security information in operation  710 . In operation  712 , the UE may transfer, to the eNB, data encrypted through use of the reused AS security information, along with an RRC connection setup complete message, or may transfer the encrypted data by including the encrypted data in the RRC connection setup complete message. 
     When a security information reuse indicator is not included in the RRC connection setup message in operation  708 , the UE may remove the previously stored AS security information in operation  716 , and may include an NAS message in the RRC connection setup complete message and transmit the RRC connection setup complete message in operation  718 . The UE may set a new AS security based on a command from the eNB in operation  720 , and may transmit the encrypted data to the eNB in operation  722 . 
       FIG. 8A  illustrates an operation of an eNB according to the third exemplary embodiment of the present invention. 
     Referring to  FIG. 8A , when the eNB receives an NAS message including IP data from a UE in operation  802 , or receives an NAS message and IP data, the eNB may transfer the received NAS message and IP data to an MME in operation  804 . In operation  806 , the eNB may receive a UE context release request message from the MME, and may release an RRC connection with the UE in operation  808 . 
       FIG. 8B  illustrates an operation of an MME according to the third exemplary embodiment of the present invention. 
     Referring to  FIG. 8B , the MME may receive an NAS message from an eNB in operation  810 , and may determine whether IP data is received in operation  812 . That is, when the IP data is received along with the NAS message, when the NAS message is provided in a form newly defined for transmitting IP data, or when an indicator indicating that the IP data is included in the NAS message is included in the NAS, the MME may determine that the IP data is received, and may proceed with operation  816  so as to transmit the IP data received from the eNB to an S-GW. In operation  818 , the MME may transmit a UE context release message to the eNB. 
     When the MME determines that the IP data is not received in operation  812 , that is, when the NAS message received from the eNB may be an NAS message for setting a context, the MME may proceed with operation  814  so as to perform a general context setting process. 
       FIG. 9  illustrates a method where an S-GW transmits received data of a UE to an MME, and the MME transfers the data to the UE again, according to a fourth exemplary embodiment of the present invention. 
     Referring to  FIG. 9 , a UE  900  transmits an Attach Request message to an eNB  902  in operation  912 , and the eNB  902  may transfer the Attach Request message to an MME  904  in operation  914 . Accordingly, in operation  916 , the MME  904  may transmit an Update Location Request message to a Home Subscriber Server (HSS)  910  so as to report identification information of the MME  904  that is provided to a subscriber, and to request subscription data. In operation  918 , the HSS  910  may include the subscription data in an Update Location Ack message, and may transfer the Update Location Ack message to the MME  904 . In operation  920 , the MME  904  may transmit, to an S-GW  906 , a Create Session Request message that requests creation of a new S1 bearer, and a data transport support indicator that indicates that the MME  904  is capable of directly transmitting data to a UE. The S-GW  906  that receives the Create Session Request message from the MME  904  may transmit, to a PDN-GW  908 , downlink S5 bearer information (S5 DL info) and a Create Request Session Request message that requests creation of an uplink S5 bearer in operation  922 . In operation  924 , the PDN-GW  908  may transfer, to the S-GW  906 , uplink S5 bearer information (S5 UL info) and a Create Session Response message in response to the Create Session Request message received in operation  922 . As circumstances demand, a condition for data transmission to the MME  904 , for example, a size of a data packet, a number of data packets, and the like, may be transferred to the S-GW  906  in operation  920  or operation  924 . In operation  926 , the S-GW  906  may transmit, to the MME  904 , uplink S1 bearer information (S1 UL info) and a Create Session Response message, in response to the Create Session Request message that requests the creation of the S1 bearer in operation  920 . In operation  928 , the MME  904  may transfer, to the eNB  902 , a UE Context Setup Request message including the S1 UL info, along with UE context information required for providing a service from the eNB  902  to the UE  900 , for example, security information, mobility limitation information of the UE  900 , and the like. The eNB  902  may transmit an RRC Connection Reconfiguration message to the UE  900  in operation  930 , and may receive an RRC Connection Reconfiguration Complete message from the UE  900  in operation  932  and thus, may generate a radio bearer to be used by the UE  900 . 
     When the UE  900  is switched into an idle mode, UE context information may be removed from the eNB  902 , and downlink S1 bearer information may be removed from the S-GW  906  in operation  934 . In this example, when the PDN-GW  908  transmits, to the S-GW  906 , IP data to be transmitted to the UE  900  in operation  936 , the S-GW  906  may determine whether to directly transmit the IP data to the MME  904  or to transmit a downlink data notification message to the MME  904 , based on a size of a data packet, a number of data packets, and whether the MME  904  provides data transport support. In operation  938 , the S-GW  906  may directly transmit the IP data to the MME  904 . In this example, information associated with a bearer to which the IP data belongs, for example, E-RAB ID may be transferred to the MME  904 , along with the IP data. The MME  904  that receives the IP data from the S-GW  906  may transmit the IP data to the UE  900  through use of an NAS message in operation  944 . The MME  904  may transmit a paging message to the UE  900  in operation  940 , and the MME  904  may receive a Service Request message from the UE  900  in response to the paging message in operation  942 . In this example, through the paging message, the IP data may be directly transferred from the MME  904  to the UE  900 . 
       FIGS. 10A and 10B  illustrate an operation of an S-GW according to the fourth exemplary embodiment of the present invention. 
     Referring to  FIG. 10A , an S-GW that receives a data transport support indicator from an MME in operation  1002  may register that the MME provides data transport support with respect to a bearer, in operation  1004 . 
     Referring to  FIG. 10B , an S-GW that receives IP data from a PDN-GW in operation  1006  may determine whether a UE is in an idle mode in operation  1008 . When the UE is in an idle mode, the S-GW may determine whether the MME provides data transport support with respect to a bearer associated with the IP data in operation  1010 . In this example, whether to transmit the IP data to the UE may be determined based on a size of a data packet, a number of data packets, and the like. 
     When it is determined that the MME is capable of transmitting the IP data to the UE, the S-GW may transmit the IP data to the MME in operation  1012 . When it is determined that the MME is incapable of transmitting the IP data in operation  1010 , the S-GW may perform buffering with respect to the IP data, and may transmit a downlink data notification message to the MME in operation  1014 . 
     When the UE is not in an idle mode in operation  1008 , the UE may transmit the IP data to an eNB that is being accessed by the UE in operation  1016 . 
     While the invention has been shown and described with reference to certain exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims and their equivalents.