Abstract:
The present invention relates to a wireless communication system and method for establishing connection between a User Equipment (UE) and a Mobility Management Entity (MME) in the wireless communication system in which the data-centric terminal requests the mobility management entity for attachment and checks, when the mobility management entity responds, data-centric features supported by the mobility management entity. According to the present invention, it is possible to connect the data-centric terminal to the mobility management entity supporting the data-centric features of the corresponding data-centric terminal efficiently in the wireless communication system.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
       [0001]    This application is a continuation application of prior application Ser. No. 13/702,200, which was a national stage entry of International application number PCT/KR2011/004439, filed on Jun. 17, 2011, which claimed the benefit of a Korean patent application filed on Jun. 17, 2010 in the Korean Intellectual Property Office and assigned Serial number 10-2010-0057693, the entire disclosure of each of which is hereby incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a wireless communication system and communication method thereof and, in particular, to a wireless communication system and method for establishing connection between a User Equipment (UE) and a Mobility Management Entity (MME) in the wireless communication system. 
         [0004]    2. Description of the Related Art 
         [0005]    Universal Mobile Telecommunications System (UMTS) is the third generation wireless communication system based on Global System for Mobile communications (GSM) and General Packet Radio Services (GPRS) and uses Wideband Code Division Multiple Access (WCDMA). The 3 rd  Generation Partnership Project (3GPP) as the UMTS standardization organization has proposed Evolved Packet System (EPS) such as Long Term Evolution (LTE). The LTE is a technology for implementing high speed packet-based communication. An LTE system includes a Mobility Management Entity (MME) which manages the mobility of the User Equipment (UE) connected thereto. 
       DISCLOSURE OF INVENTION 
     Technical Problem 
       [0006]    However, as the services provided through the wireless communication system are diversified, the UE is also being equipped various supplementary functions. The MME is embodied to support the supplementary functions of the UE. Accordingly, in order to receive the communication service in association with a certain supplementary function, the UE has to connect to the MME supporting the corresponding supplementary function. 
         [0007]    There is therefore a need of a method for connecting the UE to an MME supporting the intended supplementary function efficiently. 
       Solution to Problem 
       [0008]    In accordance with an aspect of the present invention, a method for connecting a data-centric terminal to a mobility management entity in a wireless communication system includes requesting, at the data-centric terminal, the mobility management entity for attachment; and checking, when the mobility management entity responds, data-centric features supported by the mobility management entity. 
         [0009]    Preferably, the method further includes determining, when the mobility management entity accepts the attachment, whether the data-centric terminal is to maintain the attachment to the mobility management entity according to the data-centric features; and performing, when the data-centric terminal determines to maintain the attachment, data-centric communication with the mobility management entity using the data-centric feature and, when not maintain the attachment, releasing the attachment to the mobility management entity. 
         [0010]    In accordance with another aspect of the present invention, a wireless communication system includes a data-centric terminal for performing data-centric communication using a unique data-centric feature; and a mobility management entity for managing mobility of the data-centric terminal, wherein the mobility management entity notifies, when the data-centric terminal requests for attachment, the data-centric terminal of data-centric features supported by the mobility management entity. 
         [0011]    Preferably, the data-centric terminal determines, when the mobility management entity accepts the attachment, whether to maintain the attachment to the mobility management entity according to the data-centric feature and performs, when the data-centric terminals determines to maintain the attachment, data-centric communication with the mobility management entity using the data-centric feature and, otherwise, releases the attachment to the mobility management entity. 
       Advantageous Effects 
       [0012]    In order to solve the above problems, the wireless communication system and method for establishing a connection between a UE and an MME in the system is capable of connecting the UE to the MME supporting the corresponding supplementary function efficiently. That is, the present invention is capable of connecting a data-centric terminal to a mobility management entity supporting data-centric features efficiently. Accordingly, it is possible for the mobility management entity supporting the data-centric feature to support the data-centric communication more efficiently and the data-centric terminal is capable of performing the data-centric communication more efficiently in the wireless communication system. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a diagram illustrating the architecture of a wireless communication system according to the first embodiment of the present invention, 
           [0014]      FIG. 2  is a signal flow diagram illustrating the communication procedure in the wireless communication system according to the first embodiment of the present invention, 
           [0015]      FIG. 3  is a signal flow diagram illustrating a connection procedure of the wireless communication system according to the first embodiment of the present invention, 
           [0016]      FIG. 4  is a signal flow diagram illustrating the connection procedure of the wireless communication system according to the first embodiment of the present invention, 
           [0017]      FIG. 5  is a flowchart illustrating the MME procedure in  FIG. 3 , 
           [0018]      FIG. 6  is a flowchart illustrating the MME procedure in  FIG. 4 , 
           [0019]      FIG. 7  is a flowchart illustrating the UE procedure in  FIGS. 3 and 4 , 
           [0020]      FIG. 8  is a diagram illustrating the architecture of a wireless communication system according to the second embodiment of the present invention, 
           [0021]      FIG. 9  is a signal flow diagram illustrating the connection procedure in the wireless communication system according to the second embodiment of the present invention, 
           [0022]      FIG. 10  is a flowchart illustrating the operating procedure of the MME in  FIG. 9 , and 
           [0023]      FIG. 11  is a flowchart illustrating the operating procedure of the UE in  FIG. 9 . 
       
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0024]    Exemplary embodiments of the present invention are described with reference to the accompanying drawings in detail. The same reference numbers are used throughout the drawings to refer to the same or like parts. Detailed description of well-known functions and structures incorporated herein may be omitted to avoid obscuring the subject matter of the present invention. 
         [0025]      FIG. 1  is a diagram illustrating the architecture of a wireless communication system according to the first embodiment of the present invention. 
         [0026]    Referring to  FIG. 1 , the wireless communication system of this embodiment includes an enhanced Node B (eNB)  120 , an MME  130 , a Home Subscriber Server (HSS), a Serving Gateway (S-GW)  150 , and a Packet Data Network Gateway (P-GW)  160 . 
         [0027]    The UE  110  may be fixed or mobile. Also, the UE  110  may be a normal UE capable of normal communication functions or a data-centric UE capable of specific supplementary function, e.g. data centric communication function. Although the description is directed to the data-centric UE capable of Machine Type Communication (MTC) function, the present invention is not limited thereto. Here, the MTC technology is applicable to Smart Metering for automated communication between a power company server and a home meter and an Alarm System for automated communication between a security company server and an illegal home invasion alarm. 
         [0028]    The eNB  120  controls a cell. The eNB  120  is a macro cell which is the cell of a normal cellular system. Here, the terms ‘eNB’ and ‘cell’ can be used interchangeably. The eNB  120  establishes a connection with the UE  110  through a radio channel and controls radio resource. For example, the eNB  120  generates and broadcasts system information within the cell and allocates to the UE  110  the radio resources for communicating packet data or control information with the UE.  110 . The system information may include Public Land Mobile Network Identifier (PLMN ID) for access to the PLMN via the eNB  120 , eNB Cell Global ID (ECGI), and a Tracking Area ID (TAI) of the tracking area including the cell. The eNB  120  makes a handover decision and commands handover based on the channel measurement result of the current cell and neighbor cells that is fed back by UE  110 . In order to accomplish this, the eNB  120  is provided with a control protocol such as Radio Resource Control Protocol related to radio resource management. 
         [0029]    The MME  130  manages the UE  110  in idle mode and selects the S-GW  150  and P-GW  160  for the UE  110 . The MME is also responsible for roaming and authentication-related functions. The MME  130  is also processing the bearer signal generated by the UE  110 . For this purpose, the MME  130  allocates identity information to the UE  110  and manages the UE  110  attached with the identity information. Here, the MME  130  can be a normal MME for supporting the normal UEs or the data-centric MME for supporting the data-centric UE. Although the description is directed to the MTC MME for supporting the MTC UE, the present invention is not limited thereto. 
         [0030]    The MME is connected to the eNB  120  through a radio channel and to the UE  110  via the eNB  120 . The MME  130  is connected to the eNB  120  through an S1-MME interface. At this time, the MME  130  communicates with the UE  110  using Non Access Stratum (NAS) messages. The MME  130  supports a plurality of tracking areas to connect to a plurality of eNBs  120  using the corresponding tracking area information. That is, the eNBs using the same tracking area information can connect to the same MME  130 . The eNBs using different tracking area informations can connect to different MMEs  130 . The eNBs using the different tracking area informations may connect to the same MME  130 . 
         [0031]    In order to support the data-centric communication efficiently in the wireless communication system, various data-centric proprieties should be defined. For example, the MTC feature for supporting the MTC technology efficiently in the wireless communication system may be Low Mobility, Time Controlled, Time Tolerant, Packet Switched Only (PS Only), Small Data Transmissions, Mobile Originated Only, Infrequent Mobile Terminated, Secure Connection, Location Specific Trigger, Network Provided Destination for Uplink Data, Infrequent Transmission, or Group Based MTC. 
         [0032]    For the MTC UE and MTC MME, some of the MTC features are mandatory and others are optional. For example, in the smart metering for the MTC UE to report utilization amount measured for a predetermined duration periodically, the MTC UE transmits the data less than a few hundred bytes, the ‘Small Data Transmissions’ feature is mandatory. In this case, the ‘Location Specific Trigger’ feature for the MTC UE to initiate MTC at a specific position may not be mandatory between the MTC UE and the MTC MME. In order to perform MTC efficiently, the MTC UE has to attach the MTC MME supporting the required MTC features. 
         [0033]    In the following description, the term ‘essential MTC feature’ denotes the MTC feature required mandatorily for the MTC UE to perform MTC. That is, if an essential MTC feature is supported by a radio network, the MTC UE is capable of performing MTC via the MTC MME of the radio network. The term ‘optional MTC feature’ denotes the MTC feature which is not required mandatorily for the MTC UE to perform MTC. The optional MTC feature may be required for MTC optimization in the radio network. That is, although the radio network does not support the optional MTC features, the MTC UE is capable of MTC via the MTC MME of the radio network. 
         [0034]    In the following description, the term ‘supported MTC feature’ denotes the MTC feature supported by the MTC MME of the wireless communication in order for the MTC UE to perform MTC. At this time, the supported MTC feature can be configured so as to be included in the essential MTC features of the MTC UE or not. The supported MTC feature also can be configured so as to be included in the optional MTC features of the MTC UE or not. 
         [0035]    That is, if the supported MTC feature is included in the essential features, the MTC MME is capable of supporting the MTC UE. The MTC UE is capable of performing MTC vial the MTC MME using the essential MTC feature. At this time, if the supported MTC feature includes an optional MTC feature, the MTC UE is also capable of using the optional MTC feature in performing MTC. If the supported MTC feature does not include any essential MTC feature, the MTC MME cannot support the MTC of the MTC UE. That is, the MTC UE cannot perform MTC via the MTC MME. Here, although the supported MTC feature includes an optional MTC feature, the MTC UE cannot perform MTC via the MTC MME. According, in order for the MTC UE to perform MTC via the MTC MME, the MTC UE should attach the MTC MME supporting the essential MTC feature. 
         [0036]    The HSS  150  stores the subscription data of the UE  110 . If the UE attaches to the MME  130 , the HSS  140  updates the subscription information of the UE  110 . The HSS  140  provides the MME  130  with the subscription information of the UE  110  in order for the MME  130  to control the UE  110  with the subscription information. The subscription information may include the MTC subscription information for an MTC UE. Here, the MTC subscription information may include the essential and optional MTC features of the corresponding MTC UE. 
         [0037]    The S-GW  150  connects to the eNB  120  and the MME  130  through radio channels. The S-GW  150  connects to the eNB through an S1-U interface. The S-GW  150  is responsible for the mobility control function of the UE  110 . When the UE performs handover between the eNBs  120  or between 3GPP radio networks, the S-GW  150  works as a mobility anchor of the UE  110 . 
         [0038]    The P-GW  160  is connected to the S-GW  150  through a radio channel. Here, the P-GW  160  is connected to the S-GW through a S5 interface. The P-GW  160  connects to the Internet Protocol (IP) network  170 . The P-GW  160  is responsible for the IP address allocation function and packet data-related function. That is, the P-GW  160  delivers the packet data from the IP network  170  to the UE  110  via the S-GW  150  and eNB  120 . When the UE  110  roams between the 3GPP radio network and non-3GPP radio network, the P-GW  160  works as the mobility anchor of the UE  110 . The P-GW  160  also determines the bearer band for the UE  110  and performs packet data forwarding and routing function. 
         [0039]    If it connects to the eNB  120  of the wireless communication system, the UE  110  is capable of being connected to the IP network  170  through the data path via the eNB  120 , S-GW  170 , and P-GW  160  so as to communicate packet data. The UE  110  is capable of transmitting a NAS request message to the MME  130  via the eNB  120 . At this time, the NAS request message may include at least one of an attach request, tracking area update request, or service request. Upon receipt of the NAS request message, the eNB selects the MME  130  according to a Network Node Selection Function (NNSF) to deliver the NAS request message to deliver the NAS request message. This is because the eNB  120  may be connected to plural MMEs  130  through separate S1-MME interfaces. 
         [0040]    Although the description is directed to the case where the UE  110  is an MTC UE and the eNB  120  is connected to a normal MME and an MTC MME through separate S1-MME interfaces in this embodiment, the present invention is not limited thereto. That is, although the MTC UE is replaced with another UE implemented to perform a specific supplementary function and differentiated from the normal UE and the MTC MME with another MME supporting the another UE, the present invention can be applied. In this embodiment, the description is made under the assumption that the MTC MME determines whether to accept attachment of the MTC UE according to whether the MTC MME support the essential MTC feature of the MTC UE. That is, the description is made under the assumption that all other conditions for determining whether to accept attachment of the MTC UE in the normal MME or the MME are fulfilled. 
         [0041]      FIG. 2  is a signal flow diagram illustrating the communication procedure in the wireless communication system according to the first embodiment of the present invention. 
         [0042]    Referring to  FIG. 2 , in the communication procedure of the wireless communication system of this embodiment, the MTC UE  111  first requests the MME  130  for attach via the eNB  120  at step  201 . At this time, the MTC UE  111  retains the essential and optional MTC features. That is, the MTC UE  111  selects one of the radio networks accessible through the eNB  120  and requests for the attachment to the MME  130  of the corresponding radio network. Here, the MTC UE  111  is capable of storing the information on the access PLMNs. At this time, the MTC UE  111  is capable of requesting for the attachment to the MTC MME  131  or the normal MME (as denoted by reference number  133  of  FIG. 3 ). The MTC UE  1110  is capable of transmitting International Mobile Subscriber Identity (IMSI) to the MME  130 . 
         [0043]    Next, if the MTC UE  111  requests for attachment, the MME  130  notifies the MTC UE  111  of the MTC features via the eNB  120 . At this time, the MME  130  retains the supported MTC feature supportable by the corresponding radio network. The MME  130  notifies the MTC UE  111  of the supported MTC feature. Here, the MME  130  expresses the supported MTC features in a bitmap for notifying of the MTC features and transmits the bitmap to the MTC UE  111 . With the bitmap, the MTC UE  111  is capable of checking whether the MME  130  supports MTC. The MTC UE is also capable for checking whether the MME  130  supports the essential MTC feature or optional MTC feature. That is, the MTC UE  111  is capable of identifying the MTC features supported by the MME  130  or not. 
         [0044]      FIG. 3  is a signal flow diagram illustrating a connection procedure of the wireless communication system according to the first embodiment of the present invention. 
         [0045]    Referring to  FIG. 3 , in the connection procedure of the wireless communication system according to this embodiment, the MTC UE  111  requests the MME  130  for attachment via the eNB  120  at step  211 . At this time, the MTC UE  111  is retaining the essential and optional MTC features. That is, the MTC UE  111  selects one of the radio networks accessible with the eNB  120  and requests for attachment to the MME  130  of the corresponding radio network. Here, the MTC UE  111  is capable of retaining the information on the PLMNs accessible through the eNB  120 . At this time, the MTC UE  111  is capable of attachment to the MTC MME  131  or the normal MME (denoted by reference number  133  of  FIG. 3 ). The MTC UE  111  is capable of transmitting the unique subscription identity information to the MME  130 . 
         [0046]    Next, if the MTC UE  111  requests for attachment, the MTC MME  131  requests the HSS  140  for the subscription information of the MTC UE  111  at step  213 . At this time, the MTC MME  131  reports the location of the MTC UE  111  to the HSS  140  to request for the subscription information of the MTC UE  111 . Here, the MTC MME  131  sends the subscription identity information of the MTC UE  111 . Afterward, if the subscription information of the MTC UE  111  is requested, the HSS  140  responds by sending the subscription information of the MTC UE  111  to the MTC MME  131 . At this time, the HSS  140  updates the location of the MTC UE  111  and notifies the MTC MME  131  of the update to transmit the subscription information of the MTC UE  111 . That is, the HSS  140  retrieves the subscription information of the MTC UE  111  using the subscription identity information and transmits the found subscription information to the MTC MME  131 . At this time, the subscription information includes the MTC subscription information of the MTC UE  111 . The MTC subscription information includes the essential and optional MTC features of the MTC UE  111 . 
         [0047]    If the subscription information of the MTC UE  111  is received, the MTC MME  131  analyzes the subscription information to determine whether it is possible to support the essential MTC feature of the MTC UE  111  at step  217 . At this time, the MTC MME  131  is retaining the MTC features supportable by the corresponding radio network. That is, the MTC MME  131  checks the essential MTC feature in the subscription information of the MTC UE  111  to determine whether the essential MTC feature is included in the supported MTC features. Here, if the supported MTC features include the essential MTC feature of the MTC UE  111 , the MTC MME  131  determines that the essential MTC feature of the MTC UE  111  is supportable. Otherwise, if the supported MTC features do not include the essential MTC feature of the MTC UE, the MTC MME  131  determines that the essential MTC feature of the MTC UE  111  is not supportable. 
         [0048]    If it is determined that the essential MTC feature of the MTC UE  111  is supportable, the MTC MME  131  accepts the registration of the MTC UE  111  at step  219 . At this time, the MTC MME  131  notifies the MTC UE  111  of the supported MTC features. Here, the MTC MME  131  expresses the supported MTC features in a bitmap for notifying of the MTC features and transmits the bitmap to the MTC UE  111 . 
         [0049]    The attachment to the MME  130  is accepted, the MTC UE  111  determines whether the MME  130  supports MTC at step  221 . That is, the MTC UE  111  determines whether the MME  130  is the MTC MME  131 . The MTC UE  111  determines whether the MME  130  is the MTC MME  131  based on whether the MME  130  has transmitted the MTC features. If it is determined that the MTC features has been transmitted by the MME  130 , the MTC UE  111  determines that the MME  130  is the MTC MME  131 . Otherwise, if it is determined that the MTC features has not been transmitted by the MME  130 , the MTC UE  1111  determines that the MME  130  is the normal MME  133 . Afterward, the MTC UE  111  performs MTC through the MTC MME  131  at step  223 . At this time, the MTC UE  111  is capable of performing MTC using the essential MTC feature. The MTC UE  111  is also capable of performing MTC using the supported MTC features of the MTC MME  131 . That is, the MTC UE  111  is capable of checking the MTC feature selected among the supported MTC features for use in performing MTC. 
         [0050]    If it is determined that the essential MTC feature of the MTC UE  111  is not supportable at step  217 , the MTC MME  131  rejects the registration of the MTC UE  111  at step  227 . At this time, the MTC MME  131  notifies the MTC UE  111  of the supported MTC features. Here, the MTC MME  131  expresses the supported MTC features in a bitmap for notifying of the MTC features and transmits the bitmap to the MTC UE  111 . In this way, the MTC UE  111  is capable of checks the MTC features not supported by the MTC MME  131 . The MME  131  is also capable of notifying the MTC UE  111  of the cause of the registration rejection. That is, the MTC MME  131  is capable of notifying the MTC UE  111  that the essential MTC feature is not supported. The MTC MME  131  is also capable of notifying the MTC UE  111  of a retrial period for attachment. The MTC MME  131  is also capable of notifying the MTC UE  111  of the information on PLMNs for retrial of registration. 
         [0051]      FIG. 4  is a signal flow diagram illustrating the connection procedure of the wireless communication system according to the first embodiment of the present invention. 
         [0052]    Referring to  FIG. 4 , in the connection procedure of the wireless communication system of this embodiment, the MTC UE  111  first requests the MME  130  for attachment via the eNB  120  at step  311 . At this time, the MTC UE  111  is retaining the essential and optional MTC features. That is, the MTC UE  111  selects one of the radio networks accessible through the eNB  120  to requests the MME  130  of the corresponding radio network for attachment. Here, the MTC UE  111  is capable of retaining the information on the PLMNs accessible through the eNB  120 . At this time, the MTC UE  111  is capable of requesting the MTC MME  131  or the normal MME  133  for attachment. The MTC UE  111  is capable of transmitting the unique subscription identity information to the MME  130 . 
         [0053]    Upon receipt of the registration request from the MTC UE  111 , the normal MME  133  requests the HSS  140  for the subscription information of the MTC UE  111  at step  313 . At this time, the normal MME  133  is capable of reporting the location of the MTC UE  111  to request for the subscription information of the MTC UE  111 . Here, the normal MME  133  delivers the subscription identity information of the MTC UE  111  to the HSS  140 . Afterward, if the subscription information of the MTC UE  111  is requested, the HSS  140  responds with by transmitting the subscription information of the MTC  111  to the normal MME  133 . At this time, the HSS  140  updates the location of the MTC UE  111  and notifies the normal MME  133  of the update to transmit the subscription information of the MTC UE  111 . That is, the HSS  140  retrieves the subscription information of the MTC UE  111  using the subscription identity information and transmits the found subscription information to the normal MME  133 . At this time, the subscription information includes the MTC subscription information for the MTC UE  111 . Here, the MTC subscription information includes the essential and optional MTC features of the corresponding MTC UE  111 . 
         [0054]    If the subscription information of the MTC UE  111  is received, the normal MME  133  accepts the registration of the MTC UE  111  at step  317 . At this time, the normal MME  133  is not capable of processing the MTC subscription information in the subscription information of the MTC UE  111 . That is, the normal MME  133  cannot discriminate between the MTC UE  111  and normal UE (not shown). As a consequence, the normal MME  133  regards the MTC UE  111  as a normal UE so as to accept the registration of the MTC UE  111 . 
         [0055]    If the registration is accepted by the MME  130 , the MTC UE  111  determines whether the MME  130  supports MTC at step  319 . That is, the MTC UE  111  determines whether the MME  130  is the MTC MME  131 . At this, the MTC UE  111  is capable of determining whether the MME  130  is the MTC MME  131  according to whether the MME  130  has notified of the MTC features. If the MTC features have been notified, the MTC UE  111  determines whether the MME  130  is the MTC MME  131 . Otherwise, if no MTC feature has been notified, the MTC UE  111  determines that the MME  130  is the normal MME  133 . The MTC UE  111  also detaches from the normal MME  133  at step  321 . That is, since the normal  133  cannot support the essential MTC feature, the MTC UE  111  detaches from the normal MME  133 . 
         [0056]    Although, in this embodiment, the description is directed to the exemplary case where the MTC UE  111  determines whether the MME  130  has reported the MTC features to determine whether the MME  130  is the MTC MME  131 , the present invention is not limited thereto. That is, the present invention can be implemented in such a way that the MTC UE  111  discriminates between the MTC and normal MMEs  131  and  133  based on the MTC features transmitted by both the MTC and nor MME  131  and  133 . That is, the MTC MME  131  is retaining the supported MTC features and the normal MME  133  is not retaining the supported MTC features. If the MTC UE  111  requests for attachment, the MTC MME  131  expresses the supported MTC features in a bitmap for notifying of the MTC features and transmits the bitmap to the MTC UE  111 . Meanwhile, if the MTC UE  111  request for attachment, the normal MME  133  expresses the supported MTC features in a bitmap for notifying of the MTC features and transmits the bitmap to the MTC UE  111 . Here, the normal MME  133  transmits the bitmap indicating that there is no supported MTC feature. 
         [0057]    In order to accomplish this, the MTC UE  111  is capable of determining whether the MME  130  supports MTC. Also, the MTC UE  111  is capable of determining whether the MME  130  supports the essential MTC feature or optional MTC feature. That is, the MTC UE  111  is capable of discriminating between the MTC features supported by the MME  130  and the MTC features not supported by the MME  130 . 
         [0058]      FIG. 5  is a flowchart illustrating the MME procedure in  FIG. 3 . Here, the description is made under the assumption that the MME is an MTC MME. 
         [0059]    Referring to  FIG. 5 , in the procedure according to this embodiment, the MTC MME  131  first detects the attach request of the MTC UE  111  at step  411 . At this time, the MTC MME  131  checks the subscription identity information of the MTC UE  111 . The MTC MME  131  requests the HS S 140  for the subscription information of the MTC UE  111  at step  413 . At this time, the MTC MME  131  reports the location of the MTC UE  111  to the HS S 140  to request for the subscription information of the MTC UE  111 . Here, the MTC MME  131  sends the subscription identity information of the MTC UE  111  to the HSS  140 . 
         [0060]    Subsequently, if the subscription information of the MTC UE  111  is received from the HSS  140 , the MTC MME  131  detects this at step  415  and analyzes the subscription information to determine whether it can support the essential MTC feature at step  417 . At this time, the MTC MME  131  is retaining the supported MTC features supportable in the corresponding radio network. That is, the MTC MME  131  checks the essential MTC feature in the subscription information of the MTC UE  111  to determine whether the essential MTC feature is included in the supported MTC feature. If the essential MTC feature of the MTC UE  111  is included in the supported MTC features, the MTC MME  131  determines that it is possible to support the essential MTC feature of the MTC UE  111 . Otherwise, if the essential MTC feature of the MTC UE  131  is not included in the supported MTC features, the MTC MME  131  determines that it is impossible to support the essential MTC feature of the MTC UE  111 . 
         [0061]    Finally, if it is determined that it can support the essential MTC feature of the MTC UE  111 , the MTC MME  131  accepts the attachment of the MTC UE  111  at step  419 . At this time, the MTC MME  131  notifies the MTC UE  111  of the supported MTC features. Here, the MTC MME  131  expresses the supported MTC features in a bitmap for notifying of the MTC features and transmits the bitmap to the MTC UE  111 . The MTC MME  131  performs MTC with the MTC UE  111  at step  421 . At this time, the MTC MME  131  is capable of performing the MTC with the essential MTC feature for the MTC UE  111 . The MTC MME  131  is also capable of performing the MTC with the supported MTC features for the MTC UE  111 . That is, in order to optimize the MTC, the MTC MME  131  is capable of checking MTC feature selected for the MTC UE  111  among the supported MTC features. 
         [0062]    If it is determine that it cannot support the essential MTC feature of the MTC UE  111  at step  417 , the MTC MME  131  rejects the attachment of the MTC UE  111  at step  427 . At this time, the MTC MME  131  notifies the MTC UE  111  of the supported MTC features. The MTC MME expresses the supported MTC features in a bitmap for notifying of the MTC features and transmits the bitmap to the MTC UE  111 . In this way, the MTC UE  111  is capable of checking the MTC feature not supported by the MTC MME  131 . The MTC MME  131  is also capable of notifying of the reason of the attachment rejection. That is, the MTC MME  131  is capable of notifying the MTC UE  111  that it does not support the essential MTC function. The MTC MME  131  is also capable of notifying the MTC UE  111  of the retrial period for attachment. The MTC MME  131  is also capable of notifying of the information on different PLMNs for use in retrial of attachment. 
         [0063]      FIG. 6  is a flowchart illustrating the MME procedure in  FIG. 4 . Here, the description is made under the assumption that the MME is a normal MME. 
         [0064]    Referring to  FIG. 6 , in the MME procedure of the embodiment, the normal MME  133  firsts detects the attach request of the MTC UE  111  at step  511 . At this time, the normal MME  133  checks the subscription identity information of the MTC UE  111 . The normal MME  133  requests the HSS  140  for the subscription information of the MTC UE  111  at step  513 . At this time, the normal MME  133  reports the location of the MTC UE  111  to the HS S 140  to request for the subscription information of the MTC UE  111 . Here, the normal MME  131  transmits the subscription identity information of the MTC UE  111  to the HSS  140 . 
         [0065]    Finally, if the subscription information of the MTC UE  111  is received from the HSS  140 , the normal MME  133  detects this at step  515  and accepts the attachment of the MTC UE  111  at step  517 . At this time, the normal MME  133  does not process the MTC subscription information in the subscription information of the MTC UE  111 . That is, the normal MME  133  does not discriminate between the MTC UE  111  and the normal UEs. As a consequence, the normal MME  133  regards the MTC UE  111  as a normal UE so as to accept attachment of the MTC UE  111 . Here, the normal MME  133  expresses the supported MTC features in a bitmap for notifying of the MTC features and transmits the bitmap to the MTC UE  111 . That is, the normal MME  133  is capable of transmitting the bitmap configured to indicate that there is not supported MTC feature. Afterward, the normal MME  133  releases the attachment of the MTC UE  111  at step  519 . At this time, the normal MME  133  releases the attachment according to the request from the MTC UE  111 . That is, since it cannot support the essential MTC feature, the normal MME  133  releases the attachment of the MTC UE  111 . 
         [0066]      FIG. 7  is a flowchart illustrating the UE procedure in  FIGS. 3 and 4 . Here, the description is made under the assumption that the UE is an MTC UE. 
         [0067]    Referring to  FIG. 7 , in the UE procedure of this embodiment, the MTC UE  111  first selects the MME  130  at step  611 . That is, the MTC UE  111  selects one of the radio networks accessible through the eNB  120 . At this time, the MTC UE  111  is capable of retaining the information on the operators of the radio networks accessible through the eNB  120 . The MTC UE  111  is retaining the essential MTC feature and selected MTC feature. Afterward, the MTC UE  111  requests the MME  130  for attachment at step  613 . At this time, the MTC UE  111  is capable of requesting the MTC MME  131  or the normal MME  133  for the attachment. The MTC UE  111  is also capable of transmitting the unique subscription identity information to the MME  130 . 
         [0068]    Subsequently, if the MME  130  accepts the attachment, the MTC UE  111  detects this at step  615  and determines whether the MME  130  supports MTC at step  617 . At this time, the MTC UE  111  is capable of determining whether the MME  130  is an MTC MME  131  according to whether the MTC features have been reported by the MME  130 . If the MTC features have been reported by the MME  130 , the MTC UE  111  determines that the MME  130  is the MTC MME  131 . If the MTC features have not been reported, the MTC UE  111  determines that the MME  130  is the normal MME  133 . Meanwhile, if the bitmap indicating the MTC features is received from the MME  130 , the MTC UE  111  is capable of checking the supported MTC features of the MME  130 . The MTC UE  111  is also capable of determining whether the MME  130  supports the MTC for the MTC UE  111  according to the supported MTC features of the MME  130 . 
         [0069]    Finally, if it is determined that the MME  130  supports MTC at step  617 , the MTC UE  111  performs MTC through the MME  130 , i.e. the MTC MME  131 . At this time, the MTC MME  111  is capable of performing MTC using the essential MTC feature. The MTC UE  111  is also capable of performing MTC using the supported MTC features of the MTC MME  131 . That is, the MTC UE  111  is capable of checking the MTC feature selected among the supported MTC features of the MTC MME  131  for use in performing MTC. 
         [0070]    Otherwise, if it is determined that the MME  130  does not support MTC at step  617 , the MTC UE  111  detaches from the MME  130  at step  627 . That is, since the normal MME  133  cannot support the essential MTC feature, the MTC UE  111  releases the attachment to normal MME  133 . At this time, the MTC UE  111  is capable of storing the operator information of the radio network corresponding to the normal MME  133  to reference in selecting the MME  130  afterward. That is, the MTC UE  111  is capable of storing the operator information of the corresponding radio network as forbidden PLMN ID to avoid attachment to the corresponding normal MME  133  afterward. 
         [0071]    Meanwhile, if the attachment to the MME  130  is rejected at step  615 , the MTC UE  111  detects this at step  635  and waits for the attachment retrial period at step  637 . At this time, the MTC UE  111  is capable of receiving the bitmap informing of the MTC features from the MME  130  and checks the MTC features that are not supported by the MME  130 . The MTC UE  111  is capable of waiting for a predetermined attachment retrial period. The MTC UE  111  is also capable of waiting for the attachment retrial period as notified by the MME  130 . Afterward, the MTC UE  111  reselects the MME  130  at step  639  and returns the procedure to step  615 . The MTC UE  111  performs at least a part of steps  615  to  639  again. 
         [0072]    At this time, the MTC UE  111  is capable of retaining the operator information of the radio networks, which the eNB  120  is accessible, for use in selecting another MME  130 . The MTC UE  111  is also capable of using the operation information of the different radio networks that are reported by the MTC MME  131  for selecting another MME  130 . For example, if the operation informations of the individual radio networks are stored, the MTC UE  111  selects another MME using the information and, otherwise, selects another MME  130  as notified by the MTC MME  131 . Here, the MTC UE  111  is capable of selecting another MME  130  by referencing previously stored access-forbidden information. That is, the MTC UE is capable of another MME  130  after ruling out the selection-forbidden information in the operator informations of other radio networks that are stored previously or notified by the MTC MME  131 . 
         [0073]    According to this embodiment, it is possible to connect the UE  110  to the MME  130  supporting the intended supplementary function efficiently in the wireless communication system. That is, it is possible to connect the MTC UE  111  to the MTC MME  131  supporting the essential MTC feature. Accordingly, the MTC MME  131  is capable of supporting MTC more efficiently, and the MTC UE  111  is capable of performing MTC more efficiently in the wireless communication system. 
         [0074]    Although the above-description is directed to the exemplary case for determining whether to accept the attachment of the MTC UE according to whether the MTC MME supports the essential MTC feature, the present invention is not limited thereto. That is, the present invention can be implemented in such a way that the MTC UE determines whether the MTC MME supports the essential MTC feature. At this time, criterion for determining whether to maintain the attachment of the MTC UE to the MTC MME can be configured by an external server. 
         [0075]      FIG. 8  is a diagram illustrating the architecture of a wireless communication system according to the second embodiment of the present invention. 
         [0076]    Referring to  FIG. 8 , the wireless communication system of this embodiment incudes a policy server  700 , a UE  710 , an eNB  720 , an MME  730 , an HSS, an S-GW  750 , and a P-GW  760 . In the wireless communication of this embodiment, since the configurations and functions of the UE  710 , the eNB  720 , the MME  730 , the HSS  740 , the S-GW  750 , and the P-GW  760  are similar to those described in the previous embodiment, detailed description thereof are omitted herein. 
         [0077]    The policy server  700  determines the MTC policy per MTC UE for use in association with the UE  710 . At this time, the policy server  700  sends the MTC policy to the MTC UE via the eNB  720  in order for the MTC UE to configure the MTC policy. Here, the MTC policy includes the essential MTC features for the MTC UE, selected MTC features, and information on whether it is possible to maintain the attachment to the radio network supporting no essential MTC features of the MTC UE. The policy server  700  can be an Open Mobile Alliance-Device Management (OMA-DM) server. 
         [0078]      FIG. 9  is a signal flow diagram illustrating the connection procedure in the wireless communication system according to the second embodiment of the present invention. Although the MTC UE is communicating with the server or the MTC MME via an eNB, this is omitted herein. 
         [0079]    Referring to  FIG. 9 , in the connection procedure of the wireless communication system of this embodiment, the policy server  700  first configures the MTC policy for the MTC UE  711  at step  811 . At this time, the MTC policy includes the essential MTC features, the selected MTC features, and information on whether the MTC UE  711  may maintain the attachment to the radio network which does not support the essential MTC features. Afterward, the MTC UE  711  requests the MME  730  for attachment at step  813 . That is, the MTC UE  711  selects one of the radio networks accessible via the eNB  720  and request the MME  730  of the corresponding radio network for attachment. Here, the MTC UE  711  is capable of retaining the operator informations of the radio networks accessible via the eNB  720 . At this time, the MTC UE  711  is capable of requesting the MTC MME  731  or a normal MME (not shown) for attachment. The MTC UE  711  is also capable of transmitting unique subscription identity information to the MME  730 . 
         [0080]    If the MTC UE  711  requests for attachment, the MTC MME  731  requests the HSS  740  for the subscription information of the MTC UE  711  at step  815 . At this time, the MTC MME  7312  reports the location of the MTC UE  711  to the HSS  740  to request for the subscription information of the MTC UE  711 . Here, the MTC MME  731  delivers the subscription identity information of the MTC UE  711  to the HSS  740 . Afterward, if the subscription information of the MTC UE  711  is requested, the HSS  740  responds by sending the subscription information of the MTC UE  711  to the MTC MME  731  at step  817 . At this time, the HSS  740  updates the location of the MTC UE  711  and notifies the MTC MME  731  of the update with the subscription information of the MTC UE  711 . That is, the HSS  740  retrieves the subscription information of the MTC UE  711  in match with the subscription identity information and sends the found subscription information to the MTC MME  731 . At this time, the subscription information includes the MTC subscription information for the MTC UE  711 . Here, the MTC subscription information includes the essential MTC features and the selected MTC feature of the corresponding MTC UE  711 . 
         [0081]    If the subscription information of the MTC UE  711  is received, the MTC MME  731  accepts the attachment of the MTC UE  711  at step  819 . At this time, the MTC MME  731  is retaining the MTC features supportable in the corresponding radio network. When accepting the attachment of the MTC UE  711 , the MTC MME  731  notifies the MTC UE  111  of the supported MTC features. Here, the MTC MME  731  expresses the supported MTC features in a bitmap for notifying of the MTC features and transmits the bitmap to the MTC UE  711 . 
         [0082]    If the MME  730  accepts the attachment, the MTC UE  711  determines at step  821  whether the MME  730  supports MTC. That is, the MTC UE  711  determines whether the MME  730  is the MTC MME  731 . At this time, the MTC UE  711  is capable of determining whether the MME  730  is the MTC MME  731  according to whether the MTC features have been transmitted by the MME  730 . If it is determined that the MTC features have been transmitted by the MME  730 , the MTC UE  711  determines that the MME  730  is the MTC MME  731 . Otherwise, if it is determined that no MTC feature has been transmitted by the MME  730 , the MTC UE  711  determines that the MME  730  is a normal MME. 
         [0083]    The MTC UE  711  determines whether to use the supported MTC features of the MTC MME  731  at step  823 . At this time, the MTC UE  711  determines whether to use the supported MTC features according to the MTC policy. That is, the MTC UE  711  determines based on the MTC policy whether the supported features include the essential feature. Here, if the supported MTC features include the essential MTC feature, the MTC UE  711  determines to use the supported MTC features. If the supported MTC features do not include the essential MTC feature, the MTC UE  711  determines whether to maintain the attachment to the MTC MME  731 . Here, if it is determined to maintain the attachment, the MTC UE  711  determines to use the supported MTC features. Otherwise, if it is determined not to maintain the attachment, the MTC UE  711  determines not to use the supported MTC features. 
         [0084]    If it is determined to use the supported features at step  823 , the MTC UE performs MTC via the MTC MME  731  at step  825 . At this time, if the supported MTC features include the essential MTC feature, the MTC UE  711  is capable of performing the MTC using the essential MTC features. Here, the MTC UE  711  is capable of performing MTC using the MTC feature selected among the supported MTC features of the MTC MME  731  as well as the essential MTC feature. If the supported MTC features do not include the essential MTC feature, the MTC UE  711  is capable of performing MTC using the supported MTC features of the MTC MME  731 . Here, the MTC UE  711  is capable of performing MTC with the MTC feature selected among the supported MTC features of the MTC MME  731 . 
         [0085]    Otherwise, if it is determined not to use the supported MTC features at step  823 , the MTC UE  711  releases the attachment to the MTC MME  731  at step  833 . 
         [0086]    Although the description is directed to an exemplary case where the MTC UE  711  determines whether the MTC features have been transmitted by the MME  730  to determine whether the MME  730  is the MTC MME  731  in this embodiment, the present invention is not limited thereto. That is, the present invention can be implemented in such a way that the supported MTC features are transmitted by the normal MME  733  as well as the MTC MME  731  and thus the MTC UE  711  differentiates between the MMEs. That is, the MTC MME  731  is retaining the supported MTC features while the normal MME  733  is not retaining any supported MTC feature. If the MTC UE  711  requests for attachment, the MTC MME  731  expresses the supported MTC features in a bitmap for notifying of the MTC features and transmits the bitmap to the MTC UE  711 . Meanwhile, if the MTC UE  711  request for attachment, the normal MME  733  expresses the supported MTC features in a bitmap for notifying of the MTC features and transmits the bitmap to the MTC UE  711 . Here, the bitmap is configured to indicate that the normal MME  733  has no supported MTC feature. 
         [0087]    In this way, the MTC UE  711  is capable of checking whether the MME  730  supports MTC. The MTC UE  711  is also capable of checking whether the MME  730  supports the essential MTC feature or the selected MTC feature. That is, the MTC UE  711  is capable of discriminating between the MTC features supported and not supported by the MME  730 . 
         [0088]      FIG. 10  is a flowchart illustrating the operating procedure of the MME in  FIG. 9 . In this embodiment, the description is made under the assumption that the MME is the MTC MME. In the case that the MME is a normal MME, the operating procedure of the normal MME is similar to that of the previous embodiment, the detailed description thereon is omitted herein. 
         [0089]    Referring to  FIG. 10 , in the operations procedure of the MME  730  according to this embodiment, the MTC MME  731  first detects the attach request of the MTC UE  711  at step  911 . At this time, the MTC MME  731  checks the subscription identity information of the MTC UE  711 . Next, the MTC MME  731  requests the HSS  740  for the subscription information of the MTC UE  711  at step  913 . At this time, the MTC MME  731  reports the location of the MTC UE  711  to the HSS  740  to request for the subscription information of the MTC UE  711 . Here, the MTC MME  731  transmits the subscription information of the MTC UE  711  to the HSS  740 . 
         [0090]    Subsequently, if the subscription information of the MTC UE  711  is received from the HSS  740 , the MTC MME  731  detects this at step  915  and accepts the attachment of the MTC UE  711  at step  917 . At this time, the MTC MME  731  notifies the MTC UE  711  of the supported MTC features. Here, the MTC MME  131  expresses the supported MTC features in a bitmap for notifying of the MTC features and transmits the bitmap to the MTC UE  711 . Afterward, the MTC MME  731  determines whether the attachment of the MTC UE  711  has been released at step  919 . At this time, if the MTC UE requests for detachment, the MTC MME  731  detects this and accepts the release of the detachment. 
         [0091]    Finally, if no request for detachment is detected at step  919 , the MTC MME  731  performs MTC with the MTC UE  711  at step  921 . At this time, if the supported MTC features include the essential MTC feature, the MTC MME  731  is capable of performing MTC using the essential MTC feature of the MTC UE  711 . In order to optimize MTC, the MTC MME  731  is capable of checking the selected MTC feature for the MTC UE  711  among the supported MTC features. The MTC MME  731  is capable of performing MTC with the supported MTC features for the MTC UE  711 . Here, in order to optimize MTC, the MTC MME  731  is capable of checking the selected MTC feature for the MTC UE  711  among the supported MTC features. 
         [0092]      FIG. 11  is a flowchart illustrating the operating procedure of the UE in  FIG. 9 . In this embodiment, the description is made under the assumption that the UE is the MTC UE. 
         [0093]    Referring to  FIG. 11 , in the operating procedure of the UE  110  according to this embodiment, the MTC UE  711  first configures an MTC policy according to the command of the policy server  700  at step  1001 . Here, the MTC policy includes the essential MTC features of the MTC UE  711 , selected MTC feature, and information on whether it is possible to maintain the attachment to the radio network which does not support the essential MTC feature. Afterward, the MTC UE  711  selects the MME  130  at step  1003 . That is, the MTC UE  711  selects one of the radio networks accessible via the eNB  720  to access the MME  730 . At this time, the MTC UE  711  is retaining the operator&#39;s informations of the radio networks accessible via the eNB  720 . Next, the MTC UE  711  requests the MME  730  for attachment at step  1005 . At this time, the MTC UE  711  is capable of requesting the MTC MME  731  or the normal MME for attachment. The MTC UE  711  is also capable of transmitting the unique subscription identity information to the MME  730 . 
         [0094]    Subsequently, if the MME  730  accepts the attachment, the MTC UE  711  detects this at step  1007  and determines whether the MME  730  supports MTC at step  1009 . At this time, the MTC UE  711  is capable of determining whether the MME  730  is the MTC MME  731  by checking whether the MME  730  has transmitted the MTC features. If the MTC features have been transmitted, the MTC UE  711  determines that the MME  730  is the MTC MME  731 . Otherwise, no MTC feature has been transmitted, the MTC UE  711  determines that the MME  730  is a normal MME. The MTC UE  711  receives the bitmap indicating the MTC features from the MME  730  and checks the supported MTC features of the MME  730 . The MTC UE  711  is capable of determining whether the MME  730  supports MTC for the MTC UE  711  according to the supported features of the MME  730 . 
         [0095]    Subsequently, if it is determined that the MME  730  supports MTC at step  1009 , the MTC UE  711  determines whether to use the supported MTC features of the MTC MME  731  at step  1011 . At this time, the MTC UE  711  is capable of determining whether to use the supported MTC features according to the MTC policy. Here, if the supported MTC features include the essential MTC feature, the MTC UE  711  determines to use the supported MTC features. If the supported MTC features do not include the essential MTC feature, the MTC UE  711  determines whether to maintain the attachment to the MTC MME  731  according to the MTC policy. Here, if it is determined to maintain the attachment, the MTC UE  711  determines to use the supported MTC features. If it is determined not to maintain the attachment, the MTC UE  711  determines not to use the supported MTC features. 
         [0096]    Finally, if it is determined to use the supported MTC features at step  1011 , the MTC UE  711  performs MTC through the MME  730 , i.e. MTC MME  731 , at step  1013 . At this time, if the supported MTC features include the essential MTC feature, the MTC UE  711  is capable of performing MTC using the essential MTC features. The MTC UE  711  is also capable of performing MTC using the MTC feature selected among the supported MTC features of the MTC MME  731  in addition to the essential MTC features. If the supported MTC features do not include any essential feature, the MTC UE  711  is capable of performing MTC using the supported MTC features of the MTC MME  731 . Here, the MTC UE  711  is capable of checking the MTC feature selected among the supported MTC features of the MTC MME  731  and using the selected MTC feature. 
         [0097]    If it is determined not to support MTC at step  1009  or if it is determined not to use the supported MTC features, the MTC UE  711  releases the attachment to the MME  730  at step  1021 . At this time, the MTC UE  711  is capable of retaining the operator information of the radio network corresponding to the MME  730  to reference for selecting MME  730  afterward. That is, the MTC UE  711  is capable of storing the corresponding radio network operator information as selection forbidden information so as not to request for attachment to the corresponding MME  730 . 
         [0098]    If the MME  730  does not accept the attachment at step  1007  and if the MME  730  rejects the attachment, the MTC UE  711  detects this at step  1037  and waits for the attachment retrial period at step  1039 . At this time, the MTC UE  711  is capable of waiting for a predetermined attachment retrial period. The MTC UE  711  is also capable of waiting for the attachment retrial period notified by the MME  730 . Afterward, the MTC UE  711  reselects the MME at step  1041  and returns the procedure to step  1005 . Next, the MTC UE  711  performs at least a part of steps  1005  to  1041  again. 
         [0099]    At this time, the MTC UE  711  is capable of storing the operator informations of the radio networks accessible via the eNB  720  and using the operator informations for selecting another MME  730 . The MTC UE  711  is also capable of using the other radio networks operators informations notified by the MTC MME  731  to select another MME  730 . For example, if the operator informations of the respective radio networks are stored previously, the MTC UE  711  is capable of selecting another MME  730  using these informations and, otherwise, selecting another MME  730  as notified by the MTC MME  731 . Here, the MTC UE  711  is capable of selecting another MME  730  by referencing the previously stored selection forbidden information. That is, the MTC UE is capable of ruling out the selection forbidden information in the operator informations of the respective radio networks that are stored previously or notified by the MTC MME  731  selecting another MME  730  in selecting another MME  730 . 
         [0100]    According to this embodiment, it is possible to connect the UE  710  to an MME  730  supporting the corresponding supplementary function efficiently in the wireless communication system. That is, the present invention is capable of connecting the MTC UE  711  to the MTC MME  731  supporting the corresponding essential MTC feature efficiently. As a consequence, the MTC MME  731  is capable of supporting MTC more efficiently and the MTC UE  711  is capable of performing MTC more efficiently in the wireless communication system. 
         [0101]    Although exemplary embodiments of the present invention have been described in detail hereinabove with specific terminology, this is for the purpose of describing particular embodiments only and not intended to be limiting of the invention. While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention.