Abstract:
The present invention relates to a wireless communication system and a connection method between user equipment and a mobility management entity and comprises: selecting a mobility management entity and requesting identification information for user equipment by a base station when the user equipment is connected; determining whether to assign identification information by the mobility management entity; and if the identification information is not assigned, selecting another mobility management entity by the mobility management entity, assigning identification information to the user equipment by the other mobility management entity, and performing a connection with the other mobility management entity by the user equipment. According to the present invention, user equipment can be efficiently connected with a mobility management entity in a wireless communication system.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a wireless communication system and method and, in particular, to a wireless communication system and a method for establishing a connection between a user equipment and a mobility management entity. 
     2. Description of the Related Art 
     Universal Mobile Telecommunications System (UMTS) is a third generation wireless communication system based on the Global System for Mobile communication (GSM) and General Packet Radio Services (GPRS) and using Wideband Code Division Multiple Access (WCDMA). The 3 rd  Generation Partnership Project (3GPP) for UMTS has proposed Evolved Packet System (EPS) such as Long Term Evolution (LTE). LTE is a technology for high speed packet-based communication network. An LTE mobile communication system is provided with a Mobility Management Entity (MME) which is connected to the User Equipment (UE) and responsible for managing mobility of the UE. 
     DISCLOSURE OF INVENTION 
     Technical Problem 
     With the diversification of the communication services provided by the wireless communication system, the UE is also equipped with various supplementary functions. The MME is configured to support the supplementary functions of the UE. In order to use the communication service associated with a supplementary function, the UE has to connect to the MME supporting the supplementary function. There is therefore a need of a method for a UE to connect the MME supporting the corresponding supplementary function efficiently. 
     Solution to Problem 
     In accordance with an aspect of the present invention, a method for connection between a user equipment and a mobility management entity in a wireless communication system includes requesting, at a base station when a user equipment is connected, identity information for the user equipment to a mobility management entity; determining, at the mobility management entity, whether to allocate the identity information to the user equipment; requesting, when determined not to allocate the identity information, another mobility entity for the identity information; allocating, at the other mobility entity, the identity information to the user equipment; and attempting, at the user equipment, connection to the other mobility management entity with the identity information. 
     Preferably, determining includes judging whether the mobility management entity has a function supporting the user equipment; determining, when the mobility management entity has the function supporting the user equipment, allocation of the identity information; and determining, when the mobility management entity has no function supporting the user equipment, no allocation of the identity information. 
     Preferably, determining includes judging whether a load of the mobility management entity is greater than a predetermined threshold value; determining, when the load is greater than the threshold value, not allocation of the identity information; and determining, when the load is not greater than the threshold value, allocation of the identity information. 
     In accordance with another aspect of the present invention, a wireless communication system includes a user equipment having identity information; a mobility management entity which allocates the identity information to the user equipment, establishes a connection with the user equipment using the identity information, and manages mobility of the user equipment; and a base station which selects, when the user equipment is connected, the mobility management entity to request for the identity information, wherein the mobility management entity determines, when the base station request for the identity information, whether to allocate the identity information to the user equipment and requests, when determined not to allocate the identity information, another mobility entity for the identity information. 
     Preferably, the mobility management entity judges whether the mobility management entity has a function supporting the user equipment, determining, when the mobility management entity has the function supporting the user equipment, allocation of the identity information and, otherwise, no allocation of the identity information. 
     Preferably, the other mobility management entity judges whether a load of the mobility management entity is greater than a predetermined threshold value and determines, when the load is greater than the threshold value, not allocation of the identity information and, otherwise, allocation of the identity information. 
     Advantageous Effects 
     The wireless communication system and a method for establishing a connection between the UE and MME in the wireless communication system according to the present invention to solve the above problem is capable of establishing a connection between the UE and the MME efficiently. That is, through the cooperation between the base station and the MME or among the MMEs, it is possible to establish a connection between the UE and the MME efficiently. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram illustrating a configuration of a wireless communication system according to an embodiment of the present invention, 
         FIG. 2  is a signaling diagram illustrating a connection procedure in the wireless communication system according to the first embodiment of the present invention, 
         FIG. 3  is a flowchart illustrating the operation procedure of the MME of  FIG. 2 , 
         FIG. 4  is a flowchart illustrating the operation procedure of the eNB of  FIG. 2 , 
         FIG. 5  is a signaling diagram illustrating a connection procedure in the wireless communication according to the second embodiment of the present invention, 
         FIG. 6  is a flowchart illustrating the operation procedure of the normal MME of  FIG. 5 , 
         FIG. 7  is a flowchart illustrating the operation procedure of the MTC MME of  FIG. 5 , 
         FIG. 8  is a signaling diagram illustrating a connection procedure in the wireless communication system according to the third embodiment of the present invention, 
         FIG. 9  is a flowchart illustrating the operation procedure of the normal MME of  FIG. 8 , 
         FIG. 10  is a signaling diagram illustrating a connection procedure in the wireless communication system according to the fourth embodiment of the present invention, 
         FIG. 11  is a flowchart illustrating the operation procedure of the normal MME of  FIG. 10 , 
         FIG. 12  is a signaling diagram illustrating the connection procedure in the wireless communication system according to the fifth embodiment of the present invention, 
         FIG. 13  is a flowchart illustrating the operation procedure of the normal MME of  FIG. 12 , 
         FIG. 14  is a flowchart illustrating the operation procedure of the eNB of  FIG. 12 , 
         FIG. 15  is a signaling diagram illustrating a connection procedure in the wireless communication system according to the sixth embodiment of the present invention, 
         FIG. 16  is a flowchart illustrating the operation procedure of the normal MME of  FIG. 15 , and 
         FIG. 17  is a flowchart illustrating the operation procedure of the eNB of  FIG. 15 . 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     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. 
       FIG. 1  is a block diagram illustrating a configuration of a wireless communication system according to an embodiment of the present invention. 
     Referring to  FIG. 1 , the wireless communication system of this embodiment includes a UE  10 , an enhanced Node B (eNB)  20 , an MME  30 , a Serving Gateway (S-GW)  40 , and a Packet Data Network Gateway (P-GW)  50 . 
     The UE  10  may be fixed or mobile. The UE  10  can be a normal UE for performing normal communication function or a Machine Type Communication (MTC) UE for performing MTC function. Here, MTC technology can be applied to smart metering for automated communication between the power company server and electric meter reader and alarm system for automated communication between the security company server and an illegal intrusion alarm. 
     The eNB  20  manages a cell. At this time, the eNB  20  is a macro eNB, and the cell is a macro cell as a cell of a typical cellular system. Here, the terms “eNB” and “cell” can be interchangeably used in the same meaning. The eNB  20  connects to the UE  10  through a radio channel and controls radio resource. For example, the eNB generates and broadcasts system information necessary for control within the cell and allocates radio resource for transmitting/receiving packet data or control information to/from the UE  10 . The system information is capable of including carrier information (PLMN ID), eNB Cell Global ID (ECGI), and Tracking Area ID (TAI) of each cell. The eNB is capable of collecting channel measurement result information for the serving and neighbor cells to make a handover decision and command handover. In order to achieve this, the eNB  20  is provided with the control protocol such as Radio Resource Control Protocol related to the radio resource management. 
     The MME  30  manages UE  10  in idle mode and selects the S-GW  40  and the P-GW  50 . The MME  30  is responsible for roaming and authentication functions. The MME  30  also processes bearer signals generated by the UE  10 . In order to achieve this, the MME  30  allocates identity information to the UE  10  and manages the connection with the UE  10  using the identity information. At this time, the MME  30  can be a normal MME for supporting the normal UEs or a MTC MME for supporting the MTC UEs. Here, the MME  30  is cable of having a unique entity ID which allows for identifying the normal MME and MTC MME. 
     The MME  30  connects to the eNB  20  through a radio channel and connects to the UE  10  via the eNB  20 . Here, the MME  30  connects to the eNB via S1-MME interface. At this time, the MME  30  communicates with the UE  10  using Non Access Stratum (NAS) message. The MME  30  supports a plurality of tracking areas and is connected with a plurality of eNBs  20  providing respective tracking area information. That is, a plurality of eNBs  20  providing the same tracking area information can be connected with the MME  30 . It is also possible for the plural eNBs  20  proving different tracking area informations to connect to the respective MMEs  30 . It is also possible for the plural eNBs  20  supporting different tracking areas to be connect to the same MME  30 . 
     The S-GW  40  connects to the eNB  20  and the MME  30  through radio channels. Here, the S-GW  40  connects to the eNB  20  through S1-U interface. The S-GW  320  is responsible for the UE mobility control function. That is, when the UE  10  performs handover between eNBs or roams across 3gpp radio network networks, the S-GW  40  acts as a mobility anchor of the UE  10 . 
     The P-GW  50  connects to the S-GW  40  through a radio channel. Here, the P-GW  50  connects to the S-GW via S5 interface. The P-GW  50  connects to the Internet Protocol (IP) network  60 . The P-GW  50  is responsible for IP address allocation to the UE  10  and packet data-related functions. That is, the P-GW  50  delivers the packet data received through the IP network  60  to the UE  10  via the S-GW  40  and the eNB  20 . When the UE moves between the 3GPP radio network and non-3GPP radio network, the P-GW  50  acts as the mobility anchor of the UE  10 . The P-GW  50  also determines the bearer bandwidth for the UE  10  and performs packet data forward and routing function. 
     The wireless communication system is capable of further including a Home Subscriber Server (HSS) (not shown). The HSS stores the subscriber information per UE. When the UE  10  attempts attachment to the network, the HSS provides the MME  30  with the information related to the UE  10  for use in controlling the UE  10 . 
     Once it has connected to the eNB  20  of the wireless communication system, the UE  10  connects to the IP network  60  through a data path consisting of the eNB  20 , the S-GW  40 , and the P-GW  50  so as to exchange packet data. The UE  10  is also capable of transmitting a NAS request to the MME  30  via the eNB  20 . The NAS message is capable of including request including at least one of attach request, tracking area update request, or service request. Upon receiving the NAS request message, the eNB  20  selects MME  30  according to the Network Node Selection Function (NNSF) and sends the NAS request message to the selected MME  30 . This is because the eNB  20  is capable of being connected to a plurality of MMEs  30  individually through S1-MME interface. 
     In this embodiment, although the description is directed to the case where the UE  10  is an MTC UE, the eNB  20  is connected to the respective normal MME and MTC MME, the present invention is not limited thereto. That is, although the normal UE is replaced by MTC UE implemented with a specific function and the MME is replaced by MTC MME implemented to support other type of UE, the present invention is applicable. 
       FIG. 2  is a signaling diagram illustrating a connection procedure in the wireless communication system according to the first embodiment of the present invention. 
     Referring to  FIG. 2 , the connection procedure between the MTC UE  11  and MTC MME  330  starts in such a way that the MTC UE  11  establishes an RRC connection with the eNB  20 . When it attaches to the radio network initially or enters the cell supporting the tracking area information, the MTC UE  11  is capable of performing initial RRC connection to the eNB  20  to establish the connections to the MMEs  30 ,  31 , and  33 . 
     The MTC UE  11  sends the eNB  20  an RRC Connection Request message at step  111 . Since it is the initial connection to the eNB  20 , the MTC UE  11  sends the UE ID in the form of a Random Value through in the RRC connection request message. Upon receipt of the RRC connection request message, the eNB  20  sends the MTC UE  11  an RRC Connection Setup message at step  113 . Upon receipt of the RRC Connection Setup message, the MTC UE  11  sends the eNB  20  an RRC Connection Setup Complete message at step  115 . At this time, the MTC UE  11  transmits the NAS request message to the MTC MME  33  in the RRC Connection Setup Complete message. Here, the MTC UE  11  is capable of transmitting the RRC Connection Request message or the RRC Connection Setup Complete message with an MTC indicator for indicating that the UE is the MTC UE. The MTC UE  11  is also capable of inserting the entity ID of the MME entity  30 ,  31 , or  33  to which it has connected previously in the RRC Connection Setup Complete message. 
     Once the connection has been established with the MTC UE  11 , the eNB  20  selects one of a plurality of MMEs  30 ,  31 , and  33  at step  117 . At this time, the eNB  20  determines whether the RRC Connection Setup Complete message includes an entity ID. If an entity ID is included, the eNB selects the MME identified by the entity ID. If no entity ID is included, the eNB  20  selects an MME  30 ,  31 , or  33  arbitrarily. If it has no S1-MME interface connection with the MME identified by the entity ID, the eNB  20  selects an MME  30 ,  31 , or  33  arbitrarily. Here, the eNB  20  is capable of determining whether the RRC Connection Request message or the RRC Connection Setup Complete message includes the MTC indicator. If no MTC indicator is included, the eNB  20  selects the normal MME  31 . Otherwise, if the MTC indicator is included, the eNB  20  selects the MTC MME  33 . 
     Once the MTC MME  33  has been selected, the eNB  20  sends the MTC MME  33  an Initial UE message for the MTC UE  11  at step  119 . At this time, the eNB  20  transmits the RRC Connection Setup Complete message in the NAS Request message. Upon receipt of the Initial UE Request message, the MTC MME  33  sends the MTC UE  11  an Initial UE Response message at step  121  via the eNB  20 . At this time, the MTC MME  33  generates the NAS Response message by processing the request data in the NAS Request message. The MTC MME  33  also transmits the NAS Response message in the NAS message. The MTC MME  33  is capable of transmitting Global Unique Temporary ID (GUTI) as the identity information for the MTC UE  11  in the NAS response message. Here, the GUTI includes the information on the carrier supported by the eNB  20  connected currently to the MTC MME  33 , MME Group ID of the MME  33 , entity ID of the MTC MME  33 , and MME-Temporary Mobile Subscriber ID (M-TMSI) which the MTC MME  33  allocates to the MTC UE  11 ; and the SAE Temporary Mobile Subscriber ID consists of the entity ID and M-TMSI. 
     Meanwhile, the MTC UE  11  is capable of re-attempting RRC connection with the eNB  20 . That is, when it transitions from the idle mode to the active mode or enters a cell supporting the tracking area information that has been identified already, the MTC UE  11  is capable of attempting RRC connection to the eNB  20  for re-establishing the connection to the MME  30 ,  31 , or  33  to which it has connected. 
     That is, the MTC UE  11  sends the eNB  20  the RRC Connection Request message at step  141 . Since it is a retry for connection to the eNB  20 , the MTC UE  11  includes the S-TMSI as the UE ID in the RRC Connection Request message. Upon receipt of the RRC Connection Request message, the eNB  20  sends the MTC UE  11  the RRC Connection Setup message at step  143 . Upon receipt of the RRC Connection Setup message, the MTC UE  11  sends the eNB  20  the RRC Connection Setup Complete message at step  145 . At this time, the MTC UE  11  transmits the NAS Request message for the MTC MME  33  in the RRC Connection Setup Complete message. 
     Once the MTC UE  11  has connected, the eNB  20  selects one of the plural MMEs  30 ,  31 , and  33  at step  147 . At this time, the eNB  20  determines whether the RRC Connection Setup Complete message includes the entity ID. If the entity ID is included, the eNB  20  selects the MME identified by the entity ID. That is, the eNB  20  checks the entity ID with S-TMSI included in the RRC Connection Request message and selects the entity matched with the entity ID. If no entity ID is included, the eNB  20  selects an MME  30 ,  31 , or  33  arbitrarily. In case that it has not S1-MME interface connection with the MME identified by the entity ID, the eNB  20  selects an MME  30 ,  31 , or  33  arbitrarily. 
     Once the MTC MME  33  has been selected, the eNB  20  sends the MTC MME  33  an Initial UE Request message for the MTC UE  11  at step  149 . At this time, the eNB  20  transmits the NAS Request message carried in the RRC Connection complete message. Upon receipt of the Initial UE request message, the MTC MME  33  sends the MTC UE  11  an Initial UE Response message via the eNB  20  at step  151 . At this time, the MTC MME  33  generates the NAS Response message by processing the request data in the NAS Request message. The MTC MME  33  transmits the NAS message including the NAS Response message. 
     The operation procedure between the MME  30 ,  31 , and  33  and the eNB  20  according to an embodiment of the present invention is described hereinafter. 
       FIG. 3  is a flowchart illustrating the operation procedure of the MME  30 ,  31 , or  33  of  FIG. 2 . 
     Referring to  FIG. 3 , if a NAS request message is received from the UE  10  or  11 , the MME  30 ,  31 , or  33  detects this at step  161  and determines whether to assign GUTO to the UE  10  or  11  at step  163 . That is, the MME  30 ,  31 , or  33  determines whether the GUTI has been assigned to the UE  10  or  11 . If it is determined that the GUTI has not been assigned to the UE  10  or  11  at step  163 , the MME  30 ,  31 , or  33  assigns a GUTI to the UE  10  or  11  at step  165 . The MME  30 ,  31 , or  33  also sends the UE  10  or  11  the NAS Response message including the corresponding GUTI at step  167 . 
     Otherwise, if it is determined that the GUTO has been assigned to the UE  10  or  11 , the MME  30 ,  31 , or  33  sends the UE  10  or  11  the NAS Response message via the eNB  20 . 
       FIG. 4  is a flowchart illustrating the operation procedure of the eNB  20  of  FIG. 2 . 
     Referring to  FIG. 4 , the eNB  20  of the present embodiment establishes an RRC connection with the UE  10  or  11  at step  181 . If a NAS request message is received from the UE  10  or  11 , the eNB  20  detects the message and selects an MME  30 ,  31 , or  33  at step  185 . If an entity IE is received along with the NAS request message, the eNB  20  selects the MME  30 ,  31 , or  33  matched with the entity ID. If no entity ID is received, the eNB  20  selects an MME  30 ,  31 , or  33  arbitrarily. If an MTC indicator is received along with the NAS request message, the eNB  20  selects the MTC MME  33 . Otherwise, if no MTC indicator is received, the eNB  20  selects the normal MME  31 . The eNB  20  sends the MME  30 ,  31 , or  33  the NAS request message at step  187 . If the NAS Response message is received from the MME  30 ,  31 ,  33 , the eNB  20  detects this at step  189  and delivers the NAS response message to the UE  10  or  11  at step  191 . 
     Although the above description has been directed to the exemplary case where the eNB  20  selects the MTC MME  33  for the MTC UE  11  in initial RRC connection with the MTC UE  11  in the first embodiment of the present invention, the present invention is not limited thereto. That is, when selecting an MME  30 ,  31 , or  33  arbitrarily, although the eNB  20  selects the normal MME  31 , the present invention can be implemented. Such examples are described in the second to sixth embodiments of the present invention. 
       FIG. 5  is a signaling diagram illustrating a connection procedure in the wireless communication according to the second embodiment of the present invention. 
     Referring to  FIG. 5 , the connection establishment procedure between the MTC UE  11  and the MTC MME  33  according the present embodiment starts in such a way that the MTC UE  11  attempts to establish an RRC connection to the eNB  20 . When it attempts initial attachment to the radio network or enters a cell supporting the tracking area information, the MTC UE  11  is capable of establishing the initial RRC connection to the eNB  20  to connect to a new MME  30 ,  31 , or  33 . 
     The MTC UE  11  sends the eNB  20  an RRC connection request message at step  211 . Since it is the initial connection to the eNB  20 , the MTC UE  11  transmits a random value of the UE ID in the RRC connection request message. If the RRC connection request message is received, the eNB  20  sends an RRC connection setup message to the MTC UE  11  at step  213 . In response to the RRC connection setup message, the UE  11  sends an RRC connection complete message to the eNB  20  at step  215 . At this time, the MTC UE  11  transmits an NAS request message for the MTC MME  33  in the RRC connection complete message. Here, the MTC UE  11  is capable of inserting the entity ID of the MME  30 ,  31 , or  33  to which it has connected in the RRC connection complete message. 
     If the MTC UE  11  has connected, the eNB  20  selects one of a plurality of MMEs  30 ,  31 , and  33  at step  217 . At this time, the eNB  20  determines whether the RRC connection complete message includes an entity ID. If an entity ID is included, the eNB  20  selects the MME  30 ,  31 , or  33  identified by the entity ID. Otherwise, if no entity ID is included, the eNB  20  selects an MME  30 ,  31 , or  33  arbitrarily. If there is no connection with the MME  30 ,  31 , or  33  through the S1-MME interface, the eNB  20  selects an MME  30 ,  31 , or  33  arbitrarily. 
     If the selected MME is the normal MME  31 , the eNB  20  sends the normal MME  31  an initial UE request message for the MTC UE  11  at step  219 . At this time, the eNB  20  transmits the NAS request message carried in the RRC connection complete message. If the initial UE request message in received, the normal MME  31  checks that the NAS request message is transmitted from the MTC UE  11  in the initial UE request message at step  221 . For example, the eNB  20  delivers the MTC indicator received from the MTC UE  11  to the normal MME  31  such that the normal MME  31  identifies the MTC UE  11 . Also, it is possible for the normal MME  31  to identify the MTC UE  11  based on the MTC indicator included in the subscriber information of the MTC UE  11  which is transmitted by the HSS. Also, it is possible for the normal MME  31  to identify the MTC UE  11  based on the random value selected in the range allowed for normal UE as UE ID. 
     Next, the normal MME  31  sends a GUTI allocation request message to the MTC MME  33  at step  223 . That is, the normal MME  31  requests the MTC MME  33  for the GUTI of the MTC UE  11 . In response to the GUTI allocation request message, the MTC MME  33  sends the normal MME  31  a GUTI allocation response message at step  225 . That is, the MTC MME  33  provides the normal MME  331  with the GUTI as the identity information for the MTC UE  11 . Here, the GUTI includes the information on the carrier supported by the eNB  20  connected currently to the MTC MME  33 , MME Group ID of the MME  33 , entity ID of the MTC MME  33 , and MME-Temporary Mobile Subscriber ID (M-TMSI) which the MTC MME  33  allocates to the MTC UE  11 ; and the S-TMSI consists of the entity ID and M-TMSI. If the GUTI allocation response message is received, the normal MME  31  is capable of transmits UE context of the MTC UE  11  to the MTC MME  33  at step  227 . 
     Next, the normal MME  31  sends the MTC UE  11  an initial UE response message via the eNB  20  at step  229 . At this time, the normal MME  31  generates the NAS response message by processing the request data included in the NAS request message. The normal MME  31  also includes the GUTI for the MTC UE  11  in the NAS response message. 
     Meanwhile, the MTC UE  11  is capable of retries RRC connection to the eNB  20 . That is, when it wakes up and transitions from the idle mode to the active mode or enters the cell supporting the tracking area information that has been identified already, the MTC UE  11  is capable of retrying RRC connection to the eNB  20  for reconnection to the MME  30 ,  31 , or  33 . 
     That is, the MTC UE  11  transmits the RRC connection request message to the eNB  20  at step  241 . Since it is the retry for connection, the MTC UE  11  transmits the RRC connection request message configured with the S-TMSI as the UE ID. If the RRC connection request message is received, the eNB  20  sends the MTC UE  11  the RRC connection setup message at step  243 . If the RRC connection setup message is received, the MTC UE  11  sends the RRC connection complete message to the eNB  20  at step  245 . At this time, the MTC UE  11  transmits the NAS request message for the MTC MME  33  in the RRC connection complete message. 
     Once the MTC UE  11  has connected, the eNB  20  selects one of the plural MMEs  30 ,  31 , or  33  at step  247 . At this time, the eNB  20  determines whether the RRC connection complete message includes an entity ID. If an entity ID is included, the eNB  20  selects the MME identified by the entity ID. That is, the eNB  20  checks the entity ID based on the S-TMSI included in the RRC connection request message and selects the MME  30 ,  31 , or  33  matched to the entity ID. If not entity ID is included, the eNB selects an MME  30 ,  31 , or  33  arbitrarily. If there is no connection with the MME  30 ,  31 , or  33  matched to the entity ID through S1-MME interface, the eNB  20  selects an MME  30 ,  31 , or  33  arbitrarily. 
     Once the MTC MME  33  has been selected, the eNB  20  sends the MTC MME  22  the initial UE request message for the MTC UE  11  at step  249 . Here, the eNB  20  transmits the NAS request message in the RRC connection complete message. If the initial UE request message is received, the MTC MME  33  is capable of sending the normal MME  31  a UE context request message for the MTC UE  11  at step  251 . If the UE context request message is received, the normal MME  31  is capable of sending the MTC MME  33  a UE context response message including the UE context at step  253 . Afterward, the MTC MME  33  sends the MTC UE  11  the initial UE response message via the eNB  20  at step  255 . At this time, the MTC MME  33  generates the NAS message by processing the request data included in the NAS request message. The MTC MME  33  also transmits the NAS response message in the NAS message. 
     Descriptions are made of the operation procedures of the normal MME  31  and MTC MME  33  hereinafter. Since the operation procedure of the eNB  20  in the present embodiment is similar to that of the first embodiment of the present invention, detailed description thereon is omitted herein. 
       FIG. 6  is a flowchart illustrating the operation procedure of the normal MME  31  of  FIG. 5 . 
     Referring to  FIG. 6 , if an NAS request message is received from the UE  10  or  11 , the normal MME  31  detects this at step  261  and determines whether to allocate GUTI to the UE  10  or  11  at step  263 . That is, the normal MME  31  determines whether the UE  10  or  11  has been assigned the GUTI already. If it is determined to allocate GUTI at step  263 , the normal MME  31  determines whether the UE  10  or  11  is the MTC UE  11  at step  265 . If it is determined that the UE  10  or  11  is the MTC UE  11  at step  265 , the normal MME  31  sends the MTC MME  33  a GUTI allocation request message at step  267 . Afterward, if a GUTI allocation response message is received from the MTC MME  33 , the normal MME  31  detects this at step  269  and sends the UE  10  or  11  a NAS response message including the corresponding GUTI at step  271 . 
     Otherwise, if it is determined that the UE  10  or  11  is not the MTC UE  11  at step  265 , the normal MME  31  allocates a GUTI to the UE  10  or  11  at step  270 . Next, the normal MME  31  sends the UE  10  or  11  the NAS response message including the GUTI at step  271 . If it is determined that there is no need to allocate GUTI to the UE  10  or  11  at step  263 , the normal MME  31  sends the UE  10  or  11  a NAS response message via the eNB  20  at step  275 . 
       FIG. 7  is a flowchart illustrating the operation procedure of the MTC MME  33  of  FIG. 5 . 
     Referring to  FIG. 7 , if a GUTI allocation request message is received from the normal MME  31 , the MTC MME  33  detects this at step  281  and sends the normal MME  31  a GUTI allocation response message at step  283 . If no GUTI allocation request message is received but a NAS request message is received from the UE  10  or  11 , the MTC MME  33  detects this at step  285  and sends the UE  10  or  11  the NAS response message via the eNB  20  at step  287 . 
     Although the description has been directed to the case where the normal MME  31  and MTC MME  33  communicate to each other directly in the second embodiment of the present invention, the present invention is not limited thereto. That is, even when the normal MME  31  and the MTC MME  33  are not communication directly, the present invention can be implemented. Such an example is described in the third embodiment of the present invention hereinafter. 
       FIG. 8  is a signaling diagram illustrating a connection procedure in the wireless communication system according to the third embodiment of the present invention. 
     Referring to  FIG. 8 , the connection procedure between the MTC UE  11  and the MTC  33  according to the third embodiment starts in such a way that the normal MME  31  retains the list of GUTIs, i.e. MTC GUTIs, as the identity information that can be allocated by the MTC MME  33  at step  311 . At this time, the MTC MME  33  sends the list of the MTC GUTIs directly to the normal MME  31  such that the normal MME  31  stores the MTC GUTI list. The MTC MME  33  registers the MTC GUTI list with an Operation and Management (O&amp;M) server (not shown) which provides the normal MME  31  with the MTC GUTI such that the normal MME  31  is capable of storing the list of the MTC GUTIs. Here, the GUTI includes the information on the carrier supported by the eNB  20  connected currently to the MTC MME  33 , MME Group ID of the MME  33 , entity ID of the MTC MME  33 , and MME-Temporary Mobile Subscriber ID (M-TMSI) which the MTC MME  33  allocates to the MTC UE  11 ; and the S-TMSI consists of the entity ID and M-TMSI. 
     Next, the MTC UE  11  attempts the RRC connection to the eNB  20 . When it attempts initial attachment to the radio network or enters the cell supporting the tracking area information, the MTC UE  11  is capable of attempting the initial RRC connection to the eNB  20  to establishing connection to the MME  30 ,  31 , or  33 . 
     That is, the MTC UE  11  sends the eNB  20  an RRC connection request message at step  313 . Since it is the initial attachment to the eNB  20 , the MTC UE  11  sends a random value as the UE ID in the RRC connection request message. If the RRC connection request message is received, the eNB  20  sends the MTC UE  11  an RRC connection setup message at step  315 . In response to the RRC connection setup message, the MTC UE  11  sends the eNB  20  an RRC connection complete message at step  317 . At this time, the MTC UE  11  transmits a NAS request message for the MTC MME  33  in the RRC connection complete message. Here, the MTC UE  11  is capable of further including the entity ID of the MME  30 ,  31 , or  33  to which it has connected previously in the RRC connection complete message. 
     Once the MTC UE  11  has connected, the eNB  20  selects one of the plural MMEs  30 ,  31 , and  33  at step  319 . At this time, the eNB  20  determines whether the RRC connection complete message includes an entity ID. If an entity ID is included, the eNB  20  selects the MME  30 ,  31 , or  33  matched with the entity ID. Otherwise, if no entity ID is included, the eNB  20  selects an MME  30 ,  31 , or  33  arbitrarily. If it is not connected to the MME  30 ,  31 , or  33  match with the entity ID through S1-MME interface, the eNB selects an MME  30 ,  31 , or  33  arbitrarily. 
     If the normal MME  31  is selected, the eNB  20  sends the normal MME  31  an initial UE request message addressed to the MTC UE  11  at step  321 . At this time, the eNB  20  transmits the NAS request message carried in the RRC connection complete message. If the initial UE request message is received, the normal MME  31  checks that the NAS message carried in the initial UE request message has been transmitted by the MTC MME  11  at step  323 . For example, the eNB  20  transmits the MTC indicator received from the MTC UE  11  to the normal MME  31  such that the normal MME  31  identifies the MTC UE  11 . Also, it is possible for the HSS to transmit the MTC indicator in the subscriber information of the MTC UE  11  to the normal MME  31  such that the normal MME  31  identifies the MTC UE  11 . Also, it is possible for the MTC UE  11  uses a random value selected in the range discriminated from that for the normal UE such that the normal MME  31  identifies the MTC UE  11 . The normal MME  31  determines the GUTI for the MTC UE  11  from the MTC GUTI list and marks the GUTI as being used at step  324 . The normal MME  31  is capable of transmitting the UE context of the MTC UE  11  to the MTC MME  33  at step  325  and then checking that the GUTI for the MTC UE  11  is not used from the MTC GUTI list at step  326 . 
     Next, the normal MME  31  sends the MTC UE  11  an initial UE response message via the eNB  20  at step  327 . At this time, the normal MME  31  generates a NAS response message by processing the request data in the NAS request message. The normal MME  31  transmits the NAS response message in the NAS message. The normal MME  31  is also capable of transmitting the GUTI selected from the MTC GUTI list in the NAS response message. 
     The MTC UE  11  is capable of retrying the RRC connection to the eNB  20 . After wake-up from the idle mode when it transitions from the idle mode to the active mode or enters the cell supporting the tracking area information that has been identified already, the MTC UE  11  is capable of retrying the RRC connection to the eNB  20  to reestablish the connection to the MME  30 ,  31 , or  33  to which it has connected previously. 
     That is, the MTC UE  11  sends the eNB  20  an RRC connection request message at step  341 . Since it is the retry of the connection to the eNB  20 , the MTC UE  11  transmits the RRC connection request message with the 5-TMSI as the UE ID. If the RRC connection request message is received, the eNB  20  sends the MTC UE  11  an RRC connection setup message at step  343 . In response to the RRC connection setup message, the MTC UE  11  sends the eNB  20  an RRC connection complete message at step  345 . At this time, the MTC UE  11  transmits the NAS request message for the MTC MME  33  in the RRC connection complete message. 
     If the MTC UE  11  has connected, the eNB  20  selects one of the plural MMEs  30 ,  31 , and  33  at step  347 . At this time, the eNB determines whether the RRC connection complete message includes an entity ID. If an entity ID is included, the eNB  20  selects the MME  30 ,  31 , or  33  matched with entity ID. That is, the eNB  20  checks the entity ID based on the S-TMSI included in the RRC connection request message and selects the MME  30 ,  31 , or  33  matched with the entity ID. If no entity ID is included, the eNB  20  selects an MME  30 ,  31 , or  33  arbitrarily. Also, if it has not connected to the MME  30 ,  31 , or  33  matched with the entity ID through S1-MME interface, the eNB  20  selects an MME  30 ,  31 , or  33  arbitrarily. 
     Once the MTC MME  33  has been selected, the eNB  20  sends the MTC MME  33  an initial UE request message for the MTC UE  11  at step  349 . Here, the eNB  20  transmits the NAS request message carried in the RRC connection complete message. If the initial UE request message is received, the MTC MME  33  is capable of transmitting a UE context request message for the MTC UE  11  to the normal MME  31  at step  351 . If the UE context request message is received, the normal MME  31  sends the MTC MME  33  a UE context response message including the UE context at step  353  and marks the GUTI for the MTC UE  11  as not being used in the MTC GUTI list at step  354 . Although not depicted, when the UE context request message is received, the normal MME  31  is capable of checking the GUTI for the MTC UE  11  as being not used in the MTC GUTI list and then transmits the UE context response message. Afterward, the MTC MME  33  sends the MTC UE  11  an initial UE response message via the eNB  20  at step  355 . At this time, the MTC MME  33  generates the NAS response message by processing the request data in the NAS request message. The MTC MME  33  transmits the NAS response message in the NAS message. 
     A description is made of the operation procedure of the normal MME  31  according to this embodiment hereinafter. Since the operation procedures of the eNB  20  and the MTC MME  33  according to this embodiment are similar to those in the first embodiment, detailed descriptions thereon are omitted herein. 
       FIG. 9  is a flowchart illustrating the operation procedure of the normal MME  31  of  FIG. 8 . 
     Referring to  FIG. 9 , the normal MME  31  retains the MTC GUTI list in the embodiment at step  361 . At this time, the normal MME  31  also stores a list of GUTIs that the normal MME  31  can allocate, i.e. normal GUTI list in addition to the MTC GUTI list. If a NAS request message is received from the UE  10  or  11 , the normal MME  31  detects this and determines whether to allocate GUTI to the UE  10  or  11  at step  363 . That is, the normal MME  31  determines whether it has allocated a GUTI to the UE  10  or  11  previously. If it is determined to allocate a GUTI to the UE  10  or  11  at step  365 , the normal MME  31  determines whether the UE  10  or  11  is an MTC UE  11  at step  367 . If it is determined that the UE  10  or  11  is the MTC UE  11  at step  367 , the normal MME  31  allocates an GUTI selected from the MTC GUTI list to the UE  10  or  11 . Afterward, the normal MME  31  sends the UE  10  or  11  a NAS response message including the corresponding GUTI at step  371 . 
     Otherwise, if it is determined that the UE  10  or  11  is not the MTC UE  11  at step  367 , the normal MME  31  allocates the GUTI selected from the normal GUTI rest to the UEs  10  or  11  at step  370 . Next, the normal MME  31  sends the UE  10  or  11  the NAS response message including the corresponding GUTI at step  371 . If it is not necessary to allocate a GUTI to the UE  10  or  11  at step  365 , the normal MME  31  sends the UE  10  or  11  the NAS response message via the eNB  20  at step  375 . 
     Although the description has been directed to the case where normal MME  31  delivers the GUTI allocated by the MTC MME  33  to the MTC UE  11  in the initial RRC connection between the MTC UE  11  and the eNB  20  in the second and third embodiments, the present invention is not limited thereto. That is, the present invention can be implemented in such a way that the MTC MME  33  is capable of allocating and transmitting the GUTI for the MTC UE  11 . Such an example is described hereinafter in the fourth embodiment of the present invention. 
       FIG. 10  is a signaling diagram illustrating a connection procedure in the wireless communication system according to the fourth embodiment of the present invention. 
     Referring to  FIG. 10 , the connection procedure between the MTC UE  11  and the MTC MME  33  according to the this embodiment starts in such a way that the MTC UE  11  attempts RRC connection to the eNB  20 . At this time, when it tries initial attachment to the radio network or enters the cell supporting the tracking area information, the MTC UE  11  is capable of initial RRC connection to the eNB  20  to establish the connection to a new MME  30 ,  31 , or  33 . 
     That is, the MTC UE  11  sends the eNB  20  the RRC connection request message at step  411 . Since it is the initial attachment, the MTC UE  11  transmits a random value as the UE ID in the RRC connection request message. If the RRC connection request message is received, the eNB  20  sends the MTC UE  11  an RRC connection setup message at step  413 . If the RRC connection setup message is received, the MTC UE  11  sends an RRC connection complete message to the eNB  20  at step  415 . At this time, the MTC UE  11  transmits a NAS request message for the MTC MME  33  in the RRC connection complete message. here, the MTC UE  11  is capable of further including the entity ID of the MME  30 ,  31 , or  33  to which is has connected previously in the RRC connection complete message. 
     Once the MTC UE  11  has connected, the eNB  20  selects one of a plurality of MMEs  30 ,  31 , and  33  at step  417 . At this time, the eNB  20  determines whether the RRC connection complete message includes an entity ID. If an entity ID is included, the eNB  20  selects the MME  30 ,  31 , or  33  matched with the entity ID. If no entity ID is included, the eNB  20  selects an MME  30 ,  31 , or  33  arbitrarily. Also, if it has not connected to the MME  30 ,  31 , or  33  matched with the entity ID via S1-MME interface, the eNB  20  selects an MME  30 ,  31 , or  33  arbitrarily. 
     Once the normal MME  31  has been selected, the eNB  20  sends the normal MME  31  an initial UE request message for the MTC UE  11  at step  419 . At this time, the eNB  20  transmits the NAS request message carried in the RRC connection complete message. If the initial UE request message is received, the normal MME  31  determines whether the NAS request message carried in the initial UE request message is transmitted by the MTC UE  11  at step  421 . For example, the eNB  20  transmits the MTC indicator received from the MTC UE  11  to the normal MME  31  such that the normal MME  31  identifies the MTC UE  11 . Also, it is possible for the HSS to transmit the MTC indicator in the subscriber information of the MTC UE  11  such that the normal MME  31  identifies the MTC UE  11 . Also, it is possible for the MTC UE  11  to use a random value selected in the range discriminated from that for the normal UE such that the normal MME  31  identifies the MTC UE  11 . 
     Next, the normal MME  31  sends the MTC MME  33  an initial UE request message for the MTC UE  11  at step  423 . Here, the normal MME  31  is capable of transmitting the initial UE request message using the tunneling technique. If the initial UE request message is received, the MTC MME  33  is capable of transmitting to the normal MME  31  a UE context request message for the MTC UE  11  additionally at step  425 . If the UE context request message is received, the normal MME  31  is capable of transmitting a UE context response message including the UE context to the MTC MME  33  at step  427 . Here, the MTC MME  33  and the MTC UE  11  are capable of perform NAS communication via the eNB  20  and the normal MME  31  at step  429 . That is, the MTC MME  33  and the MTC UE  11  are capable of generating and exchanging NAS messages. Here, the normal MME  31  is capable of exchanging the NAS messages with the MTC MME  33  using the tunneling technique. 
     Next, the MTC MME  33  sends the normal MME  31  an initial UE response message at step  431 . At this time, the MTC MME  33  generates the NAS response message by processing the request data in the NAS request message. Here, the MTC MME  33  is capable of transmitting the NAS response message using the tunneling technique. The MTC MME  33  is capable of transmitting the GUTI allocated as identity information of the MTC UE  11  in the NAS response message. Afterward, if the initial UE response message is received, the normal MME  31  transmits the initial UE response message to the MTC UE  11  via the eNB  20  at step  433 . 
     Meanwhile, the MTC UE  11  is capable of retrying RRC connection to the eNB  20 . After wake-up from the idle mode, when it transitions from the idle mode to the active mode or enters the cell supporting the tracking area information which has been known already, the MTC UE  11  is capable of retrying the RRC connection to the eNB  20  for reestablishing the connection to the MME  30 ,  31 , or  33  to which the MTC MME has connected previously. 
     That is, the MTC UE  11  sends the eNB  20  the RRC connection request message at step  441 . Since it is reconnection to the eNB  20 , the MTC UE  11  transmits the RRC connection request message in which the UE ID is set to the S-TMSI. If the RRC connection request message is received, the eNB  20  sends the MTC UE  11  an RRC connection setup message at step  443 . If the RRC connection setup message is received, the MTC UE  11  sends the eNB  20  an RRC connection complete message at step  445 . At this time, the MTC UE  11  transmits the NAS request message for the MTC MME  33  in the RRC connection complete message. 
     Once the MTC terminal  11  has connected, the eNB  20  selects one of the plural MMEs  30 ,  31 , and  33  at step  447 . At this time, the eNB  20  determines whether the RRC connection complete includes an entity ID. If an entity ID is included, the eNB  20  selects the MME  30 ,  31 , or  33  matched with the entity ID. That is, the eNB  20  checks the entity ID from the S-TMSI of the RRC connection request message and selects the MME  30 ,  31 , or  33  matched with the entity ID. Otherwise, if no entity ID is included, the eNB  20  selects an MME  30 ,  31 , or  33  arbitrarily. Also, if it has not connected to the MME  30 ,  31 , or  33  matched with the entity ID, the eNB  20  selects an MME  30 ,  31 , or  33  arbitrarily. 
     Once the MTC MME  33  has been selected, the eNB  20  sends the MTC MME  33  an initial UE request message for the MTC UE  11  at step  449 . Here, the eNB  20  transmits the NAS request message carried in the RRC connection complete message. If the initial UE request message is received, the MTC MME  33  sends the MTC UE  11  an initial UE response message via the eNB  20  at step  451 . At this time, the MTC MME  33  generates the NAS response message by processing the request data in the NAS request message. The MTC MME  33  transmits the NAS response message in the NAS message. 
     A description is made of the operation procedure of the normal MME  31  according to this embodiment hereinafter. Since the operation procedures of the eNB  20  and the MTC MME  33  according to this embodiment are similar to those of the first embodiment of the present invention, detailed descriptions thereon are omitted herein. 
       FIG. 11  is a flowchart illustrating the operation procedure of the normal MME  31  of  FIG. 10 . 
     Referring to  FIG. 11 , if an NAS request message is received from the UE  10  or  11 , the normal MME  31  detects this at step  461  and determines whether to allocate a GUTI to the UE  10  or  11  at step  463 . That is, the normal MME  31  determines whether the UE  10  or  11  has been allocated a GUTI already. If it is determined that the UE  10  or  11  has been allocated a GUTI already at step  463 , the normal MME  31  determines whether the UE  10  or  11  is the MTC UE  11  at step  465 . If it is determined that the UE  10  or  11  is the MTC UE  11  at step  465 , the normal MME  31  sends the MTC MME  33  a NAS request message at step  467 . Afterward, if an NAS response message including the GUTI for the UE  10  or  11  is received, the normal MME  31  detects this at step  469  and delivers the NAS response message including the corresponding GUTI to the UE  10  or  11  at step  471 . 
     Otherwise, if it is determined that the UE  10  or  11  is not the MTC UE  11  at step  465 , the normal MME  31  allocates a GUTI for the UE  10  or  11  at step  470 . The normal MME  31  delivers the NAS response message to the UE  10  or  11  at step  471 . At this time, the normal MME  31  transmits the NAS response message including the corresponding GUTI. If it is determined that there is no need to allocate a GUTI to the UE  10  or  11  at step  463 , the normal MME  31  sends the UE  10  or  11  the NAS response message via the eNB  20 . 
     Although the description is directed to the case, when the eNB  20  selects the MME  30 ,  31 , or  33  for the MTC UE  11 , the MME  30 ,  31 , or  33  performs operation for allocating GUTI to the MTC  11  in the second to fourth embodiments of the present invention, the present invention is not limited thereto. That is, the present invention is capable of being implemented in such a way that, as well as the MME  30 ,  31 , or  33 , the eNB  20  performs the operation for allocation GUTI to the MTC UE  11 . Such examples are described in the fifth and sixth embodiments of the present invention hereinafter. 
       FIG. 12  is a signaling diagram illustrating the connection procedure in the wireless communication system according to the fifth embodiment of the present invention. 
     Referring to  FIG. 12 , the connection procedure between the MTC UE  11  and the MTC MME  33  according to this embodiment starts in such a way that the MTC UE  11  attempts RRC connection to the eNB  20 . When it attempts initial connection to the radio network or enters a cell supporting the tracking area information which has not been recognized, the MTC UE  11  is capable of attempting initial RRC connection to the eNB  20  to establish the connection to a new MME  30 ,  31 , or  33 . 
     That is, the MTC UE  11  sends the eNB  20  an RRC connection request message at step  511 . Since it is the attempt for initial attachment t 0  the eNB  20 , the MTC UE  11  transmits the RRC connection request message including a random value set as the UE ID. If the RRC connection request message is received, the eNB  20  sends the MTC UE  11  an RRC connection setup message at step  513 . If the RRC connection setup message is received, the MTC UE  11  sends the eNB  20  an RRC connection complete message at step  515 . At this time, the MTC UE  11  transmits the NAS request message for the MTC MME  33  in the RRC connection complete message. Here, the MTC UE  11  is capable of transmitting the RRC connection complete message including the entity ID of the MME  30 ,  31 , or  33  to which it has connected previously. 
     Once the MTC UE  11  has connected, the eNB  20  selects one of the plural MMEs  30 ,  31 , and  33  at step  517 . At this time, the eNB determines whether the RRC connection complete message includes an entity ID. If an entity ID is included, the eNB  20  selects the MME entity  30 ,  31 , or  33  matched with the entity ID. If no entity ID is included, the eNB  20  selects an MME  30 ,  31 , or  33  arbitrarily. Also, if it has not connected to the MME  30 ,  31 , or  33  matched with the entity ID via S1-MME interface, the eNB  20  selects an MME  30 ,  31 , or  33  arbitrarily. 
     If the normal MME  31  has been selected, the eNB  20  sends the normal MME  31  an initial UE request message for the MTC UE  11  at step  519 . At this time, the eNB  20  transmits the NAS request message carried in the RRC connection complete message. Here, the eNB  20  is capable of storing the initial UE request message or the NAS request message. If the initial UE request message is received, the normal MME  31  checks that the NAS request message carried in the initial UE request message has been transmitted by the MTC UE  11  at step  521 . For example, the eNB  20  is capable of transmitting the MTC indicator received from the MTC UE  11  to the normal MME  31  such that the normal MME  31  identifies the MTC UE  11 . Also, it is possible for the HSS to transmit the MTC indicator in the subscriber information of the MTC UE  11  such that the normal MME  31  identifies the MTC UE  11 . Also, it is possible for the MTC UE  11  to use a random value selected in the range discriminated from that for the normal UE such that the normal MME  31  identifies the MTC UE  11 . 
     Next, if the MTC UE  11  has been identified, the normal MME  31  sends the eNB  20  an MME reselection request (UE Redirect Request) message at step  523 . At this time, the normal MME  31  in capable of transmitting the MME reselection request message including the information on the MTC MME  33 , e.g. entity ID. Here, the normal MME  31  is capable of transmitting the NAS request message of the MTC UE  11  in the MME reselection request message. 
     Next, if the MME reselection request message is received, the eNB  20  selects one of the plural MMEs  30 ,  31 , and  33  at step  525 . At this time, the eNB selects the MTC MME  33 . Herein, the eNB  20  determines whether the MME reselection request message includes an entity ID. If an entity ID is included, the eNB  20  selects the MTC MME  33  matched to the entity ID. Otherwise, if no entity ID is included, the eNB  20  selects an MTC MME  33  arbitrarily. Also, if it has not connected to the MME  33  matched with the entity ID via S1-MME interface, the eNB  20  selects the MTC MME  33  arbitrarily. 
     Next, if the MTC MME  33  has been selected, the eNB  20  sends the MTC MME  33  an initial UE request message for the MTC UE  11  at step  527 . The MTC MME  33  sends the MTC UE  11  an initial UE response message via the eNB  20  at step  529 . At this time, the MTC MME  33  generates the NAS response message by processing the request data in the NAS request message. The MTC MME  33  transmits the NAS response message in the NAS message. The MTC MME  33  is also capable of transmitting the NAS response message including the GUTI allocated as the identity information of the MTC UE  11 . 
     The MTC UE  11  is capable of retrying RRC connection to the eNB  20 . That is, after wake-up from the idle mode, when it transitions from the idle mode to the active mode or enters a cell supporting the tracking area information which has not been recognized until then, the MTC UE  11  is capable of retrying RRC connection to the eNB  20  to reestablish the connection to the MME  30 ,  31 , or  33  to which it has connected previously. Next, the MTC UE  11  is capable of attempting connection to the MTC MME  33  via the eNB  20 . Since the connection procedure between the MTC UE  11  and the MTC MME  33  is similar to steps  441  to  451  of  FIG. 10 , detailed description thereon is omitted herein. 
     Descriptions are made of the operation procedures of the normal MME  31  and the eNB  20  according to the present embodiment hereinafter. Since the operation procedure of the MTC MME  33  according to this embodiment is similar to that of the first embodiment of the present invention, detailed description thereon is omitted herein. 
       FIG. 13  is a flowchart illustrating the operation procedure of the normal MME  31  of  FIG. 12 . 
     Referring to  FIG. 13 , if the NAS request message is received from the UE  10  or  11 , the normal MME  31  detects this at step  561  and determines whether to allocate a GUTI to the UE  10  or  11  at step  563 . That is, the normal MME  31  determines whether the UE  10  or  11  has been allocated a GUTI already. If it is determined to allocate a GUTI to the UE  10  or  11  at step  563 , the normal MME  31  determines whether the UE  10  or  11  is the MTC UE  11  at step  565 . If it is determined that the UE  10  or  11  is the MTC UE  11 , the normal MME  31  sends the eNB an MME reselection request message at step  567 . 
     Otherwise, if it is determined that the UE  10  or  11  is not the MTC UE  11  at step  565 , the normal MME  31  allocates a GUTI to the UE  10  or  11  at step  569 . Next, the normal MME  31  sends the UE  10  or  11  a NAS response message at step  571 . At this time, the normal MME  31  transmits the NAS response message including the corresponding GUTI. If it is determined not to allocate a GUTI to the UE  10  or  11  at step  563 , the normal MME  31  sends the UE  10  or  11  a NAS response message via the eNB  20  at step  573 . 
       FIG. 14  is a flowchart illustrating the operation procedure of the eNB  20  of  FIG. 12 . 
     Referring to  FIG. 14 , the eNB  20  tries to establish RRC connection with the UE  10  or  11  at step  581 . Afterward, if a NAS request message is received from the UE  10  or  11 , the eNB  20  detects this at step  583  and selects an MME  30 ,  31 , or  33  at step  585 . At this time, if an entity ID is received in the NAS request message, the eNB  20  selects the MME  30 ,  31 , or  33  matched with the entity ID. If no entity ID is received, the eNB selects an MME entity  30 ,  31 , or  33  arbitrarily. If an MTC indicator is received in the NAS request message, the eNB  20  selects the MTC MME  33 . If no MTC indicator is received, the eNB  20  selects the normal MME  31 . The eNB  20  delivers the NAS request message to the MME  30 ,  31 , or  33  at step  587 . 
     Next, if an MME reselection request message is received from the MME  30 ,  31 , or  33 , the eNB  20  detects this at step  589  and reselects an MME  30 ,  31 , or  33  at step  591 . At this time, the eNB  20  selects the MTC MME  33 . At this time, if an entity ID is received in the MME reselection request message, the eNB  20  selects the MTC MME  33  matched with the entity ID. If no entity ID is received, the eNB  20  selects the MTC MME  33  arbitrarily. The eNB  20  delivers the NAS request message to the reselected MME  30 ,  31 , or  33  at step  593 . 
     Afterward, if a NAS response message is received from the MME  30 ,  31 , or  33 , the eNB detects this at step  595  and delivers the NAS response message to the UE  10  or  11  at step  597 . 
     Although the description is directed to the case where the eNB  20  retransmits the NAS request message in the fifth embodiment of the present invention, the present invention is not limited thereto. That is, the present invention can be implemented in such a way that the MTC UE  11  retransmits the NAS request message. Such an example is described in the sixth embodiment of the present invention of the present invention. 
       FIG. 15  is a signaling diagram illustrating a connection procedure in the wireless communication system according to the sixth embodiment of the present invention. 
     Referring to  FIG. 15 , the connection procedure between the MTC UE  11  and the MTC MME  33  starts in such a way that the MTC UE  11  attempts RRC connection to the eNB  20 . At this time, when it attaches to the network initially or enters a cell supporting the tracking information which has not been recognized yet, the MTC UE  11  is capable of trying initial RRC connection to the eNB  20  to establish a connection to a new MME  30 ,  31 , or  33 . 
     That is, the MTC UE  11  sends an RRC connection request message to the eNB  20  at step  611 . Since it is the initial connection attempt to the eNB  20 , the MTC UE  11  transmits a random value as a UE ID in the RRC connection request message. If the RRC connection request message is received, the eNB  20  sends the MTC UE  11  an RRC connection setup message at step  613 . If the RRC connection setup message is received, the MTC UE  11  sends the eNB  20  an RRC connection complete message at step  615 . At this time, the MTC UE  11  transmits a NAS request message for the MTC MME  33  in the RRC connection complete message. Here, the MTC UE  11  is capable of transmitting the entity ID of the MME  30 ,  31 , or  33  to which it has connected previously in the RRC connection complete message. 
     Next, if the MTC UE  11  has connected, the eNB  20  selects one of a plurality of MMEs  30 ,  31 , and  33  at step  617 . At this time, the eNB  20  determines whether the RRC connection complete message includes an entity ID. If an entity ID is included, the eNB  20  selects the MME  30 ,  31 , or  33  matched with the entity ID. If no entity ID is included, the eNB  20  selects an MME  30 ,  31 , or  31  arbitrarily. Also, if it has not connected with the MME  30 ,  31 , or  33  matched with the entity ID through S1-MME interface, the eNB  20  selects an MME  30 ,  31 , or  33  arbitrarily. 
     Once the normal MME  31  has been selected, the eNB  20  sends the normal MME  31  an initial UE request message for the MTC UE  11  at step  619 . At this time, the eNB  20  delivers the NAS request message carried in the RRC connection complete message. If the initial UE request message is received, the normal MME  31  checks that the NAS request message carried in the initial UE request message has been transmitted by the MTC UE  11 . For example, the eNB  20  transmits the MTC indicator received from the MTC UE  11  to the MME  31  such that the MME  31  identifies the MTC UE  11 . Also, it is possible for the HSS to transmit the MTC indicator in the subscriber information of the MTC UE  11  to the normal MME  31  such that the normal MME  31  identifies the MTC UE  11 . Also, it is possible for the MTC UE  11  to use a random value selected in the range discriminated from that for the normal UE as the UE ID such that the normal MME  31  identifies the MTC UE  11 . 
     Next, if the MTC UE  11  has been identified, the normal MME  31  sends the eNB  20  a MME reselection request message at step  623 . At this time, the normal MME  31  is capable of the information or the MTC MME  33 , i.e. entity ID, in the MME reselection request message. Afterward, the normal  31  delivers the NAS retransmission request message to the MTC UE  11  at step  625 . At this time, the normal MME  31  is capable of the NAS retransmission request message through NAS communication via the eNB  20 . If the NAS retransmission request message is received, the MTC UE  11  retransmits the NAS request for the MTC MME  33  at step  627 . At this time, the MTC UE  11  is capable of transmitting the NAS request message through NAS communication. 
     Next, if the retransmitted NAS request message is received, the eNB  20  selects one of the plural MMEs  30 ,  31 , and  33  at step  629 . At this time, the eNB  20  selects the MTC MME  33 . Here, the eNB  20  determines whether the MME reselection request message includes an entity ID. If an entity ID is included, the eNB selects the MTC MME  33  matched with the entity ID. Otherwise, if no entity ID is included, the eNB  20  selects the MTC MME  33  arbitrarily. Also, if it has not connected to the MTC MME  33  matched with the entity ID through the S1-MME interface, the eNB selects the MTC MME  33  arbitrarily. 
     Once the MTC MME  33  has been selected, the eNB  20  sends the MTC MME  33  an initial UE request message for the MTC UE  11  at step  631 . The MTC MME  33  sends the MTC UE  11  an initial UE response message via the eNB  20  at step  633 . At this time, the MTC MME  33  generates the NAS response message by processing the request data in the NAS request message. The MTC MME  33  transmits the NAS response message in a NAS message. The MTC MME  33  is also capable of transmitting the NAS response message including a GUTI allocated as the identifier information of the MTC UE  11 . 
     The MTC MME  11  is capable of retrying the RRC connection to the eNB  20 . That is, when it wakes up, i.e. transitions from the idle mode to the active mode or enters the cell supporting the tracking area information which has been recognized previously, the MTC UE  11  is capable of retrying the RRC connection to the eNB  20  to reestablish the connection to the MME  30 ,  31 , or  33  to which the MTC UE  11  has connected previously. The MTC UE  11  is capable of trying to connect to the MTC MME  33  via the eNB  20 . Since the connection procedure between the MTC UE  11  and the MTC MME  33  is similar to steps  441  to  451  of  FIG. 10  that has been described above, detailed description thereon is omitted herein. 
     The operation procedures of the normal MME  31  and the eNB  20  according to the present invention embodiment are described hereinafter. Since the operation procedure of the MTC MME  33  according to the present embodiment is similar to that of the first embodiment of the present invention, detailed description thereon is omitted herein. 
       FIG. 16  is a flowchart illustrating the operation procedure of the normal MME  31  of  FIG. 15 . 
     Referring to  FIG. 16 , if a NAS request message is received from the UE  10  or  11 , the normal me  31  detects this at step  661  and determines whether to allocate a GUTI to the UE  10  or  11  at step  663 . That is, the normal MME  31  determines whether the UE  10  or  11  has been allocated a GUTI already. If it is determined to allocate a GUTI to the UE  10  or  11  at step  663 , the normal MME  31  determines whether the UE  10  or  11  is the MTC UE  11  at step  665 . If it is determined that the UE  10  or  11  is the MTC UE  11  at step  665 , the normal MME  31  sends the eNB  20  an MME reselection request message at step  667 . Next, the normal MME  31  sends the MTC UE  11  a NAS retransmission request message via the eNB  20  at step  669 . 
     Otherwise, if it is determined that the UE  10  or  11  is no the MTC UE  11  at step  665 , the normal MME  31  allocates a GUTI to the UE  10  or  11  at step  671 . The normal MME  31  sends the UE  10  or  11  a NAS response message at step  673 . At this time, the normal MME  31  transmits the NAS response message including the corresponding GUTI. If it is determined that there is no need to allocate a GUTI to the UE  10  or  11  at step  663 , the normal MME  31  sends the UE  10  or  11  the NAS response message via the eNB  20  at step  675 . 
       FIG. 17  is a flowchart illustrating the operation procedure of the eNB  20  of  FIG. 15 . 
     Referring to  FIG. 17 , the eNB  20  establishes an RRC connection with the UE  10  or  11  at step  681 . If a NAS request message is received from the UE  10  or  11 , the eNB  20  detects this at step  683  and selects an MME  30 ,  31 , or  33  at step  685 . At this time, if an entity ID is received along with the NAS request message, the eNB  20  selects the MME  30 ,  31 , or  33  matched with the entity ID. If no entity ID is received, the eNB  20  selects an MME  30 ,  31 , or  33  arbitrarily. If an MTC indicator is received along with the NAS request message, the eNB  20  selects the MTC MME  33 . If no MTC indicator is received, the eNB  20  selects the normal MME  31 . The eNB  20  delivers the NAS request message to the MME  30 ,  31 , or  33  at step  687 . 
     Next, if an MME reselection request message is received from the MME  30 ,  31 , or  33 , the eNB  20  detects this at step  689 . Afterward, if a NAS retransmission request message is received from the MME  30 ,  31 , or  33 , the eNB  20  detects this at step  691  and delivers the NAS retransmission request message to the MTC UE  11  at step  693 . If a NAS request is received, the eNB  20  detects this at step  695  and reselects an MME  30 ,  31 , or  33  at step  697 . At this time, the eNB  20  selects the MTC MME  33 . Here, if an entity ID is received in the MME reselection request message, the eNB  20  selects the MTC MME  33 . Otherwise, if not entity ID is received, the eNB selects the MTC MME  33  arbitrarily. The eNB  20  delivers the NAS request message to the reselected entity  30 ,  31 , or  33 . If a NAS response message from the MME  30 ,  31 , or  33 , the eNB  20  detects this at step  701  and delivers the NAS response message to the UE  10  or  11  at step  703 . 
     According to the above-described embodiments, it is possible to connect the MTC UE  11  to the MTC MME  33  efficiently in the wireless communication system. That is, the MTC UE  11  can connect to the MME  33  efficiently through cooperation between eNB  20  and normal MME  31  or normal MME  31  and MTC MME  33 . 
     Although the description is directed to the connection procedure between MTC UE  11  and the MTC MME  33  in the wireless communication system, the present invention is not limited thereto. That is, the present invention also can be implemented by connecting the normal UE to the normal MME  31  efficiently through cooperation between the eNB  20  and the normal MME  31  or the normal MME  31  and MTC MME  33 . 
     In the wireless communication system, it is possible for connecting the UE  10  or  11  to the MME  30 ,  31 , or  33  corresponding to the supplementary function efficiently. That is, the UE  10  or  11  is capable being connected to the MME  30 ,  31 , or  33  efficiently through cooperation between the eNB  20  and the MME  30 ,  31 , or  33  or among the MMEs  30 ,  31 , and  33  supporting different supplementary functions. 
     Although the descriptions have been directed to the case where the connection between the UE and the MME is established in association with a specific supplementary function, the present invention is not limited thereto. That is, the present invention can be implemented in such a way that the connection between the UE and the MME is established according to the load status of the MME. 
     For example, if the eNB request for the identity information of a UE, the MME checks the current load status. At this time, the MME determines whether the current load is greater than a predetermined threshold value, i.e. whether overload occurs. If it is determined that the current load is not greater than the threshold value, i.e. no overload occurs, the MME is capable of allocating the identity information to the UE. Otherwise, if it is determined that the current load is greater than the threshold value, i.e. overload occurs, the MME requests another MME for the identity information of the UE. That is, if overload occurs, the MME suspends the connection of the UE and request another MME for the identity information. In this way, the other MME is capable of allocating identity information to the UE. Here, the MME is capable of transmitting the identity information to the UE via the other MME. Furthermore, the UE is capable of trying connection to another MME using the corresponding identity information. 
     According to the present invention, it is possible to connect a UE to an MME efficiently in the wireless communication system. That is, the UE is capable of being connected to an MME efficiently through cooperation between the eNB and the MME or among the MMEs. At this time, the MMEs is capable of cooperating among each other according to the supportable supplementary function or load status. 
     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.