Abstract:
A method and apparatus for supporting Non-Access Stratum (NAS) communication between a User Equipment (UE) and a Mobility Management Entity (MME) efficiently by addressing the signaling problems occurring between the UE and the MME in a situation where it is necessary for a network node to identify the UE and acquire UE information, if there is any, from another network node to which the UE has been attached, are provided. The method for communication between the UE and network based on the NAS protocol messages and operations is implemented with the involvement a UE, an MME, and an old MME or an old Serving General Packet Radio Service (GPRS) Support Node (SGSN) to which the UE has been attached before so as to facilitate discovering a best node using the UE information acquired from the old MME or old SGSN during the communication between the UE and the network, resulting in a reduction of a communication delay between the UE and network and an improvement of communication efficiency.

Description:
PRIORITY 
       [0001]    This application is a continuation of prior application Ser. No. 13/228,713, filed on Sep. 9, 2011, which claimed the benefit under 35 U.S.C. §119(a) of a Korean patent application filed on Sep. 9, 2010 in the Korean Intellectual Property Office and assigned Serial No. 10-2010-0088232, 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 mobile communication system. More particularly, the present invention relates to a method and apparatus for supporting Non-Access Stratum (NAS) communication between a User Equipment (UE) and a Mobility Management Entity (MME) efficiently by addressing the signaling problems occurring between the UE and MME in a situation where it is necessary for a network node to identify the UE and acquire UE information, if there is any, from another network node to which the UE have been attached after a movement between two different Radio Access Technologies (RATs) such as Evolved Universal Terrestrial Radio Access Network (EUTRAN) and Universal Terrestrial Radio Access Network (UTRAN) or Global System for Mobile Communications (GSM)/Enhanced Data Rates for GSM Evolution (EDGE) Radio Access Network (GERAN). 
         [0004]    2. Description of the Related Art 
         [0005]    As one of the representative mobile communication standard organizations, the 3 rd  Generation Partnership Project (3GPP) has defined Evolved Packet System (EPS) with the introduction of MME. 
         [0006]    The NAS protocols for the 3GPP 3G system have been revised in order to meet the requirements of high-speed data transmission in the next generation mobile communication system. The revision also has included backward compatibility to the 2G and 3G networks of 3GPP. In detail, when attaching to a network or updating a tracking area, the UE identifies the network node which it has accessed before using the node identity information of the UE identifier. 
         [0007]    In a carrier network of the related art, however, the network is configured using even the bit information indicating network node identity information, and thus there is no room to distinguish between the legacy network mobility management node and the MME introduced for supporting the EUTRAN, resulting in a node identification failure problem. There is therefore a need of a method for improving communication service quality by minimizing processing delay with the provision of the information for the UE to discover the network node to which the UE has attached before and the acquisition of the UE information based on the provided information in the communication between the UE and the network through modification of the NAS protocol or a certain procedure of the UE or the mobility management node. 
       SUMMARY OF THE INVENTION 
       [0008]    Aspects of the present invention are to address at least the above-mentioned problems and/or disadvantages and to provide at least the advantages described below. Accordingly, an aspect of the present invention is to provide a communication method and system for supporting Non-Access Stratum (NAS) communication between a User Equipment (UE) and a network node efficiently in an evolved mobile communication system including 3 rd  Generation Partnership Project (3GPP) Evolved Packet System (EPS) supporting Access Stratum (AS) and NAS protocols on layer 2, especially when the UE in idle mode moves or connects to a network or updates the tracking area or performs handover between different Radio Access Technologies (RAT) including Evolved Universal Terrestrial Radio Access Network (EUTRAN) and Universal Terrestrial Radio Access Network (UTRAN) or Global System for Mobile Communications (GSM)/Enhanced Data Rates for GSM Evolution (EDGE) Radio Access Network (GERAN)(UTRAN/GERAN). 
         [0009]    Another aspect of the present invention is to provide a communication method and system that is capable of supporting NAS authentication and NAS communication between a UE and a network entity such as a Mobility Management Entity (MME) without a processing delay by specifying the operations of the UE, MME, and Serving General Packet Radio Service (GPRS) Support Node (SGSN) in the NAS protocol during the roaming of the UE between different technology-based networks including GERAN, UTRAN, EUTRAN, and other equivalent access networks. 
         [0010]    The present invention relates to a method and system for facilitating a UE to discover a best node during or in attempt of communication with a network node using the NAS protocols, and the method for communication between the UE and network based on the NAS protocol messages and operations according to the present invention is implemented with the involvement a UE, an MME, and an old MME or old SGSN to which the UE has previously attached so as to facilitate discovering the best node using the UE information acquired from the old MME or old SGSN during the communication between the UE and the network, resulting in a reduction of communication delay between the UE and network and an improvement of communication efficiency. 
         [0011]    As aforementioned, the present invention is capable of maintaining the communication between UE and network during the handover between two different RATs such as EUTRAN and UTRAN/GERAN, resulting in reduction of communication delay. 
         [0012]    In accordance with an aspect of the present invention, a communication support method of an MME in a mobile communication system is provided. The method includes receiving a Packet-Temporary Mobile Subscriber Identity (P-TMSI) signature from a UE in an access request, and determining an old network node which the UE has accessed previously by analyzing the P-TMSI. 
         [0013]    In accordance with another aspect of the present invention, a communication support apparatus of an MME in a mobile communication system is provided. The apparatus includes a communication unit which receives a P-TMSI signature from a UE in an access request, and a determination unit which determines an old network node which the UE has accessed previously by analyzing the P-TMSI. 
         [0014]    In accordance with another aspect of the present invention, a communication support method of a UE in a mobile communication system is provided. The method includes transmitting a P-TMSI signature to an MME in an access request, and receiving an access response from the MME in response to the access request, wherein the MME analyzes the P-TMSI to determine an old network node which the UE has accessed previously. 
         [0015]    In accordance with still another aspect of the present invention, a communication support apparatus of a UE in a mobile communication system is provided. The apparatus includes a communication unit which is responsible for communication with an MME, and a control unit which transmits a P-TMSI signature to the MME in an access request and receives an access response from the MME in response to the access request, wherein the MME analyzes the P-TMSI to determine an old network node to which the UE has accessed previously. 
         [0016]    Other aspects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses exemplary embodiments of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    The above and other aspects, features, and advantages of certain exemplary embodiments of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings, in which: 
           [0018]      FIG. 1  is a schematic diagram illustrating communication environment of the mobile communication system according to an exemplary embodiment of the present invention; 
           [0019]      FIG. 2  is a signaling diagram illustrating a network attachment procedure of a User Equipment (UE) according to an exemplary embodiment of the present invention; 
           [0020]      FIG. 3  is a signaling diagram illustrating a tracking area update procedure of a UE according to an exemplary embodiment of the present invention; 
           [0021]      FIG. 4  is a signaling diagram illustrating a network attachment procedure of a UE according to another exemplary embodiment of the present invention; 
           [0022]      FIG. 5  is a signaling diagram illustrating a tracking area update procedure of a UE according to another exemplary embodiment of the present invention; 
           [0023]      FIG. 6  is a flowchart illustrating operations of a Mobility Management Entity (MME) for supporting communication between a UE and a network node according to an exemplary embodiment of the present invention; 
           [0024]      FIG. 7  is a flowchart illustrating operations of a UE for supporting communication between the UE and a network node according to an exemplary embodiment of the present invention; and 
           [0025]      FIG. 8  is a flowchart illustrating operations of an MME for supporting communication between a UE and a network node according to another exemplary embodiment of the present invention. 
       
    
    
       [0026]    Throughout the drawings, it should be noted that like reference numbers are used to depict the same or similar elements, features, and structures. 
       DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0027]    The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of exemplary embodiments of the invention as defined by the claims and their equivalents. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope and spirit of the invention. In addition, descriptions of well-known functions and constructions may be omitted for clarity and conciseness. 
         [0028]    The terms and words used in the following description and claims are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the invention. Accordingly, it should be apparent to those skilled in the art that the following description of exemplary embodiments of the present invention is provided for illustration purpose only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents. 
         [0029]    It is to be understood that the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a component surface” includes reference to one or more of such surfaces. 
         [0030]    The subject matter of the present invention is to provide a method for reducing the delay of Non-Access Stratum (NAS) communication between a User Equipment (UE) and a Mobility Management Entity (MME) by optimizing the operations of the UE, MME, and Serving General Packet Radio Service (GPRS) Support Node (SGSN) in the NAS signaling. Although the description is directed to the 3 rd  Generation Partnership Project (3GPP)-based system including Evolved Packet System (EPS), Universal Terrestrial Radio Access Network (UTRAN), and Global System for Mobile Communications (GSM)/Enhanced Data Rates for GSM Evolution (EDGE) Radio Access Network (GERAN), the present invention can be applied to other types of communication systems using NAS. 
         [0031]    In the exemplary embodiment of  FIG. 1 , the present invention proposes a communication method between a UE and an MME and operations thereof based on the NAS protocol during the movement of the UE between different Radio Access Technologies (RAT) including Evolved Universal Terrestrial Radio Access Network (EUTRAN) and Universal Terrestrial Radio Access Network (UTRAN), and it will be obvious to those skilled in the art that the disclosed communication method can be applied to other mobile communication systems implemented based on similar or different protocols but operating similarly in similar technological background and channel format with minor changes and modifications without departing from the scope of the present invention. 
         [0032]      FIG. 1  is a schematic diagram illustrating a communication environment of a mobile communication system according to an exemplary embodiment of the present invention. The description is directed to an exemplary 3GPP EPS system. Although the description is directed to the case where the UE connects to a EUTRAN and then moves to another RAT network or connects to an RAT network and then moves to the EUTRAN, the present invention can be applied to other mobile communication systems operating in a similar manner. 
         [0033]    Referring to  FIG. 1 , the base stations (referred to as Evolved Node Base Station, E Node B, and eNB, or Radio Network Controller (RNC))  112  and  133  are responsible for establishing radio links to communicate with the UE  110  within the cell as the service coverage thereof. The UE  110  is a terminal that connects to a packet data network such as the Internet via a Serving Gateway (hereinafter, referred to as Serving GW or S-GW)  116 . In the following description, the Packet Data Network Gateway (hereinafter, referred to as PDN GW)  118  as a significant network entity of the packet data network is responsible for the functions of Home Agent HA. The Mobility Management Entity/Serving GPRS Support Node (MME/SGSN)  135  is responsible for management of mobility, location, and registration of the UE. In order to manage the authentication information of the user or UE, the Home Subscriber Server (HSS)  121  is connected to the MME  114  and MME/SGSN  135  via an interface. 
         [0034]    The eNB/RNC  133 , SGW  116 , and MME/SGSN  135  are connected via data paths with the interface for managing the mobility of UE. The UE  110  and MME/SGSN  135  have an NAS protocol stack to communicate each other for the mobility management and session management. In the described exemplary embodiment, the description is directed to the situation in which the UE  100  connected to an old network (or source network) moves to connect to a new network or updates location. The source network can be one of various RATs including EUTRAN, UTRAN, and GERAN, and it is assumed that the UE moves from the source network to EUTRAN as the new network (or target network). If it moves to the target network, the UE  110  connects to the eNB  112  so as to be served by the eNB  112 , MME  114 , and HSS  121 . The MME  114  of the new network and the MME/SGSN  135  of the old network are connected with each other so as to exchange the information necessary. A description is made of the operations of the UE  110  and MME  114  operating based on the NAS protocol in the above-structured network with reference to  FIGS. 2 to 8 . In the mobile communication system according to an exemplary embodiment of the present invention, when a request message is received from the UE, the network node analyzes the request message to check the old network node to which the UE has been attached. The new network node requests the old network node for the information related to the UE. When the UE information is received from the old network node, the new network node sends a response message to the UE using the acquired UE information. 
         [0035]    In the mobile communication system of the present invention, the UE configures the request message. The UE configures the request message in order for the network node to analyze the request message to check the old network node. The UE sends the request message to the network node. Afterward, the UE receives the response message transmitted by the network node in response to the request node. 
         [0036]    Here, the request message includes the connection request message for connection to the network node and the update request message for updating the UE location. The new network node can be an MME, and the old network node can be a SGSN or MME. 
         [0037]      FIG. 2  is a signaling diagram illustrating a network attachment procedure of a UE according to an exemplary embodiment of the present invention. 
         [0038]    Referring to  FIG. 2 , the UE  110  requests attachment to the network at step  201 . At this time, the UE sends an access request message, i.e., Attach Request message, including UE identity information which is referred to as Packet-Temporary Mobile Subscriber Identity (P-TMSI) signature. The P-TMSI signature is the information to be used in the attempt of attachment to a network since the UE  110  has successfully connected to an SGSN. The Attach Request message is delivered to the MME  114  via the eNB  112  at step  203 . 
         [0039]    If it is determined that the UE  110  has accessed the old MME/SGSN  135 , the new MME  114  determines the type of the old network node at step  205 . The old network node type is determined by referencing the Most Significant Bit (MSB) of the Local Area Code (LAC) or MME Group Identity (MMEGI) in the Globally Unique Temporary Identity (GUTI) of the UE  110 . Once the old network node type is determined (if the MSB is set to 1, the old network is determined to be EUTRAN, and otherwise the old network is determined to be UTRAN/GERAN), the UE discovers the MME or SGSN in the corresponding network. In the case that the MSB is set to 1 for the UTRAN/GERAN (by some mobile carriers), if the Attach Request message transmitted by the UE  110  includes a valid P-TMSI signature, it can be determined that the UE  110  has accessed the GERAN/UTRAN previously. 
         [0040]    Next, the new MME  114  requests the MME/SGSN  135 , as the old serving network of the UE  110 , for the International Mobile Subscriber Identity (IMSI) and Mobility Management (MM) context at step  207 . The new MME  114  receives the UE information from the old MME/SGSN  135  at step  209 . Next, the authentication and security process is performed at step  211  and then the bearer creation process is performed at step  213 . Next, the new MME  114  sends an Attach Accept message to the new eNB  112  at step  215 , and the new eNB  112  forwards the Attach Accept message to the UE  110  at step  217  so as to complete the attachment procedure. 
         [0041]      FIG. 3  is a signaling diagram illustrating a tracking area update procedure of UE according to an exemplary embodiment of the present invention. 
         [0042]    Referring to  FIG. 3 , the UE  110  sends a Tracking Area Update (TAU) Request message to the network through new eNB  112  at step  301 . The TAU Request message includes a P-TMSI signature as UE identity information and a Cipher Key Sequence Number (CKSN) for referencing a cipher key when the UE  110  has accessed a GERAN/UTRAN previously. If there exists a valid CKSN and P-TMSI signature, this means that the UE has successfully connected to an SGSN previously and stored the information for use in the connection or location registration update process afterward. The TAU Request message transmitted by the UE  110  is delivered to the MME  114  via the eNB  112  at step  303 . 
         [0043]    In case that the UE has accessed the MME/SGSN  135  previously, the MME  114  determines the type of the old network node at step  305 . The old network node type is determined by referencing the MSB of the LAC or MMEGI in the GUTI of the UE  110 . Once the old network node type is determined (if the MSB is set to 1, the old network is determined to be EUTRAN, and otherwise the old network is determined to be UTRAN/GERAN), the UE discovers the MME or SGSN in the corresponding network. In case that the MSB is set to 1 for the UTRAN/GERAN (by some mobile carriers), if the Attach Request message transmitted by the UE  110  includes a valid P-TMSI signature, it can be determined that the UE  110  has accessed the GERAN/UTRAN previously. 
         [0044]    Next, the new MME  114  requests the MME/SGSN  135 , as the old serving network of the UE  110 , for the IMSI and MM context at step  307 . The new MME  114  receives the UE information from the old MME/SGSN  135  at step  309 . Next, the authentication and security process is performed at step  311  and then the bearer update process for updating Serving Gateway and UE location information is performed at step  315 . The new MME  114  sends a Context Acknowledge message to the old MME/SGSN  135  for acknowledgment of the receipt of the UE information at step  313 . After the bearer update at step  315 , the new MME  114  sends a TAU Accept message to the UE  110  at step  317  so as to complete the tracking area update procedure. 
         [0045]    According to an exemplary embodiment of the present invention, if an Attach Request or a tracking area update request message is received from the UE, the network node checks the MSB of the MMEGI or the LAC of the GUTI of the UE in the request message. If the MSB is set to 0, this means that the old network node is SGSN. Otherwise if the MSB is set to 1, the new network node determines whether the request message includes at least one of a P-TMSI signature and a CKSN. If the request message includes at least one of the P-TMSI signature and the CKSN, this means that the old network node is SGSN. Otherwise if the request message includes neither the P-TMSI signature nor the CKSN, this means that the old network node is MME. Afterward, the new network node requests the old network node for the UE information and sends a response message to the UE using the UE information received from the old network node. 
         [0046]      FIG. 4  is a signaling diagram illustrating a network attachment procedure of UE according to another exemplary embodiment of the present invention. 
         [0047]    Referring to  FIG. 4 , the UE  110  requests attachment to the network at step  401 . The Attach Request message transmitted by the UE includes the capability information on whether the UE  110  is capable of discriminating between the identifier assigned as the result of the connection to an MME and the identifier created based on the P-TMSI or Routing Area Identity (RAI). The capability information can be transmitted in a parameter, i.e., a UE network capability Information Element (IE), or in other ways. The UE  110  can transmit the Attach Request message including the information indicating whether the identifier is assigned as the result of attachment to MME or created from the P-TMSI and/or RAI. The identifier creation information can be transmitted by means of a type of identity (identification type or ID type) or other IE or discriminate between LAC and MMEGI. The Attach Request message transmitted by the UE  110  is delivered to the MME  114  via the eNB  112  at step  403 . 
         [0048]    If it is determined that the UE  110  has accessed the old MME/SGSN  135 , the new MME  114  determines the type of the old network node at step  405 . The old network node type is determined by referencing the MSB of the LAC or MMEGI in the GUTI of the UE  110 . Once the old network node type is determined (if the MSB is set to 1, the old network is determined to be EUTRAN, and otherwise the old network is determined to be UTRAN/GERAN), the UE discovers the MME or SGSN in the corresponding network. In case that the MSB is set to 1 for the UTRAN/GERAN (by some mobile carriers), if the Attach Request message transmitted by the UE  110  includes capability information, this means that the UE  110  has the capability of transmitting identification type along with the GUTI. Accordingly, the MME  114  references an identification type field or the IE related to identification type to determine whether the old network node to which the UE has attached is GERAN/UTRAN or EUTRAN. 
         [0049]    Next, the new MME  114  requests the MME/SGSN  135 , as the old serving network of the UE  110 , for the IMSI and MM context as the UE information at step  407 . The new MME  114  receives the UE information from the old MME/SGSN  135  at step  409 . Next, the authentication and security process is performed at step  411  and the bearer creation process is performed at step  413 . Next, the new MME  114  sends an Attach Accept message to the new eNB  112  at step  415 , and the new eNB  112  forwards the Attach Accept message to the UE  110  at step  417  so as to complete the attachment procedure. 
         [0050]      FIG. 5  is a signaling diagram illustrating a tracking area update procedure of a UE according to another exemplary embodiment of the present invention. 
         [0051]    Referring to  FIG. 5 , the UE  110  sends a TAU Request message to the network through new eNB  112  at step  501 . The Attach Request message transmitted by the UE includes the capability information on whether the UE  110  is capable of discriminating between the identifier assigned as the result of the connection to an MME and the identifier created based on the P-TMSI or RAI. The capability information can be transmitted in a parameter, i.e., a UE network capability IE, or in other ways. The UE  110  can transmit the Attach Request message including the information indicating whether the identifier is assigned as the result of attachment to MME or created from the P-TMSI and/or RAI. The identifier creation information can be transmitted by means of a type of identity (identification type or ID type) or other IE or discriminate between LAC and MMEGI. The Attach Request message transmitted by the UE  110  is delivered to the MME  114  via the eNB  112  at step  503 . If it is determined that the UE  110  has accessed the old MME/SGSN  135 , the new MME  114  determines the type of the old network node at step  505 . The old network node type is determined by referencing the MSB of the LAC or MMEGI in the GUTI of the UE  110 . Once the old network node type is determined (if the MSB is set to 1, the old network is determined to be EUTRAN, and otherwise the old network is determined to be UTRAN/GERAN), the UE discovers the MME or SGSN in the corresponding network. In case that the MSB is set to 1 for the UTRAN/GERAN (by some mobile carriers), if the Attach Request message transmitted by the UE  110  includes capability information, this means that the UE  110  has the capability of transmitting identification type along with the GUTI. Accordingly, the MME  114  references an identification type field or the IE related to identification type to determine whether the old network node to which the UE has attached is GERAN/UTRAN or EUTRAN. 
         [0052]    Next, the new MME  114  requests the MME/SGSN  135 , as the old serving network of the UE  110 , for the IMSI and MM context as the UE information at step  507 . The new MME  114  receives the UE information from the old MME/SGSN  135  at step  509 . Next, the authentication and security process is performed at step  511  and the bearer modification process for updating the serving gateway and UE location information is performed at step  515 . The new MME sends a Context Acknowledge message to the old MME/SGSN  135  for acknowledgment of the receipt of the UE information at step  513 . After the bearer modification at step  515 , the new MME  114  sends a TAU Accept message to the UE  110  at step  517  so as to complete the tracking area update procedure. 
         [0053]    According to this exemplary embodiment of the present invention, the UE configures an identification type indicator for discriminating the types of the temporary identifier of the network node which is transmitted in the request message such as the Attach Request and Tracking Area Update Request message. The UE transmits the request message to the network node. Afterward, the UE receives a response message from the network node in response to the request message. 
         [0054]    According to another exemplary embodiment of the present invention, if the request message such as Attach Request or Tracking Area Update Request is received from the UE, the network node determines whether the request message includes the identification type indicator for indicating the type of the old network node based on the temporary identifier. If the request message includes the identification type indicator, the network node identifies the old network node as one of SGSN and MME. At this time, the network node analyzes the identification type indicator related to the temporary identifier corresponding to the old network node to determine the old network node as one of SGSN and MME. Afterward, the network nod receives the UE information from the old network node and sends the response message to the UE using the UE information. 
         [0055]      FIG. 6  is a flowchart illustrating operations of an MME for supporting communication between a UE and a network node according to an exemplary embodiment of the present invention. 
         [0056]    Referring to  FIG. 6 , the MME  114  receives the Attach Request/TAU Request message transmitted by the UE  110  at step  701 . Upon receipt of the request message, the MME  114  checks the EPS mobile identity IE in the request message at step  703 . If the MSB of LAC/MMEGI is determined to be set to 0 at step  721 , this means that the old network node to which the UE  110  has been attached is SGSN, and thus the MME  114  discovers the corresponding one among a plurality of SGSNs to request for UE information at step  723 . 
         [0057]    If the MSB of LAC/MEGI is determined to be set to 1 at step  711 , this means that the old network node to which the UE  110  has been attached is MME or SGSN, and thus the MME  114  determines whether the Attach Request message transmitted by the UE  110  includes a valid P-TMSI signature or the TAU Request message transmitted by the UE  110  includes at least one of a CKSN or a P-TMSI signature at step  713 . If it is determined that the request message includes a valid CKSN or a P-TMSI signature, this means that the old network node to which the UE has been attached previously is SGSN, and thus the MME  114  discovers the targeted one of SGSNs to request for the UE information at step  715 . Otherwise, if it is determined that the request message includes neither a valid P-TMSI signature nor a CKSN, this means that the old network node to which the UE has been attached previously is MME, and thus the MME  114  discovers the targeted one among MMEs to request for the UE information at step  717 . 
         [0058]    According to an exemplary embodiment of the present invention, the MME includes a communication unit, a determination unit, and a control unit. 
         [0059]    The communication unit is responsible for communication with the UE. The communication unit can receive the access request message from the UE. Here, the access request message can be one of an Attach Request or a Tracking Area Update Request. 
         [0060]    The determination unit analyzes the access request message transmitted by the UE to determine the type of the old network node. Here, the determination unit analyzes the P-TMSI signature to determine the type of the old network node. The determination unit can include a judging module and an identification module. The determination unit analyzes the P-TMSI signature of the access request message. The identification module judges the old network node as one of MME and SGSN according to the analysis result of P-TMSI signature. 
         [0061]    The control unit requests the old network node for the UE information. Upon receipt of the UE information, the control unit controls such that the network node sends the response message to the UE using the acquired UE information. 
         [0062]    According to an exemplary embodiment of the present invention, the UE includes a communication unit and a control unit. The control unit controls to transmit an access request message to the MME. Here, the control unit controls such that the P-TMSI signature is transmitted in the access request message. The access request message can be one of an Attach Request and a Tracking Area Update Request of the UE. The communication unit is responsible for communication with the MME. At this time, the communication unit receives an Access Response message from the MME in response to the Access Request message. 
         [0063]      FIG. 7  is a flowchart illustrating operations of a UE for supporting communication between the UE and a network node according to an exemplary embodiment of the present invention. 
         [0064]    Referring to  FIG. 7 , the UE  110  determines whether the technology release version (hereinafter, referred to as rel) is rel — 8 or post rel — 8, i.e., rel — 9 or rel — 10, at step  801 . The operations can be defined differently according to the technology release version. In case of rel — 8, the UE  110  configures the Attach/TAU Request message with UE network capability or other indication information element indicating GUTI/mapped GUTI or without identifier at step  821  and transmits the Attach/TAU Request message to the network node at step  819 . 
         [0065]    In case of post rel —8  (i.e., rel — 9 or rel — 10), the UE  110  sets a valid UE network capability at step  811  and determines whether to use the GUTI or mapped GUTI as the identification type information, based on the identification type indication capability of the UE, at step  813 . If it is determined to use GUTI, the UE  110  configures the Attach/TAU Request message with the identification type field or identification type-related IE set to indicate GUTI at step  815 , and otherwise to use mapped GUTI, configures the Attach/TAU Request message with the identification type field or identity-related IE set to indicate mapped GUTI at step  817 . Next, the UE  110  sends the Attach/TAU Request message to the network at step  819 . 
         [0066]    According to an exemplary embodiment of the present invention the UE includes a control unit and a communication unit. The control unit configures the request message with the identification type indicator for notifying the network node of the type of the old network node corresponding to the temporary identifier. The control unit configures the request message with the identification type information of the temporary identifier corresponding to the old network node. The communication unit transmits the request message to the network node under the control of the control unit. The communication unit also receives a response message from the network node in response to the request message. 
         [0067]      FIG. 8  is a flowchart illustrating operations of an MME for supporting communication between a UE and a network node according to another exemplary embodiment of the present invention. 
         [0068]    Referring to  FIG. 8 , the MME  114  receives the Attach/TAU Request message transmitted by the UE  110  at step  901 . Upon receipt of the Attach/TAU Request message, the MME  114  analyzes the Attach/TAU Request message to check the UE network capability at step  903 . If the Attach Request message or the TAU Request message includes the identification type indication capability-related information configured, this means that the UE  110  has the identification type indication capability in transmitting GUTI-related information. In this case, the MME  114  checks the identification type field or identification type-related IE of the request message to determine whether the old network node to which the UE has been attached previously is GERAN/UTRAN or EUTRAN at step  911 . If the identification type-related information is determined to be GUTI, this means that the old network node is MME, and thus the MME  114  discovers the targeted one among the MMEs to request for the UE information at step  917 . Otherwise if the identification type-related information is the mapped GUTI, this means that the old network node is SGSN, and thus the MME  114  discovers the targeted one among the SGSNs to request for the UE information at step  913 . 
         [0069]    Returning to step  903 , if the Attach Request message or the TAU Request message does not include identification type discrimination-capability-related information, this means that the UE has no identity indication capability, and thus the MME  114  refers at step  921  to the MSB of the MMEGI or LAC in the GUTI or mapped GUTI so as to select one of the SGSNs as the old network node if the MSB is determined to be set to 0 and one of the MMEs (or one of SGSNs according to the network configuration of the carrier) as the old network node if the MSB is determined to be set to 1. In this case, the MME  114  can determine the SGSN to which the UE  110  has attached previously among a plurality of SGSNs based on the additional information such as a CKSN or a P-TMSI signature. 
         [0070]    According to an exemplary embodiment of the present invention, the MME includes a communication unit, a determination unit, and a control unit. 
         [0071]    The communication unit is responsible for communication with the UE. The communication unit can receive the Access Request message transmitted by the UE. Here, the Access Request message can be one of Attach Request and Tracking Area Update Request of the UE. 
         [0072]    The determination unit analyzes the access request message transmitted by the UE to determine the type of the old network node. The determination unit includes a judging module and an identification module. The judging unit judges whether the identification type indicator for discriminating the type of the old network is configured by the UE in association with the temporary identifier of the UE. If no identification type indicator is configured, the identification module determines the old network node to be one of the SGSNs and MMEs. At this time, the identification module analyzes the information related to the identification type of the temporary identifier corresponding to the old network node in the request message to identify whether the old network node is an SGSN or an MME. 
         [0073]    The control unit requests the old network node for the UE information. If the UE information is received from the old network node, the control unit sends the response message to the UE using the acquired UE information. 
         [0074]    In order to support communication between the UE and the MME as described above with reference to  FIGS. 2 to 8 , it is necessary to support the IE in the messages as shown in Table 1. Table 1 shows the IE indicating whether the UE has the capability of informing the network node of the identification type in the message. According to an exemplary embodiment of the present invention, the identification type indication capability is configured in octet 7. 
         [0000]    
       
         
               
               
               
               
               
               
               
               
               
             
               
               
             
               
               
               
               
               
               
               
               
               
             
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 8 
                 7 
                 6 
                 5 
                 4 
                 3 
                 2 
                 1 
                   
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 UE network capability IEI 
                 octet 1 
               
               
                 Length of UE network capability contents 
                 octet 2 
               
             
          
           
               
                 EEA0 
                 128- 
                 128- 
                 EEA3 
                 EEA4 
                 EEA5 
                 EEA6 
                 EEA7 
                 octet 3 
               
               
                   
                 EEA1 
                 EEA2 
               
               
                 EIA0 
                 128- 
                 128- 
                 EIA3 
                 EIA4 
                 EIA5 
                 EIA6 
                 EIA7 
                 octet 4 
               
               
                   
                 EIA1 
                 EIA2 
               
               
                 UEA0 
                 UEA1 
                 UEA2 
                 UEA3 
                 UEA4 
                 UEA5 
                 UEA6 
                 UEA7 
                 octet 5* 
               
               
                 UCS2 
                 UIA1 
                 UIA2 
                 UIA3 
                 UIA4 
                 UIA5 
                 UIA6 
                 UIA7 
                 octet 6* 
               
               
                 0 
                 0 
                 0 
                 ID 
                 LPP 
                 LCS 
                 1xSR 
                 NF 
                 octet 7* 
               
               
                 spare 
                 spare 
                 spare 
                 TYPE 
                   
                   
                 VCC 
               
               
                   
                   
                   
                 indication 
               
               
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 octet 8*-15* 
               
             
          
           
               
                 Spare 
                   
               
               
                   
               
               
                 Identification type indication capability (octet 7, bit 5) 
               
               
                 0 Identification type indication mechanisms not supported 
               
               
                 1 Identification type indication mechanisms supported 
               
             
          
         
       
     
         [0075]    Although exemplary embodiments of the present invention have been described in detail hereinabove, it should be clearly understood that many variations and/or modifications of the basic inventive concepts herein taught which may appear to those skilled in the present art will still fall within the spirit and scope of the present invention, as defined in the appended claims. 
         [0076]    The present invention achieves the following effects from the above described representative exemplary embodiments. 
         [0077]    The present invention provides a method and system for addressing the problem of delay in NAS protocol-based communication due to a failure of acquiring UE information from a valid network node, especially in a situation where the UE attempts network attachment or Tracking Area Update during the movement between different RATs including EUTRAN and GERAN/UTRAN. The method and system using the NAS protocol message and operations of the UE and MME that are defined according to the present invention are advantageous to facilitate communication between the UE and network node. 
         [0078]    While the invention has been shown and described with reference to certain exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims and their equivalents.