Abstract:
A method and apparatus for managing a path between nodes in a mobile communication system are provided. The method of a node for managing the path between the nodes includes transmitting/receiving a call setup message including information about a higher node for a call to/from a different node, storing the information about the higher node for the call and information of the different node by associating the two pieces of information with the call, sensing an abnormal operation of a path to a specific node, searching for a call stored in association with the specific node whose abnormal operation is sensed, and deleting information related to the call.

Description:
PRIORITY 
       [0001]    This application claims the benefit under 35 U.S.C. §119(a) of a Korean patent application filed in the Korean Intellectual Property Office on Feb. 16, 2009 and assigned Serial No. 10-2009-0012542, the entire disclosure of which is hereby incorporated by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    Aspects of the present invention relate to an apparatus and method for managing a path between nodes in a mobile communication system. More particularly, aspects of the present invention relate to an apparatus and method for managing a path for a specific node when the specific node operates abnormally in an Evolved Packet Core (EPC) system. 
         [0004]    2. Description of the Related Art 
         [0005]    Subsequent to standardization for a system and terminal of wideband code division multiple access, standardization works for next generation mobile communication are ongoing in the 3rd Generation Partnership Project (3GPP). In addition, a structure for an Enhanced Packet Core (EPC) and a related protocol are being standardized. 
         [0006]      FIG. 1  illustrates a structure of a conventional EPC system  100 . 
         [0007]    Referring to  FIG. 1 , in order for a plurality of Mobility Management Entities (MMEs)  110  to provide a user plane bearer in the EPC system  100 , a bearer is created and updated by selecting one Serving-GateWay (S-GW)  120  from a plurality of S-GWs. The S-GW  120  may act as an anchor point for performing mobility management in a 3GPP network, and a Packet Data Network (PDN) GateWay (P-GW)  130  may act as an anchor point for performing mobility management in the 3GPP network and a non-3GPP network. 
         [0008]    In the EPC system  100 , an echo request and echo response message having a format as shown in Table 1 below is used to manage a path to each node by determining whether each node operates normally. Table 1 below illustrates the format of the echo request and echo response message. 
         [0000]    
       
         
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Information elements 
                 P 
                 Condition/Comment 
                 CR 
                 IE Type 
               
               
                   
               
             
             
               
                 Recovery 
                 M 
                 NONE 
                 1 
                 Recovery 
               
               
                 Private 
                 O 
                 NONE 
                 0 
                 Private Extension 
               
               
                   
               
             
          
         
       
     
         [0009]    Herein, “Recovery” denotes a system reset count of a specific node, “P” denotes a Post condition, “M” denotes a Mandatory, “O” denotes an Optional, and ‘CR’ denotes a Change Request. 
         [0010]    As shown in Table 1 above, each node of the EPC system uses the echo request and echo response message including the system reset count to perform path management by recognizing whether a problem occurs in a path to a peer node. 
         [0011]    However, since the path management using the echo request and echo response message is a path management method performed between one node and another node, it is not suitable as a path management method of a system including an intermediary node. For example, if the MME, the S-GW, and the P-GW are used in the EPC system, when the MME operates abnormally, the S-GW may determine that the MME operates abnormally by transmitting/receiving the echo request and echo response message to/from the MME and then delete call data associated with the MME. In this case, the P-GW cannot know that the MME operates abnormally. Therefore, in order for the P-GW to release the call associated with the MME, the S-GW has to transmit a call release message to the P-GW. The number of call release messages generated in this case is equal to the number of calls which are set up in association with the MME. Each of these generated messages is transmitted to the P-GW. For example, if one million calls are set up in association with the P-GW and the MME, the S-GW instantaneously generates one million call release messages and transmits the generated messages to the P-GW. This may cause a system overload not only for the S-GW which generates and transmits the call release message but also for the P-FW which receives the call release message. Further, there is a problem in that a specific path is congested. 
         [0012]    As described above, the conventional path management method has a disadvantage in that a system overload is generated or a congestion situation occurs. Accordingly, there is a need to provide a more effective path management method. 
       SUMMARY OF THE INVENTION 
       [0013]    Aspects of the present invention 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 an apparatus and method for managing a path between nodes in a mobile communication system. 
         [0014]    Another aspect of the present invention is to provide an apparatus and method for managing a call of a specific node when the specific node operates abnormally in an Evolved Packet Core (EPC) system. 
         [0015]    Another aspect of the present invention is to provide an apparatus and for releasing a call for a specific node when a path to the specific node is abnormal by using a create session message and a modify bearer message including an address of the node in an EPC system. 
         [0016]    Another aspect of the present invention is to provide an apparatus and method in which an intermediary node between nodes in an EPC system announces to another node that a path to a specific node is in an abnormal status. 
         [0017]    Another aspect of the present invention is to provide an apparatus and method for deleting call data related to a specific node in an EPC system by receiving a message for announcing that a path to a specific node is in an abnormal status. 
         [0018]    In accordance with an aspect of the present invention, a method of a node for managing a path between nodes in a mobile communication system is provided. The method includes transmitting a call setup message including information about a higher node for a call to a different node and/or receiving the call setup message from the different node, storing the information about the higher node for the call and information about the different node by associating the two pieces of information with the call, sensing an abnormal operation of a path to a specific node, searching for a call stored in association with the specific node whose abnormal operation is sensed, and deleting information related to the call. 
         [0019]    In accordance with another aspect of the present invention, an apparatus of an intermediary node for managing a path between nodes in a mobile communication system is provided. The apparatus includes a transceiver for transmitting a call setup message comprising information of a higher node for a call to a different node and/or receiving the call setup message from the different node, a storage module for storing the information about the higher node for the call and information about the different node by associating the two pieces of information with the call, a sensor for sensing an abnormal operation of a path to a specific node, and a call session manager for searching for a call stored in association with the specific node whose abnormal operation is sensed, and for deleting information related to the call. 
         [0020]    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 
         [0021]    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: 
           [0022]      FIG. 1  illustrates a structure of a conventional Evolved Packet Core (EPC) system; 
           [0023]      FIG. 2  is a block diagram illustrating each node of an EPC system according to an exemplary embodiment of the present invention; 
           [0024]      FIG. 3  is a flowchart illustrating a call setup process for performing path management between nodes in an EPC system according to an exemplary embodiment of the present invention; 
           [0025]      FIG. 4  is a flowchart illustrating a call setup process of a Serving-GateWay (S-GW) in an EPC system according to an exemplary embodiment of the present invention; 
           [0026]      FIG. 5  is a flowchart illustrating a call setup process of a Packet Data Network (PDN) GateWay (P-GW) in an EPC system according to an exemplary embodiment of the present invention; 
           [0027]      FIG. 6  is a flowchart illustrating a path management process at the occurrence of a path failure with respect to an eNodeB (eNB) in an EPC system according to an exemplary embodiment of the present invention; 
           [0028]      FIG. 7  is a flowchart illustrating a path management process at the occurrence of a path failure with respect to a Mobility Management Entity (MME) in an EPC system according to an exemplary embodiment of the present invention; 
           [0029]      FIG. 8  is a flowchart illustrating a path management process at the occurrence of a path failure with respect to a P-GW in an EPC system according to an exemplary embodiment of the present invention; 
           [0030]      FIG. 9  is a flowchart illustrating a path management process at the occurrence of a path failure with respect to an S-GW in an EPC system according to an exemplary embodiment of the present invention; 
           [0031]      FIG. 10  is a flowchart illustrating a process of performing path management by an S-GW by recognizing occurrence of a path failure with respect to a peer node in an EPC system according to an exemplary embodiment of the present invention; 
           [0032]      FIG. 11  is a flowchart illustrating a process of performing path management by an MME or a P-GW by receiving information indicating occurrence of a path failure from an S-GW according to an exemplary embodiment of the present invention; and 
           [0033]      FIG. 12  is a flowchart illustrating a process of performing path management by an MME or a P-GW by recognizing occurrence of a path failure from an S-GW according to an exemplary embodiment of the present invention. 
       
    
    
       [0034]    Throughout the drawings, like reference numerals will be understood to refer to like parts, components, and structures. 
       DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0035]    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. Also, descriptions of well-known functions and constructions are omitted for clarity and conciseness. 
         [0036]    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 are provided for the purpose of illustration only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents. 
         [0037]    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. 
         [0038]    Hereinafter, an apparatus and for performing path management between nodes in an Evolved Packet Core (EPC) system by using a create session message and a modify bearer message including a node address and a message for announcing occurrence of a path failure for a specific node will be described. To perform path management between nodes through S5/S8/S11/S4 interfaces proposed in the EPC system, an exemplary embodiment of the present invention adds address information of a higher node for a specific call to a call setup message as shown in Table 2 and Table 3 below. 
         [0039]    Table 2 below illustrates information added to a create session request message. 
         [0000]    
       
         
               
               
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                 Information Elements 
                 P 
                 Condition/Comment 
                 CR 
                 IE Type 
               
               
                   
               
             
             
               
                 MME S11 Address for 
                 C 
                 Address information of 
                 1 
                 IP Address 
               
               
                 Path Fail Check 
                   
                 SGSN or MME for 
               
               
                   
                   
                 signaling 
               
               
                   
               
             
          
         
       
     
         [0040]    As shown in Table 2, “MME S11 Address for Path Fail Check” is an information element indicating address information of a higher node for signaling of a specific call, that is, an address of a Mobility Management Entity (MME) or a Servicing GPRS Support Node (SGSN). GPRS refers to the General Packet Radio Service. Herein, “C” denotes a Conditional. 
         [0041]    Table 3 below illustrates information added to a modify bearer request message. 
         [0000]    
       
         
               
               
               
               
               
             
           
               
                 TABLE 3 
               
               
                   
               
               
                 Information Elements 
                 P 
                 Condition/Comment 
                 CR 
                 IE Type 
               
               
                   
               
             
             
               
                 eNodeB S1-U Address 
                 M 
                 Address information 
                 1 
                 IP Address 
               
               
                   
                   
                 of RNC or eNodeB for 
               
               
                   
                   
                 Data Traffic (S1-2,S12) 
               
               
                   
               
             
          
         
       
     
         [0042]    As shown in Table 3 above, “eNodeB S1-U Address” is an information element indicating address information of a higher node for data traffic of a specific call, that is, an address of an eNodeB (eNB) or a Radio Network Controller (RNC). 
         [0043]    In an exemplary embodiment of the present invention, address information of a higher node of a specific call is transmitted by inserting the address information to a create session request message and a modify bearer request message related to call setup as shown in Table 2 and Table 3. Thus, when a node which has received the create session request message and the modify bearer request message stores the address information of the higher node in association with the call, and a path failure occurs with respect to the higher node, data of the call stored in association with the higher node is deleted. 
         [0044]    In addition, an exemplary embodiment of the present invention additionally defines a message announcing the path failure with respect to the specific node to another node in order to perform path management between nodes through the S5/S8/S11/S4 interfaces proposed in the EPC system. That is, an exemplary embodiment of the present invention additionally defines a path failure notification message announcing the path failure with respect to the specific node and a path failure acknowledgement message used as an acknowledgement for the path failure notification message. 
         [0045]    Table 4 below illustrates a message header additionally defined according to an exemplary embodiment of the present invention. 
         [0000]    
       
         
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
               
               
             
           
               
                 TABLE 4 
               
               
                   
               
               
                 Octets 
                 8 
                 7 
                 6 
                 5 
                 4 
                 3 
                 2 
                 1 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 1 
                 2 
                 FFS 
                 T = 0 
                 E = 0 
                 S = 1 
                 FFS 
               
             
          
           
               
                 2 
                 Message Type - 4 or 5 
               
               
                 3 
                 Message Length (1 st  Octet) 
               
               
                 4 
                 Message Length(2 nd  Octet) 
               
               
                 5 
                 Sequence Number(1 st  Octet) 
               
               
                 6 
                 Sequence Number(2 nd  Octet) 
               
               
                 7 
                 Spare 
               
               
                 8 
                 Spare 
               
               
                   
               
             
          
         
       
     
         [0046]    As shown in Table 4 above, in the messages additionally defined in the exemplary embodiment of the present invention, T is set to 0 to indicate that a Tunnel Endpoint ID (TEID) does not exist as in a typical path management message, and a message type is set to a number which is in a reserved state. Although the message type of the path failure notification message is set to 4 which is currently reserved and the message type of the path failure acknowledgement message is set to 5 which is also currently reserved, this is for exemplary purposes only, and thus the message type may be set to another number as long as the number is in the reserved state. 
         [0047]    Table 5 below illustrates a payload configuration of the path failure notification message additionally defined according to an exemplary embodiment of the present invention. 
         [0000]    
       
         
               
               
               
               
               
             
           
               
                 TABLE 5 
               
               
                   
               
               
                 Information 
                   
                   
                   
                   
               
               
                 Elements 
                 P 
                 Condition/Comment 
                 CR 
                 IE Type 
               
               
                   
               
             
             
               
                 Recovery 
                 M 
                 NONE 
                 1 
                 Recovery 
               
               
                 Node Type 
                 M 
                 Type of Node(eNodeB, MME, 
                 1 
                 Node Type 
               
               
                   
                   
                 S-GW, P-GW, RNC and SGSN) 
               
               
                   
                   
                 experiencing a path failure 
               
               
                 Failed Node 
                 M 
                 IP address information of Node 
                 1 
                 IP Address 
               
               
                 Address 
                   
                 experiencing a path failure 
               
               
                 Private 
                 O 
                 NONE 
                 0 
                 Private 
               
               
                 Extension 
                   
                   
                   
                 Extension 
               
               
                   
               
             
          
         
       
     
         [0048]    As shown in Table 5 above, “Recovery” denotes a system reset count of a specific node, “Node Type” denotes a type of a node experiencing a path failure, “Failed Node Address” denotes Internet Protocol (IP) address information of the node experiencing the path failure, and “Private Extension” denotes information that can be additionally added. As shown in Table 5 above, the path failure notification message additionally added in the exemplary embodiment of the present invention includes a type and address of the node experiencing the path failure so that the node receiving the path failure notification message can recognize that the path failure occurs with respect to the node indicated in the message. 
         [0049]    “Node Type” is configured as shown in Table 6 below. A type of each node is defined as shown in Table 7 below. 
         [0000]    
       
         
               
               
               
               
               
               
               
               
               
               
             
               
               
               
             
           
               
                   
                 TABLE 6 
               
               
                   
                   
               
               
                   
                 Octets 
                 8 
                 7 
                 6 
                 5 
                 4 
                 3 
                 2 
                 1 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 1 
                 Type = 138 (decimal) 
               
               
                   
                 2-3 
                 Length = 1(decimal) 
               
               
                   
                 4 
                 NODE Type 
               
               
                   
                   
               
             
          
         
       
     
         [0000]    
       
         
               
               
               
             
           
               
                   
                 TABLE 7 
               
               
                   
                   
               
               
                   
                 NODE Types 
                 Values (decimal) 
               
               
                   
                   
               
             
             
               
                   
                 &lt;reserved&gt; 
                 0 
               
               
                   
                 MME 
                 1 
               
               
                   
                 S-GW 
                 2 
               
               
                   
                 P-GW 
                 3 
               
               
                   
                 SGSN 
                 4 
               
               
                   
                 GGSN 
                 5 
               
               
                   
                 eNodeB 
                 6 
               
               
                   
                 RNC 
                 7 
               
               
                   
                 &lt;spare&gt; 
                 8-255 
               
               
                   
                   
               
             
          
         
       
     
         [0050]    In Table 7 above, a type value of each node is defined for exemplary purposes only, and thus the type value of each node may be defined to another value. Additional nodes may also be defined in Table 7, as needed. 
         [0051]    Table 8 shows a payload configuration of the path failure acknowledgment message additionally defined according to an exemplary embodiment of the present invention. 
         [0000]    
       
         
               
               
               
               
               
             
           
               
                 TABLE 8 
               
               
                   
               
               
                 Information elements 
                 P 
                 Condition/Comment 
                 CR 
                 IE Type 
               
               
                   
               
             
             
               
                 Recovery 
                 M 
                 NONE 
                 1 
                 Recovery 
               
               
                 Private Extension 
                 O 
                 NONE 
                 0 
                 Private Extension 
               
               
                   
               
             
          
         
       
     
         [0052]    As shown in Table 8 above, “Recovery” denotes a system reset count of a specific node, and “Private Extension” denotes information that can be additionally added. 
         [0053]    A structure of each node and a process of performing path management on the basis of the aforementioned description will be explained according to exemplary embodiments of the present invention. 
         [0054]      FIG. 2  is a block diagram illustrating each node of an EPC system according to an exemplary embodiment of the present invention. 
         [0055]    Referring to  FIG. 2 , each node includes a communication module  200 , a call distribution &amp; resource management module  202 , a call session management module  204 , and a call-related information storage module  206 . 
         [0056]    The communication module  200  processes a message transmitted and received to and from a peer node. 
         [0057]    The call distribution &amp; resource management module  202  properly distributes a call to each node and manages a resource. The call distribution &amp; resource management module  202  adds address information of a higher node for a specific call to a create session request message or a modify bearer request message for call setup. The call distribution &amp; resource management module  202  may also evaluate the address information of the higher node for the specific call from the create session request message or a modify bearer response message. In addition, the call distribution &amp; resource management module  202  provides information related to the specific call and the address information of the evaluated higher node to the call-related information storage module  206 . 
         [0058]    Further, the call distribution &amp; resource management module  202  determines whether a path to a peer node is normal according to an echo response message, which is a response for an echo request message for the peer node. In this case, the call distribution &amp; resource management module  202  may determine whether the path to the peer node is normal according to whether the echo response message is received within a pre-set time or whether a reset count included in the received echo response message is changed. If the echo response message is not received within the pre-set time or the reset count included in the received echo response message is changed, the call distribution &amp; resource management module  202  determines that the path to the peer node is abnormal and announces the occurrence of a path failure with respect to the peer node to the call session management module  204 . 
         [0059]    When a signal announcing the occurrence of a path failure with respect to a specific node is input from the call distribution &amp; resource management module  202 , the call session management module  204  evaluates a call for the specific node and information of other nodes associated with the call for the specific node using the call-related information storage module  206 . The call session management module  204  thereafter controls and processes a function for transmitting a path failure notification message including a type and address information of the specific node to the evaluated other nodes. Upon receiving a path failure acknowledgment message from the other nodes, the call session management module  204  controls and processes a function for deleting information related to the call for the specific node among information stored in the call-related information storage module  206 . Upon receiving a path failure notification message from the other nodes, the call session management module  204  analyzes the received path failure notification message to evaluate a type and address of a node experiencing the path failure, and controls and processes a function for deleting call-related information corresponding to the evaluated node type and address among the call-related information stored in the call-related information storage module  206 . 
         [0060]    The call-related information storage module  206  stores the call-related information. The call-related information storage module  206  stores the call-related information by associating the call-related information with information of a node for a specific call. 
         [0061]      FIG. 3  is a flowchart illustrating a call setup process for performing path management between nodes in an EPC system according to an exemplary embodiment of the present invention. 
         [0062]    Referring to  FIG. 3 , for call setup requested from an eNB/MS  300 , an MME  302  transmits a create session request message to an S-GW  304  in step  310 . Then, in step  312 , the S-GW  304  adds address information of the MME  302  to the create session request message as shown in Table 2 above, and transmits the resultant message to a P-GW  306 . 
         [0063]    In step  314 , the P-GW  306  stores the MME  302 &#39;s address information included in the create session request message by associating the address information with a call created by the create session request message. In step  316 , the P-GW  306  transmits a create session response message to the S-GW  304 . In this case, the P-GW  306  may perform steps  314  and  316  in a parallel manner, or may first perform step  316 , followed by step  314 . 
         [0064]    In step  318 , the S-GW  304  transmits the create session response message to the MME  302 . In step  320 , the S-GW  304  stores address information of the MME  302  and the P-GW  306  by associating the address information with information on a call created between the MME  302  and the P-GW  306 . The S-GW  304  may perform steps  318  and  320  in a parallel manner, or may first perform step  320 , followed by step  318 . 
         [0065]    In step  322 , the MME  302  sets up a Radio Access Bearer (RAB) with respect to the eNB/MS  300 . In step  324 , the MME  302  transmits a modify bearer request message to the S-GW  304 . In step  326 , the S-GW  304  transmits the modify bearer request message to the P-GW  306  by adding address information of the eNB  300 , which is a higher node of a specific call, to the modify bearer request message as shown in Table 3 above. 
         [0066]    In step  328 , the P-GW  306  stores the eNB  300 &#39;s address information included in the modify bearer request message by associating the address information with a call updated by the modify bearer request message. In step  330 , the P-GW  306  transmits a modify bearer response message to the S-GW  304 . The P-GW  306  may perform steps  328  and  330  in a parallel manner, or may first perform step  330 , followed by step  328 . 
         [0067]    In step  332 , the S-GW  304  transmits the create session response message to the MME  302 . In this case, the S-GW  304  may store the address of the eNB  300  by associating it with the information stored in step  320 . 
         [0068]    Although the address information of a higher node for a specific call is described above as included in the create session request message and the modify bearer request message transmitted by the S-GW  304  to the P-GW  306 , the address information of the higher node of the specific call may also be included in the create session request message and the modify bearer request message transmitted by the MME  302  to the S-GW  304 . 
         [0069]      FIG. 4  is a flowchart illustrating a call setup process of an S-GW in an EPC system according to an exemplary embodiment of the present invention. 
         [0070]    Referring to  FIG. 4 , the S-GW receives a create session request message for call setup from an MME in step  401 . In step  403 , the S-GW adds address information of the MME to the create session request message as shown in Table 2 above, and transmits the resultant message to a P-GW. In step  405 , the S-GW receives a create session response message from the P-GW. In step  407 , the S-GW stores address information of the MME and the P-GW by associating the additional information with information on a call to be created between the MME and the P-GW. In step  409 , the S-GW transmits the create session response message to the MME. 
         [0071]    In step  411 , the S-GW examines whether a modify bearer request message is received from the MME. If the modify bearer request is received, then in step  413 , the S-GW transmits the modify bearer request message to the P-GW by adding address information of an eNB, which is a higher node of a specific call, to the modify bearer request message, as shown in Table 3 above. In step  415 , the S-GW receives a modify bearer response message from the P-GW. In step  417 , the S-GW transmits the modify bearer response message to the MME. In this case, the S-GW may store the address information of the eNB by associating the address information with the information stored in step  407 . 
         [0072]      FIG. 5  is a flowchart illustrating a call setup process of a P-GW in an EPC system according to an exemplary embodiment of the present invention. 
         [0073]    Referring to  FIG. 5 , if the P-GW receives a create session request message from an S-GW in step  501 , then in step  503 , the P-GW analyzes the create session request message to evaluate address information of an MME, and stores the evaluated address information by associating the address information with a specific call corresponding to the create session request message. When the address information of the MME is stored in association with the specific call, the P-GW also stores information of the S-GW by associating the information with the specific call. In step  505 , the P-GW transmits a create session response message to the S-GW. 
         [0074]    In step  507 , the P-GW examines whether a modify bearer request message is received from the S-GW. If the modify bearer request message is received, then in step  509 , the P-GW analyzes the modify bearer request message to evaluate address information of an eNB, and stores the evaluated address information of the eNB by associating the address information with a call updated by the modify bearer request message. In step  511 , the P-GW transmits a modify bearer response message to the S-GW. 
         [0075]    As described with reference to  FIG. 3  to  FIG. 5 , the address information of the higher node for the specific call is added to the create session request message and the modify bearer message transmitted by the S-GW to the P-GW so that the P-GW can store and manage the address information of the higher node for each set-up call. 
         [0076]      FIG. 6  is a flowchart illustrating a path management process at the occurrence of a path failure with respect to an eNB in an EPC system according to an exemplary embodiment of the present invention. 
         [0077]    Referring to  FIG. 6 , an S-GW  604  transmits an echo request message to an eNB  600  in step  610 , and waits for an echo response message received from the eNB  600  for a pre-set time in step  612 . 
         [0078]    If an abnormal situation occurs in the eNB  600  or on a path to the eNB  600  and thus the S-GW  604  fails to receive the echo response message within the pre-set time, the S-GW  604  recognizes occurrence of a path failure with respect to the eNB  600 . Then, in step  614 , the S-GW  604  searches for information of an MME  602  and a P-GW  606 . The information is pre-stored in association with a call corresponding to the eNB  600 . In steps  616  and  622 , the S-GW  604  transmits a path failure notification message to the MME  602  and the P-GW  606 . The path failure notification message includes a node type and address information of the eNB  600 , that is, a node in which a path failure occurs, as shown in Table 5 above. 
         [0079]    In steps  618  and  624 , the MME  602  and the P-GW  606  respectively transmit a path failure acknowledgment message to the S-GW  604  as shown in Table 8 above. In steps  620  and  626 , the MME  602  and the P-GW  606  respectively determine that the node in which the path failure occurs is the eNB  600  by analyzing the path failure notification message, and deletes call-related information stored in association with the address information of the eNB  600 . In this case, the MME  602  may delete the call-related information by pre-recognizing the path failure with respect to the eNB  600  through an S1 interface. Meanwhile, if the path failure acknowledgment message is received from the MME  602  and the P-GW  606  respectively in steps  618  and  624 , then in step  628 , the S-GW  604  deletes the call-related information stored in association with the address information of the eNB  600 . 
         [0080]      FIG. 7  is a flowchart illustrating a path management process at the occurrence of a path failure with respect to an MME in an EPC system according to an exemplary embodiment of the present invention. 
         [0081]    Referring to  FIG. 7 , an S-GW  702  transmits an echo request message to an MME  700  in step  710 , and waits for an echo response message received from the MME  700  for a pre-set time in step  712 . 
         [0082]    If an abnormal situation occurs in the MME  700  or on a path to the MME  700  and thus the S-GW  702  fails to receive the echo response message within the pre-set time, or if the echo response message is received within the pre-set time but reset count information included in the received echo response message is changed, the S-GW  702  recognizes occurrence of a path failure with respect to the MME  700 . Accordingly, the S-GW  702  searches for information of a P-GW  704  in step  714 . The information is pre-stored in association with the MME  700 . In step  716 , the S-GW  702  transmits a path failure notification message to the P-GW  704 . The path failure notification message includes a node type and address information of the MME  700 , that is, a node in which a path failure occurs, as shown in Table 5 above. 
         [0083]    In step  718 , the P-GW  704  transmits a path failure acknowledgment message to the S-GW  702  as shown in Table 8 above. In step  720 , the P-GW  704  determines that a node in which the path failure occurs is the MME  700  by analyzing the path failure notification message, and deletes call-related information stored in association with the address information of the MME  700 . When the path failure acknowledgment message is received from the P-GW  704 , the S-GW  702  deletes the call-related information stored in association with the address information of the MME  700  in step  722 . 
         [0084]      FIG. 8  is a flowchart illustrating a path management process at the occurrence of a path failure with respect to a P-GW in an EPC system according to an exemplary embodiment of the present invention. 
         [0085]    Referring to  FIG. 8 , an S-GW  802  transmits an echo request message to a P-GW  804  in step  810 , and waits a pre-set time for an echo response message received from the P-GW  804  in step  812 . 
         [0086]    If an abnormal situation occurs in the P-GW  804  or on a path to the P-GW  804  and thus the S-GW  802  fails to receive the echo response message with the pre-set time, or if the echo response message is received within the pre-set time but reset count information included in the received echo response message is changed, the S-GW  802  recognizes occurrence of a path failure with respect to the P-GW  804 . Accordingly, the S-GW  802  searches for information of an MME  800  in step  814 . The information is pre-stored in association with the P-GW  804 . In step  816 , the S-GW  802  transmits a path failure notification message to the MME  800 . The path failure notification message includes a node type and address information of the P-GW  804 , that is, a node in which a path failure occurs, as shown in Table 5 above. 
         [0087]    In step  818 , the MME  800  transmits a path failure acknowledgment message to the S-GW  802  as shown in Table 8 above. In step  820 , the MME  800  determines that a node in which the path failure occurs is the P-GW  804  by analyzing the path failure notification message, and deletes call-related information stored in association with the address information of the P-GW  804 . In this case, the MME  800  may transmit a cell delete request message to a specific eNB sequentially with a time interval in the process of deleting the call-related information, so that the eNB can be avoided from overhead caused by instantaneous call release. When the path failure acknowledgment message is received from the MME  800  in step  818 , the S-GW  802  deletes the call-related information stored in association with the address information of the P-GW  804  in step  822 . 
         [0088]      FIG. 9  is a flowchart illustrating a path management process at the occurrence of a path failure with respect to an S-GW in an EPC system according to an exemplary embodiment of the present invention. 
         [0089]    Referring to  FIG. 9 , an MME  900  transmits an echo request message to an S-GW  902  in step  910 , and waits for an echo response message received from the S-GW  902  for a pre-set time in step  912 . 
         [0090]    If an abnormal situation occurs in the S-GW  902  or on a path to the S-GW  902  and thus the MME  900  fails to receive the echo response message within the pre-set time, or if the echo response message is received within the pre-set time but reset count information included in the received echo response message is changed, the MME  900  recognizes occurrence of a path failure with respect to the S-GW  902 . Accordingly, in step  914  the MME  900  searches for and deletes call-related information stored in association with address information of the S-GW  902 . In this case, the MME  900  may also transmit a cell delete request message to a specific eNB sequentially with a time interval in the process of deleting the call-related information, so that the eNB can be avoided from an overhead caused by instantaneous call release. 
         [0091]    Meanwhile, a P-GW  904  transmits an echo request message to the S-GW  902  in step  920 , and waits for an echo response message received from the S-GW  902  for a pre-set time in step  922 . If an abnormal situation occurs in the S-GW  902  or on a path to the S-GW  902  and thus the P-GW  904  fails to receive the echo response message within the pre-set time, or if the echo response message is received within the pre-set time but reset count information included in the received echo response message is changed, the P-GW  904  recognizes occurrence of a path failure with respect to the S-GW  902 . Accordingly, the P-GW  904  searches for and deletes call-related information stored in association with the address information of the S-GW  902  in step  924 . 
         [0092]      FIG. 10  is a flowchart illustrating a process of performing path management by an S-GW by recognizing occurrence of a path failure with respect to a peer node in an EPC system according to an exemplary embodiment of the present invention. 
         [0093]    Referring to  FIG. 10 , the S-GW transmits an echo request message to the peer node in step  1001 , and examines whether an echo response message is received from the peer node within a pre-set time in step  1003 . The peer node may be, for example, an eNB, an MME, and/or a P-GW. 
         [0094]    If the echo response message is not received within the pre-set time, the procedure proceeds to step  1007 . If the echo response message is received within the pre-set time, then in step  1005 , the S-GW examines whether reset count information included in the received echo response message is changed. 
         [0095]    If the reset count information is not changed, the S-GW recognizes that the peer node operates normally, and then the process of  FIG. 10  ends. If the reset count information is changed, proceeding to step  1007 , the S-GW recognizes occurrence of a path failure since a system of the peer node is down or an abnormal situation occurs on a path to the peer node. In step  1009 , the S-GW searches for information of a node associated with the peer node. In step  1011 , the S-GW transmits to the found node a path failure notification message including a type and address information of the peer node as shown in Table 5 above. 
         [0096]    In step  1013 , the S-GW receives a path failure acknowledgment message from the found node. In step  1015 , the S-GW deletes data related to a call associated with the peer node and the found node. 
         [0097]      FIG. 11  is a flowchart illustrating a process of performing path management by an MME or a P-GW by receiving information indicating occurrence of a path failure from an S-GW according to an exemplary embodiment of the present invention. Although the following description will be explained with respect to the P-GW, the same also applies to the MME. 
         [0098]    Referring to  FIG. 11 , the P-GW receives a path failure notification message from a peer node (i.e., the S-GW) in step  1101 , and analyzes the path failure notification message to evaluate a type and address information of a node in which the path failure occurs in step  1103 . In step  1105 , the P-GW searches for call-related data stored in association with a node corresponding to the evaluated node type and address. In step  1107 , the P-GW deletes the found call-related data. 
         [0099]      FIG. 12  is a flowchart illustrating a process of performing path management by an MME or a P-GW by recognizing occurrence of a path failure from an S-GW according to an exemplary embodiment of the present invention. Although the following description will be explained with respect to the P-GW, the same also applies to the MME. 
         [0100]    Referring to  FIG. 12 , the P-GW transmits an echo request message to a peer node (i.e., the S-GW) in step  1201 , and thereafter examines whether an echo response message is received from the S-GW within a pre-set time in step  1203 . If the echo response message is not received within the pre-set time, the procedure proceeds to step  1207 . If the echo response message is received within the pre-set time, proceeding to step  1205 , the S-GW examines whether reset count information included in the received echo response message is changed. 
         [0101]    If the reset count information is not changed, the S-GW recognizes that the peer node operates normally, and then the process of  FIG. 12  ends. If the reset count information is changed, then in step  1207 , the S-GW recognizes occurrence of a path failure since a system of the peer node is down or an abnormal situation occurs on a path to the peer node. In step  1209 , the P-GW searches for call-related data stored in association with the S-GW. In step  1211 , the P-GW deletes the found call-related data. 
         [0102]    In the aforementioned description, when call-related information is deleted in each node, call release information and accounting information should be managed normally. 
         [0103]    According to exemplary embodiments of the present invention, path management is performed between nodes in an Evolved Packet Core (EPC) system by using a create session message and a modify bearer message including a node address and a message for announcing an abnormal status of a specific node. Therefore, unnecessary call-release message creation and transmission are avoided, and thus generation of an overload of an intermediary node and a peer node can be prevented and waste of resources can be prevented. In addition, exemplary embodiments of the present invention can simplify a procedure of handling a path failure and thus there is an advantage in terms of system reliability and resource saving. 
         [0104]    While the present 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 present invention as defined by the appended claims and their equivalents.