Patent Publication Number: US-9413822-B2

Title: System and method for providing mobile P2P service

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to and the benefit of Korean Patent Application No. 10-2010-0120818 filed in the Korean Intellectual Property Office on Nov. 30, 2010, the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     (a) Field of the Invention 
     The present invention relates to a system and method for providing a mobile P2P service. 
     (b) Description of the Related Art 
     As many people use mobile devices such as cell phones and PDAs nowadays, Peer-to-Peer (hereinafter, ‘P2P’) networking in mobile environments is getting more and more attention. 
     The P2P in mobile environments is different from the P2P in fixed environments that has been studied a lot in the past because mobile devices are objects with mobility and each of them has limited communication coverage. 
     Moreover, as the performance of smartphones has seen much improvement, a wide variety of application services are being delivered. Especially, the demand for large volumes of multimedia traffic is sharply growing. 
     Meanwhile, distributed service technologies, such as Peer-to-Peer (P2P), are widely used in wired networks in order to accept large volumes of traffic like IPTV, distribute the load of a server, and prevent bottlenecks in a particular network segment. 
     However, in the case that a distributed service technology such as P2P is applied to wireless networks, it is not appropriate to adapt the technology as it is because wireless link fees imposed on subscribers are high, compared to wired ones, and transfer rates are low and unstable. 
     The following problem is expected to appear when a mobile P2P service is realized. That is, if a receiving mobile peer is disconnected during movement, or loses its connection because the battery has run out, a transmitting mobile peer will continuously transmit content without knowing about the disconnection while the mobile peer on the other side cannot receive the content, resulting in a loss of the content. However, if the mobile peer resumes its connection later, it will seek retransmission, and the mobile peer on the other side will repeat transmission. Thus, the overload and waste of wireless traffic are expected. Moreover, the probability of such a situation is considerably high, compared to wired links, because wireless links are unstable than the wired ones. 
     The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in an effort to provide a system and method for providing a mobile P2P service, which can provide traffic stably in an appropriately distributed fashion, and keep a mobile P2P communication path in its optimum state depending on the movement and status change of a mobile peer. 
     An exemplary embodiment of the present invention provides a mobile P2P system. This system includes: a mobile tracker node that is located in a dedicated wired network operating in conjunction with an internet network to which a plurality of peer nodes are connected, manages information of a plurality of mobile peer nodes connected to a wireless access network, and transmits, to the mobile peer nodes, a peer list containing information on one or more peer nodes having the content queried by the plurality of mobile peer nodes, the one or more peer nodes including the mobile peer nodes and the peer nodes on the internet network; and 
     a super peer node that is connected to the mobile tracker node via wires, located for each wireless access network, forwards a content query received from the mobile peer nodes to the mobile tracker node, and receives the queried content from the peer nodes in the peer list received from the mobile tracker node and transmits the same to the mobile peer nodes. 
     Another exemplary embodiment of the present invention provides a mobile P2P service method. This method includes: a mobile tracker node&#39;s registering information received from a plurality of mobile peer nodes connected to a wireless access network, the mobile tracker node being located in a dedicated wired network operating in conjunction with an internet network to which a plurality of peer nodes are connected; providing the plurality of mobile peer nodes with information on a super peer node located in the wireless access network and connected via wires to the mobile tracker node; receiving, from the super peer node, a content query transmitted by the plurality of mobile peer nodes; and creating a peer list containing information on one or more peer nodes having the queried content based on the received information, and transmitting the same to the super peer node, the one or more peer nodes including the mobile peer nodes and the peer nodes on the internet network. 
     Yet another exemplary embodiment of the present invention provides a mobile P2P service method. This method includes: a super peer node&#39;s receiving a content query from a plurality of mobile peer nodes and forwarding the same to a mobile tracker node, the super peer node being connected via wires to the mobile tracker located in a dedicated wired network operating in conjunction with an internet network to which a plurality of peer nodes are connected; receiving, from the mobile tracker node, a peer list containing information on one or more peer nodes having the queried content, the one or more peer nodes including the mobile peer nodes and the peer nodes on the internet network; and receiving the queried content from a certain peer node included in the peer list and transmitting the same to the mobile peer nodes. 
     According to an exemplary embodiment of the present invention, the rapid increase in wireless data traffic caused by the increase in smartphone users in the mobile communication market can be dealth with efficiently by adapting a distributed service technology, such as P2P, to multiple wireless networks. 
     Moreover, a super peer capable of replacing the function of a mobile peer can be introduced to minimize traffic load in a wireless segment. 
     Furthermore, a P2P communication path can be optimized by taking into account distance, cost, and wireless node traffic condition. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view showing the configuration of networks for providing a mobile P2P service according to an exemplary embodiment of the present invention. 
         FIG. 2  is a block diagram showing the configuration of a super peer node according to an exemplary embodiment of the present invention. 
         FIG. 3  is a block diagram showing the configuration of a mobile tracker to node according to an exemplary embodiment of the present invention. 
         FIG. 4  is a flowchart showing a peer registration process of a mobile peer node according to an exemplary embodiment of the present invention. 
         FIG. 5  is a flowchart showing a P2P content transmission process according to an exemplary embodiment of the present invention. 
         FIG. 6  is a flowchart showing in details a P2P content transmission operation of the super peer node according to an exemplary embodiment of the present invention. 
         FIG. 7  is a flowchart showing a method for controlling a content transmission path according to one exemplary embodiment of the present invention. 
         FIG. 8  is a flowchart showing a method for controlling a content transmission path according to another exemplary embodiment of the present invention. 
         FIG. 9  is a view showing a mobile P2P content transmission path according to an exemplary embodiment of the present invention. 
         FIG. 10  is a flowchart showing a method for controlling a content transmission path according to still another exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     In the following detailed description, only certain exemplary embodiments of the present invention have been shown and described, simply by way of illustration. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature and not restrictive. Like reference numerals designate like elements throughout the specification. 
     Throughout the specification, unless explicitly described to the contrary, the word “comprise” and variations such as “comprises” or “comprising”, will be understood to imply the inclusion of stated elements but not the exclusion of any other elements. 
     In this specification, a mobile peer node may designate a mobile station (MS), a terminal, a mobile terminal (MT), a subscriber station (SS), a portable subscriber station (PSS), user equipment (UE), an access terminal (AT), and so on. Moreover, the mobile peer node may include all or a part of functions of the mobile terminal, the subscriber station, the portable subscriber station, the user equipment, and so on. 
     In this specification, a base station (BS) may designate an access point (AP), a radio access station (RAS), a node B (Node B), an evolved node B (eNode B), a base transceiver station (BTS), a mobile multihop relay (MMR)-BS, and so on. Further, the base station may include all or a part of functions of the access point, the radio access station, the node B, the eNode B, the base transceiver station, the MMR-BS, and so on. 
     Hereinafter, a system and method for providing a mobile P2P service according to an exemplary embodiment of the present invention will be described in detail with reference to the drawings. 
       FIG. 1  is a view showing the configuration of networks for providing a mobile P2P service according to an exemplary embodiment of the present invention. 
     Referring to  FIG. 1 , the networks for providing a mobile P2P service include wireless access networks  100 , a dedicated wired network  200 , and an internet network  300 . 
     The wireless access networks  100 , which are connected to a mobile peer node  400 , include, for example, a WCDMA (Wideband Code Division Multiple Access) network, a WiBro network, and a WiFi network. 
     Such a wireless access network  100  includes an edge router  101 , and is connected to the dedicated wired network  200  through the edge router  101 . The edge router  101  serves to interconnect the wireless access network  100 , to which it belongs, to the dedicated wired network  200 . 
     The dedicated wired network  200  includes edge routers  201  and a core router  203 . The edge routers  201  are connected to the edge router  101  of each wireless access network  100  and the core router  203  to connect the wireless access networks  100  and the dedicated wired network  200 . Further, the core router  203  is connected to an edge router  301  of the internet network  300  to connect the wireless access networks  100  and the internet network  300 . 
     At this time, a traffic monitoring device  205  is connected to the core router  203  to collect traffic information. 
     Moreover, the internet network  300  includes the edge router  301  connected to the edge router  201  of the dedicated wired network  200 , and the edge router  301  is connected to a tracker node  303 . The tracker node  303  collects information of peer nodes  305  and provides a peer list. 
     Among the wireless access networks  100 , the WCDMA network and the to WiBro network each include a base station  103  and an EMS (Element Management System)  105 . 
     The EMS  105  remotely monitors and controls information of IP (Internet Protocol) equipment, for example, the base station  103 , to collect traffic information of the base station  103  and transmit it to the traffic monitoring device  205  of the dedicated wired network  200  through the edge router  101 . 
     Among the wireless access networks  100 , the WiFi network includes an access point (AP)  107 . The access point  107  transmits traffic information to the traffic monitoring device  205  through the edge router  101 . 
     At this point, the wireless access networks  100  are connected to one or more mobile peer nodes  400 . 
     The mobile peer nodes  400  are handheld mobile terminals, such as cell phones, PDAs (Personal Digital Assistants), smartphones, laptops, and iPads. 
     Such a mobile peer node  400  includes the Content Upload Function (CUF) for sending content and the Content Download Function (CDF) for receiving content. 
     A virtual server, i.e., super peer node  500 , which replaces the function of the mobile peer node  400 , is located in each wireless access network  100 . 
     Such a super peer node  500  in the form of a virtual server is fixedly located at the boundary of the wireless access network  100 , and connected to the dedicated wired network  200  via wires. Also, the super peer node  500  receives content in place of the mobile peer node  400  and transmits it to the mobile peer node  400 , and registers a content list of the mobile peer node  400  to a mobile tracker node  600 . 
     In a mobile P2P environment, a peer list may be frequently updated according to the movement and status changes of the mobile peer nodes  400 . With these changes in the mobile peer nodes  400 , frequent control messages may be generated between the mobile peer nodes  400  and the mobile tracker node  600 . To reduce such status changes, the super peer node  500  replacing the function of the mobile peer nodes  400  is located at a boundary end point of the wireless access network  100  so as to be connected to the dedicated wired network  200  via wires. 
     As the super peer node  500  can receive and forward the content of the mobile peer nodes  400  in place of the mobile peer nodes  400 , the received content can be re-transmitted later to the mobile peer nodes  400  even under a situation where no content cannot be received because the mobile peer nodes  400  are disconnected or the battery runs out, thereby preventing the problem of content loss. 
     Further, the dedicated wired network  200  includes a mobile tracker node  600  connected to the core router  203 . Like the tracker node  303  of the internet network  300 , the mobile tracker node  600  provides a peer list by collecting information of the mobile peer nodes  400 . That is, the mobile tracker node  600  provides a list of the mobile peer nodes  400  where the content requested by the mobile peer nodes  400  can be downloaded. 
     At this point, the super peer node  500  and the mobile tracker node  600  can be implemented in the form of a large-capacity server. 
     Now, detailed configurations of the super peer node  500  and the mobile tracker node  600  will be described with reference to  FIGS. 2 and 3 . 
       FIG. 2  is a block diagram showing the configuration of a super peer node according to an exemplary embodiment of the present invention. 
     Referring to  FIG. 2 , the super peer node  500  includes a routing unit  501 , a content transmission/reception control unit  503 , a content reception unit  505 , a content transmission unit  507 , a content DB  509 , and a path control unit  511 . 
     The routing unit  501  receives ‘peer registration’ and ‘content query’ from the mobile peer nodes  400 , and routes them to the mobile tracker node  600 . 
     The content transmission/reception control unit  503  receives a peer list from the mobile tracker node  600 . 
     The peer node contains information on peer nodes having the content, and includes information on content transmission priority of the peer nodes. Hereinbelow, the peer nodes having the content and included the peer list are commonly referred to as ‘content transmission peers’. 
     Such content transmission peers include peer nodes  305  located in the internet network  300 , the mobile peer nodes  400  located in the wireless access network  100  to which the mobile peer node  400  that has transmitted content query belongs, and mobile peer nodes  400  located in a different wireless access network  100 . Although described later, the super peer node  500  has the content storage function. Thus, the content transmission peers also include the super peer node  500  of the wireless access network  100  to which the mobile peer node  400  that has transmitted content query belongs, and the super peer node  500  of a different wireless access network  100 . 
     The content transmission/reception unit  503  sends a content request to the content transmission peer with the highest priority among the content transmission peers listed in the peer list, and transmits the content to the mobile peer node  400  that has transmitted the content query. 
     If there is pre-stored content in the content DB  509 , the stored content can be transmitted to the mobile peer node  400  that has transmitted the content query. 
     Moreover, if a content storage request is received from the mobile tracker node  600  during reception of the content from the content transmission peer, content transmission to the mobile peer node  400  that has transmitted the content query is stopped, and the received content is stored in the content DB  509 . Of course, if a content transmission request is received later from the mobile tracker node  600 , content transmission is resumed, and the content stored in the content DB  509  is transmitted to the mobile peer node  400  that has transmitted the content query. 
     The content reception unit  505  downloads the content from the content transmission peer under control of the content transmission/reception control unit  503 , and can be implemented as a large-capacity buffer. 
     The content transmission unit  507  transmits the content received by the content reception unit  505  or the content stored in the content DB  509  to the mobile peer node  400  that has transmitted the content query under control of the content transmission/reception control unit  503 . 
     The content DB  509  stores the content received by the content reception unit  505  under control of the content transmission/reception unit  503 . 
     Upon receipt of a super peer handover request from the mobile tracker node  600 , the path control unit  511  performs super peer handover to a different super peer node  500  or mobile peer node  400  based on the information contained in the super peer handover request. As used herein, the super peer handover is defined as an ‘operation for handing over the content transmission rights’. 
     During the super peer handover, information on the mobile peer node  400  that is currently transmitting the content can be transmitted together with the content already received by the content reception unit  505 . 
       FIG. 3  is a block diagram showing the configuration of a mobile tracker node according to an exemplary embodiment of the present invention. 
     Referring to  FIG. 3 , the mobile tracker node  600  includes a meta information DB  601 , a terminal status information DB  603 , an access network traffic information DB  605 , a peer locality information DB  607 , a super peer information DB  609 , a mobile peer management unit  611 , a terminal status monitoring unit  613 , a network traffic monitoring unit  615 , and a service control unit  617 . 
     The meta information DB  601  stores user content information, i.e., meta information. Such meta information includes a list of content for each mobile peer node  400  received from the mobile peer nodes  400 . 
     Moreover, the meta information includes content path information provided for each mobile peer node  400 . 
     Other meta information includes a variety of information related to mobile P2P content, such as mobile P2P service subscription information, connection quality information of mobile P2P service, upload speed information, download speed information, number of existing peer connections, amount of available peer content, historical peer behavior information, forecast peer behavior information, local resources, type of internet address, and node accessibility, predicted pairwise connectivity. 
     The terminal status information DB  603  stores information related to the terminal status of the mobile peer nodes  400 . In other words, it stores terminal status change information, such as Power On/Off, terminal performance information of the mobile peer nodes  400 , and information about the connection status of the mobile peer nodes  400  to the access network  100 . 
     The access network information DB  605  stores information about the nodes constituting the access network  100 . These nodes include an edge router  101 , a switch (not shown), a super pier node  500 , a base station  103 , ACR (Access Control Router) for a Wibro network, and SGSN (Serving GPRS Support Node) and GGSN (GPRS Gateway Support Node) for a WCDMA network. 
     Moreover, the access network information DB  605  stores information about the traffic information of each cell, i.e., load information indicating the traffic conditions of a base station  103  and an access point  107 . 
     The peer locality information DB  607  stores the type of a wireless access network  100  to which a mobile peer node  400  is connected, information about a connected cell, and real-time location information. Such locality information includes internet protocol addresses, network coordinate system information, internet protocol address to geolocation database results, information about whether peers are in a public or a private network region, postal address information, and global positioning system information. 
     The super peer information DB  609  includes location information of each of the super peer nodes  500  located in the wireless access networks  100 , server information, and so on. 
     Moreover, the super peer information DB  609  stores mapping information between the mobile peer node  400  and the super peer node  500  of the wireless access network  100  to which the mobile peer node  400  is connected. A mapping between the mobile peer node  400  and the super peer node  500  functions to suppress traffic on a wireless interface that is unnecessarily generated from the mobile peer node  400 . Further, a client mobile peer requesting a service continuously performs a relay function through the super peer even if communication is cut off due to changes in the wireless environment, thereby enhancing service continuity and the mobility of the mobile peer. 
     The mobile peer management unit  611  performs the meta information processing function (MIPF) for managing content information of the mobile peer node  400 . The mobile peer management unit  611  performs peer registration of the mobile peer node  400 , and updates content information received from the mobile peer node  400  in the meta information DB  601 . 
     At this point, the mobile peer management unit  611  receives, from the super peer node  500 , the peer registration transmitted by the mobile peer node  400 . 
     The terminal status monitoring unit  613  performs the user equipment status monitoring function (UEMF) for managing the status of the mobile peer node  400 . The terminal status monitoring unit  613  operates in conjunction with the wireless access network  100  to which the mobile peer node  400  is connected so as to monitor the power on/off, connection status, etc. of the mobile peer node  400 , and updates the monitoring result to the terminal status information DB  603 . 
     In this case, the terminal status monitoring unit  613  can periodically receive terminal status information of the mobile peer node  400  through the mobile peer node  400  or through the super peer node  500 . Alternatively, it can receive terminal status information of the mobile peer node  400  through the base station  103  or access point  107  of the wireless access network  100  to which the mobile peer node  400  is connected. 
     The network traffic monitoring unit  615  performs the access network traffic monitoring function (ATMF) for monitoring the traffic condition of the wireless access network  100 . The network traffic monitoring unit  615  collects, from the traffic monitoring device  205 , base station load information of the wireless access network  100  collected by the traffic monitoring device  205 , and updates it in the access network information DB  605 . 
     The service control unit  617  performs the mobile P2P service control function (MPSF). 
     That is, the service control unit  617  receives, from the mobile peer node  400 , a content query for requesting a content download, and searches the meta information DB  601  and provides the mobile peer node  400  with a peer list containing information about peers from which the content can be downloaded. 
     Unlike P2P in a wired (fixed) network, in a mobile P2P network, the peer list is created by selecting content transmission peers, taking into account the to following criteria: 
     {circle around (1)} terminal mobility 
     {circle around (2)} terminal status change (Power On, Off) 
     {circle around (3)} abrupt change in connection quality (i.e., it is difficult to ensure QoS due to variations in transmission rate) 
     {circle around (4)} Terminal performance is lower than computer performance in wired (fixed) network 
     {circle around (5)} High fees to be charged for connecting links 
     {circle around (5)} Billing for transmission as well as for reception Moreover, the service control unit  617  determines an optimum peer list by analyzing network traffic information of the content transmission peers based on the information obtained from searching of the terminal status information DB  603  and the access network traffic information DB  605 . 
     In other words, network traffic information including the types of connected networks of the content transmission peers and the load of connected cells are analyzed so that any content transmission peer belonging to a base station  103  or access point  107  with heavy traffic should not be included in the peer list. 
     The service control unit  617  can select content transmission peers according to the following order of content transmission priority, which may differ more or less depending on the type of the wireless access network  100 . 
     For example, if the wireless access network  100  to which the mobile peer node  400  requesting a content query is connected is a WCDMA network, content transmission peers are selected according to the following order of to content transmission priority shown in Table 1. 
     
       
         
           
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Priority 
                   
               
               
                 order 
                 object 
               
               
                   
               
             
            
               
                 1 
                 Super peer on WCDMA network 
               
               
                 2 
                 Peer connected to wired network or super peer on other network 
               
               
                 3 
                 Mobile peer connected to WiFi 
               
               
                 4 
                 Mobile peer connected to Wibro with light load (less than 
               
               
                   
                 40%) on base station 
               
               
                 5 
                 Mobile peer connected to WCDMA with little load (less than 
               
               
                   
                 10%) on base station 
               
               
                 6 
                 Mobile peer connected to WiBro with bearable load (less than 
               
               
                   
                 70%) on base station 
               
               
                 7 
                 Mobile peer connected WCDMA with bearable load (less than 
               
               
                   
                 50%) on base station 
               
               
                   
               
            
           
         
       
     
     Moreover, if the wireless access network  100  to which the mobile peer node  400  requesting a content query is connected is a WiFi network, content transmission peers are selected according to the following order of content transmission priority shown in Table 2. 
     
       
         
           
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                 Priority 
                   
               
               
                 order 
                 object 
               
               
                   
               
             
            
               
                 1 
                 WiFi mobile peer that can constitute AD hoc network 
               
               
                 2 
                 Super peer on WiFi network 
               
               
                 3 
                 Peer connected to wired network or super peer on other network 
               
               
                 4 
                 WiFi-connected mobile peer that cannot constitute AD 
               
               
                   
                 hoc network 
               
               
                 5 
                 Mobile peer connected to Wibro with light load (less than 
               
               
                   
                 40%) on base station 
               
               
                 6 
                 Mobile peer connected to WCDMA with little load (less than 
               
               
                   
                 10%) on base station 
               
               
                 7 
                 Mobile peer connected to WiBro with bearable load (less than 
               
               
                   
                 70%) on base station 
               
               
                 8 
                 Mobile peer connected WCDMA with bearable load (less than 
               
               
                   
                 50%) on base station 
               
               
                   
               
            
           
         
       
     
     Further, as a result of searching the terminal status information DB  603  and the super peer information DB  609 , if it is determined that the mobile peer node  400  is in a content unreceivable state due to the power off of the mobile peer node  400  or the disconnection of the wireless access network  100 , a request is sent to the super peer node  500  mapped to the current mobile peer node  400  to stop content transmission to the mobile peer node  400  and store the content being transmitted. Next, when the mobile peer node  400  goes back into the content receivable state, a request is sent to the super peer node  500  to transmit the stored content to the mobile peer node  400 . 
     In addition, as a result of searching the peer locality information DB  607 , if it is determined that the mobile peer node  400  has moved, the service control unit  617  configures an optimum P2P transmission path by taking into account the traffic load, cost, etc. of the wireless access network  100  to which the mobile peer node  400  is connected, based on the information obtained from searching of the access network traffic information DB  605 . 
     Next, a method for providing a mobile P2P service will be described based on the above-explained configuration of  FIGS. 1 to 3 . 
     Like components to those of  FIGS. 1 through 3  are indicated with like reference numerals of  FIGS. 1 through 3 . 
     First,  FIG. 4  is a flowchart showing a peer registration process of a mobile peer node according to an exemplary embodiment of the present invention. 
     Referring to  FIG. 4 , the mobile peer node  400  connected to a certain wireless access network  100  executes a mobile P2P service (S 201 ). This involves executing a process in which a user sends a request to use the mobile P2P service and all the relevant operations are carried out. 
     Then, the mobile peer node  400  is connected to the mobile tracker node  600  and performs peer registration (S 203 ). As the connection is an initial connection to the mobile tracker node  600 , the peer registration is transmitted to the mobile tracker node  600 . 
     The peer registration is an operation of reporting peer-related information defined in the mobile P2P service to the mobile tracker node  600  periodically or on every change in the information on the content the mobile peer node  400  has. Also, the peer-related information can include information on the content the mobile peer node  400  has, terminal performance information, information about the connected access network, current location information, and so on. 
     Meanwhile, the mobile peer management unit  611  of the mobile tracker node  600  stores the peer-related information received from the mobile peer node  400  in the peer registration step S 203  (S 105 ). 
     Next, the mobile peer management unit  611  of the mobile tracker node  600  searches the super peer information DB  609  for the super peer node located in the wireless access network  100  to which the mobile peer node  400  is connected (S 107 ), and determines whether the super peer node  500  is present or not (S 109 ). 
     As a result of the search, if the super peer node  500  is present, information about the searched super peer node  500  is transmitted to the mobile peer node  400  (S 111 ). Then, the mobile peer node  400  and the super peer node  500  are mapped and stored in the super peer information DB  609  (S 113 ). 
     Afterwards, when the time for peer registration arrives, the mobile peer node  400  determines whether super peer node information has been received from the mobile tracker node  600  or not (S 115 ). 
     If the super peer node information has been received, the mobile peer node  400  performs peer registration to the super peer node  500  (S 117 ). Then, the super peer node  500  forwards the peer registration to the mobile tracker node  600  (S 119 ). 
     On the other hand, if it is determined in the step S 115  that no super peer node information has been received, the mobile peer node  400  performs peer registration to the mobile tracker node  600  (S 121 ). 
     The mobile tracker node  600  updates the peer-related information received in the step S 119  or the step S 121  (S 123 ). 
       FIG. 5  is a flowchart showing a P2P content transmission process according to an exemplary embodiment of the present invention. 
     Referring to  FIG. 5 , when a P2P content query requested by the user is issued (S 201 ), the mobile peer node  400  determines whether there exists super peer node information of the connected wireless access network  100  (S 203 ). That is, it is determined whether ther super peer node information received upon registration of  FIG. 4  is stored or not. 
     If there exists super peer node information, the content query is transmitted to the super peer node  500  (S 205 ). Then, the routing unit  501  of the super peer node  500  routes the content query to the mobile tracker node  600  (S 207 ). 
     Next, the service control unit  617  of the mobile tracker node  600  searches the meta information DB  601  for peer-related information (S 209 ), and selects one or more content transmission peers having the content queried in the step S 207  (S 211 ). These content transmission peers include the mobile peer node  400 , a super peer node  500 , and the peer node  305  of the internet network  300 . 
     Moreover, the service control unit  617  of the mobile tracker node  600  analyzes the status of a network to which a content transmission peer is connected by searching the access network traffic information DB  605  and the peer locality information DB  607  (S 213 ). 
     In other words, if the content transmission peer is the mobile peer node  400  or the super peer node  500 , base station (or cell) load information of the wireless access network  100  stored in the access network traffic information DB  605  is checked. 
     Also, if the content transmission peer is the peer node  305  of the internet network  300 , the tracker node  303  of the internet network  300  is requested to check network load information. 
     The service control unit  617  of the mobile tracker node  600  creates a peer list consisting of one or more content transmission peers that meet a defined order of content transmission priority as an analysis result of the connected network status obtained in the step S 213 , among one or more content transmission peers selected in the step S 211  (S 215 ). That is, any content transmission peer not included in the orders of content transmission priority of Tables 1 and 2 is not included in the peer list. 
     Once the peer list is created (S 215 ), the service control unit  617  of the mobile tracker node  600  transmits the peer list to the super peer node  500  (S 217 ). The peer list includes an order of content transmission priority. 
     Afterwards, the content transmission/reception control unit  507  of the super peer node  500  sends a content download request to the content transmission peer with the highest priority according to the peer list received in the step S 217 , and the content reception unit  505  of the super peer node  500  downloads the content (S 219 ). Next, the content transmission unit  507  of the to super peer node  500  transmits the content downloaded in the step S 219  to the mobile peer node  400  (S 221 ). 
     On the other hand, if the mobile peer node  400  determines in the step S 203  that there exists no super peer node information, i.e., the super peer node  500  is not present in the wireless access network  100  to which the mobile peer node  400  is connected, a content query is transmitted to the mobile tracker node  600  (S 223 ). 
     The service control unit  617  of the mobile tracker node  600  searches the metal information DB  601  (S 225 ), and selects one or more content transmission peers having the queried content (S 227 ). Then, the connected network status is analyzed (S 229 ) to create a peer list consisting of optimum content transmission peers that meet the order of content transmission prirotiy (S 231 ), and the created peer list is transmitted to the mobile peer node  400  (S 233 ). Here, the steps S 225  to S 231  are identical to the steps S 209  to S 215 . 
     Meanwhile, the mobile peer node  400  sends a content request to the content transmission peer with the highest priority among the content transmission peers included in the peer list received in the step S 233 , and receives the content (S 235 ). 
       FIG. 6  is a flowchart showing in details a P2P content transmission operation of the super peer node according to an exemplary embodiment of the present invention. 
     Referring to  FIG. 6 , the content transmission/reception control unit  503  of the super peer node  500  that has received the peer list from the mobile tracker node  600  searches the content DB  509  (S 303 ), and determines whether the content queried by the mobile peer node  400  is stored or not (S 305 ). 
     If the content has been stored, the content transmission/reception control unit  503  of the super peer node  500  extracts the stored content from the content DB  509  (S 307 ), and transmits it to the mobile peer node  400  (S 309 ). 
     Otherwise, if the content is determined not to have been stored, the content transmission/reception control unit  503  of the super peer node  500  searches the peer list received in the step S 301  (S 311 ), and sends a content transmission request to the content transmission peer (not shown) with the highest priority (S 313 ). Then, the content transmission unit  505  of the super peer node  500  receives the content from the content transmission peer (not shown) (S 315 ), and the content transmission unit  507  of the super peer node  500  transmits the content being buffered (S 317 ) to the mobile peer node  400  (S 319 ). 
     In the case of failing to receive the content in the step S 315 , the content transmission/reception control unit  503  of the super peer node  500  sends a content transmission request to the content transmission peer (not shown) with the next highest priority included in the peer list and receives the content. 
     Meanwhile, the terminal status monitoring unit  613  of the mobile tracker node  600  monitors the status of the mobile peer node  400  (S 321 ). Then, a monitoring result is stored in the terminal status information DB  603 . The monitoring method may involve receiving terminal status information periodically from the base station  103 , the EMS  105 , and the wireless access point  107 . Alternatively, the terminal status information may be received from the mobile peer node  400  if the mobile peer node  400  has performed peer to registration. 
     At this point, the service control unit  617  of the mobile tracker node  600  determines if content transmission to the mobile peer node  400  is not available by referring to the terminal status information DB  603  (S 323 ). For example, it is determined if the mobile peer node  400  is powered off or has a wireless network connection error. 
     If it is determined that content transmission to the mobile peer node  400  is not available in the step S 323 , the service control unit  617  of the mobile tracker node  600  sends a content storage request to the super peer node  500  (S 325 ). 
     Next, the content transmission/reception control unit  503  of the super peer node  500  stops content transmission to the mobile peer node  400  (S 327 ), and stores the content received from the content transmission peer (not shown) in the content DB  509  (S 329 ). Then, a content storage response is transmitted to the service control unit  617  of the mobile tracker node  600  (S 331 ). 
     Afterwards, the service control unit  617  of the mobile tracker node  600  determines the availability of content transmission while continuously monitoring the terminal status of the mobile peer node  400  by referring to the terminal status information DB  603  (S 333 ). 
     If content transmission is available, the service control unit  617  of the mobile tracker node  600  sends a content transmission request to the super peer node  500  (S 335 ). 
     Then, the content transmission/reception control unit  503  of the super peer node  500  resumes content transmission and transmits the content stored in the content DB  509  in the step S 329  to the mobile peer node  400  (S 337 ). 
     In what follows,  FIGS. 7 through 10  illustrate various exemplary embodiments of the process in which the mobile P2P content transmission path is changed when the mobile peer node moves, i.e., the method in which the content transmission path is controlled. 
     First,  FIG. 7  is a flowchart showing a method for controlling a content transmission path according to one exemplary embodiment of the present invention. 
     As used herein, a home super peer node  500  means a super peer node located in a wireless access network  100  to which a mobile peer node  400  has been previously connected, and a visiting peer node  500  means a super peer node located in a wireless access network  100  to which the mobile peer node  400  has moved. 
     Referring to  FIG. 7 , if the mobile peer node  400  moves while receiving content from the home super peer node  500  (S 401 ), the peer locality information DB  607  is updated, and the service control unit  617  of the mobile tracker node  600  detects the movement of the mobile peer node  400  (S 403 ). 
     At this point, the service control unit  617  of the mobile tracker node  600  determines if the mobile peer node  400  is moving within the same network (S 405 ). That is, it is determined a cell change occurs within the same network. 
     When the mobile peer node  400  is detected as moving within the same network, the service control unit  617  of the mobile tracker node  600  determines if the mobile peer node  400  is moving to an AD hoc network having the content the mobile peer node  400  is receiving (S 407 ). That is, it is determined whether to the mobile peer node  400  is entering the AD hoc network or not. 
     If the mobile peer node  400  has not moved to the AD hoc network, no operation is carried out at all, and the step S 403  is performed again. 
     On the contrary, if the mobile peer node  400  has moved to the AD hoc network, the service control unit  617  of the mobile tracker node  600  sends the home super peer node  500  a request to perform super peer handover to the mobile peer node  400  in the AD hoc network (S 409 ). At this point, information of the mobile peer node in the AD hoc network is transmitted as well. 
     Then, the home super peer node  500  forwards the super peer handover request to the content receiving mobile peer node  400  (S 411 ), and stops the content transmission (S 413 ). 
     The mobile peer node  400  sends a content download request to the mobile peer node  400 , present in the AD hoc network and requested to take over the super peer in the step S 411 , and receives the content (S 415 ). 
     On the other hand, if it is determined in the step S 405  that the mobile peer node  400  has moved not within the same network but to a different network, the service control unit  617  of the mobile tracker node  600  determines whether the visiting super peer node  500  has the content being received by the mobile peer node  400  (S 417 ). A list of content that the visiting super peer node has is obtained through a content storage response in the step S 331  of  FIG. 6 , and stored in the super peer information DB  609 . Accordingly, the service control unit  617  of the mobile tracker node  600  searches the super peer information DB  609  to check the content of the visiting super peer node  500 . 
     In the step S 417 , if the visiting super peer node  500  is determined as having no content, the flow returns to the step S 403 . 
     Otherwise, if the visiting super peer node  500  is determined as having content, the service control unit  617  of the mobile tracker node  600  sends the home super peer node  500  a request to perform super peer handover (S 419 ). 
     The home super peer node  500  hands over the content transmission rights to the visiting super peer node  500  (S 421 ). At this point, information about the mobile peer node and a peer list containing content information are transmitted as well so that the visiting super peer node  500  can download content based on this information and transmit it to the mobile peer node  400 . 
     Moreover, once the content transmission rights are handed over, the content that has been already downloaded to the home super peer node  500  but not transmitted yet to the mobile peer node  400  can be transmitted, too. 
     Then, the visiting super peer node  500  transmits the content handed over to itself to the mobile peer node  400  (S 423 ). 
       FIG. 8  is a flowchart showing a method for controlling a content transmission path according to another exemplary embodiment of the present invention. 
     Referring to  FIG. 8 , a content transmission peer is a mobile peer node. A content receiving mobile peer node  400  is referred to as mobile peer node  1 , and a content transmission peer is referred to as mobile peer node  2 . 
     While mobile peer node  1  is receiving content from mobile peer node  2  (S 501 ), the service control unit  617  of the mobile tracker node  600  detects a movement of mobile peer node  1  (S 503 ). 
     Then, the service control unit  617  of the mobile tracker node  600  to determines whether mobile peer node  1  has entered the network where the super peer node  500  is present (S 505 ). That is, the service control unit  617  determines whether the super peer node exists or not in the wireless access network  100  to which mobile peer node  1  is connected by referring to the peer locality information DB  607  and the super peer information DB  609 . 
     If mobile peer node  1  has not entered the network where the super peer node  500  is present, the step S 503  is performed again. 
     On the contrary, if mobile peer node  1  has entered the network where the super peer node  500  is present, the service control unit  617  of the mobile tracker node  600  sends a super peer handover request to mobile peer node  2  (S 507 ). Information on mobile peer node  2  can be checked in the meta information DB  601 . 
     Then, mobile peer node  2  hands over the content transmission rights to the super peer node  500  requested in the step S 507  (S 509 ). At this point, information on mobile peer node  1  is transmitted as well. 
     Afterwards, mobile peer node  2  transmits content not to mobile peer node  1  but to the super peer node  500  (S 511 ). Then, the super peer node  500  transmits the content received in the step S 511  to mobile peer node  1  (S 513 ). 
     Meanwhile, the P2P content transmission path can be changed by taking into account inter-node distance and traffic condition, which will be hereinafter explained with reference to  FIGS. 9 and 10 . 
       FIG. 9  is a view showing a mobile P2P content transmission path according to an exemplary embodiment of the present invention.  FIG. 10  is a flowchart showing a method for controlling a content transmission path according to still another exemplary embodiment of the present invention. 
     First, referring to  FIG. 9 , an arbitrary wireless access network  100  to which the mobile peer node  400  is connected includes a plurality of wireless nodes, super peer nodes, and nodes. 
     As used herein, the plurality of wireless nodes indicate base stations, which refer to RAS (remote access services) in a WiBro network, Node-B in a WCDMA network, and AP (Access Point) in a WiFi network. 
     The nodes refer to ACR (Access Control Router), an edge router, SGSN, GGSN, and so on. 
     In this way, a plurality of wireless nodes are present under a single super peer node, and nodes are present over the super peer node. 
     In this case, a mobile peer node connected to a certain wireless node may be moved and connect to another wireless node. As used herein, the super peer node connected to the wireless node before movement is referred to as the home super peer node, and the super peer node connected to the wireless node after movement is referred to as the visiting super peer node. 
     A method of path control when the mobile peer node  400  has moved will be described below. 
     Referring to  FIG. 10 , while the mobile peer node  400  is receiving content from the home super peer node  500  (S 601 ), the service control unit  617  of the mobile tracker node  600  detects a movement of the mobile peer node  400  (S 603 ). The movement detection is identical to that of  FIGS. 7 and 8 . 
     The service control unit  617  of the mobile tracker node  600  calculates the handover condition values of the home super peer node  500  and the visiting super peer node  500  by the following Equation 1 (S 605 ). 
     
       
         
           
             
               
                 
                   T 
                   = 
                   
                     
                       
                         ∑ 
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                       ⁢ 
                       
                         ( 
                         
                           
                             D 
                             i 
                           
                           × 
                           
                             C 
                             i 
                           
                         
                         ) 
                       
                     
                     - 
                     
                       
                         ( 
                         
                           1 
                           - 
                           L 
                         
                         ) 
                       
                       / 
                       α 
                     
                   
                 
               
               
                 
                   ( 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     1 
                   
                   ) 
                 
               
             
           
         
       
     
     where D represents the distance between the nodes present on the transmission path of the content received by the mobile peer node  400 . 
     C represents the cost of the nodes. The node cost mainly includes the cost of network constituent elements such as the cost of cable between the nodes. That is, the node cost represents the costs (CAPEX) of network constituent elements present on a network path and operating costs (OPEX), both required for mobile P2P traffic transfer. 
     L represents the traffic load of wireless nodes (to be described in  FIG. 9 ) present on the transmission path. The traffic load is stored in the access network traffic information DB  605 . 
     Referring to  FIG. 9 , D of the handover condition value of the home super peer node includes the distance between the home super peer node and the wireless nodes and the distance between the wireless nodes and the mobile peer node  400 . C includes the cost of the home super peer node and the cost of the wireless nodes. L includes the traffic load of the home super peer node and the traffic load of the wireless does. 
     Moreover, D of the handover condition value of the visiting super peer node includes the distance between the visiting super peer node and the wireless nodes and the distance between the wireless nodes and the mobile peer node  400 . C includes the cost of the visiting super peer node and the cost of the wireless nodes. L includes the traffic load of the visiting super peer node and the cost of the wireless nodes. 
     The service control unit  617  of the mobile tracker node  600  determines if the handover condition value of the visiting super peer node is higher than the handover condition value of the home super peer node by comparing the handover condition values calculated in the step S 605  (S 607 ). 
     If the handover condition value of the visiting super peer node is determined to be higher than the handover condition value of the home super peer node, the service control unit  617  of the mobile tracker node  600  sends the home super peer node  500  a request to perform super peer handover (S 609 ). 
     Then, the home super peer node  500  performs super peer handover to the visiting super peer node  500  (S 611 ), and the visiting super peer node  500  transmits content to the mobile peer node  400  (S 613 ). Here, the steps S 609  to S 613  are identical to the steps S 419  to S 423 . 
     While this invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. 
     
       
         
           
               
             
               
                   
               
               
                 &lt;Description of symbols&gt; 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                 100: wireless access network 
                 101, 201, 301: edge router 
               
               
                 103: base station 
                 105: EMS 
               
               
                 107: AP 
                 200: dedicated wired network 
               
               
                 203: core router 
                 205: traffic monitoring device 
               
               
                 300: Internet network 
                 303: tracker node 
               
               
                 305: peer node 
                 400: mobile peer node 
               
               
                 500: super peer node 
                 501: routing unit 
               
               
                 503: content transmission/reception 
               
               
                 control unit 
               
               
                 505: content reception unit 
               
               
                 507: content transmission unit 
                 509: content DB 
               
               
                 511: path control unit 
                 600: mobile tracker node 
               
               
                 601: meta information DB 
                 603: terminal status information 
               
               
                   
                 DB 
               
               
                 605: access network information DB 
                 607: peer locality information DB 
               
               
                 609: super peer information DB 
                 611: mobile peer management unit 
               
               
                 613: terminal status monitoring unit 
               
               
                 615: network traffic monitoring unit 
               
               
                 617: service control unit