KR20050002456A - Apparatus and method for searching optimal nodes for use in P2P data communication, and computer readable medium on which program for executing the method is recorded - Google Patents

Abstract

PURPOSE: A device and a method for searching an optimal node for the P2P(Peer-to-Peer) data communication, and a computer-readable recording medium storing a program for executing the same are provided to shorten a search time and waste no system resource by searching the optimal transfer node with regional information, ISP(Internet Service Provider) information, and line sort information. CONSTITUTION: A node information storage(104) stores node information of the nodes(30) connected through the network. A file information storage(105) stores file information of files stored in a file server(40) connected to a search device(10). A file information receiver(101) receives the file information the including node information of the requesting node from the requesting node(20). An optimal node searcher(102) searches the optimal transfer node by using the file information of the requesting node, the node information stored in the node information storage, and the file information stored in the file information storage. A searched information transmitter(103) transmits a node ID of the determined optimal transfer node to the requesting node.

Description

Apparatus and method for searching optimal nodes for use in P2P data communication, and computer readable medium on which program for executing the method is recorded}

According to the present invention, a node having an optimal transmission condition among nodes holding a corresponding file (hereinafter referred to as a 'transport node') to a node (hereinafter, referred to as a 'request node') to receive a specific file in P2P communication. The present invention relates to a searchable technology, and more particularly, to an apparatus and method for searching for an optimal node based on a region of a transmitting node, an ISP, a circuit type, and an IP class.

In the traditional server-client file transfer method, there is a limitation that the client side cannot guarantee a satisfactory transmission speed due to the limited network band. Recently, P2P-based services have been spread to overcome these limitations. However, although many P2P service programs such as eDonkey, eMule, and Sori Sea, which are representative of file sharing are active, network up / down bands are extremely limited due to the fact that file transfer is performed using a user-based PC. There was a problem that it could not provide a better file transfer service, especially when supporting split file downloads such as eDonkey or eMule can provide a better transfer environment, but also incurs a burden on user resources This also has a problem that there are many irrationalities in stable service.

Therefore, the requesting node needs to search for the transport node that is most suitable for file transfer. Currently, when the requesting node requests the file server to transfer a specific file, the file server requests a list of the transport nodes that hold the specific file. The requesting node calculates a hop count for all nodes included in the transmitting node list or searches for an optimal transmitting node using a ping signal. However, finding an optimal transport node directly at the requesting node takes considerable time and wastes resources of the requesting node.

In addition, in P2P communication, a technique (eg, an eDonkey or FlashGet program) that divides and transmits a file into a plurality of blocks in order to overcome the limited up band of each node is a general trend. Compared to the method of receiving the files sequentially, it is difficult to calculate when the transmission is completed and there is a problem that the contents of the file can be confirmed when the transmission is completed.

The present invention has been made to solve the above problems, and an object of the present invention is to search for the optimal transmission node using the region information, ISP company information, line type information and IP class information of the transmission node in the optimal node search apparatus. It is to provide an optimal node searching apparatus and method that shortens the searching time and does not waste system resources of the requesting node, compared to each requesting node connected through P2P directly looking for the optimal transmitting node.

In addition, another object of the present invention is to divide the file into a plurality of blocks, the optimum node having the effect of receiving the files sequentially by transmitting the file block from the plurality of transmitting nodes to the requesting node in proportion to the uploading speed of the transmitting node It is to provide a search apparatus and method.

1 is a block diagram of a search apparatus according to an embodiment of the present invention.

2 is a flowchart of an optimal node search method according to an embodiment of the present invention.

3 is an explanatory diagram for explaining a specific example of the method of FIG.

4 is a conceptual diagram illustrating a file division transmission method according to an embodiment of the present invention.

5 is a conceptual diagram illustrating a file division transmission method according to another embodiment of the present invention.

6 is a block diagram of a search apparatus for implementing the transmission method of FIG.

7 is a flowchart of a method for determining whether to allocate an optimal transmitting node or update download information of a requesting node according to a signal of a requesting node.

In order to achieve the above object, the present invention provides an apparatus for searching for an optimal node, which searches for an optimal transport node among transport nodes holding a file according to a request of a requesting node to receive a file. A node information storage unit storing node information of nodes, a file information storage unit storing file information of a file stored in a file server connected to the search apparatus, and node information of the requesting node from the requesting node. Optimal node search for searching for an optimal transmitting node using a file information receiver for receiving file information, including file information of the requesting node and node information and file information stored in the node information storage unit and the file information storage unit. And a node identifier of the optimum transmitting node determined by the searching unit. And a search information transmitting unit for transmitting the search information, wherein the node information includes region information, ISP company information, line type information, and IP class information of the corresponding node, and the file information of the requesting node includes a request block of a file to be transmitted; The optimal node search unit includes a request rate, and the optimal node search unit includes IP class information, line type information, ISP company information, and local information among transport nodes that hold the request block and have node information that matches the node information of the request node. Record the optimal node search device, the optimal node search method corresponding to the technical idea of the device, and the program for executing the method. Provide a computer readable recording medium.

On the other hand, the optimal node searcher is to determine the transmission node as the optimal transmission node when the upload speed is greater than or equal to the requested rate among the transmission nodes that match the IP class information. At this time, when the upload speed is smaller than the requested speed, the last forwarding node whose IP matches the requesting node may be determined as an optimal forwarding node. On the other hand, when the upload speed is smaller than the requested rate, the node having the highest upload rate among the transport nodes that match the IP class may be determined as the optimal transport node.

In addition, the search information transmitting unit together with the node identifier, the requesting node receives block allocation information in which the optimal transmitting node determines the location of the file block to be transmitted to the requesting node in proportion to the uploading speed of the optimal transmitting node determined by the searching unit. It is desirable to send to. At this time, the search apparatus calculates a time point at which the connection with the requesting node is disconnected before the transmission of the file block allocated to the optimal transmission node is completed, and the search result is determined by the optimum node search unit before a predetermined time of the disconnection time point. It is preferable to further include a transmission status monitoring unit for requesting to reassign the optimal transmission node. The transmission state monitoring unit determines whether the signal from the requesting node is an allocation request or download state information of the optimal transmission node, and, if the allocation request is an allocation request, requests the optimal node searcher to search for the optimal transmission node and downloads the information. In the case of, the node information of the requesting node is updated.

Hereinafter, with reference to the accompanying drawings will be described an embodiment of the present invention.

1 is a block diagram of an apparatus for searching for an optimal node according to the present embodiment. According to FIG. 1, the search apparatus 10 includes a file information receiver 101, an optimal transmission node searcher 101, a search information transmitter 103, a node information storage 104, and a file information storage 105. Consists of

The node information storage unit 104 stores node information of all nodes, and the node information includes region information of the node, ISP company information, line type information, IP class information, upload / download speed, and the like. The area information can be classified into national unit, state / province (or state), etc. ISP information refers to a company that provides Internet communication services, and line type is a type of serviced line such as ADSL or VDSL. The IP class information refers to information on which IP class the node belongs to. The reason for classifying each information is that the communication environment such as access speed or upload / download speed for each node varies greatly according to the same and different information of each information, and the best communication environment is provided between nodes having the same information. This is because the probability is high. The file information storage unit 105 stores information about a file stored in the file server 40, and the file information includes a protocol version of the file, a file name, a file size, and a list of transfer nodes holding the file. Information such as this is included.

The file information receiving unit 101 receives file information of a request node, and the file information includes a protocol version, a file name, a file size, a request block, a request speed, node information, etc. of a file to be transmitted, and node information corresponds to the corresponding node information. It consists of the node's local information and network information including the ISP's ISP, line type, IP class, and upload / download speed of the node.

On the other hand, the file is divided into a plurality of blocks having a predetermined size (for example, 1M bytes), the requesting node can request transmission from the file block of the desired point. Therefore, the request block information means the location of a specific block of a file that the requesting node wants to receive. The demand rate refers to the speed assigned to each node on the web by policy (for example, the speed at which the download rate is set differently depending on the paid or free members of the website). It will be different. In addition, before receiving file information, a communication path must be secured between the requesting node and the retrieval apparatus by detecting a request signal of the requesting node to generate a server socket and connecting the generated server socket to the requesting node's client socket.

The optimal transmission node retrieval unit 102 uses the file information of the requesting node, the node information of the transmission node stored in the node information storage unit 104, and the file information stored in the file information storage unit 105. FIG. The searcher transmits the search information to the search information transmission unit 103 by searching for an optimal transmission node according to the algorithm shown in FIG. According to FIG. 2, in step S201, node information of the first transmitting node Tn1 among all transmitting nodes included in the node information storage unit 104 is read, and in step S203, a request block exists in the corresponding node. Check if it is. If there is a request block, step S205 checks whether or not the area information of the request node and the current node match, and if the area information matches, step S207 compares the best node and the current node to determine the best node. Since it is about the first transmitting node, the first transmitting node is determined to be the best node. Steps S209, S213, and S217 check whether the ISP company information, line type information, and IP class information of the requesting node and the current node match, and if the information matches, the optimal node and the current node in steps S211, S215, and S219. Compare nodes to determine the best node. Since it is currently about the first node, if the information matches, the current node will be determined as the best node. Meanwhile, in steps S211, S215, and S219, as in step S204, the optimal node is compared with the current node to determine the optimal node. If the information of the optimal node and the current node matches up to the present, the optimal node is determined. Determine the best node as the new best node.

In step S221, it is checked whether the required speed is smaller than the upload speed of the node. If the required speed is smaller than the upload speed of the corresponding node, since no other transmitting node is needed anymore, go to step S223 and determine the current corresponding node as the optimal node, and determine the determined optimal transmitting node information by the search information transmitting unit 103. To send). On the other hand, if the required speed is larger than the upload speed, another transmission node is needed to satisfy the required speed, and therefore, the process proceeds to step S225, in which the transmission node having the higher upload speed among the optimal node and the current node is the optimal node. The process then proceeds to step S227. Therefore, in step S225, among the nodes having an upload speed lower than the required speed, the transmission node having the largest transmission speed is determined as the optimal node. However, step S225 is only for sequentially arranging the transmission nodes having the highest upload speed, and step S225 is omitted so that the last transmission node is determined to be the optimal node among the transmission nodes having an upload speed smaller than the required speed. You may make it possible.

In step S227, it is checked whether the current transmitting node is the last transmitting node. If it is not the last transmitting node, the node information of the next transmitting node is taken and the previous steps are repeated. If the last transmitting node, the process proceeds to step S223. Finally, the optimal transmission node is determined as the optimal transmission node.

3 illustrates a specific example using the algorithm of FIG. 2, in which there are five transmitting nodes in total, the first transmitting node Tn1 matches the request node and the circuit type, and the second transmitting node Tn2 corresponds to the requesting node and the ISP. The third transmission node Tn3 matches up to the requesting node and the IP class, the upload speed is 200K, the fourth transmission node Tn4 matches up to the requesting node and the IP class, and the upload speed is 300K. It is assumed that the transmitting node Tn5 matches up to the requesting node and the IP class and the upload speed is 100K. In addition, it is assumed that the required speed is 500K.

At this time, in the first cycle of the algorithm of FIG. 2, the first transport node Tn1 will be determined to be an optimal node, and the second transport node Tn1 that matches up to the circuit type in the second cycle also matches only the ISP company. Since the priority is higher than the transmission node Tn2, the first transmission node Tn1 will be determined to be an optimal node. In the third cycle, since the IP class has a higher priority than the line type, the third transport node Tn3 will be determined to be the best node. In the fourth cycle, the fourth transport node Tn4 will upload more than the third transport node Tn3. Since the speed is high, the fourth transmitting node Tn4 will be determined as the optimal node. In the fifth cycle, since the upload speed of the fifth transmission node Tn5 is lower than that of the fourth transmission node Tn3, the fourth transmission node Tn4 will finally be determined as an optimal node. At this time, if step S225 is omitted, the fifth transmitting node Tn5, which is the last transmitting node of which the IP class matches, will be determined as the optimal node.

The search information transmitter 103 may transmit a node identifier of the optimal node determined by the optimal node searcher 102 to the requesting node 20 so that the requesting node 20 may receive a file from the determined optimal transmission node 30. Make sure

On the other hand, the requesting node 20 is connected to the optimal node and is ready to receive a file. At this time, if the uploading speed of the optimal node is smaller than the required speed, the requesting node 20 divides the file from another transmitting node and is currently optimized at the required speed. When file information is transmitted to the retrieval apparatus 10 at a speed equal to the required speed minus the upload speed of the node, the retrieval apparatus 10 determines the new optimal transmission node through the algorithm of FIG. To send.

4 shows that the request node 20 is assuming that the request speed of the request node 20 is 800K, the nodes determined as optimal nodes are A, B, C, and D nodes, and that the upload speeds are 100K, 300K, 200K, and 200K, respectively. ) Is a diagram for explaining that a file is divided and transmitted from a transmitting node. According to FIG. 4, a file of n Mbytes is divided into blocks of 1M units, and each transmitting node is allocated a file block in proportion to the upload speed. Therefore, in the case of FIG. 4, the first 1M block of the file is transmitted from the node A, the 2M to 4M blocks of the file are received from the node B, and the 5M, 6M and 7M, Receive 8M. By changing the size of the divided blocks in proportion to the upload speed, the same effect as downloading the files sequentially can be obtained. In the case of FIG. 4, transmission of 1M to 8M blocks of the file is completed after 10 seconds. The transmission of blocks is completed from 9M to 16M blocks, and the request node 20 can receive files up to nM blocks in this manner. On the other hand, when a request node 20 receives a file from a transmitting node and a transmitting node (for example, a node C) cannot transmit a file for any reason, the other transmitting node (for example, A and B) occurs. And a file block to be transmitted from each transmitting node in proportion to the upload speed of the node D).

Therefore, in order to expect the same effect of receiving files sequentially when split files are received from multiple transmitting nodes, the location of the file block to be transmitted by each transmitting node is determined in proportion to the uploading speed of the optimal transmitting node. Although necessary, the retrieval information transmitting unit 103 also transmits block allocation information that determines a file block to be transmitted from each optimal node to the requesting node with reference to the upload speed along with the determined node identifier of the optimal node. For example, the search information transmitter 103 transmits the first 1Mbyte (100K / 800K) of the eight file blocks (8Mbytes in total) if the upload speed of the first optimal node determined when the requested speed is 800K is 100K. If the optimal speed of the next optimal node is 300K, 3Mbytes (300K / 800K) are allocated to the transport blocks, ranging from 2M blocks to 4M blocks. Send it to the requesting node with the node identifier.

FIG. 4 illustrates that each transport node holds the entire block of the file, but according to the present embodiment, if only a request block exists in the transport node, the transport node can receive the file block from the transport node even if the transport node does not have the entire block of the file. have.

FIG. 5 is a diagram for describing a method of dividing and downloading a file from a node currently receiving a file from the file server 40 or other transmission nodes. According to FIG. 5, it is assumed that node A and node B are receiving files from the file server at speeds of 100K and 200K, respectively, and that the amount of transmission is 10M bytes and 2M bytes, respectively, and the upload speeds are 50K and 150K, respectively. . At this time, when the node C, which is the request node 20, tries to receive a file of 100M bytes at a request rate of 300K, if the optimal nodes determined by the search apparatus 10 are nodes A and B, then node A and node B Since the sum of upload speeds is smaller than the required speed, the file server 40 is directly sent to the file server 40 for the remaining speed. First, node A's download completion time is (100 (full size) -10 (transmitted size)) / 0.1 = 90 * 1024K / 100K = 921.6 seconds = 15.36 minutes, and node B's download completion time is (100- 2) /0.2=98*1024/200=501.75 seconds = 8.36 minutes, and the estimated time to complete download of node C is (100 * 1024) / 300 = 341 seconds = 5.68 minutes, so node C will download files from both A and B. Can be sent. On the other hand, after C node 51.2 seconds (y = 100x + 10 * 1024, y '= 300x, x = 51.2), the node C surpasses the file download speed of node A and can no longer download files from node A. After 20.48 seconds, it will not be able to download files from node B. Therefore, the search apparatus 10 needs to reassign the optimum node before the connection disconnection time predetermined time in anticipation of the connection disconnection time at which the requesting node (C node) will exceed the download speed of the transmitting nodes (A and B nodes). have.

6 shows a configuration example of such a search apparatus 10 ', which includes all of the components of the search apparatus 10 of FIG. 1, and further has a transmission status monitoring unit 106 added thereto. Therefore, the transmission state monitoring unit 106 expects the request node to disconnect from the transmitting node and reassigns the optimum node to the optimal node search unit 102 before a predetermined time of the disconnection time. . In this case, the disconnected upload speed may be secured by requesting reassignment using the upload speed of the forwarding node that is expected to be disconnected as the required speed. The optimal node searching unit 102 determines a new optimal node according to the algorithm of FIG. 2, and the search information transmitting unit 103 transmits the node identifier of the newly determined optimal node to the requesting node so that the file from the new optimal node can be found after disconnection. Allow a block to be sent.

Meanwhile, the request node 20 first requests the search apparatus 10 to allocate an optimal transmission node, and at any time even while the transmission node is assigned and receives a file, the requesting node 20 transmits its download status information (eg, to the search apparatus 10). , The download rate of the file, the download speed, etc.), and the transmission state monitoring unit 106 receives and processes the delivery information of the request node 20. FIG. 7 illustrates a method for determining whether the requesting node 20 requests the search apparatus 10 to allocate the transmission node or transmits the download information to allocate the transmission node or update the download information. Is a flow chart. First, the search apparatus 10 determines whether the signal from the requesting node 20 is an allocation request of the optimal transmitting node in step S701 and receives file information from the file information receiving unit 101 of the requesting node if the allocation request is made. (S711) The optimal node searching unit 102 searches for the optimal node (S713), and the search information transmitting unit 103 transmits the identifier and the block allocation information of the optimal transmitting node to the requesting node 20 (S715). If not, the process proceeds to step S703 to determine whether the signal from the requesting node 20 is download information, and if so, updates the requested node information of the node information storage unit 104 (step S705). In step S703, it is determined whether the connection of the request node 20 is disconnected, and in step S703, the flow proceeds to step S707 to determine whether the request node 20 is disconnected. If it is determined in step S707 that the connection is terminated, the flow advances to step S709 to close the server socket with the request node 20 and delete the request node from the node information storage unit 104. The flow advances to step S701 to wait for a signal from the request node 20 again.

Although the embodiments of the present invention have been described above, the scope of the technical idea of the present invention is not limited to this embodiment, and those skilled in the art should not depart from the scope of the technical idea of the present invention. It should be noted that variations can be made without making any difference.

As described above, according to the present invention, the search time is shortened and system resources of the user node are wasted as compared to the conventional technology in which each node connected through P2P directly searches for the optimal node by searching for the optimal node in the optimal node search apparatus 10. It is possible to obtain an effect of preventing the occurrence.

In addition, according to the present invention, by dividing a file into a plurality of blocks and transmitting a file block from a plurality of transmitting nodes to a requesting node in proportion to the uploading speed of the transmitting node, the effect of receiving the files sequentially can be obtained. have.

Claims (21)

In the optimum node searching apparatus for searching for the optimal transmission node among the transmission nodes holding the file in response to a request of the requesting node to receive the file, A node information storage unit storing node information of nodes connected via a network, a file information storage unit storing file information of a file stored in a file server connected to the search apparatus, and the request node from the request node. A file information receiver for receiving file information including node information of the node; and searching for an optimal transmission node using file information of the requesting node, node information and file information stored in the node information storage unit and the file information storage unit; An optimal node searching unit and a search information transmitting unit for transmitting the node identifier of the optimal transmitting node determined by the searching unit to the requesting node, The node information includes local node information, ISP company information, line type information, and IP class information of the node, and the file information of the requesting node includes a request block and a request rate of a file to be transmitted. The optimum node retrieval unit determines priority in order of IP class information, line type information, ISP company information, and region information among transmission nodes that hold the request block and have node information that matches the node information of the request node. And determine the best transmission node having the highest priority. 2. The apparatus of claim 1, wherein the optimal node searcher determines the corresponding transport node as an optimal transport node when the upload speed is greater than or equal to the required speed among transport nodes with matching IP class information. . 3. The apparatus of claim 2, wherein when the upload rate is smaller than the requested rate, the last transmitting node that matches the requesting node and the IP class is determined as an optimal transmitting node. 3. The apparatus of claim 2, wherein when the upload rate is smaller than the requested rate, the node having the highest upload rate among the transmission nodes that match the IP class is determined as the optimum transfer node. The block allocation information of claim 1, wherein the search information transmitter determines, together with the node identifier, a location of a file block to be transmitted to the requesting node by the optimal forwarding node in proportion to the uploading speed of the optimal forwarding node determined by the searcher. The node search apparatus, characterized in that for transmitting to the requesting node. The optimal node of claim 5, wherein the search apparatus calculates a time point at which the connection with the requesting node is disconnected before the transmission of the file block allocated to the optimal transmission node is completed, and the predetermined time point before the disconnection time point. And a transmission status monitoring unit for requesting to reassign the optimal transmission node to the searching unit. 7. The method of claim 6, wherein the transmission state monitoring unit determines whether the signal from the requesting node is an allocation request or download state information of the optimal transmitting node, and if the allocation request is an allocation request, searches for the optimal transmitting node for the optimal node searching unit. And requesting and downloading information, updating node information of the requesting node. In the optimal node search method for searching for the optimal transmission node among the transmission nodes holding the file in response to a request of the requesting node to receive the file, Receiving file information including node information of the requesting node, determining an optimal transmitting node using file information of the requesting node, file information and node information of the transmitting node, and determining the determined optimal transmitting node Transmitting the node identifier of to the requesting node; The node information includes local node information, ISP company information, line type information, and IP class information of the node, and the file information of the requesting node includes a request block and a request rate of a file to be transmitted. The optimal node searching step prioritizes IP class information, line type information, ISP company information, and region information among transport nodes that have the request block and have node information that matches the node information of the request node. Determining and determining the highest priority node as the optimal transmission node. 10. The method of claim 8, wherein the step of searching for an optimal node determines that the transport node is an optimal transport node when the upload speed is greater than or equal to the required speed among transport nodes with matching IP class information. Way. 10. The method of claim 9, wherein when the upload rate is smaller than the requested rate, the last transmitting node having the same IP class as the requesting node is determined as an optimal transmitting node. 10. The method of claim 9, wherein when the upload rate is smaller than the required rate, the node having the highest upload rate among the transmission nodes that match the IP class is determined as the optimal transfer node. 10. The method of claim 8, wherein the transmitting of the search information comprises, together with the node identifier, a block allocation in which the optimal transmitting node determines a location of a file block to be transmitted to the requesting node in proportion to the uploading speed of the optimal transmitting node determined in the searching step. And further transmitting information to the requesting node. The optimal node of claim 12, wherein the search method calculates a time point at which the connection with the requesting node is disconnected before the transmission of the file block allocated to the optimal transmission node is completed, and the predetermined time point before the disconnection time point. And a transmission status monitoring step of returning to the searching step. The method according to claim 13, wherein the transmission state monitoring step determines whether the signal from the requesting node is an allocation request or download state information of the optimal transmitting node, and returns to the optimum node searching step when the allocation request is an allocation request. And if necessary, updating the node information of the requesting node. A computer-readable recording medium having recorded thereon a program for executing an optimal node searching method for searching for an optimal transmitting node among transport nodes holding a file according to a request of a requesting node to receive a file. : Receiving file information including node information of the requesting node, determining an optimal transmitting node using file information of the requesting node, file information and node information of the transmitting node, and determining the determined optimal transmitting node Transmitting the node identifier of to the requesting node; The node information includes local node information, ISP company information, line type information, and IP class information of the node, and the file information of the requesting node includes a request block and a request rate of a file to be transmitted. The optimal node searching step prioritizes IP class information, line type information, ISP company information, and region information among transport nodes that have the request block and have node information that matches the node information of the request node. And determine the optimum transmission node having the highest priority. 16. The recording medium of claim 15, wherein the searching for the optimal node determines that the transmitting node is an optimal transmitting node when the uploading rate is greater than or equal to the required rate among the transmitting nodes having the matching IP class information. 17. The recording medium of claim 16, wherein when the uploading speed is lower than the demanding speed, the last transmitting node that matches the requesting node and the IP class is determined as an optimal transmitting node. 17. The recording medium of claim 16, wherein when the upload speed is smaller than the required speed, the node having the highest upload speed among the transmission nodes having the same IP class is determined as the optimal transmission node. 16. The method of claim 15, wherein the retrieving information transmitting step is a block allocation in which the optimal transmitting node determines a location of a file block to be transmitted to the requesting node in proportion to the upload speed of the optimal transmitting node determined in the retrieving step together with the node identifier. And transmitting the information to the requesting node. 20. The optimal node of claim 19, wherein the search method calculates a time point at which the connection with the requesting node is disconnected before the transmission of the file block allocated to the optimal transmission node is completed. And a transmission state monitoring step of returning to the searching step. 21. The method according to claim 20, wherein the transmission state monitoring step determines whether the signal from the requesting node is an allocation request or download state information of the optimal transmission node, and returns to the optimum node search step when the allocation request is made. And if necessary, updating the node information of the requesting node.