CN102821316A - Improved video on demand (VOD) transmission method based on peer-to-peer computing core algorithm - Google Patents

Abstract

An improved video-on-demand transmission method based on the core algorithm of peer-to-peer computing. The topology structure includes a seed file production server, an electronic program guide server (EPG), an improved index server (Tracker), a streaming media server and an improved BitTorrent client. The invention improves the segment selection algorithm and node selection algorithm in the BitTorrent protocol, introduces an adaptive sliding window mechanism, fully utilizes the efficient file distribution capability of the BitTorrent protocol, and can meet the real-time requirements of video-on-demand. This method can not only solve the problem of server single point failure and connection server bottleneck, but also reduce the load pressure on the server side.

Description

An improved video-on-demand transmission method based on peer-to-peer computing core algorithm

technical field

The present invention is an improved video-on-demand system transmission method based on the peer-to-peer computing core algorithm. The peer-to-peer computing protocol used is the BitTorrent protocol. It improves the segment selection algorithm and node selection algorithm in BitTorrent, and introduces an adaptive sliding window mechanism. Restricting slice selection requests to meet the real-time requirements of video on demand belongs to the field of peer-to-peer network applications.

Background technique

Video on demand technology is an important application technology of distributed streaming media. Video on Demand is also known as VOD, the full name is Video on Demand, that is, video streaming on demand. Video-on-demand technology is a cutting-edge technology in the current streaming media communication application, and it is a new technology that combines future-oriented information, communication and other related technologies. At the same time, video on demand is another business, which generally refers to an interactive multimedia application service that uses interactive networks to transmit audio and images in real time to realize video on demand, information query, TV shopping, distance education and other services.

Traditional streaming media systems on the Internet are generally based on the C/S model, usually including one or more servers and several clients. In the C/S mode, the capacity of the streaming media system (the number of clients served at the same time) is mainly determined by the network output bandwidth of the server, and sometimes the processing power, memory size, and I/O rate of the server also affect the system capacity. In the C/S mode, due to the large bandwidth and long duration of streaming media transmission, and the limited network bandwidth available on the server side, even if a high-end server is used, its system capacity is only a few hundred clients, which is not economical. Scale. In addition, due to the uncertainty of the Internet, if the client is far away from the server, indicators such as delay, jitter, bandwidth, and packet loss rate during streaming media transmission will also be more uncertain. The server sends streaming media content once for each client separately, so the consumption of network resources is also very huge. Therefore, under the current condition of limited resources, how to meet the ever-increasing user needs and reduce the service cost of streaming media while ensuring service quality is an important topic in the research of streaming media technology. The P2P technology that has emerged in recent years can use each node in the Internet to perform peer-to-peer computing, make full use of idle resources on the Internet, and allow two clients to directly exchange information, so it has received widespread attention. Applying P2P technology to streaming media business provides a new way of thinking to solve the problem of server-side network bandwidth and server capacity limitations. In this context, P2P-based video-on-demand technology emerged.

BitTorrent is an efficient P2P file sharing download tool. Through a central Tracker server, the BitTorrent client obtains the node list of the current download task, and then complete peer-to-peer collaboration between each node completes the download of each file segment. File slice sharing improves download efficiency without any other server involvement.

The fragment selection algorithm used in the BitTorrent protocol is: the local minimum fragment first, that is, each peer node first selects the fragments with the fewest neighbor nodes to download, and those relatively more fragments in the system are downloaded later .

The node selection algorithm adopted in the BitTorrent protocol is: in the case of keeping the proportion of seeds close to the proportion of global seeds, randomly select node information and return it to the requesting node.

Contents of the invention

Technical problem: the purpose of the present invention is to improve the segment selection algorithm and node selection algorithm in the BitTorrent protocol, and introduce an adaptive sliding window mechanism to meet the real-time requirements of video on demand. Compared with the traditional VOD system, it can not only transmit data efficiently, ensure the smoothness of VOD, but also reduce system load and operation cost.

Technical scheme: a kind of improved video-on-demand transmission method based on peer-to-peer computing core algorithm of the present invention adopts improved BitTorrent client and improved index server Tracker to improve the transmission speed of streaming media resource files, and the algorithm involves seed file production server, electronic program list Server EPG, improved index server Tracker, streaming server and improved BitTorrent client module; the transmission process of the entire video on demand is as follows:

Step.11: The seed file production server makes the streaming media file to be released into a seed file, and then

Afterwards, the seed file is sent to the electronic program list server EPG;

Step 12: The electronic program guide server EPG downloads the seed file, and at the same time makes a TV program according to the seed information.

sub program list;

Step 13: The video-on-demand client will automatically request the electronic program list server EPG after starting.

Sub program list, the electronic program list server EPG verifies whether the user belongs to the registered user according to the user's information, if the user passes the verification, the electronic program list server EPG will send the electronic program list to the user, and then the on-demand program will appear on the user's client menu;

Step 14: According to the on-demand menu, the user orders the program he wants to watch, and then sends it to the electronic program list server EPG

Request the seed file, and then the electronic program list server EPG sends the seed file to the user;

Step 15: When the user receives the torrent file, enter the download process immediately, first through the improved

The BitTorrent client establishes a connection with the improved index server Tracker to obtain neighbor node information;

Step 16: The improved BitTorrent client passes the information of these neighbor nodes, using a sliding window

The mechanism part downloads streaming media files in an orderly manner, plays them while downloading, and also provides uploading services for other neighbor nodes; after the client downloads, it becomes a seed node, and the seed node provides uploading for other nodes through an improved segment selection algorithm.

The improved BitTorrent client uses an improved fragment selection algorithm, which can solve the even distribution of file fragments. The improvement steps are as follows:

Step 21: For the uniform distribution of fragments in the network, abolish the seed upload strategy, no longer according to

Download speed to provide upload;

Step 22: Set a list in the download completion node Seed, and put all the fragment numbers at initialization

In the list, when the fragment is uploaded by the client node, delete the fragment number from the list;

Step 23: When the download node uses the method of downloading the least fragments first to request fragments from the Seed,

If the download fragment is in the list, Seed sends the fragment file to the download node, and deletes the fragment number from the list; slice, and then delete the slice from the list, if the above two conditions do not meet, then block the node;

Step 24: When the fragment numbers in the list are all deleted, that is, when the list is empty, re-initialize,

Add all fragment numbers back to the list for node download.

The improved index server Tracker adopts an improved node selection algorithm, which can make full use of the upload efficiency of nodes. The improvement steps are as follows:

Step 31. Expand the communication between the node and the tracking server, so that the Tracker can know the node's next

loading progress;

Step 32. On the Tracker server side, establish a sequence for each torrent file according to the download progress

ascending list of

Step 33. When a seed file is published, the node Seed is first added to the list, and its

The download progress is set to 1;

Step 34. When a peer node communicates with the Tracker, if the node is a newly added node, it will be inserted into the corresponding position of the list according to the download progress. If the peer node is already in the list, the previous position of the list will be deleted, and it will be The progress is reinserted into the list;

Step 35. Find 40 nodes with the smallest progress gap with the node according to the node position;

Step 36. Return the list of neighbor nodes to the requesting node.

In step 16, the sliding window mechanism is used to partially and orderly download streaming media files, so that the fragments near the playback point can be downloaded first; during the operation, each time a new file fragment needs to be requested, first check the Whether the file fragments are all requested or downloaded, if not, first request the fragments in the sliding window, if the request is completed, take the file fragments from the non-sliding window to request, with the movement of the playback point, the sliding window Also make a corresponding slide; and the size of the sliding window can be adaptively adjusted according to the decoding speed and playback delay during playback, which not only meets the real-time requirements of video on demand, but also makes full use of BitTorrent's efficient transmission efficiency.

Beneficial effects: the method of the present invention proposes an improved video-on-demand transmission method based on the BitTorrent core algorithm, aiming to solve the problems of heavy load pressure and low efficiency of the streaming media server in the video-on-demand system by combining the efficient file distribution mechanism of BitTorrent. The technical method proposed in this invention is not a simple list of existing technologies, but is refined through continuous practice according to the characteristics of existing technologies, and realizes an efficient P2P video-on-demand transmission system by effectively combining various mechanisms. A specific description is given below.

Data island : If only server A owns resource S in the network, then when server A goes down or is damaged for some reason, all nodes in the network cannot access or obtain resource S until server A works normally again. This state of A is called "data island". Data islands seriously affect the stability and flexibility of the system, and a few nodes in the network can affect the overall performance. Data islands are very common in traditional music on-demand systems. All resources of on-demand users come from the media server. Once the media server goes down, all on-demand users cannot obtain media resources. One solution is to set up multiple backup media servers. But this will bring great cost overhead. In our BitTorrent-based VOD transmission system, the resources of VOD users do not necessarily come from media services, and in many cases can be completely separated from the media server, thus getting rid of the problem of data islands.

Load balancing : refers to the balanced sharing of service requests among each processing unit of the system. That is, the load in the network is distributed to multiple servers or nodes, thereby effectively avoiding the overload of some servers or nodes in the network, so that all nodes can share the load in the network evenly, and ensure more efficient operation of the network. The load balancing technology in the traditional multimedia on-demand system usually only performs load balancing on all media servers in the system, so that all media servers have a similar load, so as to prevent a few media servers from being overwhelmed, while some are not effectively utilized , such as the load balancing technology in the shared multimedia on-demand system. In the P2P music on-demand system, the load balancing technology uses client nodes to share the load of the media server to reduce the load of the media server. Compared with the load balancing technology in the traditional multimedia on-demand system, this load balancing technology has a wider role , is also more thorough and effective.

Improved BitTorrent core algorithm: What the segment selection algorithm in the BitTorrent agreement adopted is the local minimum priority strategy of the number of fragment copies, this strategy can not make the uniformity of the number of fragments close to optimal, the present invention adopts the improved seed node upload strategy to This strategy is improved, and the experiment proves that the uniformity of the number of fragments, the download speed, and the average download time have been greatly improved compared with the traditional strategy and the strategy before the improvement. The Tracker node selection algorithm is similar to a random selection strategy. The algorithm has uncertainty and strong randomness, and it may take a long search time to find a suitable service provider. To solve this problem, the present invention adopts an improved node selection algorithm to help nodes find a suitable node in the shortest time. Experiments have proved that the download speed of the improved algorithm has been significantly improved, and the download speed of the final stage mode has not been significantly reduced.

Description of drawings

Figure 1 is the flow chart of the improved seed node upload,

Figure 2 is a flow chart of the improved node selection algorithm,

Fig. 3 is a flow chart of BitTorrent-based VOD transmission,

Figure 4 is the specific flow chart of the system during operation.

Detailed ways

The method of the invention emphasizes improving the core algorithm in BitTorrent, and introduces an adaptive sliding window mechanism to meet the real-time requirements of video on demand.

． Improved Fragment Selection Algorithm

In the BitTorrent system, the Local Rarest First strategy is adopted, that is, the node only needs to know the distribution of the file slices of the shared file among its neighbor nodes (usually 50 nodes). The least file block priority strategy is implemented in the node. This reduces system load and maintains an even distribution of file blocks locally. But there are some problems in BitTorrent's fragment selection strategy: because the local least priority is only based on local information, the local least does not mean the global least, so the selection of file blocks is blind to a certain extent.

The improved fragment selection algorithm is as follows: by improving the seed upload strategy, the upload strategy indirectly affects the balance of file fragment distribution.

The traditional seed upload strategy is: when all the fragments of the client node are downloaded, if it does not leave the network immediately, it will become a seed node. Since the seed node will not download file fragments from other nodes, it will not Then use the node selection strategy to select nodes for uploading, but choose several nodes that get the fastest download speed from this node to provide uploading, so that the uploading bandwidth can be utilized as much as possible.

The present invention proposes an improved fragment selection algorithm, the algorithm idea is as shown in Figure 1, and its process is:

1. For the uniform distribution of fragments in the network, the upload strategy of seeds is abolished, and no longer based on the download speed

degrees to provide uploads.

2. The fragment selection algorithm of the download node remains unchanged, that is, the previous random first fragment,

Least-first, strict-priority, last-stage modes.

3. Set a list in Seed, all fragment numbers are placed in the list at initialization, when the fragment is

After the Seed node is uploaded, the segment number is deleted from the list.

4. When the download node uses the least priority to request fragments from Seed, if the download fragment is in the list,

Seed sends the fragment file to the download node and deletes the fragment number from the list. If not, the Seed can be sent to the download node through the bitfield field of the download node to the fragment that the download node does not have and the fragment number is in the list, and then delete the fragment from the list. If the above two conditions do not meet, block the fragment node.

5. When the fragment numbers in the list are all deleted, that is, when the list is empty, re-initialize and set all

There are fragment numbers to re-join the list for nodes to download.

． Improved Node Selection Algorithm

In order to make full use of the upload bandwidth of neighbor nodes, the neighbor nodes of the node should preferably contain the file fragments required by the node. The traditional Tracker algorithm uses a method of randomly selecting neighbor nodes, which affects the download efficiency of nodes to a certain extent, and is not conducive to the efficient distribution of file fragments. This situation is especially obvious in the final stage of node downloading. Since the number of fragments required for the final node to be downloaded is relatively small, if a node with fewer fragments is selected as a neighbor node, the probability of obtaining fragments is often very low. It also causes the download speed of the node in the final stage to be significantly reduced.

The present invention proposes an improved node selection algorithm, the algorithm idea is shown in Figure 2, and its flow is:

1. Extend the communication between peer nodes and Tracker, so that Tracker can know the download progress of the node.

2. On the Tracker server side, create an upgrade list for each torrent file according to the download progress.

sequence listing.

3. When a seed file is released, the Seed node is first added to the list, and its download is entered into

degree is set to 1.

4. When the peer node communicates with the Tracker, if the peer node is a newly added node, it will be inserted into the corresponding position of the list according to the download progress. If the peer node is already in the list, the previous position of the list will be deleted, and will be The progress is reinserted into the list.

5. Find 40 nodes with the smallest progress gap with the node according to the node position.

6. Return the list of neighbor nodes to the requesting node.

． Adaptive sliding window mechanism

The sliding window maintains a window about the media data receiving buffer. This window will move forward according to the state changes of the data consumed by the player and the data received by the peer node. Once the data within the sliding window is consumed by the player, the sliding window will Move forward to get the media data needed by the player for subsequent playback. Data within the sliding window will be requested from the server or other partner nodes in priority order according to urgency.

From the previous discussion, we can know that the larger the sliding window, the faster the urgent data can be obtained. At the same time, since each fragment in the sliding window requests multiple peer nodes (to achieve and ensure the rapid acquisition of fragments), Undoubtedly, it will increase the redundancy of fragmentation requests and responses in the system, and the smaller the sliding window is, correspondingly, the ratio of data requests outside the sliding window will increase. For the data outside the sliding window, we still adopt BitTorrent's "least first" strategy except for the part of setting "anchor point" later, so the redundancy of the system will be relatively smaller, which can effectively reduce the System load, but this may not be able to meet the player's demand for the data to be played in time. This mainly depends on the changes in the receiving and consuming speed of the player's buffered data. When the receiving speed is greater than the consumption speed, obviously the buffer can meet the consumption speed of the player. At this time, the sliding window should be reduced to reduce the system load. The sliding window will be used to ensure that the "least first" strategy does not have urgent data requests for downloaded players (we know that "least first" always downloads the less replicated parts in the cluster first in order to balance the system load) slices, this method of out-of-order download cannot meet the needs of the player to play sequentially), when the receiving speed is lower than the consumption speed, because the buffer data consumption of the player is faster, in order to reduce the waiting time for the user to play, we should increase the The sliding window is used to obtain the data required by the player as soon as possible. Therefore, in order to dynamically reflect the data changes in the sliding window and achieve a better balance of system load, we propose an adaptive sliding window scheme.

相对应，客户端应该在这个播放等待时间内填充满滑动窗口缓冲，而后开始播放媒体流，在播放的同时，不断地继续填充这个缓冲，以保证播放的连续性。这样关于滑动窗口的最佳大小，根据试验统计，滑动窗口的大小应该静态的设置为能够缓冲300s的媒体数据。根据

（其中

表示播放器的播放延迟，即从客户端请求节目到播放器开始播放之间的时间间隔；

表示分片的大小，用于保存在对等节点的媒体数据的最小单位，大小为256K字节；

表示媒体文件的解码速度）的滑动窗口大小计算公式，前提都在于假设分片获取的速度总是至少大于或等于播放器流媒体的解码速度，这在实际应用中，特别对于广大的ADSL用户和具有高质量QoS保证的流媒体数据，具有极大的不现实性。我们滑动窗口的初始大小同样采取的计算方案，同时鉴于BitTorrent分片获取的波动性，以及前述所讨论的滑动窗口对系统整体性能的影响，我们的自适应大小滑动窗口将根据分片获取的速度动态地自我调整大小。 From the above discussion, we can clearly realize that the size of the sliding window is a crucial parameter that affects the performance of the system. We believe that the size of the sliding window should be related to the playback start wait time

Correspondingly, the client should fill the sliding window buffer within the playback waiting time, and then start playing the media stream, and continue to fill the buffer while playing, so as to ensure the continuity of the playback. In this way, regarding the optimal size of the sliding window, according to experimental statistics, the size of the sliding window should be statically set to be able to buffer 300s of media data. according to

(in

Indicates the playback delay of the player, that is, the time interval between the client requesting a program and the player starting to play;

Indicates the size of the fragment, which is the smallest unit of media data stored in the peer node, with a size of 256K bytes;

Indicates the decoding speed of the media file), the premise of the sliding window size calculation formula is that the speed of fragmentation acquisition is always at least greater than or equal to the decoding speed of the player's streaming media. In practical applications, especially for the majority of ADSL users and Streaming media data with high-quality QoS guarantee is extremely unrealistic. The initial size of our sliding window also adopts the same calculation scheme, and in view of the volatility of BitTorrent fragmentation acquisition and the impact of the sliding window on the overall performance of the system discussed above, our adaptive sliding window will be based on the speed of fragmentation acquisition Dynamically resizes itself.

1. Architecture

The purpose of system design is to implement a new system, but if the new system is too different from the original system, the cost of system upgrade will be huge, especially for large-scale network systems, a major upgrade of the system will bring considerable cost and time cost. Therefore, when designing a BitTorrent-based video-on-demand system, the original system architecture should be fully considered in order to realize a simple upgrade between the two systems. It can be seen from the traditional video-on-demand system that its problems mainly come from the bottleneck of the media server, but there are no serious problems for other parts of the network. According to the common shared video-on-demand system to simply balance the load among the media servers, the bottleneck of the media server cannot be completely solved, but the bottleneck problem of the media server can be completely realized by balancing the load of the server to each node in a P2P manner completely resolved.

Figure 3 shows the overall architecture of the BitTorrent-based video-on-demand system, which is based on the existing mature large-scale video-on-demand system, while taking into account the characteristics of P2P. It not only realizes the video-on-demand system based on BitTorrent, but also guarantees the performance and scalability of the system.

As can be seen from Figure 3, in terms of overall architecture, it is very similar to the traditional video-on-demand system, which also ensures that the changes in the system upgrade will be relatively small. The main change of the whole system is on the client side, and at the same time, the function of the server will also change. It no longer simply returns the information of the media server, but also returns the information of the neighbor nodes. The change of the client node is mainly aimed at the client running on the client node, and the upgrade process is relatively simple.

Two, the embodiment

As shown in Figure 4, the specific process of the system during operation is as follows:

1. The seed file making server makes the streaming media file to be released, and then sends the seed file

EPG server.

2. The EPG server downloads the seed file, and at the same time makes an electronic program list based on the seed information.

3. After the VOD client is started, it will automatically request the electronic program list from the EPG server, and the EPG

The server verifies whether the user belongs to the registered user according to the information of the user. If the user passes the verification, the EPG server will send the electronic program list to the user, and then the program menu on demand will appear on the user's client.

4. According to the on-demand menu, users can order the programs they want to watch, and then request the seed file from the EPG server

file, and then the EPG server sends the seed file to the user.

5. When the user receives the torrent file, he immediately enters the download process. First, the improved

The BitTorrent client establishes a connection with the Tracker server, and obtains neighbor node information according to the improved Tracker algorithm.

6. The client passes the information of these neighbor nodes, according to the improved BitTorrent client part

Download streaming media files in an orderly manner, play while downloading, and provide upload services for other neighbor nodes at the same time, so that users can watch on-demand programs immediately until the files are played.

The following describes the implementation of the adaptive sliding window.

First give the following definition:

：节点

下载分片的速度之和，是实时动态的反映，根据我们上面的讨论，可得知的大小有如下计算公式： 

:node

The sum of the speed of downloading fragments is a reflection of real-time dynamics. According to our discussion above, we can know The size of is calculated by the following formula:

: Initial sliding window size (ideal sliding window size), the size can be calculated by the following formula

：

时刻的自适应滑动窗口大小

:

Adaptive sliding window size for moments

then we define The calculation formula is as follows:

，

是调整滑动窗口大小的频度。 Where N is the number of fragments of the file requested by the node,

,

is how often to resize the sliding window.

的时候，即起始的时候，。 when

when, at the beginning, .

Therefore, the adaptive size sliding window algorithm can be easily implemented as follows:

，而

为滑动窗口的最小值，理论上，按顺序下载的话，当分块获取速度大于缓冲区消耗速度时，可以趋近于0，即是不需要滑动窗口的存在，但是正如我们前面说讨论的，由于BT无序下载的特性，我们必须保留滑动窗口为一定的大小，通过试验，我们发现当解码速度为4Mbps，播放延迟为5s时，

取值为10~20为最佳，而

取值15%~20%为最佳。 From the previous we know is the number of fragments, assuming a 512MB video file, then

,and

It is the minimum value of the sliding window. In theory, if downloading in sequence, when the block acquisition speed is greater than the buffer consumption speed, It can be close to 0, that is, there is no need for the existence of the sliding window, but as we discussed earlier, due to the characteristics of BT out-of-order downloading, we must keep the sliding window at a certain size. Through experiments, we found that when the decoding speed is 4Mbps, when the playback delay is 5s,

The value of 10~20 is the best, and

The value of 15%~20% is the best.

Claims (4)

1. A video-on-demand transmission method improved based on the peer-to-peer computing core algorithm, characterized in that an improved BitTorrent client and an improved index server Tracker are used to improve the streaming media resource file transmission speed, and the topology adopted includes a seed file production server, Electronic program list server EPG, improved index server Tracker, streaming media server and improved BitTorrent client; the transmission process of the entire video on demand is as follows: Step.11: The seed file production server makes the streaming media file to be released into a seed file, and then Afterwards, the seed file is sent to the electronic program list server EPG; Step 12: The electronic program guide server EPG downloads the seed file, and at the same time makes a TV program according to the seed information. sub program list; Step 13: The video-on-demand client will automatically request the electronic program list server EPG after starting. Sub program list, the electronic program list server EPG verifies whether the user belongs to the registered user according to the user's information, if the user passes the verification, the electronic program list server EPG will send the electronic program list to the user, and then the on-demand program will appear on the user's client menu; Step 14: According to the on-demand menu, the user orders the program he wants to watch, and then sends it to the electronic program list server EPG Request the seed file, and then the electronic program list server EPG sends the seed file to the user; Step 15: When the user receives the torrent file, enter the download process immediately, first through the improved The BitTorrent client establishes a connection with the improved index server Tracker to obtain neighbor node information; Step 16: The improved BitTorrent client passes the information of these neighbor nodes, using a sliding window The mechanism part downloads streaming media files in an orderly manner, plays them while downloading, and also provides uploading services for other neighbor nodes; after the client downloads, it becomes a seed node, and the seed node provides uploading for other nodes through an improved segment selection algorithm. 2. according to the improved video-on-demand transmission method based on peer-to-peer computing core algorithm according to right 1, it is characterized in that improved BitTorrent client, adopts improved segment selection algorithm, can solve the even distribution of file fragmentation, and the improvement steps are as follows: Step 21: For the uniform distribution of fragments in the network, abolish the seed upload strategy, no longer according to Download speed to provide upload; Step 22: Set a list in the download completion node Seed, and put all the fragment numbers at initialization In the list, when the fragment is uploaded by the client node, delete the fragment number from the list; Step 23: When the download node uses the method of downloading the least fragments first to request fragments from the Seed, If the download fragment is in the list, Seed sends the fragment file to the download node, and deletes the fragment number from the list; slice, and then delete the slice from the list, if the above two conditions do not meet, then block the node; Step 24: When the fragment numbers in the list are all deleted, that is, when the list is empty, re-initialize, Add all fragment numbers back to the list for node download. 3. According to the improved VOD transmission method based on the peer-to-peer computing core algorithm according to right 1, it is characterized in that the improved index server Tracker adopts the improved node selection algorithm, which can make full use of the upload efficiency of the node, and the improvement steps are as follows: Step 31. Expand the communication between the node and the tracking server, so that the Tracker can know the node's next loading progress; Step 32. On the Tracker server side, establish a sequence for each torrent file according to the download progress ascending list of Step 33. When a seed file is published, the node Seed is first added to the list, and its The download progress is set to 1; Step 34. When there is a peer node communicating with the Tracker, if the node is a newly added node, it will be inserted into the corresponding position of the list according to the download progress. If the peer node is already in the list, the previous position of the list will be deleted, and will be The progress is reinserted into the list; Step 35. Find 40 nodes with the smallest progress gap with the node according to the node position; Step 36. Return the list of neighbor nodes to the requesting node. 4. according to the improved video-on-demand transmission method based on the peer-to-peer computing core algorithm according to right 1, its special The feature is that in step 16, the sliding window mechanism is used to download the streaming media files in an orderly manner, so that the fragments near the playback point can be downloaded first; Whether all the file fragments in the window have been requested or downloaded. If not, first request the fragments in the sliding window. If the request is completed, request the file fragments from the non-sliding window. With the movement of the playback point, The sliding window also slides accordingly; and the size of the sliding window can be adaptively adjusted according to the decoding speed and playback delay during playback, which not only meets the real-time requirements of video-on-demand, but also makes full use of BitTorrent's high-efficiency transmission efficiency.

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