A p2p approaches to extend the ability of Video on Demand systems to serve more users. In the proposed system users share with each other the media data obtained and the media server is no longer the only source to get data from, thereby, the load on the media server could be greatly alleviated and the overall system capacity increases and more users could be served. The p2p streaming system introduces efficient searching; data transfer dynamically monitoring and initial buffering to maintain a high quality of playback. Its provider selection policy helps to reduce the load of the underlying network by avoiding remote data transfer.
1. Introduction
Recently, with the rapid development of large-scale storage, high performance workstation and broadband network technology, the information transferred on the Internet consists of not only text and images, but also varieties of multimedia communication, which is possible on technical and economic aspects. Multimedia communication makes video, audio, text, images as one kind, and provides richer user experience, so that it is used more and more extensive. Streaming media technology makes it possible to transfer audio, video or animation to users’ PC continuously and in real-time mode instead of waiting for the whole completion.
However, the traditional client-server based network streaming media system consumes large network bandwidth and server resource, which prevents the development of the network media services. For example, a video needs 300 kbps bandwidth, and 1000 users watch it at the same time, so that we need 300 Mbps bandwidth, which is over the server limit. If there were much more users, then we could only add more servers to support the service. So, a new kind of transfer mode is needed.
In order to solve the problem above, many kinds of solutions have been brought up in research field and industry field in recent years; some important ones include Content Delivery Network CDN and IP multi-cast. But these solutions need special hardware to run, for example, several CDN servers are needed worldwide to set up CDN; IP multi-cast needs the modification of the current Internet routing method and more routers supporting the multi-cast ability. Such solution is too expensive and can not solve our problem completely.
Then, P2P network gets in. A peer-to-peer, commonly abbreviated to P2P, is any distributed network architecture composed of participants that make a portion of their resources directly available to other network participants, without the need for central coordination instances. Peers are both suppliers and consumers of resources, in contrast to the traditional client-server model where only servers supply, and clients consume.
BT has many advantages we can learn, such as pipeline, choking algorithm, tit-for-tat theory. It uses SHA1 hash function to index file chunks uniquely, and apply random policy to the missing chunks in order to provide data resource to clients more efficient and balance each file trunks’ copies in the network. For the finishing file trunk, the client can request other clients to provide the trunk so that this file trunk can be finished transferring earlier.
2. Simple VOD System Model
As the P2P media technology improves and develops, the VOD system based on P2P technology has more and more applications. Now there exists mature P2P stream software such as PPLIVE and PPSTREAM. For the P2P streaming media service has many advantages, lots of research institutions dive into the P2P transfer mode. University of Stanford in USA raised Spread system, which combines the Peers to a single grouped tree and use the Peer to forward media stream. University of Florida got the ZIGZAG, which organized the Peers into layered groups and set up the grouped tree based on some policies to achieve large-scale broad-casting. An American researcher brought up the PROP system, which achieves extensible streaming media live using proxy. University of Massachusetts designed and implemented DirectStream, a directory based video live broadcast system. The directory maintains the video information index and all the peers’ information in the grouped tree on the server. New peer will look up the index and determine whether to join the existing tree or create a new tree. Microsoft designed the SplitStream streaming media technology after CoopNet. This system aims to lower the load of each grouped tree by setting up several trees. The internal nodes in the tree are the sub nodes of another tree. The complete stream is split into some parts to be transferred in every tree. Thus, the load will be gone shares on the trees.
Relative to the video broadcast system, VOD is asynchronous. For the users who playing the same program, the startup time among each user are not the same, and the Pause, Resume etc executive by the users need more complex catch and transmission strategies to achieve the advantages of P2P. Therefore, the main idea of this article is that model for a broadcast system, and deal with some basic problem of this system model. First of all, let’s see the structure of the whole system.
The VOD system model in this article will get involved with a super peer. The basic system structure will be given as follows.
P2P Streaming Media Play System is consisting with the P2P streaming media servers and other child nodes. Each network nodes of P2P network is equal, each two nodes is server and client. To ensure the system work effectively, we set P2P streaming media server as Web information management server of other child node that manages the system’s users’ information and program resources information.
System structure is shown in Figure 1. The server and client connect through the Internet.
The P2P streaming media server not only provide general streaming media server primary function, but also play a role of the contents of the index server, its functions are as follows:
1) network management: To monitor the operational status of the child nodes, display the network status, traffic statistics and so on.
2) resource management: to storage media files,
Figure 1. P2P broadcast system structure.
media resources search (locate), maintain the system node resource information, exchange resources and information with other master node. For each block of streaming media, maintain a online streaming media client list of all downloaded and cached this block, provide the download address of all requests for streaming media blocks for new customers.
3) User Management: To register node user information, implement user authorization management, control user system permissions to verify the legitimacy of the visitor.
4) media server: to provide the child nodes of the system with the original streaming media content.
5) When necessary, the server would do block, encoding, packaging and transport and so on on multimedia content.
The functions of child nodes are as follows:
1) streaming media services: as the streaming media server of other child nodes to provide streaming media services.
2) Local media resources: management media files have been downloaded, maintain node resource information.
3) media play: re-sorted the received streaming media data to achieve broadcast with media player controls.
Figure 2 shows the specific process on broadcast.