P2P视频点播系统外文翻译文献
P2P视频点播系统外文翻译文献
(文档含中英文对照即英文原文和中文翻译)
原文：
Recent Advances in Peer-to-Peer Media Streaming Systems
ABSTRACT
Recently, there is great interest in using the peer-to-peer (P2P) network in media streaming. A great number of P2P media streaming systems have been developed. In this paper, we first give a brief survey on some key techniques and algorithms in the field of P2P streaming research. We also analyze the market view of P2P streaming media service, and give a brief descrip-tion about the current mainstream P2P streaming systems deployed in China.
I.
INTRODUCTION
P2P视频点播系统外文翻译文献
The rapid development of the Internet has changed the conven-tional ways that people access and consume information.Besides sending and receiving e-mails, browsing web pages, and downloading data files, people also hope to call telephone, watch movie and TV, and conduct other entertainments via the same Internet. The ideal objective is that anyone can access anything (contents) from anywhere at any time. It is commonly conceived that the next generation Internet should be a multi-media communication network based on the core of IP protocol. Besides traditional data services, other multimedia contents such as voice, image, and video, would also be delivered over the same IP network, among which the streaming media service will play a very more important role.
Streaming media enables real-time and continuous delivery of video and audio data in a fashion of “flow”, i.e., once the sender begins to transmit, the receiver can start playback almost at the same time while it is receiving media data from the sender, instead of waiting for the entire media file to be ready in the local storage. Unlike normal data file, a streaming media file is huge, thus requires high channel bandwidth. Moreover, streaming media also carries stringent demand in the timing of packet delivery. The large size of the streaming media as well as its delivery timing requirement causes a streaming media server to be expensive to set up and run. In traditional client/server-based media streaming systems, all clients access the same server resource. In this scenario, on the one hand, the processing power, storage capacity, and I/O throughput of the server may become the bottleneck; on the other hand, large number of long-distance network connections may also lead to traffic congestion, thus cannot afford better quality of service (QoS) comparable with that of other tradi-tional Internet services, such as WWW and FTP, and cannot meet the performance requirements of large-scale real-time media streaming applications, especially in the aspects of scalability, adaptability, fault-tolerance and robustness. To address these problems, recently researchers have pro-posed many solutions, such as IP multicast and CDN (content delivery network). However, both of them need supports from special hardware. For IP multicast network, large-scale multicast-capable routers must be redeployed in the Internet. For content delivery network, a large number of CDN servers should be placed at the network edge, close to any receiver, and cooperate with each other to distribute multimedia data. The costs of infrastructure setup and administration are expensive, and cannot resolve the problems fundamentally. In recent years, Peer-to-Peer (P2P) networking technology has gained tremendous attention from both academy and industry. In a P2P system, peers communicate directly with each other for the sharing and exchange of data as well as other resources such as storage and CPU capacity, each peer acts both as a client who consumes resources from other peers, and also as a server who provides service for others. P2P systems can benefit from their following characteristics: adaptation, self-organization, load-balancing, fault-tolerance, availability through massive replication, and the ability to pool together and harness large amounts of resources. For example, file-sharing P2P systems distribute the main cost of sharing data - bandwidth and storage - across all the peers in the network, thereby allowing them to scale without the need for powerful and expensive servers. P2P systems are originally applied in network file sharing, and have achieved great success, such as Napster, Gnutella, Emule, and BitTorrent. However, different from general P2P file sharing, P2P media streaming poses more stringent timing and resource requirements for real-time media data transmis-sion and rendering, therefore it is needed to provide more restricted functions in the respects of resource management, scheduling, and control. Various P2P media streaming systems have been proposed and developed recently. Even in
P2P视频点播系统外文翻译文献
China, nowadays there are about more than a dozen of P2P streaming applications de-ployed in the Internet. In this paper, we first give a brief survey on some key research issues and algorithms of P2P streaming systems, and then analyze and summarize the current status and development trend of P2P streaming market in China.
II. RESEARCH PROGRESS OF P2P MEDIA STREAMING
A simple and straightforward way of P2P streaming implemen-tation is to use the technique of application-layer multicast (ALM). With ALM, all peer nodes are self-organized into a logical overlay tree over the existing IP network and the stream-ing data are distributed along the overlay tree. The cost of providing bandwidth is shared among the peer nodes, reducing the burden of the media server. In application-layer multicast, data packets are replicated and forwarded at end hosts, instead of at routers inside the network. Compared with IP multicast, application-layer multicast has several advantages. On the one hand, since there is no need for supports from routers, it can be deployed gradually based on the current Internet infrastructure; on the other hand, application-layer multicast is more flexible than IP multicast, and can adapt different distribution demands of various upper level applications.
Thus, how to construct and maintain an efficient ALM-based overlay network has became one of the key problems of P2P streaming research. To address this problem, mainly three questions should be answered. The first relates to the P2P network architecture, i.e., what topologies should the overlay network be constructed? The second concerns routing and scheduling of media data, i.e., once the overlay topology is determined, how to find and select appropriate upstream peers from which the current peer receives the needed media data? The third is membership management, i.e., how to manage and adapt the unpredictable behaviors of peer joining and departure?
Recently, several P2P streaming systems and algorithms have been proposed to address the above issues. From the view of network topology, current systems can be classified into three categories approximately: tree-based topology, forest-based (multi-tree) topology, and mesh topology. In the following we give a brief summarization of P2P streaming techniques accord-ing to this classification. 2.1 Tree-based topology
The typical model of tree-based P2P streaming system is PeerCast. In PeerCast, nodes are organized as a single multicast tree, where the parent provide service only directly to its sons.
The node joining and departure strategies used in PeerCast are simple. For node joining, a new node n first request services from the root node S. If the S has enough resources, it provides service for n directly; otherwise, S redirects the request of n to one of its sons. The son then repeats this process, until the parent of n is found. Since each node only maintains the information of its parent and sons, unbalanced tree may be constructed.
Generally, there exist four route selection strategies in PeerCast: random selection, round-robin selection, smart selection accord-ing to physical placement, and smart selection according to bandwidth. To achieve a balanced multicast tree, custom routing policy should be chosen carefully for individual peer node.
ZIGZAG is another tree-based P2P streaming system which can construct more balanced