International Journal of Computer Applications (0975 – 8887) Volume 5– No.5, August 2010 33 Comparison between Centralized & Decentralized Overlay Networks for Media Streaming Sachin Yadav Department of CSE SGIT, Ghaziabad, INDIA Ranjeeta Yadav Department of ECE SGIT, Ghaziabad, INDIA Shailendra Mishra Department of CSE KEC, Dwarahat, INDIA ABSTRACT In this paper we examine the performance of two types of Overlay networks i.e. Peer-to-Peer (P2P) & Content Delivery Network (CDN) media streaming using Multiple Description Coding (MDC). In both the approaches many servers simultaneously serve one requesting client with complementary descriptions. This approach improves reliability and decreases the data rate a server has to provide. We have implemented both approaches in the ns-2 network simulator. The experimental results indicate that the performance of Multiple Description Coding-based media streaming in case of P2P network is better than CDN. Keywords: MDC, CDN, Video Streaming, P2P, Overlay Network 1. INTRODUCTION We Media streaming received lot of attention in the past few years. As a consequence, live and on-demand media streaming is today widely used to stream TV & radio channels, TV shows, or arbitrary audio & video media. During this time several approaches have been devised to tackle the media-streaming problem. The first one is to use a client-server model, where a single server is the media provider and multiple clients are the media consumers. The second one is to use a peer-to-peer approach where the clients help the server in delivering the media content by having the roles of consumers and providers at the same time. Both schemes have their advantages and disadvantages. The client-server approach has the advantage that the client receives the content directly from the server with the minimum delay but at the cost of overwhelming the server in particular situations (for instance at high rate hours: e.g. football / basketball games etc). As a result, the server’s bandwidth can quickly become a bottleneck in the system due to the large number of client requests. On the other hand, in the peer-to-peer approach algorithms are devised to multicast the content between clients. In this case the clients have an active role in distributing the media content to other clients and thus remove the pressure from the server node. In this way, scaling the system functionality to a large number of consumers becomes a reality. However, this solution has its drawbacks too. Specifically, these algorithms have to tackle a high dynamic system, where clients can come and leave suddenly without any prior knowledge or guarantees. Today’s video streaming systems are mostly based on the client server model of Content Delivery Networks (CDN) which leads to several problems. The most important ones are: 1. Flash Crowd: Large numbers of streaming servers are not able to feed more than a few hundred streaming sessions simultaneously [14]. 2. Bandwidth cost: It can be a significant problem to the content provider. In contrast, these costs are shared by every participant in the P2P streaming network. 3. Single Point of failure: Like any client-server model, the server is the single point of failure. P2P networks offer characteristics and possibilities which cannot be provided by CDNs as proposed in [7]. As we show in this work, the performance of media streaming can he better in a P2P network, although the probability that one stream breaks is higher [10] [11]. The reason for this is that the replication rate of the video streams in a P2P network is typically significantly higher than in a CDN, due to the large number of participating hosts. In Gnutella for example, every peer shares an average of 500 files [6] and many peers host the same file. Figure 1: Distributed video streaming using multiple description coding in a P2P network. Peer P1 is simultaneously serve by the closest available peers P6 & P3 with descriptions D1 & D2 respectively. Using MDC in a P2P streaming scenario is illustrated in Figure 1. Peer p1 wants to receive video file S which is available in the MDC format on p3, p5 and p6. In this example the video is encoded using two descriptions D1 & D2. Peers p3 and p6 are chosen based on the distance from server to the receiver, and they simultaneously serve the video file S, each one providing a complementary description. If both the descriptions are received at the receiving peer p1, it will experience the highest quality. If any of the descriptions are affected by packet loss or excessive delay, the receiver can still decode and display video S but at the expense of a degradation of the quality, as the descriptions are independently decodable.