Large Scale Multimedia Streaming in Heterogeneous Network Environments.

Introduction Video-on-demand (VoD) is an enabling technology [1] allowing geographically distributed users to interactively access video files from remote VoD servers. With this technology, users can playback the video content without waiting for the entire file to arrive and also enjoy the flexible control of video playback with VCR-like functions. Compared with conventional data communications, delivery of video data has more stringent requirements on network bandwidth, delay and loss [2]. However, the current Internet is inherently a packet-switched network that was not designed to handle isochronous (continuous time-based) traffic such as audio and video. The Internet can only provide best-effort services and has no guarantee on the quality of service (QoS) for audio and video transmission. In addition, a large-scale VoD system must have a large storage capacity to archive hundreds or even thousands of videos and a high performance I/O bandwidth to handle an enormous number of concurrent video streams. Also, in practical situations, clients can connect to the network, says Internet, with different communication technologies such as modem, ASDL and wireless link and their downstream rates may vary from 56 kbps to 10 Mbps or above. To cater for the heterogeneous requirement, the system will deliver different qualities of video streams to the clients according to their capacity constraints. If the clients have a low bandwidth connection such as 56 Kbps, they will receive the videos encoded at a low bit rate. On the other hand, the high quality video will be delivered to the customers having the broadband access capability. As a result, there are still many open issues in designing protocols and transmission strategies for VoD systems in such environment. There are three main approaches for building a large scale VoD system in heterogeneous network environment in a cost-efficient way. The first one is based on the hierarchical architecture. The second one makes use of peer-to-peer (P2P) technology to support video services. The third one is a hybrid approach that combines with the use of the first two approaches.