Video multicast over the Internet

Multicast distribution of video is an important component of many existing and future networked services. The Internet lacks support for quality of service (QoS) assurance, which makes the transmission of real-time traffic challenging. In addition, the heterogeneity of the Internet's transmission resources and end-systems makes it extremely difficult, if not impossible, to agree on acceptable traffic characteristics among multiple receivers of the same video stream. We survey techniques that have been proposed for transmitting video in this environment. These generally involve adaptation of video traffic carried over the network to match receiver requirements and network conditions. In addition to their applicability to the near-term capabilities of the Internet, they also are of relevance to a future, QoS-aware Internet environment. We first consider source-based techniques in which the source adjusts the video stream traffic to match some consensus among the receivers about its desired characteristics. These techniques can result in an unfair treatment for receivers, especially those whose capability is significantly above or below the group consensus. We then consider techniques that aim to improve the fairness among the receivers by sending the video in multiple (layered or replicated) streams. We also discuss several error control mechanisms, using timely retransmission of missing data to further improve the quality of the received video. Finally, we discuss some of the issues in the development of Internet video multicast protocols.