Video multicast over the Internet

Multicast (multipoint) distribution of video is an important component of m any existing and future networked services. Today's Internet lacks support For quality of service (QoS) assurance, which makes the transmission of rea l-time traffic (such as video) 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 characteristi cs among multiple receivers of the same video stream. in this article we su rvey techniques that have been proposed for transmitting video in this envi ronment. These techniques generally involve adaptation of the video traffic carried over the network to match receiver requirements and network condit ions. In addition to their applicability to the near-term capabilities of t he Internet, they also are of relevance to a future, QoS-aware Internet env ironment because of the inevitable inaccuracies in traffic and resource res ervation specifications. 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 resul t in an unfair treatment for receivers, especially those whose capability i s significantly above or below the group consensus. We then consider techni ques that aim to improve the Fairness among the receivers by sending the vi deo in multiple (layered or replicated) streams. We also discuss several er ror control mechanisms, using timely retransmission of missing data to Furt her improve the quality of the received video. Finally, we discuss some of the issues that remain to be resolved in the development of Internet video multicast protocols.