We study the problem of localizing repair packets when packets are lost during multicasts. When repair packets are multicast, a highly lossy receiver may swamp the entire multicast "group" with duplicate repair packets thereby wasting bandwidth; thus, the protocols need repair locality. We present a multicast layering scheme where the sender proactively distributes FEC repair packets among multiple multicast groups. Each receiver can selectively tune in to a subset of these multicast groups to obtain packets close in number to what it needs. We develop an efficient algorithm that dynamically determines the optimal distribution of FEC repair packets to a given (small constant) number of multicast groups. The running time of this algorithm is independent of the number of receivers in the multicast session, and is hence highly scalable. However, the optimal algorithm requires the knowledge of the FEC repair requirements of all the receivers in the multicast group, and hence is subject to the implosion problem. To handle the implosion problem, we develop an heuristic algorithm that achieves repair locality very similar to that of the optimal algorithm, but does not require as much global knowledge. Our multicast layering scheme can be integrated into known reliable multicast protocols to make them more scalable. For concreteness, we focus on: (i) singly scoped SRM, (ii) hierarchically scoped SRM, and (iii) a tree-based reliable multicasting protocol RMTP, and present combined protocols incorporating our solutions into each of them. Simulation experiments show that our solutions can substantially enhance the scalability of these reliable multicast protocols.

The current Internet is not reliable; packet loss rates are frequently high, and varying over time. Transmitting high-quality interactive video over the Internet is challenging because the quality of compressed video is very susceptible to packet losses. Loss of packets belonging to a video frame manifests itself not only in the reduced quality of that frame but also in the propagation of that distortion to successive frames. This error propagation problem is inherent in many motion-based video codecs due to the interdependence of encoded video frames. This paper presents a dynamic loss recovery scheme, called RESCU, to address the error propagation problem. In this new scheme, picture coding patterns are dynamically adapted to current network conditions in order to maximize the effectiveness of hybrid transport level recovery (employing both forward error correction and retransmission) in reducing error propagation. Since RESCU does not introduce any playout delay at the receiver, it is suitable for interactive video communication. An experimental study based on actual Internet transmission traces representing various network conditions shows that dynamic hybrid RESCU exhibits better error resilience and incurs much less bit overhead than existing error recovery techniques such as NEWPRED and Intra-H.261.

Real-time interactive video transmission in the current Internet has mediocre quality because of high packet loss rates. Loss of packets in a video frame manifests itself not only in the reduced quality of that frame but also in the propagation of that distortion to successive frames. This error propagation problem is inherent in any motion compensation-based video codec. In this paper, we present a new error recovery scheme, called recovery from error spread using continuous updates (RESCU), that effectively alleviates error propagation in the transmission of interactive video. The main benefit of the RESCU scheme is that it allows more time for transport-level recovery such as retransmission and forward error correction to succeed while effectively masking out delays in recovering lost packets without introducing any playout delays, thus making it suitable for interactive video communication. Through simulation and real Internet experiments, we study the effectiveness and limitations of our proposed techniques and compare their performance to that of existing video error recovery techniques including H.263+ (NEWPRED). The study indicates that RESCU is effective in alleviating the error spread problem and can sustain much better video quality with less bit overhead than existing video error recovery techniques under various network environments.