Abstract
Videoconferencing is an important topic on the current Internet. The heterogeneity of the network, its access-to-all approach and the varying amount of available bandwidth present many challenges to researchers. Most of the available videoconferencing implementations send video and audio in a monolithic stream with an adaptive rate. In one-to-many sessions, the available end-to-end bandwidth between the source and a receiver might sharply differ from one end-user to another. It is clear that one rate cannot satisfy all the online users because that would force the source to use a least common denominator strategy. Earlier work of graduate students at the TAMU Multimedia and Networking Laboratory has focused on multi-layered encoding. The video is "multiplexed" on several streams. Receivers with more bandwidth can request more streams for a better picture quality. In this research, CafeMocha (the videoconferencing tool developed by Sazzad and Brown at Texas A&M) is enhanced from a two layer codec to a six layer codec. Layer control methods are then tested using the improved codec. A simplified version of the Receiver-driven Layered Multicast protocol (RLM) proposed by McCanne at UC Berkeley, is implemented and tested. Later, RLM itself is implemented, and tested in the one-to-one case. A new metric is defined whereby each layer control scheme subscription path, under various rate limits, is compared to a defined "ideal" layer subscription sample path. We defined performance as the ratio of the cumulative bandwidth delivered in the actual case to the cumulative bandwidth delivered in the "ideal" case. RLM performance values of 99.6% were recorded when the performance was still good at 72.6% when the ideal highest subscription layer was bursty. RLM was found to be a good control mechanism for moderately bursty layered streams. Propositions for possible improvements are suggested in the conclusion.
Gholmieh, Ralph Akram (1997). Multicast multilayer videoconferencing: enhancement of a multilayer codec and implementation of the receiver driven layered multicast protocol. Master's thesis, Texas A&M University. Available electronically from
https : / /hdl .handle .net /1969 .1 /ETD -TAMU -1997 -THESIS -G46.