Celerity: a low-delay multi-party conferencing solution.

In this thesis, we attempt to revisit the problem of multi-party conferencing from a practical perspective, and tore think the design space involved in this problem. We believe that an emphasis on low end-to-end delays between any two parties in the conference is a must, and the source sending rate in a session should adapt to bandwidth availability and congestion. We present Celerity, a multi-party conferencing solution specifically designed to achieve our objectives. It is entirely Peer-to-Peer(P2P), and as such eliminating the cost of maintaining centrally administered servers. It is designed to deliver video with low end-to-end delays, at quality levels commensurate with available network resources over arbitrary network topologies where bottlenecks can be anywhere in the network. This is in contrast to commonly assumed P2P scenarios where bandwidth bottlenecks reside only at the edge of the network. The highlight in our design is a distributed and adaptive rate control protocol, that can discover and adapt to arbitrary topologies and network conditions quickly, converging to efficient link rate allocations allowed by the underlying network. In accordance with adaptive link rate control, source video encoding rates are also dynamically controlled to op-timize video quality in arbitrary and unpredictable network conditions. Celerity runs on the application layer and uses UDP to deliver the data. With the distributed rate control protocol, Celerity can deliver video at quality levels without the acknowledge of the underlying network topology, bandwidth, and the routing. We have implemented Celerity in a prototype system, and demonstrateits su¬perior performance over existing solutions in a local experimental test bed and over the Internet. In addition, using Celerity we have developed a multi-party conferencing system which provides real-time video and audio communication and allows users to dynamically join and leave, it achieves better user experience(low delay and high throughput) than existing products.Chen, Xiangwen.Thesis (M.Phil.)--Chinese University of Hong Kong, 2012.Includes bibliographical references (leaves 66-68).Abstract --- p.iAcknowledgement --- p.iiiChapter 1 --- Introduction --- p.1Chapter 1.1 --- Motivation --- p.1Chapter 1.2 --- Contribution --- p.2Chapter 1.3 --- Thesis Organization --- p.4Chapter 2 --- Related Work --- p.5Chapter 3 --- Problem Formulation and Celerity Overview --- p.7Chapter 3.1 --- Settings --- p.7Chapter 3.2 --- Problem Formulation --- p.9Chapter 3.3 --- Celerity Overview --- p.10Chapter 4 --- Packing Delay-bounded Trees --- p.13Chapter 5 --- Overlay Link Rate Control --- p.18Chapter 5.1 --- Considering Both Delay and Loss --- p.18Chapter 5.2 --- A Loss-Delay Based Primal-Subgradient-Dual Algorithm --- p.20Chapter 5.3 --- Computing Subgradients of R{U+2098}(c{U+2098}, D) --- p.23Chapter 6 --- PRACTICAL IMPLEMENTATION --- p.26Chapter 6.1 --- Peer Functionality --- p.26Chapter 6.2 --- Critical Cut Calculation --- p.29Chapter 6.3 --- Utility Function --- p.29Chapter 6.4 --- Opportunistic Local Loss Recovery --- p.29Chapter 6.5 --- Fast Bootstrapping --- p.30Chapter 6.6 --- Operation Overhead --- p.30Chapter 6.7 --- Peer Computation Overhead --- p.31Chapter 6.8 --- System Implementation --- p.32Chapter 7 --- Experiments --- p.34Chapter 7.1 --- LAN Testbed Experiments --- p.34Chapter 7.1.1 --- Absence of Network Dynamics --- p.36Chapter 7.1.2 --- Cross Traffic --- p.39Chapter 7.1.3 --- Link Failure --- p.40Chapter 7.2 --- Peer Dynamics Experiments --- p.41Chapter 7.3 --- Internet Experiments --- p.42Chapter 8 --- Concluding Remarks --- p.46Chapter A --- Packing Delay-bounded Trees in the Presence of Helpers --- p.47Chapter B --- Proof of Theorem 1 and Theorem 3 --- p.50Chapter C --- Proof of Corollary 1 and Corollary 2 --- p.56Chapter D --- Proof of Proposition 1 --- p.58Chapter E --- Proof of Theorem 2 --- p.60Bibliography --- p.6