Browse Theses

An enduring trait of the Internet is its heterogeneity. These heterogeneities present significant barriers to the transmission of real-time multimedia data across groups.

This dissertation presents a solution to the problems posed by heterogeneity in the context of real-time multimedia transmission over the Internet. Our solution exploits software agents--called media gateways--that are placed throughout the network at points of a change in the network environment. These agents process the multimedia streams in ways that accommodate the disparities in network and end-system capabilities. In this way our solution enables transmission of real-time media over heterogeneous environments.

Our solution leverages the advantages of an "in-the-network" solution to offer a wide range of flexible adaptation parameters, while maintaining an architecture that is dynamic, flexible and robust. It consists of three distinct components. First, we developed a high-performance media gate-way, the RTP Gateway, that serves as the core adaptation mechanism in our solution. Due to the dominance of video bandwidth in multimedia sessions, we focused in particular on the design and implementation of a video gateway. Our video gateway architecture lends itself to a very efficient implementation, while maintaining a high degree of flexibility in the range of input and output formats that it can process.

The second component of our system is a protocol for media gateway control. Our protocol, called SCUBA, presents a novel approach to video bandwidth allocation in real-time multi-media sessions by enabling media sources to intelligently account for receiver interest in their rate-adjustment algorithms. SCUBA is orthogonal to and complements existing rate-adaptation schemes and can interoperate with either sender- or receiver-directed control systems. To scale the SCUBA protocol with multicast session size, we decouple the receiver-feedback process from the session size through sampling. This approach introduces a "tunable" tradeoff between convergence time and sampling accuracy that for large sessions is solely dependent on the control traffic bandwidth. In addition to its application to media gateway control, we present several other applications of SCUBA including end-to-end conferencing, floor control, and cross-media synchronization.

Finally, since the Internet infrastructure does not support the deployment media gateways within the network in the manner which we require, we developed an architecture for active services: a general framework for the deployment of application-level computation within the network. We describe a design and implementation of an architecture for active services: the AS 1 framework. (Abstract shortened by UMI.)