An Agent-based Approach to Real-time Multimedia Transmission over Heterogeneous Environments
Elan Amir
EECS Department, University of California, Berkeley
Technical Report No. UCB/CSD-98-1006
, 1998
An enduring trait of the Internet is its heterogeneity. Evidence of this heterogeneity includes the wide range of network transmission rates, varying across many orders of magnitude, and the vast differences in computing power, ranging from PDA's to supercomputers. These heterogeneities present significant barriers to the transmission of real-time multimedia data across groups. The barriers stem from the fact that in order to accommodate the entire gamut of group member characteristics, e.g., bandwidth availability or computing power, a source is required to transmit its data with properties matching the most constrained receiver. Instead, we would like to transmit media to multiple receivers at heterogeneous rates and properties that match those of each individual receiver. <p> Recent proposals for "end-to-end" solutions -- i.e, solutions which require only the participation of the end-applications -- offer the advantage of not requiring modifications within the network. However, these solutions are relatively limited in the granularity and flexibility of their adaptation. On the other hand, existing "in-the-network" approaches, such as the H.323 MCU architecture, while offering a higher degree adaptation flexibility, maintain a static and inflexible design that is at odds with the dynamic nature of Internet communication. <p> 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. <p> 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 gateway, 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. <p> 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 multimedia 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. <p> 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.
Advisors: Randy H. Katz and Steven R. McCanne
BibTeX citation:
@phdthesis{Amir:CSD-98-1006,
Author= {Amir, Elan},
Title= {An Agent-based Approach to Real-time Multimedia Transmission over Heterogeneous Environments},
School= {EECS Department, University of California, Berkeley},
Year= {1998},
Url= {http://www2.eecs.berkeley.edu/Pubs/TechRpts/1998/6413.html},
Number= {UCB/CSD-98-1006},
Abstract= {An enduring trait of the Internet is its heterogeneity. Evidence of this heterogeneity includes the wide range of network transmission rates, varying across many orders of magnitude, and the vast differences in computing power, ranging from PDA's to supercomputers. These heterogeneities present significant barriers to the transmission of real-time multimedia data across groups. The barriers stem from the fact that in order to accommodate the entire gamut of group member characteristics, e.g., bandwidth availability or computing power, a source is required to transmit its data with properties matching the most constrained receiver. Instead, we would like to transmit media to multiple receivers at heterogeneous rates and properties that match those of each individual receiver. <p> Recent proposals for "end-to-end" solutions -- i.e, solutions which require only the participation of the end-applications -- offer the advantage of not requiring modifications within the network. However, these solutions are relatively limited in the granularity and flexibility of their adaptation. On the other hand, existing "in-the-network" approaches, such as the H.323 MCU architecture, while offering a higher degree adaptation flexibility, maintain a static and inflexible design that is at odds with the dynamic nature of Internet communication. <p> 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. <p> 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 gateway, 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. <p> 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 multimedia 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. <p> 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.},
}
EndNote citation:
%0 Thesis %A Amir, Elan %T An Agent-based Approach to Real-time Multimedia Transmission over Heterogeneous Environments %I EECS Department, University of California, Berkeley %D 1998 %@ UCB/CSD-98-1006 %U http://www2.eecs.berkeley.edu/Pubs/TechRpts/1998/6413.html %F Amir:CSD-98-1006