Zegura, Ellen W.

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Now showing 1 - 4 of 4
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    Network Support for Multicast Video Distribution
    (Georgia Institute of Technology, 1998) Bhattacharjee, Samrat ; Calvert, Kenneth L. ; Zegura, Ellen W.
    Multicast video distribution in a best-effort environment presents challenges to system designers, including heterogeneity in the bandwidth availability on the paths from the sender to the receivers and dynamic behavior in the network and set of receivers over time. Classic approaches to dealing with dynamic conditions involve adaptation at the sender (for unicast) and adaptation driven by the receivers (for multicast). Both approaches have limitations that affect the quality of video received. In this paper, we consider a third option for the location of adaptation, namely: in the network. We demonstrate that a modest amount of state and computation at network routers can yield significant performance gains for multicast video distribution. Our schemes maintain the advantages of receiver-based adaptation, while overcoming the limitation. Since the network applies the adaptation, the time and place for adaptation can better match network conditions. Further, the adaptation can occur more rapidly, without the need for route changes. Finally, the adaptation can occur at finer granularity, providing better quality and more graceful degradation to receivers.
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    An Architecture for Active Networking
    (Georgia Institute of Technology, 1996) Bhattacharjee, Samrat ; Calvert, Kenneth L. ; Zegura, Ellen W.
    Active networking offers a change in the usual network paradigm: from passive carrier of bits to a more general computation engine. The implementation of such a change is likely to enable radical new applications that cannot be foreseen today. Large-scale deployment, however, involves significant challenges in interoperability, security, and scalability. In this paper we define an active networking architecture in which user control the invocation of pre-defined, network-based functions through control information in packet headers. After defining our active networking architecture, we consider a problem (namely, network congestion) that may benefit in the near-term from active networking, and thus may help justify migration to this new paradigm. Given an architecture allowing applications to exercise some control over network processing, the bandwidth allocated to each application's packets can be reduced in a manner that is tailored to the application, rather than being applied generically. Our results show that the ability to gracefully adapt to congestion makes a good case for active networking.
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    Core Selection Methods for Multicast Routing
    (Georgia Institute of Technology, 1995) Calvert, Kenneth L. ; Zegura, Ellen W. ; Donahoo, Michael J.
    Multicast routing is an important topic of both theoretical and practical interest. Some recently-proposed multicast routing algorithms involve the designation of one or more network nodes as the "center" of the routing tree for each multicast group address. The choice of this designated router (which we refer to as the "core") influences the shape of the multicast routing tree, and thus influences performance of the routing scheme. In this paper we investigate the relationship between the choice of core and three performance measures. Specifically, we compare various methods of selecting a core with respect to their effect on bandwidth, delay, and traffic concentration. We conclude that simple methods are adequate for widely distributed groups, but that the addition of group information can be leveraged to improve performance especially when the group is small or exhibits a high degree of locality. We also conclude that core choice has a significant impact on traffic concentration, in fact traffic concentration effects can be ameliorated by appropriate core choice policies.
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    A Comparison of Two Practical Multicast Routing Scheme
    (Georgia Institute of Technology, 1994) Calvert, Kenneth L. ; Madhavan, Ramesh ; Zegura, Ellen W.
    Designing an interdomain multicast routing scheme that makes efficient use of network resources while delivering good performance to applications is a significant challenge. A variety of schemes have been proposed, but little has been done to compare the schemes systematically over a rich set scenarios. In this work we develop a framework to do systematic evaluation of multicast routing schemes, and apply it to two practical schemes: Distance Vector Multicast Routing Procotol and Core Based Trees. We conclude that Core Based Trees has the potential to make more efficient use of resources, with modest performance penalty. However, this requires mechanisms to choose good cores. We suggest a heuristic for evaluating the goodness of a core and moving towards a good core.