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Zegura, Ellen W.

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Author: Bhattacharjee, Samrat ×

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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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    A Novel Server Selection Technique for Improving the Response Time of a Replicated Service
    (Georgia Institute of Technology, 1997) Bhattacharjee, Samrat ; Zegura, Ellen W. ; Ammar, Mostafa H. ; Fei, Zongming
    Server replication is an approach often used to improve the ability of a service to handle a large number of clients. One of the important factors in the efficient utilization of replicated servers is the ability to direct client requests to the best server, according to some optimality criteria. In this paper we target an environment in which servers are distributed across the Internet, and clients identify servers using our application-layer anycasting service. Our goal is to allocate servers to clients in a way that minimizes a client's response time. To that end, we develop an approach for estimating the performance that a client would experience when accessing particular servers. Such information is maintained in a resolver that clients can query to obtain the identity of the server with the best response time. Our performance collection technique combines server push with client probes to estimate the expected response time. A set of experiments is used to demonstrate the properties of our performance determination approach and to show its advantages when used within the application-layer anycasting architecture.
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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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    Application-Layer Anycasting
    (Georgia Institute of Technology, 1996) Ammar, Mostafa H. ; Zegura, Ellen W. ; Shah, Viren ; Fei, Zongming ; Bhattacharjee, Samrat
    Server replication is a key approach for maintaining user-perceived quality of service within a geographically wide-spread network. The anycasting communication paradigm is designed to support server replication by allowing applications to easily select and communicate with the "best" server, according to some performance or policy criteria, in a group of content- equivalent servers. We examine the definition and support of the anycasting paradigm at the application layer, providing a service that maps anycast domain names into one or more IP addresses using anycast resolvers. In addition to being independent from network-layer support, our definition includes the notion of filters, functions that are applied to groups of addresses to affect the selection process. We consider both metric-based filters (e.g., server response time) and policy-based filters; we further allow filtering both at the anycast resolver and local to the anycast client. A key input to the filtering process is metric information describing the relative performance of replicated servers. We examine the use of various techniques for maintaining this information at anycast resolvers.