Person:

Zegura, Ellen W.

Permanent Link

https://hdl.handle.net/1853/71879

Associated Organization(s)

Organizational Unit

School of Computer Science

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Publication Search Results

Now showing 1 - 10 of 10

Multiple-Channel Multicast Scheduling for Scalable Bulk-data Transport

(Georgia Institute of Technology, 1998) Ammar, Mostafa H. ; Zegura, Ellen W. ; Donahoo, Michael J.

A key technique for allowing a server to handle a large volume of requests for file transfers is to multicast the data to the set of requesting clients. Typically, the paths from the server to the clients will be heterogeneous in bandwidth availability. Multiple-Channel Multicast (MCM) is an approach that can be used to handle this heterogeneity. In this approach the data is multicast over multiple channels, each addressed as a separate multicast group. Each receiver subscribes to a set of channels (i.e., joins the corresponding multicast groups) commensurate with its own rate capabilities. Of particular interest in the design of MCM schemes is the scheduling of data transmission across the multiple channels to accomodate asynchronous requests from clients. In this paper, we present and analyze a new multiple-channel multicast approach called Partition Organization (PO) scheduling. The scheme is designed to result in good reception efficiency when compared to existing proposals while improving on their performance when other measures of interest (which we introduce) are considered.
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.
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.
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.
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.
Distributed Laboratories: A Research Proposal

(Georgia Institute of Technology, 1996) Schwan, Karsten ; Ahamad, Mustaque ; Hudson, Scott E. ; Limb, J. O. (John O.) ; Ammar, Mostafa H. ; Ezquerra, Norberto F. ; Mukherjee, Amarnath ; Potts, Colin ; Ramachandran, Umakishore ; Zegura, Ellen W. ; Fujimoto, Richard M.

The continuing merger of computer and communication technologies is leading to a new computing/communications infrastructure of unprecedented magnitude, enabling new applications with broad economic and social impact. Yet, such applications pose major challenges to researchers in Computer Science and in application domains. The topic of the proposed research program is the realization of Distributed Laboratories, where individuals can interact with each other, and more importantly, with powerful, distributed computational tools as readily as if all were located in a single site. Our intent is to permit scientists, engineers, and managers at geographically distinct locations (including individuals 'tele-commuting' from home) to combine their expertise in solving shared problems, by allowing them to simultaneously view, interact with, and steer sophisticated computations executing on high performance distributed computing platforms.
Core Migration for Dynamic Multicast Routing

(Georgia Institute of Technology, 1995) Donahoo, Michael J. ; Zegura, Ellen W.

Efficient multicast communication provides one of the best avenues for scaling bandwidth intensive applications. Current multicast routing mechanisms perform well for multicast groups which reach a long-term, steady-state distribution of membership. However, when the membership migrates throughout the network, current routing techniques may perform poorly. One type of multicast routing technique involves selection of a "core" router through which all multicast communication is routed. We propose to adapt this routing scheme to efficiently support dynamic groups, by allowing the core to migrate. As part of our work we provide solutions to several problems that are more general, including estimating multicast bandwidth using unicast information and soliciting responses from a limited number of participants to avoid message implosion.
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.
Generation and Analysis of Random Graphs to Model Internetworks

(Georgia Institute of Technology, 1994) Thomas, Megan ; Zegura, Ellen W.

Graph models are commonly used in studying solutions to internetworking problems. This paper considers several random graph models that have been used to model internetworks, and considers ways to characterize the properties of these graphs. By matching the characteristics of the random graphs to the characteristics of real internetworks, more accurate modeling can be achieved.
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.