Department of Computer Science

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https://hdl.handle.net/10919/19035
The Department of Computer Science has an accredited undergraduate program that offers specialized ‘tracks’ of study in key areas. Undergraduates are prepared by graduation for pursuing a computing career or for graduate study. Our active corporate partners program offers internships and permanent employment to our students. Students are encouraged to participate in research experiences during their studies. Capstone courses provide significant team project experiences. The graduate program offers M.S. and Ph.D. degrees, emphasizing thesis work both at the main campus in Blacksburg and at the Northern Virginia Center. About two-thirds of the graduate students are pursuing the Ph.D. degree. The faculty, among whom there are 12 NSF or DOE CAREER Award winners, are active researchers who are visible contributors to the profession and have achieved significant honors.

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Browsing Department of Computer Science by Author "Abdulla, Ghaleb"

Now showing 1 - 8 of 8
  • Caching Proxies: Limitations and Potentials
    Abrams, Marc; Standridge, Charles R.; Abdulla, Ghaleb; Williams, Stephen; Fox, Edward A. (Department of Computer Science, Virginia Polytechnic Institute & State University, 1995-07-01)
    As the number of World-Wide Web users grow, so does the number of connections made to servers. This increases both network load and server load. Caching can reduce both loads by migrating copies of server files closer to the clients that use those files. Caching can either be done at a client or in the network (by a proxy server or gateway). We assess the potential of proxy servers to cache documents retrieved with the HTTP protocol. We monitored traffic corresponding to three types of educational workloads over a one semester period, and used this as input to a cache simulation. Our main findings are (1) that with our workloads a proxy has a 30-50% maximum possible hit rate no matter how it is designed; (2) that when the cache is full and a document is replaced, least recently used (LRU) is a poor policy, but simple variations can dramatically improve hit rate and reduce cache size; (3) that a proxy server really functions as a second level cache, and its hit rate may tend to decline with time after initial loading given a more or less constant set of users; and (4) that certain tuning configuration parameters for a cache may have little benefit.
  • Characterizing World Wide Web Queries
    Abdulla, Ghaleb; Liu, Binzhang; Saad, Rani A.; Fox, Edward A. (Department of Computer Science, Virginia Polytechnic Institute & State University, 1997-02-01)
    Locating information on the WWW is a major activity for users, and Web Information Retrieval Systems (IRS) are becoming more important to support their endeavors. In this paper we characterize queries performed by Web users to such systems and give distributions for accesses to different Web IRS. We characterize clients' accesses, queries and user sessions. Our purpose is to reduce network and bandwidth by identifying ways to optimize interactions with the Web. We characterize clients' sessions by a sequence of Browsing, Searching, and Next steps, and demonstrate that more search steps correlate with a reduction in the number of bytes transferred.
  • Modeling Correlated Proxy Web Traffic Using Fourier Analysis
    Abdulla, Ghaleb; Nayfeh, Ali H.; Fox, Edward A. (Department of Computer Science, Virginia Polytechnic Institute & State University, 1997-11-01)
    We analyze the arrival rate of accesses to Web proxy caching servers. The results show that the data display strong periodic autocorrelation. The examined data sets show a consistent behavior in terms of having periods corresponding to daily and weekly cycles that can be explained in terms of daily and weekly cyclic behavior of Web users. While these results confirm the correlation in the network traffic noticed by other researchers, we emphasize that this correlation is periodic. A new approach is introduced to model data that exhibit such characteristics by a combination of Fourier and statistical analysis techniques. The source of high correlation in the data is shown to come from the periodic and hence the deterministic part. Synthesized data that results from this modeling approach is shown to have a long-range dependent and self-similar behavior.
  • Multimedia Traffic Analysis Using CHITRA95
    Abrams, Marc; Williams, Stephen; Abdulla, Ghaleb; Patel, Shashin; Ribler, Randy; Fox, Edward A. (Department of Computer Science, Virginia Polytechnic Institute & State University, 1995-04-01)
    We describe how to investigate collections of trace data representing network delivery of multimedia information with CHITRA95, a tool that allows a user to visualize, query, statistically analyze and test, transform, and model collections of trace data. CHITRA95 is applied to characterize World Wide Web (WWW) traffic from three workloads: students in a classroom of network-connected workstations, graduate students browsing the Web, undergraduates browsing educational and other materials, as well as traffic on a courseware repository server. We explore the inter-access time of files on a server (i.e., recency), the hit rate from a proxy server cache, and the distributions of file sizes and media types requested. The traffic study also yields statistics on the effectiveness of caching to improve transfer rates. In contrast to past WWW traffic studies, we analyze client as well as server traffic; we compare three workloads rather than drawing conclusions from one workload; and we analyze tcpdump logs to calculate the performance improvement in throughput that an end user sees due to caching.
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    NMFS: Network Multimedia File System Protocol
    Patel, Sameer H.; Abdulla, Ghaleb; Abrams, Marc; Fox, Edward A. (Department of Computer Science, Virginia Polytechnic Institute & State University, 1992)
    We describe an on-going project to develop a Network Multimedia File System (NMFS) protocol. The protocol allows "transparent access of shared files across networks" as Sun's NFS protocol does, but attempts to meet a real-time delivery schedule. NMFS is designed to provide ubiquitous service over networks both designed and not designed to carry multimedia traffic.
  • Scaling the World-Wide Web
    Abdulla, Ghaleb; Abrams, Marc; Fox, Edward A. (Department of Computer Science, Virginia Polytechnic Institute & State University, 1996-03-01)
  • Web Response Time and Proxy Caching
    Liu, Binzhang; Abdulla, Ghaleb; Johnson, Tommy; Fox, Edward A. (Department of Computer Science, Virginia Polytechnic Institute & State University, 1998-03-01)
    It is critical to understand WWW latency in order to design better HTTP protocols. In this paper we characterize Web response time and examine effects of proxy caching on response time. We show that at least a quarter of the total elapsed time is spent in setting up TCP connections. We also characterize the effect of a user's network bandwidth on response time. Average connection time from a client via a 33.6 K modem is two times longer than that from a client via switched Ethernet. Contrary to the typical thought about Web proxy caching, this study finds that a single stand alone proxy cache does not always reduce response time. Implications of these results to the HTTP-NG protocol and Web application design also are discussed in the paper.
  • WWW Proxy Traffic Characterization with Application to Caching
    Abdulla, Ghaleb; Fox, Edward A.; Abrams, Marc; Williams, Stephen (Department of Computer Science, Virginia Polytechnic Institute & State University, 1997-02-01)
    Characterizing World Wide Web proxy traffic helps identify parameters that affect caching, capacity planning and simulation studies. In this paper we identify invariants that hold across a collection of ten traces representing traffic seen by caching-proxy servers. The traces were collected from governmental, industry, university, high school, and an online service provider environment, with request rates that range from a few accesses to millions of accesses per hour. We also show that the examined traffic is semi-similar. We explore sources of Web self-similarity and we conclude that a strong source is the periodicity in the users behavior. The tests revealed that there is a strong connection between access rate from hour to hour. We also report the hit rate and weighted hit rate obtained by running a trace driven simulation on the workloads to simulate a proxy with infinite cache, similarly, accesses to unique servers and URLs are a small portion of the total. By considering these characteristics of traffic we can improve the utility of caching for WWW clients.