Institute for Systems Research Technical Reports

For this new computing landscape, this thesis advocates creating highly scalable dataservices based on adaptive hybrid data delivery. It introduces air-caching, a technique thateffectively integrates broadcasting for massive dissemination of popular data, and unicastingfor upon-request delivery of the rest. It describes the special properties, performance goals,and challenges of air-caching. Then, it presents adaptive cache management techniques forthree different settings: servicing large numbers of data requests over heavily accessed databases, propagating data updates to mobile clients intermittently connected toinformation sources, and implementing publish/subscribe services again in the context ofmobile computing. In all cases, performance experiments demonstrate the scalability,efficiency, and versatility of this technique, even under rapidly changing data access patterns.

In this thesis we consider an alternative network architecture, where largeheterogeneous networks are built from small homogeneous networksinterconnected by carefully designed proxy systems. We describe the designand implementation of such a proxy and demonstrate marked performanceimprovements over both actual and simulated satellite channels. We alsodiscuss some benefits and drawbacks of using proxies in networks andexplore some tradeoffs in proxy design.

However, there are certain performance problems withproviding Internet over satellite due to the nature of TCP/IP protocol suite and the satellite link characteristics. In this paper, we describe a simulation study of an architecture for improving the performance of TCP/IP over satellite links.

On each end of the satellite link, there are gateways that split the TCP connection so that the satellite link is transparent to the end hosts.

The split TCP connection over the satellite segment is then optimized.TCP congestion control is maintained on each segment of the split connection.

We simulated such an architecture in OPNET and present results showing improved throughput over the satellite link.

Even if these professions succeed in their endeavors, computer researchers will still have much work to do. They will have to deal with the difficult question: How can information and communication services be made usable for every citizen? Designing for experienced, frequent users is difficult enough, but designing for a broad audience of unskilled users is a far greater challenge. Computing technology is still too hard to use for many people. We can define universal usability as having more than 90 percent of all households as successful users of information and communication services at least once a week. A 1998 survey of US households shows that 42% have computers and 26% use Internet-based e-mail or other services. The percentage declines in poorer and less educated areas. While cost is an issue for many, hardware limitations,the perceived difficulty and lack of utility discourages others. This paper presents a research agenda based on three challenges in attaining universal usability for web-based and other services: --Technology variety: Supporting a broad range of hardware, software and network access,--User diversity: Accommodating users with different skills, knowledge, age, gender, handicaps, literacy, culture, income, etc., and --Gaps in user knowledge: Bridging the gap between what users know and what they need to know