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We consider the problem of providing vehicular Internet access using roadside 802.11 access points. We build on previous work in this area [18, 8, 5, 11] with an extensive experimental analysis of protocol operation at a level of detail not previously explored. We report on data gathered with four capture devices from nearly 50 experimental runs conducted(More)
We study the problem of processor scheduling for n parallel jobs applying the method of competitive analysis. We prove that for jobs with a single phase of parallelism, a preemptive scheduling algorithm without information about job execution time can achieve a mean completion time within 2− 2 n+1 times the optimum. In other words, we prove a competitive(More)
A multiprocessor system is unlikely to have access to information about the execution characteristics of the jobs it is to schedule. In this work, we are interested in scheduling algorithms for batch jobs that require no such knowledge (such algorithms are called non-clairvoyant). Preemptive scheduling (i.e., redistribution of processors) is important to(More)
In three-tiered web applications, some form of admission control is required to ensure that throughput and response times are not significantly harmed during periods of heavy load. We propose Q-Cop, a prototype system for improving admission control decisions that considers a combination of the load on the system, the number of simultaneous queries being(More)
The rapid proliferation of the World-Wide Web has been due to the seamless access it provides to information that is distributed both within organizations and around the world. In this paper, we describe the design and implementation of a system, called Ajents, which provides the software infrastructure necessary to support a similar level of seamless(More)
User-level virtual memory (VM) primitives are used in many different application domains including distributed shared memory, persistent objects, garbage collection, and checkpointing. Unfortunately, VM primitives only allow traps to be handled at the granularity of fixedsized pages defined by the operating system and architecture. In many cases, this(More)
In this paper, we describe the design of a system, called ParaWeb, for utilizing Internet or intra-net computing resources in a seamless fashion. The goal is to allow users to execute serial programs on faster compute servers or parallel programs on a variety of possibly heterogeneous hosts. ParaWeb provides extensions to the Java programming environment(More)
In systems that support garbage collection, a tension exists between collecting garbage too frequently and not collecting it frequently enough. Garbage collection that occurs too frequently may introduce unnecessary overheads at the risk of not collecting much garbage during each cycle. On the other hand, collecting garbage too infrequently can result in(More)
When a roadside 802.11-based wireless access point is shared by more than one vehicle, the vehicle with the lowest transmission rate reduces the effective transmission rate of all other vehicles. This <i>performance anomaly</i> [9] degrades both individual and overall throughput in such multi-vehicular environments. Observing that every vehicle eventually(More)
In this paper, we extensively tune and then compare the performance of web servers based on three different server architectures. The &mu;server utilizes an event-driven architecture, Knot uses the highly-efficient Capriccio thread library to implement a thread-per-connection model, and WatPipe uses a hybrid of events and threads to implement a(More)