Computer Science Technical Reports

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https://hdl.handle.net/1911/94827

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Browsing Computer Science Technical Reports by Author "Aron, Mohit"

Now showing 1 - 6 of 6
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    A Resource Management Framework for Predictable Quality of Service in Web Servers
    (2003-07-07) Aron, Mohit; Druschel, Peter; Iyer, Sitaram
    This paper presents a resource management framework for providing predictable quality of service (QoS) in Web servers. The framework allows Web server and proxy operators to ensure a probabilistic minimal QoS level, expressed as an average request rate, for a certain class of requests (called a service), irrespective of the load imposed by other requests. A measurement-based admission control framework determines whether a service can be hosted on a given server or proxy, based on the measured statistics of the resource consumptions and the desired QoS levels of all the co-located services. In addition, we present a feedback-based resource scheduling framework that ensures that QoS levels are maintained among admitted, co-located services. Experimental results obtained with a prototype implementation of our framework on trace-based workloads show its effectiveness in providing desired QoS levels with high confidence, while achieving high average utilization of the hardware.
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    Differentiated and Predictable Quality of Service in Web Server Systems
    (2000-10-31) Aron, Mohit
    As the World Wide Web experiences increasing commercial and mission-critical use, server systems are expected to deliver high and predictable performance. The phenomenal improvement in microprocessor speeds, coupled with the deployment of clusters of commodity workstations has enabled server systems to meet the continually increasing performance demands in a cost-effective and scalable manner. However, as the volume, variety and sophistication of services offered by server systems increase, effective support for providing differentiated and predictable quality of service has also become important. For example, it is often desirable to differentiate between the resources allocated to virtual web sites hosted on a server system so as to provide predictable performance to individual sites, regardless of the load imposed upon others. Server systems lack adequate support for providing predictable performance to hosted services in terms of metrics that are meaningful to server applications, such as average throughput, response time, etc. This is because conventional systems multiplex resources by dealing with system level metrics such as CPU/disk bandwidth, memory pages etc. Maintaining predictable levels of performance in application level metrics, therefore, requires a corresponding mapping to system level metrics that is not supported in conventional systems. High performance server systems based upon cluster-based architectures also lack adequate support for providing differentiated quality of service. This is because providing differentiated quality of service in a cluster-based server system requires global resource management not found in current clusters. This dissertation is concerned with support for both differentiated as well as predictable quality of service in server systems. The specific requirements of server applications and their interactions with the resource management facilities in the operating system software are studied. This leads to a concerted design of a resource management framework for providing effective quality of service in server systems.
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    End-to-End TCP Congestion Control over ATM Networks
    (1997-02-12) Aron, Mohit; Druschel, Peter
    It is well documented that the effective throughput of TCP can suffer on plain ATM networks. Several research efforts have aimed at developing additions to ATM networks like Early Packet Discard that avoid TCP throughput degradation. This paper instead investigates improvements to TCP that allow it to perform well on ATM networks without switch-level enhancements, thus avoiding additional complexity and loss of layer transparency in ATM switches. We present an enhanced version of TCP Vegas and show that it performs nearly as well on plain ATM networks as on packet-oriented networks. Moreover, like the original TCP Vegas, our version achieves a significant increase in throughput over the BSD 4.4-Lite TCP. We also present an analysis of TCP dynamics over ATMnetworks, and a simulation based study of the various enhancements in our TCPimplementation and their impact on TCP performance over ATM and packet-oriented networks.
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    TCP Implementation Enhancements for Improving Webserver Performance
    (1999-07-06) Aron, Mohit; Druschel, Peter
    This paper studies the performance of BSD-based TCP implementations in Web servers. We find that lack of scalability with respect to high TCP connection rates reduces the throughput of Web servers by up to 25% and imposes a memory overhead of up to 32 MB on the kernel. We also find that insufficient accuracy in TCP's timers results in overly conservative delays for retransmission timeouts, causing poor response time, low network utilization and throughput loss. The paper proposes enhancements to the TCP implementation that eliminate these problems, without requiring changes to the protocol or the API. We also find that conventional benchmark environments do not fully expose certain significant performance aspects of TCP implementations and propose techniques that allow these benchmarks to more accurately predict the performance of real servers.
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    TCP: Improving Startup Dynamics by Adaptive Timers and Congestion Control
    (1998-06-03) Aron, Mohit; Druschel, Peter
    This paper studies the startup dynamics of TCP on both high as well as low bandwidth-delay network paths and proposes a set of enhancements that improve both the latency as well as throughput of relatively short TCP transfers. Numerous studies have shown that the timer and congestion control mechanisms in TCP can have a limiting effect on performance in the startup phase. Based on the results of our study, we propose mechanisms for adaptingTCP in order to yield increased performance. First, we propose a framework for the management of timing in TCP. Second, we show how TCP can utilize the proposed timer framework to reduce the overly conservative delay associated with a retransmission timeout. Third, we propose the use of packet pacing in the initial slow-start to improve the performance of relatively short transfers that characterize the web traffic. Finally, we quantify the importance of estimating the initial slow-start threshold in TCP, specially on high bandwidth-delay paths.
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    Techniques for Efficient Cell-Level ATM Simulations
    (2000-02) Aron, Mohit; Brakmo, Lawrence
    This paper investigates the efficiency of a network simulator in simulating ATM networks with UBR service and compares it to the the efficiency of simulating conventional packet networks. A network simulator can be highly inefficient for cell-level ATM simulations as compared to analogous packet network simulations. We motivate and describe three techniques for improving the efficiency of ATM simulations. These techniques afford an increase inefficiency of 29-34% for ATM simulations.