9 research outputs found

    Multi-class Latency Bounded Web Services

    No full text
    Masters ThesisTwo recent advances have resulted in significant improvements in web server quality-of-service. First, both centralized and distributed web servers can provide isolation among service classes by fairly distributing system resources. Second, session admission control can protect classes from performance degradation due to overload. The goal of this thesis is to design a general "front-end" algorithm that uses these two building blocks to support a new web service model, namely, multi-class services which control response latencies to within pre-specified targets. Our key technique is to devise a general service abstraction to adaptively control not only the latency of a particular class, but also to assess the inter-class relationships. In this way, we capture the extent to which classes are isolated or share system resources (as determined by the server architecture and system internals) and hence their effects on each other's QoS. We validate the scheme with trace driven simulations.National Science Foundatio

    Distributed scheduling and multi-channel opportunistic media access for ad hoc networks

    No full text
    Current wireless ad hoc networks suffer from two main performance limitations. First, current ad hoc networks do not efficiently utilize the scarce and dynamic wireless spectrum. As a result, the goodput of current ad hoc networks is often lower than the maximum radio transmission rate. Second, current ad hoc networks provide only best effort service, and there is little related work to provide general mechanisms to enable more powerful services (such as guaranteed services, differentiated services and flow protection). Consequently, current ad hoc networks are unable to provide quality-of-service (throughput or delay targets, QoS differentiation and fairness) and can incur severe unfairness even in simple topologies. In this thesis I design and evaluate mechanisms that together address the above mentioned two main performance limitations of current ad hoc networks. In particular this thesis has two main contributions. First, I propose and evaluate Distributed Wireless Ordering Protocol (DWOP), which provides a framework for design of join scheduling and MAC in ad hoc networks. The goal of DWOP is to ensure that to the closest extent possible, packets are serviced in the order as defined by a centralized reference scheduler. By ensuring that packets access the medium in an exact reference order, DWOP serves as a framework to apply the wealth of packet scheduling service disciplines developed for wireline networks to wireless ad hoc networks thereby making it possible to achieve the desired goals of fairness, throughput and delay targets and service differentiation in such networks. Second, I propose MAC mechanisms to opportunistically exploit the scarce and variable wireless channel to maximize net system throughput of ad hoc networks. In particular I devise Multi-channel Opportunistic Auto Rate (MOAR), a distributed MAC protocol which exploits the presence of frequency diversity in ad hoc networks to maximize the net throughput of such networks. MOAR is opportunistic across both users and channels and exploits temporal variations across multiple frequency channels present at the physical (PHY) layer to opportunistically transmit data at a higher rate on high quality channels. The two contributions, namely joint design of distributed MAC and scheduling and design of multi-channel opportunistic MAC protocol, together form a frame-work for high performance ad hoc networks which not only support QoS but also achieve high throughput by efficiently exploiting the scarce and dynamic wireless channel

    Multi-class latency bounded Web services

    No full text
    Two recent advances have resulted in significant improvements in web server quality-of-service. First, both centralized and distributed web servers can provide isolation among service classes by fairly distributing system resources. Second, session admission control can protect classes from performance degradation due to overload. The goal of this thesis is to design a general "front-end" algorithm that uses these two building blocks to support a new web service model, namely, multi-class services which control response latencies to within pre-specified targets. Our key technique is to devise a general service abstraction to adaptively control not only the latency of a particular class, but also to assess the inter-class relationships. In this way, we capture the extent to which classes are isolated or share system resources (as determined by the server architecture and system internals) and hence their effects on each other's QoS. We validate the scheme with trace driven simulations
    corecore