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      • HARVEST
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      Scalable download protocols

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      Date
      2006-12-15
      Author
      Carlsson, Niklas
      Type
      Thesis
      Degree Level
      Doctoral
      Metadata
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      Abstract
      Scalable on-demand content delivery systems, designed to effectively handle increasing request rates, typically use service aggregation or content replication techniques. Service aggregation relies on one-to-many communication techniques, such as multicast, to efficiently deliver content from a single sender to multiple receivers. With replication, multiple geographically distributed replicas of the service or content share the load of processing client requests and enable delivery from a nearby server.Previous scalable protocols for downloading large, popular files from a single server include batching and cyclic multicast. Analytic lower bounds developed in this thesis show that neither of these protocols consistently yields performance close to optimal. New hybrid protocols are proposed that achieve within 20% of the optimal delay in homogeneous systems, as well as within 25% of the optimal maximum client delay in all heterogeneous scenarios considered.In systems utilizing both service aggregation and replication, well-designed policies determining which replica serves each request must balance the objectives of achieving high locality of service, and high efficiency of service aggregation. By comparing classes of policies, using both analysis and simulations, this thesis shows that there are significant performance advantages in using current system state information (rather than only proximities and average loads) and in deferring selection decisions when possible. Most of these performance gains can be achieved using only “local” (rather than global) request information.Finally, this thesis proposes adaptations of already proposed peer-assisted download techniques to support a streaming (rather than download) service, enabling playback to begin well before the entire media file is received. These protocols split each file into pieces, which can be downloaded from multiple sources, including other clients downloading the same file. Using simulations, a candidate protocol is presented and evaluated. The protocol includes both a piece selection technique that effectively mediates the conflict between achieving high piece diversity and the in-order requirements of media file playback, as well as a simple on-line rule for deciding when playback can safely commence.
      Degree
      Doctor of Philosophy (Ph.D.)
      Department
      Computer Science
      Program
      Computer Science
      Supervisor
      Eager, Derek L.
      Committee
      Soteros, Chris; Keil, J. Mark; Grassmann, Winfried K.; Deters, Ralph
      Copyright Date
      December 2006
      URI
      http://hdl.handle.net/10388/etd-12152006-085440
      Subject
      Peer-assisted streaming
      Probabilistic piece selection
      Performance evaluation
      Batching
      Content delivery
      Scalable download
      Multicast protocols
      Required server bandwidth
      Service aggregation
      Replica selection
      BitTorrent-like systems
      Digital fountain
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      • Graduate Theses and Dissertations
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