performance evaluation of redirection schemes in content distribution networks
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Performance Evaluation of Redirection Schemes in Content Distribution Networks. Jussi Kangasharju, Keith W. Ross Institut Eurecom. Jim W. Roberts France Telecom R&D. Outline. Content Distribution Networks Redirection Schemes Simulations Experiments Discussion Future Work Conclusion.

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performance evaluation of redirection schemes in content distribution networks

Performance Evaluation of Redirection Schemes inContent Distribution Networks

Jussi Kangasharju, Keith W. Ross

Institut Eurecom

Jim W. Roberts

France Telecom R&D

outline
Outline
  • Content Distribution Networks
  • Redirection Schemes
  • Simulations
  • Experiments
  • Discussion
  • Future Work
  • Conclusion
content distribution networks
Content Distribution Networks
  • Content distribution on the Web is changing
  • Content placed on content servers
  • Clients redirected to nearby content servers
  • Better performance for clients
  • Load balancing on content servers
  • Better fault tolerance
redirection schemes
Redirection Schemes
  • Full redirection
    • All client requests directed to content servers
    • Advantage: Simple
    • All content servers must be able to serve any content -> full mirrors or proxies
  • Selective redirection
    • Only some requests redirected
    • Need to select what content to serve from content server
dns redirection
DNS Redirection
  • Currently CDNs use DNS redirection
  • Two strategies
    • CDN controls the DNS resource records of the origin server
    • References to objects are changed to point to a content server
  • First strategy = Full redirection
  • Second strategy = Selective redirection
simulation model
Simulation Model
  • Use the NS network simulator
  • Simple model: Client, Server, and Link
  • Vary RTT, bandwidth, and loss rate on link
  • Client requests HTML file, then requests images
  • Look at user-perceived performance (total time)
  • Does not account for server load (yet)
effects of bandwidth
Effects of Bandwidth
  • After 1.5 Mbps, download time mostly based on RTT
  • Study only RTT and loss rate
different clients
Different Clients
  • Two different clients: Pipelining and parallel
  • Assumption: Parallel client cannot retrieve all objects with one set of connections
  • Baseline: Retrieve all from origin server
  • RTTs: 10, 20, 60, 100, 120, and 160 ms
  • Does not include DNS lookup delay
  • Assume parallel connections to be independent
test files
Test Files
  • 100 pages from Hot100.com
  • Typical homepage 20 KB + 50 KB
loss free network baseline
Loss Free Network, Baseline
  • Big gains possible, up to 90%
loss free network switch
Loss Free Network, Switch
  • Parallel connections, Medium page
  • Gains limited, maximum 30%
loss in network baseline
Loss in Network, Baseline
  • Big gains still possible, up to 85%
  • Not as good as no-loss case (slow-start)
loss in network switch
Loss in Network, Switch
  • Parallel connections, Medium page
  • Maximum gains 20% (slow-start, loss of SYN)
experiments
Experiments
  • Repeat simulated experiment on Internet
  • Exclude DNS lookups
  • Results confirm results from simulations
discussion
Discussion
  • Switching servers limits performance:
    • Either new server is not fast enough or the client should have used it for all the objects
  • Easy with full redirection, can be done with selective redirection, but have to be careful
  • Persistent connections
  • No server load -> switching degraded
  • No redirection cost -> switching improved
future work
Future Work
  • Improve simulation topology and model
  • Take into account server load in simulations
  • Include cost of redirection
  • Perform more extensive experiments
  • Evaluate the server selection schemes of existing CDNs
conclusion
Conclusion
  • Evaluate effects of redirection on user-perceived performance
  • Both simulations and experiments
  • Switching servers during download of a page hurts performance
  • Need to replicate Web pages with images to guarantee best performance
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