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Content Delivery Networks (CDN)


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Content Delivery Networks (CDN). Active, passive, application, and naming based CDN

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Content Delivery Networks (CDN)

  1. 1. Content Delivery Networks (CDN) CS4262 Distributed Systems Dilum Bandara Some slides extracted from Dr. Srinath Perera & Dr. Rajkumar Buyya’s Presentation Deck
  2. 2. Internet Content Providers End Users The Web – Simple on Outside…
  3. 3. NAP NAP UUNet Qwest AOL Network Providers Content Providers End Users Peering Points …But Problematic on Inside
  4. 4. Issues  Latency  Browser takes a long time to load pages  Packet loss  Browser hangs, user needs to hit refresh  Jitter  Streams are jerky  Server load  Browser connects but doesn’t fully load the page  Bandwidth aggregation  Broken/missing content 4
  5. 5. Solution – Content Delivery Networks (CDNs) Servers at Network Edge Content Providers End Users NAP NAP
  6. 6. Content Delivery Networks (CDNs)  Passive  Through browser cache & proxies  If content is static, not much investment is needed from content provider  Significant fraction of HTTP objects not cacheable  Need investment from content provider  Provider lacks of control & customization  Active  Replicate content on a distribution network  HTTP redirects  DNS-based  Provider has control & customization  Low investment from content provider side 6
  7. 7. Conventional vs. CDN 7 Source:
  8. 8. CDN Challenges  How to replicate content?  Where to replicate content?  How to find replicated content?  How to choose among known replicas?  How to direct clients towards a replica? 8
  9. 9. CDN 9
  10. 10. CDN Options – HTTP Redirects  Origin server rewrites pages to serve content via CDN 10Page that distributes content via CDN Traditional Web page on server
  11. 11. CDN Options – DNS Based 11A. Su, D. R. Choffnes, A. Kuzmanovic, & F. E. Bustamante, “Drafting behind Akamai (travelocity- based detouring), “ ACM SIGCOMM Comput. Commun. Rev. 36, 4, Aug. 2006, pp. 435-446.
  12. 12. CDN Options  Application based (HTTP redirects)  Pros  Application-level, fine-grained control  Cons  Additional load & high RTTs, hard to cache  Naming based (DNS selection)  Pros  Well-suitable for caching, reduce RTTs  Cons  Request by resolver not client, request for domain not URL, hidden load factor of resolver’s population 12