Choosing the Right FDO Deployment Model for Your Application _ Geoffrey at In...
Introduction to Content Delivery Networks
1. Content Delivery
Networks
CS4482 High Performance Networking
Dilum Bandara
Dilum.Bandara@uom.lk
Some slides extracted from "Content Delivery Networks -
Principles & Practice" by Ravi Sundaram
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
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5. Solution – Content Delivery Networks
(CDNs)
Servers
at Network Edge
Content
Providers
End
Users
NAP
NAP
7. CDNs
A system of computing devices networked
together (across Internet) that cooperate to
deliver content to end users
Pros
Improved end-user experience
Reduce latency, packet loss, & jitter
Transparent to users
Reduced network congestion
Increased scalability
Improved fault-tolerance
Reduced vulnerability
Reduced costs 7
8. CDNs (Cont.)
Cons
Application-level solution
Reliance on a CDN provider
ISPs vs. CDN providers
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9. CDN Mechanisms
Passive
Through browser cache & proxies
If content is static, not much investment is needed from
content provider
Significant fraction of HTTP objects uncatchable
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 9
10. CDN Challenges
How to replicate content?
Where to replicate content?
How to find replicated content?
How to choose among know replicas?
How to direct clients towards replica?
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12. CDN Options – HTTP Redirects
Origin server rewrites pages to serve content via CDN
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Page that distributes content via CDN
Traditional Web page on server
13. CDN Options – DNS Based
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A. 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.
14. 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
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