Introduction to Content Delivery Networks. CDN design options such as HTTP Redirects, DNS Based, Application Based, Name Based

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

2. Internet
Content
Providers
End
Users
The Web – Simple on Outside…

3. NAP
NAP
UUNet
Qwest
AOL
Network
Providers
Content
Providers
End
Users
Peering
Points
…But Problematic on Inside

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. Solution – Content Delivery Networks
(CDNs)
Servers
at Network Edge
Content
Providers
End
Users
NAP
NAP

6. Conventional vs. CDN
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www.labnol.org/internet/setup-content-delivery-network-with-amazon-s3-cloudfront/

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?
10

11. CDN
11

12. CDN Options – HTTP Redirects
 Origin server rewrites pages to serve content via CDN
12
Page that distributes content via CDN
Traditional Web page on server

13. CDN Options – DNS Based
13
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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