Content Delivery Networks: Status and Trends Speaker: Shao-Fen Chou Advisor: Dr. Ho-Ting Wu 5/8/2012 1

Outline Introduction CDN Overview Content Distribution and Management Request-Routing Mechanisms Performance Measurement Conclusion Reference 2

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Introduction With the proliferation of the Internet, popular Web services often suffer congestion and bottlenecks due to large demands. Proxy servers partially address the need for rapid content delivery by a shared cache. 4

Introduction Web caching has three primary benefits: ▪It reduces bandwidth consumption, network congestion, and network traffic. ▪It reduces external latency. ▪It improves reliability. ▪But caching has significant drawbacks: ▪Clients might receive stale data. ▪“Flash crowds” event. 5

Introduction Researchers have considered CDN to reducing these disadvantages: ▪It reduces origin server load, and latency for end users. ▪It increases throughput. ▪CDN can also improve Web scalability and disperse flash-crowd event. 6

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CDN Overview The differences between proxies and CDNs: ▪Proxies store the most frequently and most recently requested content. ▪CDNs store content specified by the network administrator. 8

CDN Overview Three key components of a CDN architecture: ▪Content provider ( or customer) ▪CDN provider ▪End-users (or clients) 9

CDN Overview CDN providers use caching or replica servers located in different geographical locations. CDN cache servers are also called edge servers or surrogate servers. 10

CDN Overview 11 source: wikipedia

CDN Overview Four basic steps for CDN: ▪Surrogate servers cache the origin servers’ content. ▪Routers deliver the client’s content request to a suitable surrogate server. ▪Network elements distribute the requested content form the origin to the surrogates. ▪Accounting mechanism provides logs to the origin servers. 12

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Content Distribution and Management 14

Content Distribution and Management Surrogate placement: ▪Greedy method ▪Topology-informed Placement Strategy ▪Hot Spot ▪Tree-based Replica Placement 15

Content Distribution and Management Optimal number of surrogates: ▪Single-ISP approach: deploy at least 40 surrogate servers around its network’s edge. ▪Multi-ISP approach: locates numerous surrogate servers in global ISP points of presence as many as possible. 16

Content Distribution and Management Content selection and delivery: ▪Full-site ▪Partial-site : Empirical-based Popularity-based Cluster-based 17

Content Distribution and Management Content outsourcing: ▪Cooperative push-based ▪Non-cooperative pull-based ▪Cooperative pull-based 18

Content Distribution and Management Cache organization: ▪Caching techniques ▪Cache update 19

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Request-Routing Mechanisms ▪Global Server Load Balancing (GSLB) ▪DNS-based request routing ▪HTTP redirection ▪URL rewriting ▪Anycasting ▪CDN Peering 21

Request-Routing Mechanisms An example of a content delivery process: 22

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Performance Measurement CDN customer evaluate CDN performance using five key metrics: ▪Cache hit ratio ▪Saved bandwidth ▪Latency ▪Surrogate server utilization ▪Reliability 26

Performance Measurement From a client’s perspective, the most important CDN criteria: ▪Cost ▪Performance ▪Availability 27

Conclusion With replication technologies, CDN can offer efficient multicast delivery of content. Without scalable and reliable distributed storage and surrogate servers, CDN are vulnerable to attackers. The challenge for such CDNs will be to offer secure content delivery with high QoS guarantees. 28

Reference [1] A. Vakali, and G. Pallis, “Content Delivery Networks: Status and Trends,” IEEE Internet Computing, IEEE Computer Society, 2003, pp [2] A. M. K. Pathan and R. Buyya,“A Taxonomy and Survey of Content Delivery Networks,” Technical Report,GRIDS- TR , Grid Computing and Distributed Systems Laboratory, The University of Melbourne, Australia, February [3] Content delivery network, Retrieved 08.May.2012 from 29

Q&A Thanks for your attention. 30