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Benefits of Content Delivery Networking to
E-Learning and E-Communications.
Michel Eboueya, Michel Menard and Pascal
Estraillier Laboratoire dInformatique et
dImagerie Industrielle (L3i), Department of
Computer Sciences Université de La Rochelle
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Summary

• Introduction
• What is caching
• What is a Content Delivery/Distribution Network?
• The content delivery block
• The content routing block.
• Performance Measurement.
• Benefits of Content Distribution and Management
• Conclusion

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Content Delivery Networking

• A Content Delivery Network (CDN) is a
  Co-ordinated network of devices (Content Engines)
  that cache content for end users
• CDNs are a multi-million-dollar business already.

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Content Delivery Networking why?

• Interconnections Contribute to Slow, Unreliable
  Content Delivery
• Content and Usage Continue to Increase.

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Interconnections Contribute to Slow, Unreliable
Content Delivery

• Each Web-object requires multiple round-trips
  between end-users and the source of Web content
• Data transit currently governed by FIFO manner,
  limited accountability
• Surges in demand for content often unpredictable
• Packet loss at interconnection points may exceed
  20 during peak hours
• For every 1 of packet loss that occurs, an end
  users download time is doubled.

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Content and Usage Continue to Increase.

• Demands on Internet backbone are rising
• Internet usage rising 76 annually to 2,990 Gbps
  by 2003 (Pioneer Consulting).
• By year 2005, there will be over 750 million
  people online (International Data Corporation).
• Internet content is becoming increasingly complex
  and mission-critical(Gartner Group).

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Summary

• Introduction
• What is caching
• What is a Content Delivery/Distribution Network?
• The content delivery block
• The content routing block.
• Performance Measurement.
• Benefits of Content Distribution and Management
• Conclusion

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What is caching (1/2)

• A Web cache
• sits between Web servers (or origin servers) and
  a client or many clients,
• and watches requests for HTML pages, images and
  files come by
• saving a copy for itself.
• Then, if there is another request for the same
  object,
• it will use the copy that it has,
• instead of asking the origin server for it again.

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What is caching (2/2)

• There are two main reasons that Web caches are
  used
• To reduce latency
• To reduce traffic

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Summary

• Introduction
• What is caching
• What is a Content Delivery/Distribution Network?
• The content delivery block
• The content routing block.
• Performance Measurement.
• Benefits of Content Distribution and Management
• Conclusion

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  What is a Content Delivery Network? (1/4)

• It is a service offered by a service provider.
• maintains multiple locations with copies of the
  same content
• uses information about the user and the content
  requested
• to route the user to the most appropriate
  site.

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  What is a Content Delivery Network? (2/4)

• At least three independent building blocks
• (in addition to the network infrastructure)
• the content delivery block,
• the content routing block,
• the performance measurement block

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Content Delivery and caching

• Concerns
• the entire content workflow,
• encoding
• indexing
• edge delivery,
• how to secure
• and manage the content.

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Content Routing

• Consists of technologies to match end-users with
  the right content from the right place, i.e. DNS
  redirection,

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Content Routing

• Client requests content of a web page residing at
  the content provider's website - www.content.com.
• 2. Since content.com doesn't host their own
  streaming media, but uses cdn.com as their CDN
  provider, the URL redirects the media clients to
  the cdn.com site.
• 3. Using redirection algorithms the media client
  gets redirected to the most appropriate cache. In
  this case, the CDN doesn't have a cache directly
  placed at the ISP.

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Content Routing

• 4. If the CDN has a cache placed at the client's
  ISP, the client gets redirected to that point.
• 5. The CDN cache serves the content to the
  client. Since the cache isn't close to the client
  in this case, the performance might not be as
  good as expected.

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Performance Measurement What? And Why? (1/6)

• Content distribution networks are coordinated
  caching systems.
• CDNs are a multi-million-dollar business already.
• Wed like to have a figure of merit for them.

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Performance Measurement a DNS-redirecting CDN
DNS redirector
Client
http//example.com/foo
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Performance Measurement Client Actions (3/6)

• R Resolve domain name
• F Fetch content
• Ordinary client use of CDN RF
• Instead of doing (RF) , do R then F
• This allows to compare the server chosen to some
  other servers that could have been chosen, over a
  large number of fetches.

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Performance Measurement Procedure (4/6)

• R Collect a set of servers by repeated DNS
  queries
• to a variety of name servers
• over a number of hours
• F Fetch a particular piece of content from each
  member of the set, measuring latency

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Performance Measurement Important Details

• Interleaved fetches
• Fetch1 at server1, fetch1 at server2, etc.
• Not fetch1 at server1, fetch2 at server1, etc.
• Unmeasured fetch before measured fetch
• Avoids cache misses
• Measure only HTTP fetch latency
• CDN not penalized for cost of DNS resolution

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Performance Measurement (6/6)

• CDNs do add measurable value compared to random
  selection
• They arent perfect or optimal
• You can measure them yourself!
• Hard to know what explains performance
  differences
• Internal structures are secret

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Summary

• Introduction
• What is caching
• What is a Content Delivery/Distribution Network?
• The content delivery block
• The content routing block.
• Performance Measurement.
• Benefits of Content Distribution and Management
• Conclusion

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Benefits of Content Distribution and Management

• CDNs bring order and quality of service (QoS)
• to the Internet's IP backbone
• to eliminate or minimize the infamous "World Wide
  Wait."
• CDNs address these stringent response-time
  demands
• by minimizing the number of Internet backbones
  that
• a Web request
• and resulting streaming or downloadable
  content
• must cross .

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Benefits of Content Distribution and Management
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Poor Content Delivery High Opportunity/Operating
Costs

• Traffic delays and packet loss translate into
  lost revenue opportunities and damage to
  reputation/brand.
• Despite 8 second rule, average page download
  for a consumer site 15 seconds (Keynote,
  7/2000).
• Abandon rates increase as site download times
  increases

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Poor Content Delivery High Opportunity/Operating
Costs
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Summary

• Introduction
• What is caching
• What is a Content Delivery/Distribution Network?
• The content delivery block
• The content routing block.
• Performance Measurement.
• Benefits of Content Distribution and Management
• Conclusion

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  Who need CDN?

• The customers of a CDN will be companies that
  wish to offer their content to a geographically
  distributed, potentially large, audience
• As it maintains multiple locations with copies
  of the same content
• uses information about the user and the content
  requested
• to route the user to the most appropriate
  site.

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Conclusion

• CDN
• is an overlay network to the Internet that has
  been
• for the high-performance delivery of rich
  multimedia content.
• A raison d'être is to make the Internet a trusted
  delivery network for mission-critical,
  content-rich CDN services.
• To maintain the distributed copies of content,
  the CDN will usually collocate their content
  servers with strategic ISPs. This offers a number
  of advantages, including
• lower latency for delivery,
• higher robustness,
• lower cost and higher capacity,
• which are needed advantages by e-learning and
  e-commence applications.

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Content Caching Solutions

• Caching solutions enable ISPs to retain Internet
  content on specialized servers housed in ISP POP
  facilities near end users. Reduces need to
  repeatedly pull down same content from origin
  server
• Reduces strain/origin server costs of content
  provider reduces ISPs bandwidth costs by 30-50
• Improves end user experience by expediting the
  delivery of content
• Difficult for ISPs to manage on on-going basis,
  particularly for dynamic content
• Weakens ability of a content provider to record
  site traffic page views used to determine
  advertising charges.
• Not designed to cache all relevant content, still
  highly dependent on network

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Solutions for Each Point of Content Delivery Path

• Network Capacity Building bigger and faster
  pipes, routers and switches in long-haul and last
  mile (Qwest, Level 3, Covad,Excite_at_Home, Cisco,
  Lucent)
• Satellite Multicasting Extending reach beyond
  terrestrial pipes, leveraging point-to-multipoint
  solution (Edgix, iBeam, Cidera)
• Intelligent Routing Avoiding congestion and
  network failures, finding the most direct paths
  from origin to end-user
• (InterNAP, AboveNet)
• Content Caching Solutions Enabling ISPs to copy
  and store content for their own customers
  (CacheFlow,Cisco, InfoLibria, Inktomi)
• Content Distribution Services Managing and
  coordinating ISP caches, returning control to
  content providers
• (Akamai, Digital Island/Sandpiper, Epic Realm,
  Speedera)

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Some trends to Watch in Content Delivery

• More ISPs hosting companies outsource content
  delivery to specialized serviceproviders.
• Growing market opportunity attracts more
  competition raising potential for pricing
  pressure. Content providers welcome less
  expensive service.
• Hosting companies want control over content in
  the data centers, not at local ISP POPs.
• Despite high expectations for future, streaming
  media services not overwhelming anyone so far.