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					Benefits of Content Delivery Networking to E-Learning and E-Communications.
                    Michel Eboueya, Michel Menard and Pascal Estraillie r

           Université de La Rochelle, Laboratoire d’Informatique et d’Imagerie Industrielle (L3i),
                      Avenue Michel Crépeau , Fr-17042 La Rochelle cedex 1, France.
           [ | |]

ABSTRACT: The Web has emerged as one of the most powerful ways for businesses and consumers to
communicate and learn. Its global reach, availability and speed has changed the way organizations do
business. Effective E-Learning and E-Communication are critical elements determining organizational
success. This success will be determined by how efficiently an organization can: effectively communicate
and share knowledge across the enterprise of employees, partners, suppliers and customers; educate,
motivate and retain employee resources.
A Content Delivery Network (CDN) is a Co-ordinated network of devices (Content Engines) that cache
content for end users. CDN allows service providers to distribute content closer to the end user and
overcome issues such as network bandwidth availability, distance or latency obstacles, origin server
scalability, and congestion issues during peak usage periods. So, in addition to service provider customer
benefits, CDNs enable enterprises to accelerate their deployment of advanced e -business applications
such as e-learning and live streaming.

Key word: Content delivery, web caching, active network, dynamic content.

1 Introduction

An International Conference on "New Horizons in Industry and Education" cannot afford a paper about
"Content Delivery Networks" as it is one of the hottest new technologies in the Information Technology
arena in this beginning of the 21th century. When we started to write this paper, such good references as
the Matthew List guide [8] the Stardust White Paper [10] didn't exit but the subject is so hot that it is now
more important to seek for clarity, not only for originality (as there is the same information in many
different papers) along with a “fil d'ariane”.

The Internet has matured to the point where its value is transcending mere IP connectivity for the support
of static Web pages and the exchange of text-based email. Content providers and, publishers and e-
businesses are looking to the Web as a high-performance, reliable vehicle for delivering bandwidth-
intensive, rich multimedia content such as e-commerce transactions, special events, news and
entertainment services [7].

The efforts to develop dynamic, often interactive multimedia content are shifting the IP networking
industry's focus from Layer 3 connectivity issues to the construction of intelligent, Layer 4 - 7
infrastructures that can better support the stringent response-time requirements of these new content types.
In particular, the industry emphasis is turning to specially- tuned overlays to the Internet called content
delivery networks or content distribution networks (CDNs) [9].

In this paper, we will explain what are Content Services are and what they include, and then demonstrate
some benefits like Distributed Web Hosting, Applications Hosting, and E-Commerce, Static image
acceleration, Large Scale On-Demand and Live Streaming, Media Delivery and Hosting, Content Rating
and Filtering, Distributed Dynamic Content, Personalization.
We will conclude by showing how CDNs improve an enterprise’s ability to effectively deploy a new
generation of Web-based, content-rich, E-learning and communications solutions resulting in accelerated
content delivery and improved content.

2 What is a Content Delivery/Distribution Network?

A CDN is a service offered by a service provider, either an established one, or a CDN-only provider.
Fundamentally, a CDN maintains multiple locations with copies of the same content, and uses
information about the user and the content requested to “route” the user to the most appropriate site. The
customers of a CDN will be companies that wish to offer their content to a geographically distributed,
potentially large, audience [2].

A CDN, could be seen as consisting of at least three independent building blocks in addition to the
network infrastructure: the content routing block, the content delivery block and the performance
measurement block [8]:

                                 Fig. 1. The CDN chain from CISCO

2.1-The content delivery block concerns the entire content workflow, from encoding of any type of media
sources (audio, video, Web pages, documents, software…) and indexing to edge delivery, and how to
secure and manage the content [3].
                                             Fig. 2. Content caching

If all the content was to be served from the same point, i.e., servers in one location, all the media clients
would get their content delivered from that point, both for live and on-demand content. This would have a
huge impact on both the network and servers.

 To avoid this scenario, a caching structure would be in place at each strategic POP (Point-of-Presence) or
location that would serve the content directly instead of from the centralized point. This is transpa rent to
the end-user; it appears to them that they are getting served from the central server. These distribution
service, comprise a distributed set of surrogate servers that cache content and work on behalf of a Web
owner's origin server, enabling requests to bypass congested areas of the Internet and be delivered from
the edge. IP Multicast is one technology that might be used as a component of distribution services as a
network-efficient vehicle for updating mirrored caches [7] [8].

2.2-The content routing block consists of technologies to match end-users with the right content from the
right place, i.e. DNS redirection for example. In other words, redirection services aim at making sure that
a user's Web request is directed to the cache server that is closest and most available [5] [11].
There are two different aspects to content routing. The first is the global routing algorithm, which routes
the client to the most appropriate Point-of-Presence(POP). The second addresses the local routing, which
spreads requests amongst multiple servers in a (POP.

In the following figure (Fig. 3)
1. The client requests content of a web page residing at the content provider's website -
2. Since doesn't host their own streaming media, but uses as their CDN provider, the
URL redirects the media clients to the site.
3. Using redirection algorithms (which we shall discuss later), 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.
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.
6. The cache peering at the client's ISP1 serves the content, and will offer low latency and good
throughput due to the close proximity of the end-client. Forms of redirection are addressed in [8].

                                   Fig. 3. An example of content routing

2.3-Performance Measurement – The customer utilising the service needs feedback on the performance of
the CDN as a whole. This involves usage of internal measurement technologies as well as external
services such as MediaMetrics [4] [5]. So, an accounting and billing system enables the CDN provider to
measure, log and bill the content provider based on usage (the amount of bandwidth consumed by users
who tap into the content provider's site). In addition, these systems are evolving to enable CDN providers
to cross-bill one another for CDN internetworking services.

3. Benefits of CDNs come from the way they work

CDNs bring order and quality of service (QoS) to the Internet's IP backbone[6] to eliminate or minimize
the infamous "World Wide Wait." Slight network delays or somewhat inconsistent response times go
almost unnoticed when the Internet application at hand is text-based email or a static Web page download.
In a multimedia world of entertainment services, gaming, live videoconferences and streaming broadcasts,
which are sensitive to response-time delays, though, extra steps must be taken to ensure delivery of a
quality experience.

CDNs address these stringent response-time demands in large part by minimizing the number of Internet
backbones that a Web request and resulting streaming or downloadable content must cross. One way they
do this is by hosting replicas of a developer's content in cache servers called surrogates , located within
network edge points of presence (PoPs) . The setup enables CDN service providers, in many cases, to
deliver content stored in cache servers just one hop away from the user.
A user request to a content provider's Web site is redirected to a data center of the CDN provider.
Typically, the content provider must set up this redirection itself using the tools and encoding method
dictated by the CDN service provider. The CDN contains a lookup service that steers a content request to

  ISP - An IP network service p rovider that provides access to the public Internet. May or may not also be a CDN
service provider.
the content surrogate that is closest (geographically or shortest travel time) to the user and/or is the least

To determine the content server that is most available to a user at the time of a request for content, CDN
service providers make use of load-balancing technology. This technology can be homegrown by the
CDN service provider or delivered in the form of router software or a network appliance from a third-
party vendor. Load-balancing capabilities front-end a content server cluster and direct traffic to the least-
loaded server, much like a traffic warden steers vehicles around congestion at a street intersection.
Increasingly, CDNs are also making use of Web switching , also called content switching or application-
layer switching to further enhance QoS levels. These software capabilities enable the network
connectivity elements in a CDN (routers and switches) to examine not only IP address information when
determining a best path through the network, but also to take into account the specific response-time
requirements of the application or content being requested.

Meanwhile, the surrogates contain software that extracts logging, usage and billing information that is
aggregated up to a central database in the CDN service provider's data center. The CDN service provider
uses this information to determine what to charge the content provider for the CDN services rendered.
Pricing models are generally usage based, with a fixed fee per megabit per second of usage. The usage
information collected and aggregated by the surrogates is also used to deliver content management
capabilities, usage trending, and performance information to the content provider customer as a part of the
CDN service package.

Content Distribution Content Routing     Content S witching       Content Edge Delivery     Intelligent   Networks
and Management                                                                              services

Global / Centralized Scalability         Flash Crowd Protection High-performance Content Leverage        Existing
Provisioning                                                    Delivery for PoPs        Network Infrastructure

Real-time monitoring   Routing to Best Optimal handling for Integrated Caching for QoS
                       M ost   Proximate Non-cacheable content Transparent Insertion into
                       Content           as (e-commerce and e- the Network

Ensuring Fresh Content Adaptive Routing E-learning     and    e- Full    Scalable    Range M ulticast
                       Around           commerce                 Product

Self        Organizing Failures/         Core         Distribution Range     with   common VPN’s
Distribution Network   Congestion        Capabilities              Architecture

                           Fig. 5. Li nes giving the key features and benefits of CDNs

4 Who need CDNs

Organizations that build content for the Web are faced with the challenge of delivering content with
increasingly dynamic characteristics to customers with consistent, high service levels. As users get
increasingly Internet-savvy and demanding, the QoS levels in content delivery can make or break
customer attraction and retention. Some examples of organizations that fall in the content provider
category are the following: owners of e-commerce sites (concerned about response times for browsers and
transaction times for buyers) and E-learning developers such as virtual universities or traditional leader-
led sales automation training companies that are adding Web-based versions of their offerings: in fact, all
organizations wishing to offer Web-based video news coverage and any and all businesses whose
Internet-based content is mission-critical.

To date, the lion's share of content providers have been hosting and managing their own Internet-
connected content sites, sometimes supporting mirrored content servers in two or three locations. The
reasons include CDNs being a relatively new and little-known phenomenon and the perception of high
costs associated with CDN services.

Today, services from well-known CDN providers, list for $1,995 per megabit per second of usage. At a
glance, these prices often seem high to content providers, particularly compared with the approximate
$600 per megabit per second of usage charged for vanilla Internet hosting and connectivity services from
collocation.. However, content providers find themselves needing to run multiple data centers to
efficiently serve local content around the world, totaling up the hardware resources, network connectivity
costs and, most significantly, the human resource requirements to support their 24-by-7 sites which makes
the build-it-yourself alternative less cost-effective.

5 Conclusion

In this paper, we have shown that a CDN is an overlay network to the Internet that has been built
specifically 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

6 References

[1]     A. Beck, M. Hofmann and M. Condry, Example Services for Network Edge Proxies, Internet
Engineering Task Force, {Internet Draft}
e Nov. 2000.

[2] Cisco White Paper - The Ins and Content Based Services» .«Cisco Delivers Complete System for
Content Delivery Networks and Next Generation {Internet Draft}

[3] Syam Gadde and Jeff Chase, Duke and Misha Rabinovich, Web Caching and Content Distribution:
A View from the Interior. Proceedings of the 5th International Web Caching and Content Delivery
Workshop , Portugal, Lisbon , 22-24 May 2000. See also
[4] Kirk L. Johnson, John F. Carr, Mark S. Day and M. Frans Kaashoek The Measured Performance of
Content Distribution Networks (SightPath, Inc. USA). ) Proceedings of the 5th International Web Caching
and Content Delivery Workshop , Portugal, Lisbon , Portugal 22-24 May 2000.

[5] Jussi Kangasharju,Keith W. Ross and James W. Roberts, Performance Evaluation of Redirection
Schemes in Content Distribution Networks Proceedings of the 5th International Web Caching and
Content Delivery Workshop , Portugal, Lisbon, Portugal 22-24 May 2000.

[6] Terence Kelly and Daniel Reeves, Optimal Web Cache Sizing: Scalable Methods for Exact Solutions
(University of Michigan, USA) Proceedings of the 5th International Web Caching and Content Delivery
Workshop , Portugal, Lisbon , Portugal 22-24 May 2000.

[7] Brian Neil Levine, Jon Crowcroft, Christophe Diot, J. J. Garcia-Luna-Aceves and James F. Kurose,
Consideration of Receiver Interest for IP Multicast Delivery in infocom, (Tel Aviv, Israel), Mar. 2000.

[8] Matthew List Content Delivery Networks (CDNs) – A Reference Guide {Internet Draft} Thrupoint

[9] G. MacLarty and M. Fry, Policy-based content delivery: an active network approach comcom, vol.
24, no. 2, pp. 241--248, Feb. 2001.

[10] White Paper - The Ins and Outs of Content Delivery Networks.What they are, why we
need       them,        and      how        to       build        them.       {Internet       Draft} February 2001.

[11] R. Penno and A. de Albuquerque, User Identification on the Internet Internet Engineering Task
Force, {Internet Draft}, Feb. 2001.