YouTube Science & Engineering Camps for Kids - ESD

Servers in Toronto
Servers in
Moscow
Fig. 1: An Illustration of a Simple
Content Delivery Network with
Many Distributed Servers
Origin
server
in
Seattle
Servers
in Paris
CDN
Content
Distributor
Servers in
Casablanca
Servers in
Aman
Servers in Salvador
ince its official launch in November 2005,
www.YouTube.com has grown tremendously
in popularity and has recently emerged as
the third most popular Internet website,
according to Alexa Web Traffic Ranking. The
market research company comScore reported
that YouTube attracted five billion online
video views from the U.S. alone during July
2008. This social video website is geared for hosting
User-Generated Content (UGC). The widespread use
of this content on the Internet significantly blurred the
distinction between a publisher and a user. In particular,
publishers and users are no longer restricted to entirely
separate roles, as users can capture videos using cell
phones, digital cameras, and other portable devices and
share them with the world at no charge.
SERVING YOUTUBE
Video streaming to a huge number of users is very
demanding of server and network resources. Videos
require high data transfer rates and thus high bandwidth
capacities and must be continuously received in time with
minimal delay. Amazingly, it was reported that in 2007
YouTube consumed as much bandwidth as the entire
Internet in 2000. The question now arises as to how
YouTube can support all this data traffic. In other words,
what is the technology behind it?
The technology behind YouTube is called Content
Delivery Network (CDN). As illustrated in Fig. 1, the
content in the origin server(s) is automatically stored
in surrogate servers, located in many cities around
the world. (A server is a computer system that runs a
computer program to provide services to other computer
programs and their users.) Thus, the user’s request
for streaming a video is transparently transferred to a
surrogate server close to the user’s geographical location.
The delivery of the content by a server close to the user
leads to fast and reliable video streaming and reduces the
contention on the Internet. An accounting mechanism
is typically employed to relay access information and
detailed logs to the origin server(s).
As most other content providers, YouTube does not
have its own CDN. Instead, CDNs are paid services offered
by specialized companies, called CDN providers, such as
Akamai Technologies and Limelight Networks. Akamai
for instance has more than 12,000 servers for over 1,000
networks in 62 countries. The use of such infrastructures
relieves YouTube and other online video companies from
the tedious task of maintaining a huge number of servers
worldwide and also reduces the overall cost.
As a final note, YouTube’s bandwidth costs as of March
2008 were estimated to be $1 million a day. If you are
wondering how YouTube makes money, considering these
bandwidth expenses and other operational costs, it is
through advertisements.
Nabil J. Sarhan is Assistant Professor
of electrical and computer engineering
and the Director of the Media Research
Lab at Wayne State University. He has
worked on NSF-sponsored projects
in the area of multimedia computing
and networking and has published
extensively in top conferences and
journals in this area.
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