Content Delivery Network - Report

1. CONTENT DELIVERY NETWORK­PEERING CDN
DIMPLE BADIANI
008081710

2. ABSTRACT:
The proliferation of Content Delivery Networks (CDN) reveals that existing content
networks are owned and operated by individual companies. As a consequence, closed
delivery networks are evolved which do not cooperate with other CDNs and in
practice, islands of CDNs are formed. Moreover, the logical separation between
contents and services in this context results in two content networking domains. But
present trends in content networks and content networking capabilities give rise to the
interest in interconnecting content networks. Finding ways for distinct content
networks to coordinate and cooperate with other content networks is necessary for
better overall service. In addition to that, meeting the QoS requirements of users
according to the negotiated Service Level Agreements between the user and the
content network is a burning issue in this perspective. This paper presents a scalable
and Service­Oriented Architecture based system to assist the creation of open Content
and Service Delivery Networks (CSDN). It deals with peering of CDN and why is it
necessary. The open CSDNs scale and support sharing of resources through peering
with other CSDNs[1].
INTRODUCTION:
What is Content Delivery Network(CDN) ?
A content delivery network or content distribution network (CDN) is a large
distributed system of servers deployed in multiple data centers in the Internet. Content
delivery networks (CDNs) help content providers deliver text, pictures, audio, video,

3. applications and services to users. The purpose of CDNs is to overcome the limitations
of the Internet in terms of user perceived Quality of Service (QoS) when accessing
content. A CDN replicates content from the origin server to cache servers called
replica servers, spread across the globe. Content requests are directed to the cache
server closest to the user, and that server delivers the requested content.
A CDN has a combination of a content delivery infrastructure, request­routing
infrastructure, distribution infrastructure and an accounting infrastructure. CDNs
improve network performance by maximizing bandwidth, improving accessibility
and maintaining correctness through content replication. As a result, CDNs offer fast
and reliable applications and services by distributing content to cache servers located
close to end­users.
CDN providers ensure the fast delivery of any digital content. They host a third­party
content like images, software patches, streaming media and file transfer service. The
source of content are web service providers or media companies, whereas, the end
users interact with the CDN through cell phone, PDA or laptop.
Why Peering of CDNs?
Presently the CDNs are owned and operated by individual companies, who have
created their own closed delivery network which is somewhat expensive to maintain.
Even though there are many CDN providers, they do not specifically cooperate in
delivering content to end­users in a scalable manner. So one have to utilize the service
of a CDN provider at a time, one cannot use multiple CDNs offering different services
together. As a result use of one specific CDN creates isolation of CDNs and it
increases the cost for the company using it. To minimize the cost CDN providers must
collaborate with each other so that services can be supplied and received in a
cooperative manner which cannot be provided by the other CDN providers and vice
versa. Through collaboration with another CDN provider, content networks can
emphasize on customer satisfaction meeting end­user’s QoS requirements, and hence

4. it can minimize the exposed business impact of service level violations.
To make content services an Internet infrastructure service, vendors have implemented
content service networks, which act as another network infrastructure layer built upon
CDNs and provide next generation of CDN services. CSN appears to be another
variation of the conventional CDN as it is just another layer of network infrastructure
built around CDN. This logical separation between content and services under the
Content Delivery/Distribution and Content Services domain, is undesirable
considering the on­going trend in content networking. Hence, a unified content
network which supports the coordinated composition and delivery of content and
services, is highly desirable.
This paper presents the idea of creation of open Content and Service Delivery
Networks(CSDNs). The CSDNs scale and support sharing of resources through
peering with other CSDNs. A virtual organization model for CSDN supports sharing
of web servers within their own networks as well as other CSDN. It also defines the
key areas related to CSDN by identifying issues to be addressed.
STATE OF ART:
In content delivery network, end user requests are served from the web servers
distributed around the internet that cache the original content stored in the origin
server. CDNs are dedicated to web caching content for the users to access it faster;
whereas, peer2peer sharing networks are integrated vertically to achieve a single goal,
and execute the data intensive applications on remote data. Some of the
representatives of CDN are described below.
Limelight Networks: It is a content delivery network service provider. The advanced
content delivery network provides high performance delivery of digital media and
software. It supports distributed on­demand and live delivery of video, music and
games[2].
Mirror Image: It is a global network for online content, application and transaction

5. delivery, provides content delivery, streaming media, web computing and reporting
solutions that offer customers a way to create web experiences for users[3].
Ignite Technologies: It provides the leading enterprise content delivery solution,
enabling businesses to efficiently publish, deliver and manage digital assets from rich
media content
for training and communications, to software patches and virus
updates to anyone at any time[4].
Issues involved in CDN:
As CDNs spread over various geographical locations and uses distributed components,
there are various technical issues concerned with CDN content delivery. Some of them
are as follows:
CDN selection: The choice of content to be delivered to the end user is of utmost
important. Content can be delivered in full or partial, to the customers. In full content
delivery, the servers perform entire replication in order to deliver total content to the
end user. Whereas, in partial delivery, only embedded objects are delivered.
Request Routing: To select most appropriate server for content routing, several
routing schemes can be used. Some of them are CDN peering, URL rewriting , client
multiplexing[5]. In CDN peer approach, peer­to­peer content networks are formed by
symmetrical connections between host computers. When CDNs are peered, they
deliver content on behalf of each other.
Content Replication and Caching: Replicating of the content is very common in
large scale distributed environment of CDN. Caching can be done on intra­cluster or
inter­cluster basis.
Content outsourcing: After selecting the proper servers for CDN infrastructure and

6. proper content selection, it is necessary to decide which method to follow for content
outsourcing. The various types of content outsourcing methods are cooperative
push­based, non cooperative pull­based and cooperative pull­based.
REFERENCES:
en.wikipedia.org/wiki/Content_delivery_network
Limelight networks ­ www.limelight.com
Mirror Image ­ www.mirror­image.com/site
Ignite Technologies ­ www.ignitetech.com/platform.aspx
G. Peng, CDN: Content Distribution Network, Technical Report.