A DIFFERENTIATED SERVICE BASED CONTENT

DISTRIBUTION METHOD IN CDN

Binjie Zhu, Ke Xu and Renjie Pi

Beijing University of Posts and Telecommunications, Beijing, China

Keywords: Content delivery, Overlay network, Differentiated service.

Abstract: With the development of Internet applications, there are more and more problems about delay in the

Internet. Content distribution network is an overlay network to distributing the content to the edge of

Internet to reducing the user perceived delay. This paper focuses on the content distribution problem in the

content delivery network. A differentiated service based content distribution algorithm was designed in this

paper. Clustering algorithm was used to get pedigree chart of the edge server, and then ant algorithm was

used to search for the optimal edge server based on the pedigree chart. The analysis shows that this

algorithm combines the clustering method and ant colony algorithm, and it has a good distribution of

results.

1 INTRODUCTION

CDN (Content Delivery Network) use distributed

caching and the load balancing techniques on the

Internet to build a distributed overlay network. This

overlay network pushing the content from the source

to the network edge equipment. On one hand, it

allows the user to access to near location server with

the desired content, reducing the end to end delay,

improved customer service quality; On the other

hand, the central server bottleneck was broken, and

reducing the backbone network traffic. It effectively

alleviating the throughput of backbone network, and

increasing of system capacity.

There are three layers in the CDN overlay

network. The first layers is source server where the

source content object come from. The second layer

is the copies server layer. This layer is used to

storage the copy of the content for distribution. The

third layer is the user layer, obtains the content from

the copy servers. The copy server is put in the edge

of internet, so the network traffics are pushed to the

edge of the Internet (George Palls, 2006). It is the

basic idea of content delivery network (CDN).

We designed a P2P-CDN with two layers, shown

as figure 1. The edge server in the CDN is divided

into two layers: the wide-area and the local level.

Wide-area node was distribution in different

locations, for the purpose of pushing the content into

the edge of Internet. Local level nodes were in the

same location, and the function is to increasing load

capacity.



Figure 1: P2P-CDN with two layers.

2 BACKGROUND AND

PREVIOUS WORK

After a contract was signed between the CDN pro-

576

Zhu B., Xu K. and Pi R..

A DIFFERENTIATED SERVICE BASED CONTENT DISTRIBUTION METHOD IN CDN.

DOI: 10.5220/0003589705760579

In Proceedings of the 13th International Conference on Enterprise Information Systems (SSE-2011), pages 576-579

ISBN: 978-989-8425-53-9

 2011 SCITEPRESS (Science and Technology Publications, Lda.)

vider and the CDN user, the contents were delivery

to a CDN provider. All the content files were copied

in the source server by the CDN providers. CDN

content were transmission to the edge cache server

by distribution module of CDN according to a

certain distribution means, shown as figure 2.

Figure 2: Content distribution.

The existing distribution method (Adrian J. 2006)

(S. S. H., 2003) does not support service

differentiation. All content objects as a whole, does

not distinguish the different server quality

requirements between different content. The

proposed method in this paper supports

differentiated Service and supports optimization for

each content object. A contract was signed between

the CDN provider and the CDN user in which

contain the service level requirements of each

content object. Different levels of service

corresponding to different number of copies. Every

content objects has the attributes of service level

requirements. How to distribute the contents of an

object with differentiated Service effectively is the

aim of this paper.



3 DIFFSERV-BASED CONTENT

DISTRIBUTION METHOD

CDN systems included source server, edge servers,

and the CDN management system. CDN

management system including the content

distribution related modules: service differentiation

module, content distribution control module, ant

search module, the delay measurement module,

shown as figure3. Content distribution module's

function is to distribute the content object to the edge

server node.

Delay measurement module is to measure the

network delay between the edge servers. If there are

N edge servers, n

(0 )nN<≤ points selected from

the edge servers randomly. The delay data were

statistics to get the delay date of other points to the n

points. The hierarchical diagram was obtained

through clustering these data. The pedigree chart was

transformed into a standard pedigree tree for a

heuristic algorithm of content distribution.



Figure 3: CDN system modules.

If there are n copies for one content, then n ants

climb out in ant colony search modules. For a set of

content objects, there may be a crowding

phenomenon, in which a lot of content was assigned

to one location, causing unbalance distribution.

However, this distribution unbalanced is necessary

from the view of all the point of positions. The

purpose content distribution network is to reducing

the delay, the best performance in a position to do

distribution copy is necessary. However, it is

necessary to balance distribution in the peer position

with the same effect. In another word, the balance is

necessary form the view of local area or the nearby

position. According to this principle, ants were

crawling, and sprinkle pheromone. Distribution

balance guided by the pheromone information.

The service level argument was obtained from

the service distinction module. The service level

information contains the number of copies for a

content object. The service level as an argument was

transmitted to ant search module. The ant searching

module run heuristic search in the space of edge

server based on the pedigree tree. Contents were

distribution to the optimal position based on the ant

search result. It is shown as figure 4.

A DIFFERENTIATED SERVICE BASED CONTENT DISTRIBUTION METHOD IN CDN

577

Figure 4: Distribution Flow.

4 EXAMPLE

For a detailed description of the algorithm process,

there will be an example. Assuming the six edge

points in the content distribution system, N = {A, B,

C, D, E, F}, every point is one edge server, shown as

the figure 5. Because there are fewer number of

point, so all the six points were selected for the delay

monitoring points. All the edge server point has a

distance to this 6 monitoring points, and it is forms a

matrix.

Figure 5: The edge servers.

Pedigree chart was obtained through the

hierarchical clustering of these points base on the

matrix. As shown in figure 6.

The chart was transformed into a pedigree tree,

as shown in Figure 7. Suppose there is a content

object, the content object needs to have three copies.

Because there are n copies of the content to be

distributed, so there are three ants crawling in the

pedigree tree. After the ants search in pedigree tree,

three positions got for the three copies.

Figure 6: Pedigree chart.

Figure 7: Standard pedigree tree.

Ants crawl in the pedigree tree with 3 deep. As

ants climb with a depth of 3, each ant is faced with

two choices. For example, there was an ant facing

the choice of points 2 and 6. According to the crawl

rules in front, it can randomly select the point, but

the pheromone was sprinkled in the choice path, in

order to facilitate the next ants to choose a different

path for load balancing purposes. Finally, the three

servers choose are shown in Table 1.

Table 1: The result of distribution.

Copies C1 C2 C3

Edge servers 2 1 4

5 CONCLUSIONS AND FUTURE

WORK

This paper studies the content delivery network

content distribution problem. Different quality of

service has a different number of copies, was

distributed with service differentiation. The contents

ICEIS 2011 - 13th International Conference on Enterprise Information Systems

578

with high QoS level were distributed to the optimal

position to achieve utility maximization. This paper

presents a hierarchical clustering based heuristic

method and ant colony algorithm to solve this

problem. Future work is to further optimize this

method.

ACKNOWLEDGEMENTS

This work is supported by the National Key project

of Scientific and Technical Supporting Programs of

China (Grant Nos. 2008BAH24B04,

2008BAH21B03, 2009BAH39B03); the National

Natural Science Foundation of China (Grant No.

61072060); the Program for New Century Excellent

Talents in University (No. NECET-08-0738);

Engineering Research Center of Information

Networks. Ministry of Education.

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Adrian J. Cahill, Cormac J. Sreenan, 2006, An efficient

resource management system for a streaming media

distribution network, Intreactive Technology and

Smart Education, Vo. 3, No. 1

George Palls, Athena, Vakali, 2006, Insight and

Perspectives for content delivery networks,

Communications of the ACM, January, Vol. 49, No. 1

S. S. H. Tse, 2003, Approximate Algorithms for Document

Placement in Distributed Web Servers, IEEE

Transactions on Parallel and Distributed Systems,

Vol. 16, No. 6, pp. 489-496

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