Quality-of-Experience for Multimedia

Chapter 3

Content Distribution Network

In this chapter, first, we present the general architecture of a content distribution network (CDN) system with its components and functions. Then, we describe in detail its two main layers: the routing layer and the meta-routing layer.

3.1. Motivation

Nowadays, the demand for content on the Internet is increasing rapidly. This needs an efficient and scalable content distribution solution. Implementing multiple servers placed at geographically distributed locations replaces using single-server schemes. The general idea of this evolution is to bring the servers geographically closer to clients. This new architecture, called CDN, will improve the performance of the system, reduce network load and provide better fault tolerance. Currently, there are many successful CDN providers such as Akamai [AKA 98] and Digital Island [DIG 96].

The general operation mechanism of a CDN service is depicted in Figure 3.1. When a customer (e.g. a Website and VoD service) subscribes to a CDN service, the customer provides data to the CDN provider. The latter will implement a distribution network in using replica server scheme. More precisely, a CDN provider replicates the content data from the origin server of the customer to the replica servers scattered over the Internet. The operation mechanism of a user’s request is described step by step as follows. First, the end user sends a request to the Website (step 1). Then, the Website forwards the request to the CDN ...