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Complex Networks by Kayhan Erciyes

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Chapter 12
The Internet and the Web
12.1 Introduction
Computer networks consist of computers which communicate using communication
links. The Internet and the World Wide Web (Web) are the two widely used computer
networks as we have seen in Chapter 1. The Internet which is the largest computer
network in the world is organized hierarchically from home or office computers to
networks in organizations and then to service providers which are connected via
backbone networks. The Web is functionally an information network that uses the
underlying Internet for data transfer.
In this chapter, we will first investigate the structure and the properties of the
Internet. We will model the Internet using undirected graphs, nodes of which are
routers or autonomous systems. We will then look at the results of various projects
that have performed tests on the Internet using these two models and summarize the
results of these tests. We will use directed graph model of the Web and find that it
has a specific structure. We will describe the widely used page rank algorithm and
the hubs and authorities algorithm. In both the Internet and Web analysis, we will
restrict our investigation to complex network properties.
12.2 The Internet
The Internet is a worldwide computer network which connects millions of computers
in the world. These computers called hosts may be personal computers, workstations,
servers, sensors, mobile phones or various other computational devices. The hosts
are physically connected to the Internet using communication links such as coaxial
cable, fiberoptics or wireless medium. A data packet is the basic data unit transferred
over the Internet and a router is a device in the Internet that inputs a packet from one
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Complex Networks: An Algorithmic Perspective
Tier 1
Tier 2
Tier 3
Figure 12.1: Internet tier structure
of its input ports and transfers this packet to one of its output ports. Packet switching
is the process of transferring packets from the sending hosts to the receiving hosts
using suitable paths called routes.
The hosts are connected to the Internet using Internet service providers (ISPs)
which may provide different modes of connection to the Internet such as wireless or
broadband access. The ISPs are organized hierarchically such that lower-tier ISPs are
connected to the higher-tier ISPs which have more efficient routers and high-speed
fiberoptic links between these routers as shown in Figure 12.1.
12.2.1 Services
We will first look at the services offered by the Internet before analyzing its structure.
These services can be broadly classified as connection methods, circuit provision and
the protocols offered.
12.2.1.1 Services of Connection
The hosts, routers and other devices in the Internet exchange information using
protocols which enable correct and timely delivery of data between the users. A
protocol is a set of rules and procedures that specify the ways of communication
between the Internet devices. The Internet provides two types of services to the ap-
plication as connection-oriented service and connectionless service. In a connection-
oriented service, the applications that want to communicate first establish a connec-
tion between them by exchanging control messages. This is analogous to two people
who first greet each other before transferring any information. In a connectionless

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