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sense. In fact, traffic from most of the traditional

applications on IP-based networks is quite toler-

ant with respect to variations in transfer times

(also referred to as elastic traffic flows). How-

ever, too wide changes in the behaviour (such

as longer response time) would likely be consid-

ered a great annoyance for a human user.

The main topics addressed in this article are re-

lated to IP and how it can be utilised. Accompa-

nying articles consider the aspects more related

to Traffic Engineering (TE). Concepts on

domains and layers are described in the follow-

ing chapter. Chapter 3 addresses selected topics

on optics from an “IP point of view”. Mobility

and multicast are discussed in Chapter 4 and

Chapter 5, respectively. Authentication and

other security issues are treated in Chapter 6. A

few scenarios and examples, including Virtual

Private Network, Web browsing and telephony

are given in Chapter 7. The main objective of

this article is to provide a soft introduction to the

application of IP and some core functions that

have to be present in a wide area network.

2 Network Components

2.1 Concepts

Being no surprise to anyone, a network is put

together by a number of components; each of

them having its characteristics. Moreover, some

of the components can be grouped based on cer-

tain characteristics. This is commonly useful

when discussing appropriate solutions for the

components and how they can be put together to

compose a network. That is, each of the compo-

nents would implement certain mechanisms, be

designed according to an architecture, and so

forth.

Looking at studies deriving systematic network

descriptions, one frequently observes a division

into domains and strata, see Figure 2. Domain

refers to geographical separation, while stratum

refers to a functional separation. These are

depicted by horizontal and vertical separations.

A basic example of a set of strata is the 7-layer

Open System Interconnection (OSI) model.

Here, however, stratum is used in a more general

interpretation, although similarities with the OSI

model can be recognised.

Figure 2 Identifying components in the network

Figure 3 User, control and management activities

service

logic/data

router/

switch

transport/

line/cable

Customer

equipment

Access Edge Centre

domain

solution/

implementation

stratum

layers (strata)

management plane

user plane control plane