Computer Networks 1
Lecture -5-
Introduction to Computer Networks
In this course we will use the term ‘‘computer network’’ to mean a
collection of autonomous computers interconnected by a single
technology. Two computers are said to be interconnected if they are able
to exchange information.
The connection need not be via a copper wire; fiber optics, microwaves,
infrared, and communication satellites can also be used. Networks come
in many sizes, shapes and forms, as we will see later. They are usually
connected together to make larger networks, with the Internet being the
most well-known example of a network of networks.
In this lecture, you will learn to: Uses of computer networks, identify the
key components of computer network, networks classification, network
software, reference models, and others.
1.1 Uses of Computer Networks
Among all of the essentials for human existence, the need to interact with
others ranks just below our need to sustain life. Communication is almost
as important to us as our reliance on air, water, food, and shelter. The
methods that we use to share ideas and information are constantly
changing and evolving. Whereas the human network was once limited to
face-to-face conversations, media breakthroughs continue to extend the
reach of our communications. From the printing press to television, each
new development has improved and enhanced our communication. As
with every advance in communication technology, the creation and
interconnection of robust data networks is having a profound effect. Early
data networks were limited to exchanging character-based information
between connected computer systems. Current networks have evolved to
,Computer Networks 2
carry voice, video streams, text, and graphics between many different
types of devices.
We will start with traditional uses at companies, then move on to home
networking and recent developments regarding mobile users, and finish
with social issues.
1.1.1 Business Applications
Most companies have a substantial number of computers. For example, a
company may have a computer for each worker and use them to design
products, write brochures, and do the payroll. Initially, some of these
computers may have worked in isolation from the others, but at some
point, management may have decided to connect them to be able to
distribute information throughout the company.
Put in slightly more general form, the issue here is resource sharing. The
goal is to make all programs, equipment, and especially data available to
anyone on the network without regard to the physical location of the
resource or the user as shown in Figure 1.1.
Figure 1-1.Business applications can be accessed remotely as if
employees were on site.
In the simplest of terms, one can imagine a company’s information
system as consisting of one or more databases with company information
, Computer Networks 3
and some number of employees who need to access them remotely. In
this model, the data are stored on powerful computers called servers.
Often these are centrally housed and maintained by a system
administrator. In contrast, the employees have simpler machines, called
clients, on their desks, with which they access remote data, for example,
to include in spreadsheets they are constructing. In the client/server
model, the device requesting the information is called a client and the
device responding to the request is called a server. The client and server
machines are connected by a network, as illustrated in Figure 1.2.
Figure 1-2. A network with two clients and one server.
The most popular realization is that of a Web application, in which the
server generates Web pages based on its database in response to client
requests that may update the database. The client-server model is
applicable when the client and server are both in the same building (and
belong to the same company), but also when they are far apart.
If we look at the client-server model in detail, we see that two processes
(i.e., running programs) are involved, one on the client machine and one
on the server machine. Communication takes the form of the client
process sending a message over the network to the server process. The
client process then waits for a reply message. When the server process
Lecture -5-
Introduction to Computer Networks
In this course we will use the term ‘‘computer network’’ to mean a
collection of autonomous computers interconnected by a single
technology. Two computers are said to be interconnected if they are able
to exchange information.
The connection need not be via a copper wire; fiber optics, microwaves,
infrared, and communication satellites can also be used. Networks come
in many sizes, shapes and forms, as we will see later. They are usually
connected together to make larger networks, with the Internet being the
most well-known example of a network of networks.
In this lecture, you will learn to: Uses of computer networks, identify the
key components of computer network, networks classification, network
software, reference models, and others.
1.1 Uses of Computer Networks
Among all of the essentials for human existence, the need to interact with
others ranks just below our need to sustain life. Communication is almost
as important to us as our reliance on air, water, food, and shelter. The
methods that we use to share ideas and information are constantly
changing and evolving. Whereas the human network was once limited to
face-to-face conversations, media breakthroughs continue to extend the
reach of our communications. From the printing press to television, each
new development has improved and enhanced our communication. As
with every advance in communication technology, the creation and
interconnection of robust data networks is having a profound effect. Early
data networks were limited to exchanging character-based information
between connected computer systems. Current networks have evolved to
,Computer Networks 2
carry voice, video streams, text, and graphics between many different
types of devices.
We will start with traditional uses at companies, then move on to home
networking and recent developments regarding mobile users, and finish
with social issues.
1.1.1 Business Applications
Most companies have a substantial number of computers. For example, a
company may have a computer for each worker and use them to design
products, write brochures, and do the payroll. Initially, some of these
computers may have worked in isolation from the others, but at some
point, management may have decided to connect them to be able to
distribute information throughout the company.
Put in slightly more general form, the issue here is resource sharing. The
goal is to make all programs, equipment, and especially data available to
anyone on the network without regard to the physical location of the
resource or the user as shown in Figure 1.1.
Figure 1-1.Business applications can be accessed remotely as if
employees were on site.
In the simplest of terms, one can imagine a company’s information
system as consisting of one or more databases with company information
, Computer Networks 3
and some number of employees who need to access them remotely. In
this model, the data are stored on powerful computers called servers.
Often these are centrally housed and maintained by a system
administrator. In contrast, the employees have simpler machines, called
clients, on their desks, with which they access remote data, for example,
to include in spreadsheets they are constructing. In the client/server
model, the device requesting the information is called a client and the
device responding to the request is called a server. The client and server
machines are connected by a network, as illustrated in Figure 1.2.
Figure 1-2. A network with two clients and one server.
The most popular realization is that of a Web application, in which the
server generates Web pages based on its database in response to client
requests that may update the database. The client-server model is
applicable when the client and server are both in the same building (and
belong to the same company), but also when they are far apart.
If we look at the client-server model in detail, we see that two processes
(i.e., running programs) are involved, one on the client machine and one
on the server machine. Communication takes the form of the client
process sending a message over the network to the server process. The
client process then waits for a reply message. When the server process
