INTRODUCTION TO COMPUTER
NETWORK
WHAT IS A COMPUTER NETWORK?
A network consists of two or more computers that are connected to share resources (
printers, CDROM, programs …), and to communicate (emails, chat …).
The computers on a network may be linked using cables (twisted pair, coaxial, fiber optic)
or wireless technologies (WIFI, Infrared …) .
HISTORY OF NETWORKS :
In the beginning, computer systems were highly centralized within a single large room. The
first networks were time-sharing networks consisting of Mainframes and Dumb Terminals.
Mainframes :
multi-user systems, are large and powerful computers used primarily by large organizations for critical
applications. They are capable of communicating with hundreds of users simultaneously.
A dumb terminal :
is a device which consists of a keyboard and a monitor, and a connection to an intelligent computer
( mainframe or server computer).
dumb terminals have no data processing power and depend entirely on the server for
computations, data storage, and retrieval.
ARPANET (1969 – 1990)
In the late 1960s (when the U.S. military was afraid of a nuclear attack from the Soviet
Union) DOD (department of defense-USA) turned to its research arm ARPA (Advanced
Research Projects Agency) to design a global computer network that would connect
military bases and allow university-based researchers working for the Defense
Department to share information with their colleagues in other U.S cities.
In 1969 the ARPANET were developed in secret by the Department of Defense in
conjunction with several universities.
In the early 1980s, ARPANET gradually became what we now call the internet.
VINTON CERF
Vinton cerf (born June 23, 1943) is an American internet inventor, who is recognized as
one of the fathers of the internet sharing this title with the American engineer Bob Kahn.
Vinton cerf is also known as the developer of TCP/IP technology
In 1971, the electronic mail (email) was invented.
In the mid-1980s, people began viewing the collection of networks as the Internet.
In 1988, the first forum for real time chat was provided through the creation of IRC
(Internet Relay Chat).
In 1989, Tim Berners-Lee developed the first version of the World Wide Web, but it
was non-graphic. Then be developed the HTML (Hypertext Mark-up Language) in
1990.
In 1993, Mosaic , the first graphical Internet interface or web browser, was developed
by Marc-Andresen.
In 1995 the Microsoft Internet Explorer 1.0 browser was introduced.
ADVANTAGES OF NETWORKS
1. Sharing of resources: expensive devices such as laser printers, programs and
folders can be shared by many users.
2. Remote access.
3. Reduction of distance and time.
4. Speed : fast transfer of files.
5. Centralized management.
6. Workgroup computing : allows many users to work on a project concurrently.
DISADVANTAGES OF NETWORKS
1. Cost : cost of equipment and network installation.
2. Security problems : hacking, viruses , spying…
3. Networks maintenance : requires experts and considerable time.
4. Server failure : Network connectivity between clients and servers may fail, which
will interrupt the work.
WHAT IS A NETWORK HOST?
A network host is a computer or other device connected to a computer network. A network
host may offer information resources, services, and applications to users or other nodes of
the network, and it can be identified by its IP address.
To test/check the connectivity with a remote host ( PC, Router, printer, DSL, modem…), you
can use the tool : PING
Example : ping 192.168.1.1
A replay of 4 packets means that a connection exists. Otherwise, there is a
connection problem.
COMPUTER ROLES IN A NETWORK
Computers on a network can be configured either as clients or either as-Servers.
-A Client-Computer is one that requests services and resources from a
Server on a
network.
-A server-Computer is a powerful computer that provides services and resources for the
Clients on a network.
TYPES OF SERVERS
1.
File server : a computer server that store common files and share them for clients over a network.
2.
Print server : a computer server on which one or more printers are attached. Its function is to provide
and manage printing services on a network.
3.
Web server : a computer server that hosts website and delivers web pages over the internet.
4.
Mail server : a computer server that hosts an mail application. It allows sending, storing and retrieving
email messages over a network.
5.
FTP server : is a software application running the File Transfer Protocol (FTP), which is the protocol for
exchanging files over the Internet.
6.
Proxy server : is computer that function as an intermediary between a web browser and the Internet.
Proxy servers help improve web performance by storing a copy of frequently used webpages
(caching).
7.
DNS server : short for Domain Name System ( or service or Server), an Internet service that translates
domain name into IP address.
NETWORKS ARCHITECTURES
1.
Peer-to-Peer Architecture:
An efficient way to connect less than 10 computers. In a Peer to Peer network, each computer can access the files
stored on any other computer. There is no dedicated server.
All computers are equals and have the same priority. A popular Peer to Peer network is the Microsoft’s Windows for
Workgroups.
-Advantages of Peer to Peer architecture:
simple configuration.
cheap requirements : No Server or special operating system is needed.
-Disadvantages/limitations of Peer to Peer architectures:
no dedicated server is used. So, there is no centralized management on the network.
Difficult maintenance.
Backups are not centralized.
Weak security.
Limited number of computers.
2. Client/server Architectures:
Client/server architectures is ideal for large-scale networks. One of the computers is configured
as a centralized server that will public files and common applications. The other computers are
called “clients” and can share the resources of the server.
-Advantages of Client/Server architectures:
Centralized management.
Centralized backup on the server.
Easier maintenance.
Improved/better security.
Scalability: It is easier to add more computers and more resources without affecting the network performance.
-Disadvantages of Client/Server architectures:
Server cost.
Complex configuration.
The server is a critical point of failure. It if goes down, the entire network may fail
TYPES AND SIZE OF NETWORKS
Networks can be distinguished based on their reach (scope or size). Typically, there
are three main types of networks : LAN, WAN and Man
LAN - LOCAL AREA NETWORK
A Local Area Network (LAN) connects computers within a small geographic area;
usually within the same building. (E.g. school LAB, office, home….)
Typically, the connection is high speed and relatively inexpensive. The maximum
number of computers on a LAN is 1024. data transfer speeds can reach up to 10
Mbps (Ethernet), 100 Mbps (Fast Ethernet) and 1 Gbps (Gigabit Ethernet).
WAN – WIDE AREA NETWORK
A wide area network (WAN) interconnects multiple LANs over great geographic
distances. The internet is an example of worldwide WAN. For example, WANs are
used to establish international banks networks. WANs operate using routers and
protocols like ATM, X.25, and Frame Relay. The speed available on a WAN varies
depending on the cost of the connections and may be low (1 Mbps, 2 Mbps….)
MAN – METROPOLITAN AREA NETWORK
a Metropolitan Area Network (MAN) is a larger network that usually spans several
buildings in the same city or different towns to interconnect LANs using high-speed
connections, such as fiber-optic links or leased lines. For example a MAN can used to
interconnect a University dispersed campuses.
Comparison Table
LAN
MAN
WAN
Designation:
Local Area Network
Metropolitan Area Network
Wide Area Network
Speed:
Fastest
100 Mbps  10 Gbps
Slower than LAN
Slowest
1Mbps  8 Mbps (DSL)
Distance:
Small geographic area;
usually within the same
building
Larger network which covers A Large network that spans
an area equivalent to a city great geographic distance
or different towns
such as the Internet
Security:
High security
Lower security than LAN
Lowest security
Equipment:
-Twisted pair cable and
wi-fi connections
-Hubs, switches and
repeaters…
-Fiber optic cables
Leased lines/telephone links
-Switches, bridges and
repeaters
-Fiber optic and Satellite
links.
-Wan switches and routers
Protocols:
TCP/IP, file and print
sharing…
TCP/IP
TCP/IP, ATM ….
Setup Costs:
Low costs
Higher costs than LAN
Highest costs
N.B of Users or
Computers:
Smallest/limited
1024 computer max
Large
Largest/unlimited