1. CHAPTER 3
COMPUTER NETWORKS & COMMUNICATIONS
1.1 BASIC CONCEPTS OF COMPUTER NETWORKS
Definition of Computer Networks
A computer network is a collection of computers and
devices connected together via communication devices and
transmission media. For example it may connect
computers, printers and scanners.
Definition of Communication
Communication describes a process in which two or more
computer or devices transfer data, instructions and
information.

2. 1.2 THE IMPORTANCE/ADVANTAGES OF COMPUTER
NETWORKS
i. Sharing of devices such as printer and scanner
ii. Sharing of program/software
iii. Sharing of files
iv. Sharing of data
v. Sharing of information
vi. Sharing of single high-speed internet connection
vii. Can access server centered database
viii. Better communication using Internet services such as
e-mail, mailing list and Internet Relay Chat(IRC)

3. Types of computer network
LAN MAN WAN

4. Network Architecture
Client/server Peer to peer

5. Types of computer network
Bus Star Ring

6. Network communications technology
Intranet Extranet Internet

7. 1.3 TYPES OF COMPUTER NETWORKS
A local area network is a network that connects computers
Local Area Network and devices in a limited geographical area such as a home,
(LAN) school computer laboratory, office building.
A metropolitan area network (MAN) is a high speed network
Metropolitan Area that connects local area networks in a metropolitan area
Network (MAN) such as city or town and handles bulk of communications
activity across the region.
A MAN typically includes one or more LAN but covers a
smaller geographic area than a WAN.
A wide area network is a network that covers a large
Wide Area Network geographical area such as country or the world.
(WAN)
WAN combines many types of media such as telephone lines,
cables and radio waves. A WAN can be one large network or
can consist of two or more LANs connected together.
The Internet is the worlds largest WAN.

9. 1.3.1 DIFFERENCES BETWEEN LAN & WAN
WAN Different LAN
A wide area network is a Geographical A local area network is a network
network that covers a large Area that connects computers and
geographical area such as devices in a limited geographical
city, country or the world. area such as a home, school
computer lab and office building
In case of WAN the cost of Cost Cost of data transmission in LAN
data transmission is very is less because the transmission
high because the medium is owned by a single
transmission mediums organization
used are hired either
telephone lines or satellite
links
The speed of data Speed The speed of data transmission is
transmission is lower than much higher in LAN than in WAN
LAN

10. 1.3.1 DIFFERENCES BETWEEN LAN & WAN
WAN Different LAN
Geographical
Area
Cost
Speed

11. 1.4 TYPES OF NETWORK ARCHITECTURE
A server is a
computer that
provides
services to
clients and
control access
to hardware,
software and
other
resources A client is a
computer that
request
services from
a server
computer

12. 1.4 TYPES OF NETWORK ARCHITECTURE
Client/Server
On a client/server network, one computer act as a server
that provides services and the other computers (client) on
the network request services from the server.
A server is a computer that controls access to the hardware,
software and other resources on the network and provides
a centralized storage area for program. There are many type
of server such as mail server, web server, file server and ftp
server.
A client is a computer that requests services from a server
computer.

14. 1.4 TYPES OF NETWORK ARCHITECTURE
Peer-to-peer
Peer-to-peer is a simple, inexpensive network that typically
connects fewer than 10 computers. All computers in the network
have equal capabilities to use the resources (hardware, software,
data and files) available on the network. With peer-to-peer
networks, there is no central server.

16. 1.5 TYPES OF NETWORK TOPOLOGIES
Network topology is the physical arrangement of computers in a
network. Common network topologies include the bus, star and ring.
i) Ring Topology
On a ring network, a cable forms a closed loop(ring) with all
computers and devices arranged along the ring. Data transmitted on
the network travels from device to device around the entire ring, in
one direction. When a computer or device send data, the data
travels to each computer on the ring until it reaches its destination.
If computer or device on a ring network fails, all devices before the
failed device are unaffected but those after the failed device cannot
function. A ring network can span a larger distance than a bus
network, but it is more difficult to install. The ring topology
primarily is used for LANs, but also used in WANs.

17. Advantages
 A physical ring topology has minimal cable requirements
 No wiring center or closet needed
 The message can be automatically acknowledge
 No collision exist between nodes
Disadvantages
 If any node goes down, the entire ring goes down
 Troubleshooting is difficult because communication is only one
way
 There will be a limit on the distance between nodes

19. 1.5 TYPES OF NETWORK TOPOLOGIES
ii) Bus Topology
A bus network consists of single central cable, to which all
computers and other devices connect. The bus is physical cable that
connects the computers and others devices.
The bus in a bus network transmit data, instructions, and
information and information in both directions. When sending
device transmits data, the address of the receiving device is
included with the transmission with the transmission so the data is
routed to the appropriate receiving device. Bus networks are
popular on LANs because they are inexpensive and easy to install.
One advantage of the bus network is that computers and other
devices can be attached and detached at any point on the point on
the bus without disturbing the rest of the computers. The
transmission simply by passes the failed device.

20. Advantages
 Easy to implement and extend
 Cost effective as only a single cable is used
 Cable faults are easily identified
Disadvantages
 Limited cable length and number of stations
 If there is a problem with the cable, the entire network goes
down
 Maintenance costs may be higher in the long run
 Performance degrades as additional computers are added or on
heavy traffic.
 Proper termination is required (loop must be in closed path)

22. 1.5 TYPES OF NETWORK TOPOLOGIES
iii) Star Topology
On a star network, all of the computers and devices(node) on the
network connect to central device, thus forming a star. The central
device that provides a common connection point for nodes on the
network is called the hub.
Similar to bus network, star networks are fairly easy to install and
maintain. Nodes can be added to and removed from the network.
On star network, if one node fails, one that node effected. The other
nodes continue to operate normally. If the hub fails, however, the
entire network inoperable until the hub is repaired. Most star
networks, therefore, keep backup hubs available in case primary hub
fails. A star network generally requires more cable.

23. Advantages
 Easy to install and wire
 No disruptions to the network then connecting or removing
devices.
 Easy to detect faults and to remove parts
 More suited for larger networks
 Easy to expand network
 Easy to troubleshoot because problem usually isolates itself
Disadvantages
 Failure of the central hub causes the whole network failure
 It is slightly more expensive than using bus topology
 Requires more cable

25. 1.6 DIFFERENCES BETWEEN BUS, RING & STAR TOPOLOGY
Topology Bus Ring Star
Configuration
Central device Not available Not available Hub or switch
Data Both direction One direction Both direction
transmitted
Installation and Easy Difficult Easy
maintenance
If one node fails Does not effect The entire Does not effect
the rest of network stop the rest of nodes
nodes working

26. 1.7 TCP/IP as a protocol to facilitate communication over
computer network
A protocol is a set of rules for the exchange of data between a terminal
and computer or between two computers. Think of protocol as a sort of
precommunication agreement about the form in which a message or
data is to be sent and receipt is to be acknowledge.
TCP/IP is short for Transmission Control Protocol/Internet Protocol.
TCP/P is a network standard, specifically a protocol, that defines how
messages are routed from one end of a network to the other, ensures
the data arrives correctly.

27. 1.8 NETWORK COMMUNICATIONS TECHNOLOGY
INTERNET
An internet is a public network. It is worldwide collection of networks
that links millions of business, government agencies, educational
institutions and individuals.
INTRANET
An intranet is a private network within an organization that resembles
the internet. Organizations use intranets to provide information to their
employees.
Typically applications include electronic telephone directories, email
addresses, employee information, internal job opening, and much more.
Employees find surfing their organizational intranets to be as easy and
as intuitive as surfing the Internet.

28. Like the public internet, intranet use browsers, web sites, and web
pages. Intranet typically provides e-mail, mailing lists, newsgroup, and
FTP services accessible only to those within the organization.
EXTRANET
An extranet is a private network that connects more than one
organizations.
Many organizations use the Internet technologies to allow suppliers,
customers and business partner limited access to their network.
The purpose is to increase efficiency and reduce costs.
For examples, Generals Motors has thousands of suppliers for parts that go
into making an automobile. By having access to the production schedules,
suppliers can schedule and deliver parts as they are needed at the General
Motors assembly plants. In this way, General Motors can be assured of
having adequate parts without maintaining large inventories.

29. DIFFERENCES INTERNET, INTRANET & EXTRANET
DIFFERENCES Internet Intranet Extranet
Used for Public Private Private
Types of users Provide Provide information Provide information
information for for organization to suppliers,
public employees customers and
business partner
Usages Access all kinds of Telephone Access data, Check
information directories, Internal status Place orders,
job openings, send email
employee
information
Security Loose High Use virtual private
network (VPN)
technology to
communication
over the internet
more secure

30. 2.0 HARDWARE REQUIREMENTS FOR NETWORKING
COMMUNICATION DEVICES
NETWORK INTERFACE CARD (NIC) is a communication device that
enables a computer or device to access a wired network (via cable).
A WIRELESS NETWORK INTERFACE CARD is a communication device
that enables a computer or device to access a wireless network (via
radiowave).
A MODEM is a communication device that enables a computer to
transmit data over telephone or cable line. Modem converts digital
signals from your computer into analog signals to send over the phone
lines and converts the phone’s analog signals into digital for the
computer.

32. A HUB is a communication device that is used for connecting wired
computers or devices on a Local Area Network (LAN). A hub provides a
common connection point for nodes on a star network.
A WIRELESS ACCESS POINT is a communication device that is used for
connecting wireless computers or devices on a Local Area Network
(LAN)
A ROUTER is a communication device that connects multiple
computers and transmits data to its correct destination on the
network. A router allows multiple computers to share a single high-
speed internet connection.

34. TRANSMISSION MEDIA
Transmission media
PHYSICAL TRANSMISSION WIRELESS TRANSMISSION
MEDIA MEDIA
Send communication signal Send communication signal
through tangible material such through air or space using
as wire and glass using radiowave, microwave and
electrical signal and pulses of infrared.
light. 1. Infrared
1. Twisted pair cable 2. Radiowave
2. Coaxial cable 3. Satellite
3. Fiber optic

35. 2.3 TYPES OF CABLES
(a) Twisted pair cable
Description:
Twisted pair cable consists of two strands of insulated copper
wire, twisted around each other. Multiple twisted pairs can be
combined into a single cable. This twisted-pair configuration
somewhat reduces interference from electrical field.
How signal pass through:
Transmit data by means electrical signal

36. (b) Coaxial Cable
Description:
Coaxial cable consists of a single copper wire surrounded by at
least three layer an insulating material, braided wires, plastic
coating.
How signal pass through:
Transmit data by means electrical signal
(b) Fiber Optic
Description:
Fiber consists of dozens or hundreds of thin strands of glass
that use light to transmit signal. Each strand, call optical fiber, is
as thin as human hair.
How signal pass through:
Transmit data as pulses of light through tiny tubes of glass

38. 2.4 WIRELESS TRANSMISSION MEDIA
(a) Infrared
Type of wireless transmission medium that sends signals using infrared
light waves. To communicate each other, Infrared devices often must
be within about 5 meters (15 feet)
(b) Radio wave
IEEE 802.15.1
Bluetooth technology uses short-range radio waves to transmit data
between two Bluetooth devices. The data transfers between devices
at rate of 1 Mbps. To communicate each other, Bluetooth devices often
must be within about 10 meters (33 feet).

39. IEEE 802.11 b/ IEEE 802.11 g
WiFi (Wireless Fidelity): The data transfers between devices at a rate
of 11 – 54 Mbps. To communicate each, WiFi devices often must be
within about 30 meters (100 feet)
(c) Satellite
A satellite is a space station that receives microwaves signals from an
earth-based station, amplifies (strengthens) the signals, and
broadcasts the signal back over a wide area to any number of earth-
based stations.

40. 3.0 SOFTWARE REQUIREMENTS
3.1 DEFINITION OF NETWORKING OPERATING SYSTEM
Networking Operating System is an operating that is designed to
support a network. Network operating system organizes and
coordinate how multiples users access and resources on a network.
Resources include hardware, software, data and information. For
example, NOS allows multiple uses to share a printer, internet access,
files and programs.
Examples of Network Operating Systems
i) Netware vi) Linux (Red Hat, SUSE, KDE, Ubuntu)
ii) Window Server 2000
iii) UNIX
iv) Windows NT
v) Solaris

41. 3.2 CLIENT SOFTWARE
1. Web browser
• A web browser is application software that allows users to
access and view web pages.
• Web browsers have several main functions.
a. Retrieve and view internet-based information. They enables
us to retrieve and view information from World Wide Web.
b.Interact with servers. They allow us to interact with server-
based systems to submit information to this system.
c.View electronic documents. They are the foundation tool for
viewing electronic documents.
d.Download and upload information. They let us download
digital information, then view and/or hear the downloaded
video, images, music, and so on. They let us upload information,
as well.
e.E-mail. They allow us to send and receive e-mail.
• Examples: Internet Explorer 7, Mozilla Firefox, Netscape
Communicator 7, Opera 6.0, Camino 1.0, Safari 1.2, GoSurf

42. 2. Network utilities
• Ping : to provide a check that a particular IP address is available
and reachable
3. Network file manager
• My network places replaces the Network Neighborhood
feature that you used in both Window 98 and Windows NT 4.0
• Function: to access files and folders on other computer in the
network

43. 4. Email client
• There are several function of e-mail client
a. To create e-mail messages
b. To send e-mail messages
c. To receive e-mail messages
d. To forward e-mail messages
e. To store e-mail messages
f. To print e-mail messages
g. To delete e-mail messages
• Examples : Outlook Express, Mozilla Thunderbird