Chapter 8
Basic Concepts of a Computer Network
Objectives
•
Understand why a computer network is needed
•
Understand what types of services are available on a
network
•
Understand how computers can be connected locally to
form a Local Area Network (LAN) and over long distances
to form a Wide Area Network (WAN)
•
Be aware of how and why computers are connected to
form a network at home, in school and in workplace
•
Be able to use and describe the common services
available in a networked environment
Modern Computer and Information Technology (HKCEE) Core Module
Section B Computer Systems and Networking
p.1
Chapter 8
8.1 Need for a Computer Network
8.1.1 Case Studies
• Case 8.1: In school, Jane needs to save
her working files in A1 computer laboratory
into a floppy disk and give it to her classmate
in A2 laboratory for review.
With computer network: Jane can
save files in a file server. When Jane
amends files in A1 computer laboratory,
her classmates can see the new
updates in A2 computer laboratory at
the same time.
Modern Computer and Information Technology (HKCEE) Core Module
Section B Computer Systems and Networking
p.2
Chapter 8
• Case 8.2 : John works in a shipping
company. He is responsible for data entry and
often needs to print the shipping orders of the
company. However, no printer is connected to
his computer. John must save all files into a
floppy disk and use another computer to print
the shipping orders. This is very inconvenient
for John.
With computer network: John can now
directly print the shipping orders to a
networked printer from his computer.
One printer can handle all the printing
tasks.
Modern Computer and Information Technology (HKCEE) Core Module
Section B Computer Systems and Networking
p.3
Chapter 8
8.1.2 Why do We Need a Computer Network ?
A network is a way to
connect computers for :
• Communication
• Data exchange
• Resource sharing
Most companies have PCs connected to form a network
in their offices
Modern Computer and Information Technology (HKCEE) Core Module
Section B Computer Systems and Networking
p.4
Chapter 8
Three of the most important
benefits that are brought by
network include the
following:
• It allows many users to
access the same programs
and data simultaneously
• It makes electronic
communications easier
• It allows users to share
peripheral devices, such as
printers and scanners
Modern Computer and Information Technology (HKCEE) Core Module
Section B Computer Systems and Networking
Video conferencing is available in the network
environment
p.5
Chapter 8
8.2 Types of Network
When two or more computers are connected, a network is formed.
There are two main types of network:
• Local Area Network (LAN)
• Wide Area Network (WAN)
Modern Computer and Information Technology (HKCEE) Core Module
Section B Computer Systems and Networking
p.6
Chapter 8
8.2.1 Local Area Network (LAN)
• A Local Area Network (LAN)
consists of computers that
are relatively near to each
other
• It can consist of just two or
three PCs connected together
to share resources. It can
also connect hundreds of
computers of different kinds
• The connection can be made
either by cables, infrared links,
or small wireless devices
Modern Computer and Information Technology (HKCEE) Core Module
Section B Computer Systems and Networking
An example of a local area network connecting
several PCs, printers, a file server and a
network gateway
p.7
Chapter 8
8.2.2 Wide Area Network (WAN)
•
A typical Wide Area Network (WAN) consists of two or
more local area networks connected together across a wide
geographical area
•
Public utilities, such as the telephone line system, are
usually used for the transmission of data
•
The cost associated with transmitting data is another major
difference between WAN and LAN. It is relatively more
expensive in WAN than that of in LAN.
8.2.3 Metropolitan Area Network (MAN)
Metropolitan Area Network (MAN) is a network that
interconnects computers in a geographic area larger than that
covered by LAN but smaller than that covered by WAN.
Modern Computer and Information Technology (HKCEE) Core Module
Section B Computer Systems and Networking
p.8
Chapter 8
An illustration of a Wide Area Network (WAN)
Modern Computer and Information Technology (HKCEE) Core Module
Section B Computer Systems and Networking
p.9
Chapter 8
8.3 Network Models
8.3.1 Peer-to-peer Model
• A peer-to-peer model is
a LAN where computers
are simply connected
together
• Each computer has equal
relations with each other
and controls which
computer can use its
resources
A peer-to-peer model
Modern Computer and Information Technology (HKCEE) Core Module
Section B Computer Systems and Networking
p.10
Chapter 8
8.3.2 Client/Server Model
In a client/server network
model, we have:
client
• Server: A computer that has
central control over all
network resources.
• Clients: Other computers
connected to the server.
Server
client
client
A client/server model
Modern Computer and Information Technology (HKCEE) Core Module
Section B Computer Systems and Networking
p.11
Chapter 8
Network model
Peer-to-peer
Advantages
Disadvantages
Inexpensive and easy to set up Lacks of management software to effectively
monitor the activities of a network
Client/server
Handles very large networks
efficiently
Table 8.1
The cost of installation and administration is high
Advantages and disadvantages of peer-to-peer and client/server models
Modern Computer and Information Technology (HKCEE) Core Module
Section B Computer Systems and Networking
p.12
Chapter 8
8.4 Basic Requirements for Establishing
a Computer Network
The basic requirements of a network are:
• Each computer must have a network card
• Network protocol
• A hub or a router
• Cables or microwaves
• Network operating system
Modern Computer and Information Technology (HKCEE) Core Module
Section B Computer Systems and Networking
p.13
Chapter 8
8.4.1 Protocols
Networks are governed by protocols, which are rules for
sending and receiving data. Devices on the network must be
able to “talk the same language ” or use the same protocol.
Two common protocols used today are:
• NetBEUI : It is a protocol that broadcasts messages
to every computer on the network.
• TCP/IP : It is the protocol of the Internet and is
required on any computers that communicate across
the Internet. It is a very powerful protocol to connect
every computer in the world.
Modern Computer and Information Technology (HKCEE) Core Module
Section B Computer Systems and Networking
p.14
Chapter 8
8.4.2 Network Operating System (NOS)
A network operating system (NOS) is an operating system
that has the ability to control the networking components of a
computer system.
It also provides services such as:
• Printer sharing
• File sharing
• Database sharing
• Application sharing
• The ability to manage a naming directory for the
network
Modern Computer and Information Technology (HKCEE) Core Module
Section B Computer Systems and Networking
p.15
Chapter 8
8.4.3 Network Interface Card (NIC)
•
•
In a network, each
computer must have a
network interface card
to connect to other
computers and devices.
In a wireless connection,
a wireless adapter is
required.
A network cable is
plugged into the
network interface card
and physically connects
a computer to a
network
The main function of a network interface card is to
convert data of a computer into electrical signals
Modern Computer and Information Technology (HKCEE) Core Module
Section B Computer Systems and Networking
p.16
Chapter 8
8.4.4 Types of Communication Media
•
In a wired network, data
is transmitted through
physical media, mostly
cables, such as twistedpair cable , coaxial
cable and fibre-optic
cable.
•
In a wireless network,
data is transmitted
through microwave.
Modern Computer and Information Technology (HKCEE) Core Module
Section B Computer Systems and Networking
A fibre-optic cable is a thin strand of glass that transmits
pulsating beams of light instead of electric current.
p.17
Chapter 8
8.4.5 Connecting Devices
A connecting device acts as a switching board for transmitting
data from one computer to another.
Hub
Computer
Computer
Computer
Computer
A network hub is used to connect different computers together by joining all the network cables
Modern Computer and Information Technology (HKCEE) Core Module
Section B Computer Systems and Networking
p.18
Chapter 8
Connecting Device
Hub
Bridge
Router
Access point
Functions
A hub is a device that connects all network cables together. We can
think of the hub as being a joining point of all network media.
A bridge is a device that connects different networks together, e.g.
connecting an electrical network to an optical network, or a wired
network to a wireless network.
A router is a sophisticated device that connects different networks.
Network data is routed to different networks based on the rules that
are programmed in the router. We can think of a router as a kind of
highway roundabout for data traffic.
An access point is a station that transmits and receives data in a
wireless network. It connects users to other users within the network.
Each access point can serve multiple users within a defined network
area. When users move beyond the range covered by
Table 8.2
Functions of different connecting devices
Modern Computer and Information Technology (HKCEE) Core Module
Section B Computer Systems and Networking
p.19
Chapter 8
8.4.6 Network Topologies
Topology is the physical or logical layout of cables and devices
that make up a network. There are three main types of network
topology:
• Star topology : Several
nodes are connected to a
central one. All the
communications travel
through this central node.
It requires the largest
amount of connecting cables.
Star topology
Modern Computer and Information Technology (HKCEE) Core Module
Section B Computer Systems and Networking
p.20
Chapter 8
•
Bus topology : Nodes are
connected by a common
bus, which can be as
simple as a single wire.
It is less expensive than the
star topology.
Bus topology
Modern Computer and Information Technology (HKCEE) Core Module
Section B Computer Systems and Networking
p.21
Chapter 8
•
Ring topology : Each node
is connected to two others
forming a ring. Data is
transmitted around this ring.
There are usually two rings
running in parallel so that
when one segment of the
ring is broken, the other ring
can take over immediately.
Ring topology
Modern Computer and Information Technology (HKCEE) Core Module
Section B Computer Systems and Networking
p.22
Chapter 8
Topology
Bus
Advantages
• Easy to connect a computer or
peripheral to a linear bus
• Requires less cable length than a star
topology
Star
• Easy to install and wire
• No disruptions to the network when
connecting or removing devices
• Easy to detect faults and to remove
parts
• Does not rely on a single hosting
computer and can function even though
one of the nodes is broken
Ring
Table 8.3
Disadvantages
• Entire network shuts down if there is a
break in the main cable
• Terminators are required at both ends of
the backbone cable
• Difficult to identify the problem if the entire
network shuts down
• Requires more cable length than a bus
topology
• If the hub fails, nodes attached are disabled
• More expensive than the bus topology
• The channel can handle only one message
at a time
• Performance will be degraded if there is a
high-volume of network traffic
Advantages and disadvantages of the three different network topologies
Modern Computer and Information Technology (HKCEE) Core Module
Section B Computer Systems and Networking
p.23
Chapter 8
8.4.7 Network Technologies
•
Network technology is the type of cabling equipment used
to create a LAN
•
Each network technology is designed to work with a certain
type of network topology.
•
Each one has certain standard features
•
The most common types of network technology include:
• Ethernet
• Local Talk
• Token Ring
• Asynchronous Transfer Mode (ATM)
Modern Computer and Information Technology (HKCEE) Core Module
Section B Computer Systems and Networking
p.24
Chapter 8
Ethernet is the most popular network technology because it
is inexpensive to implement. It is essentially a bus topology
where every node “taps ” into a central cable.
Network technology
Ethernet
Fast Ethernet
Gigabit Ethernet
Data transfer rate
Cable
Twisted Pair, Coaxial, 10 Mbps
Fibreoptic
Twisted Pair, Fibre100 Mbps
optic
Twisted Pair,
1 Gbps
Fibre-optic
Table 8.4
Modern Computer and Information Technology (HKCEE) Core Module
Section B Computer Systems and Networking
Topology
Bus, Star
Star
Star
A summary of different types of Ethernet
p.25
Chapter 8
8.5 Common Services Available in
a Networked Environment
8.5.1 Simultaneous Access
Simultaneous access of information is one of the three
common services that can be provided by a network.
Modern Computer and Information Technology (HKCEE) Core Module
Section B Computer Systems and Networking
p.26
Chapter 8
client
PC
PC
Server
client
PC
client
Without a network, each computer has its own
copy of data file. It is hard to decision which
one is the most up-to-dated.
In a client/server network, the data is stored at
the central server. Staffs can retreive the file
at any time and changes on the data can be
seen immediately.
Example Quarterly sales report of a company
Modern Computer and Information Technology (HKCEE) Core Module
Section B Computer Systems and Networking
p.27
Chapter 8
8.5.2 Shared Peripheral Devices
The ability to share peripheral devices is one of the most
important services that a network can provide.
Client A
Print Server
Printer
Client B
Print queue
Client C
Example Sharing of Printers
Modern Computer and Information Technology (HKCEE) Core Module
Section B Computer Systems and Networking
p.28
Chapter 8
8.5.3 Communications
Another useful application of a network is electronic
mail (e-mail), which is a system for exchanging written
messages through a network.
An illustration of how an e-mail is sent and received over a network
Modern Computer and Information Technology (HKCEE) Core Module
Section B Computer Systems and Networking
p.29
Chapter 8
8.6 Wireless Network
•
Wireless network
connections perform the
same functions as wired
connections.
•
To connect to a wireless
network, we need wireless
adapters and wireless
network
An illustration of how notebook computers can
connect to a network through access points
Modern Computer and Information Technology (HKCEE) Core Module
Section B Computer Systems and Networking
p.30
Chapter 8
8.7 Case Studies of Setting a
Computer Network
8.7.1 Network at Home
( Click here for a larger view )
Modern Computer and Information Technology (HKCEE) Core Module
Section B Computer Systems and Networking
p.31
Chapter 8
8.7.2 Network in Workplace
( Click here for a
larger view )
Modern Computer and Information Technology (HKCEE) Core Module
Section B Computer Systems and Networking
p.32
Chapter 8
End of Chapter 8
Modern Computer and Information Technology (HKCEE) Core Module
Section B Computer Systems and Networking
p.33