Download Why Network Computers?

Study Unit
4
COMPUTER SYSTEMS AND DATA COMMUNICATION
Introduction
Computerised information systems use hardware and software to generate
information. This information must then be communicated to the user by using
specific communication methods. In this study unit, we look at information
systems, accounting information systems and modern methods of communication.
Communication Theory
Communication is the transfer of information from a sender to a receiver. It refers to
the means and methods whereby data is transferred between processing locations
through the use of communication systems. Communication systems are defined as
systems for creating, delivering and receiving electronic messages. The
communication system comprises of the following
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A device to send the message
The channel or communication media
A device to receive the message
An information system is a system that comprises people, machines and methods by
which data is collected, processed, transferred and distributed. The system may be
manual or automatic. This study unit will focus on the automatic system. An
accounting information system measures business activities (data), processes the data
and communicates usable information to decision makers.
What is a Network?
Before the evolution of networks, organisations made use of stand-alone computer
systems. Computers would be found in strategic places in the organisation but were
not linked to each other. Stand-alone computers are now used mainly by sole
proprietors and for personal use.
Computer networks are now more accessible to organisations and individuals on a
large scale. Terminals are linked to a mainframe and this gives users access to a
central processing function. These terminals can be linked via internal or external
communication channels.
A network consists of two or more computers that are linked in order to share
resources, such as printers and CD-ROMs, exchange files, or allow electronic
communications.
There are different configurations that can be used to ensure connectivity.
Configuration refers to the way that hardware devices are connected to each other.
The computers on a network may be linked through cables, telephone lines, radio
waves, satellites, or infrared light beams.
Fig 4.1 gives an example of a network in an organisation comprising a local area
network or LAN connecting computers with each other, the Internet, and various
servers.
The three basic types of networks include:
 Local Area Network (LAN)
 Wide Area Network (WAN)
 Metropolitan Area Network (MAN)
Local Area Network
The Local Area Network (LAN) enables multiple users in a relatively small
geographical area to exchange files and messages, as well as access shared
resources such as file servers. Rarely are LAN computers more than a mile apart.
It is generally limited to a geographic area such as a writing lab, school, or
building.
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In a typical LAN configuration, one computer is designated as the file server. It
stores all of the software that controls the network, as well as the software that can
be shared by the computers attached to the network. Computers connected to the
file server are called workstations. The workstations can be less powerful than the
file server, and they may have additional software on their hard drives. On most
LANs, cables are used to connect the network interface cards in each computer.
Wide Area Network
The Wide Area Network (WAN) is an interconnection of various LANs through
telephone network to unit geographically distributed users. Dedicated
transoceanic cabling or satellite uplinks may be used to connect this type of
network.
Using a WAN, anybody in Zimbabwe can communicate with countries like Japan
in a matter of minutes, without paying enormous phone bills. For example when
we log on to the Internet, we become a part of a WAN. A WAN uses special
communication tools such as multiplexers to connect local and metropolitan
networks to global communications networks like the Internet. To users, however,
a WAN will not appear to be much different than a LAN or a MAN.
Metropolitan Area Network
The Metropolitan Area Network (MAN) is usually the interconnection between
various LANs in a particular geographical area like a metropolitan city like
Harare.
Computer Networks configurations
Basically, there are two types of network configuration, peer-to-peer networks
and client/server networks.
A network is referred to as peer-to-peer if most computers are similar and run
workstation operating systems. Peer-to-peer networks are more commonly
implemented where less then ten computers are involved and where strict security
is not necessary. All computers have the same status, hence the term 'peer', and
they communicate with each other on an equal footing. Files, such as word
processing or spreadsheet documents, can be shared across the network and all
computers on the network can share devices, such as printers or scanners, which
are connected to any one computer. Other computers can access these resources
but a computer that has a particular resource must be turned on for other
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computers to access the resource it has. For example, if a printer is connected to
computer A and computer B wants to print to that printer, computer A must be
turned on.
A computer network is referred to as client/server if (at least) one of the
computers is used to "serve" other computers referred to as "clients". Besides the
computers, other types of devices can be part of the network. Client/server
networks are more suitable for larger networks. A central computer, or 'server',
acts as the storage location for files and applications shared on the network.
Usually the server is a higher than average performance computer. The server also
controls the network access of the other computers which are referred to as the
'client' computers. Typically, teachers and students in a school will use the client
computers for their work and only the network administrator (usually a designated
staff member) will have access rights to the server.
In a client/server environment, each computer still holds (or can still hold) its (or
some) resources and files. Other computers can also access the resources stored in
a computer, as in a peer-to-peer scenario. One of the particularities of a
client/server network is that the files and resources are centralized. This means
that a computer, the server, can hold them and other computers can access them.
Since the server is always On, the client machines can access the files and
resources without caring whether a certain computer is On.
Another big advantage of a client/server network is that security is created,
managed, and can highly get enforced. To access the network, a person, called a
user must provide some credentials, including a username and a password. If the
credentials are not valid, the user can be prevented from accessing the network.
The client/server type of network also provides many other advantages such as
centralized backup, Intranet capability, Internet monitoring, etc.
Table 4.1 provides a summary comparison between Peer-to-Peer and
Client/Server Networks.
Table 1: Peer-to-Peer Networks vs Client/Server Networks
Peer-to-Peer Networks vs Client/Server Networks
Peer-to-Peer Networks
Easy to set up
Less expensive to install
Client/Server Networks
More difficult to set up
More expensive to install
A variety of operating systems can be
supported on the client computers, but the
server needs to run an operating system that
supports networking
Can be implemented on a wide range of
operating systems
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More time consuming to maintain the
software being used (as computers must be
managed individually)
Less time consuming to maintain the
software being used (as most of the
maintenance is managed from the server) 
Very low levels of security are supported or
none at all. These can be very cumbersome
to set up, depending on the operating
system being used
High levels of security are supported, all of
which are controlled from the server. Such
measures prevent the deletion of essential
system files or the changing of settings
Ideal for networks with less than 10
computers
No limit to the number of computers that
can be supported by the network
Requires a server running a server operating
system
Does not require a server
Demands that the network administrator has
a high level of IT skills with a good working
knowledge of a server operating system
Demands a moderate level of skill to
administer the network
Why Network Computers?
The primary purpose of a computer network is to share resources. Computers
networks allow people to share information, software, and any resources,
including hardware, more efficiently. For example:
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You can play a CD music from one computer while sitting on another
computer
You may have a computer with a CD writer or a backup system but the
other computer doesn’t have it; In this case, you can burn CDs or make
backups on a computer that has one of these but using data from a
computer that doesn’t have a CD writer or a backup system
You may have a computer that doesn’t have a DVD player. In this case,
you can place a movie DVD on the computer that has a DVD player, and
then view the movie on a computer that lacks a DVD player
You can connect a printer (or a scanner, or a fax machine) to one
computer and let other computers of the network print (or scan, or fax) to
that printer (or scanner, or fax machine)
You can place a CD with pictures on one computer and let other
computers access those pictures
You can create files and store them in one computer, then access those
files from the other computer(s) connected to it
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Components of a Network
In order to set up a computer network relevant network hardware and software
are required.
Network hardware
Networking hardware includes all computers, peripherals, interface cards and
other equipment needed to perform data-processing and communications within
the network.
This section provides information on the following components:
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File Servers
Workstations
Network Interface Cards
Switches
Repeaters
Bridges
Routers
File Server
A File server is a high capacity computer that provides various resources to the
network. It is the heart of a network and must have the following things:
 need a very fast computer with a large amount of RAM and storage space,
a fast network interface card, and a tape back-up device
 need network operating system such as Novell Netware, Windows NT
server, or Apple Share
 control the communication of information between the nodes on a network
If you plan to use one of your existing computers as the server, check its hardware
and make sure it meets the following requirements:
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A processor with 133-MHz or higher speed; 550-MHz recommended; up
to eight processors supported on one server
128 MB of RAM minimum required; 256 MB or more recommended; 32
GB maximum
1.25 to 2 GB of available hard disk space
CD-ROM or DVD-ROM drive
VGA or hardware that supports console redirection required; Super VGA
supporting 800 x 600 or higher-resolution monitor recommended
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Workstations
A computer in a network is called a workstation or client. This computer needs a
network interface card to enable it to be connected to the network backbone. It
does not necessarily need floppy disk drives or hard disks since files can be saved
on the file server.
When you are planning to use a computer as a workstation as a network, you
should make sure that computer meets the necessary requirements. In some cases,
it may only meet the hardware requirements without any software. In some cases,
something could be missing. If you decide to purchase brand new computers, as a
reminder of what we reviewed in chapter one, here are the hardware requirements
the computer must meet:
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A processor with 300 megahertz or higher processor clock speed
recommended; 233 MHz minimum required (single or dual processor
system); Intel Pentium/Celeron family, or AMD K6/Athlon/Duron family,
or compatible processor recommended
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128 megabytes (MB) of RAM or higher recommended (64 MB minimum
supported; may limit performance and some features)
1.5 gigabytes (GB) of available hard disk space
Super VGA (800 x 600) or higher-resolution video adapter and monitor
CD-ROM or DVD drive
Keyboard
Microsoft Mouse or compatible pointing device
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Network Interface Cards (NICs)
A network interface card (NIC) which is pronounced 'nick', is also known as a
network card. It connects the computer to the cabling, which in turn links all of
the computers on the network together. Each computer on a network must have a
network card. The three common network interface connections are Ethernet
cards, LocalTalk connectors, Token Ring cards. Most modern network cards are
10/100 NICs and can operate at either 10Mbps or 100Mbps Only NICs supporting
a minimum of 100Mbps should be used in new installations schools. Most of
these are internal, with the card fitting into an expansion slot inside the computer
and some build on the motherboard.
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Fig 5: Network Interface Cards (NICs)
We mentioned that a network card could also be used or installed externally. This
can be done using USB. Here is another example:
Hubs/Concentrators
A hub is a device used to connect multiple devices, including PC, printers, and
scanners, to the network. It serves as a central meeting place for cables from
computers, servers and peripherals. To make this possible, a hub is equipped with
small holes called ports. They usually have 4, 8, 12, or 24 RJ-45 ports. The entire
network shuts down if there is a problem on a hub. Here are some examples of
commonly found hubs.
Fig 6a: An 8 port Hub
Fig 6b: 2 Examples of 24 port Switches
When configuring a hub, you connect an RJ-45 cable from the network card of a
computer to one port of the hub.
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The function of a hub is to direct information around the network, facilitating
communication between all connected devices. However in new installations
switches should be used instead of hubs as they are more effective and provide
better performance.
Switches
Switches are the more recent technology and the accepted way of building today's
networks. They are essentially high-speed multi-port bridges which are more
efficient than with any other type of hub.
With switching, each connection gets "dedicated bandwidth" and can operate at
full speed. As a result, a switch is often termed a 'smart hub'. In contrast, a hub
shares bandwidth across multiple connections such that activity from one PC or
server can slow down the effective speed of other connections on the hub.
Now more affordable than ever, Dual-speed 10/100 autosensing switches are
recommended for all school networks. Schools may want to consider upgrading
any hub based networks with switches to improve network performance, that is,
the speed of data on the network.
Repeaters
A repeater is a device that regenerates and amplifies signals to create longdistance networks. They simply receive, amplify and rebroadcast the signals
although some repeaters can provide basic error-checking. They are used to
overcome distance limitations. Repeaters can be separate devices or they can be
incorporated into a concentrator.
Bridges
A bridge is a device that links two homogenous packet-broadcast local networks.
A bridge is used to connect two or more networks using the same address method
or protocol. It is often used when LANs reach their capacity of nodes. It accepts
all packets from each network addressed to devices on the other, buffers them,
and retransmits them to the other network. It also monitors and manages the
traffic to maintain optimum performance on both sides of the network.
Routers
Like a hub, a router is another type of device that acts as the central point among
computers and other devices that are part of a network. Here is an example of a
wired router.
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Routers are similar to bridges in that they link two or more physically separate
network segments. The network segments linked by a router, however, remain
logically separate and can function as independent networks.
A router functions a little differently than a hub. In fact, a router can be
considered a little "intelligent" than the hub.
Like a hub, the computers and other devices are connected to a router using
network cables. To make this possible, a router is equipped with holes, called
ports, in the back. Here is an example.
Network Operating System
A network operating system is a supervisory software program that resides on the
server. It controls how the network operates by defining who can use the network
and how information and peripherals are shared among users. The most
commonly used network operating systems in schools are from the Microsoft
windows family, which include Windows NT, Windows 2000 Server. Novel
Netware, UNIX, LYNX and others are not common in our schools.
Network Media
Network Cables
Cable is the medium through which information usually moves from one network
device to another. There are several types of cables which are commonly used
with LANs. In some cases, a network will utilize only one type of cable, other
networks will use a variety of cable types. The type of cable chosen for a network
is related to the network's topology, protocol, and size. You need to understand
the characteristics of different types of cables and how they relate to other aspects
of a network in order for you to develop a successful network.
In this section we discuss the following types of cables used in networks:
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Unshielded Twisted Pair (UTP) Cable
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Shielded Twisted Pair (STP) Cable
Coaxial Cable
Fiber Optic Cable
Wireless LANs
The two most popular types of structured network cabling are twisted-pair (also
known as 10BaseT) and thin coax (also known as 10Base2).
Unshielded Twisted Pair (UTP) Cable
Twisted pair cabling comes in two varieties: shielded and unshielded. Unshielded
twisted pair (UTP) is the most popular and is generally the best option for school
networks (See fig. 1). This cable looks like ordinary telephone wire, except that it
has 8 wires inside instead of 4.
It consists of two insulated copper wires arranged in a regular spiral pattern to
minimize the electromagnetic interference between adjacent pairs. It is a low
frequency transmission medium.
This cable is the most popular and is generally the best option for school
networks, because of its low cost and easy installation. It is also ideal for short
distance, usually less than 100 meters.
Fig 4a: Cat5e Cable and a close up of RJ-45 connector
Fig 4c: Cat5e Patch Panel
Fig 4b: Cat5e Wall Outlets
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Fig4d: Wall Mounted Cabinet
Categories of Unshielded Twisted Pair
Type
Category 1
Category 2
Category 3
Category 4
Category 5
Use
Voice Only (Telephone Wire)
Data to 4 Mbps (LocalTalk)
Data to 10 Mbps (Ethernet)
Data to 20 Mbps (16 Mbps Token Ring)
Data to 100 Mbps (Fast Ethernet)
10BaseT cabling is available in different grades or categories. Some grades, or
"cats", are required for Fast Ethernet networks, while others are perfectly
acceptable for standard 10Mbps networks--and less expensive, too. All new
networks use a minimum of standard unshielded twisted-pair (UTP) Category 5e
10BaseT cabling because it offers a performance advantage over lower grades.
The standard connector for UPT cable is an RJ-45 connector, which looks like a
large telephone modular connector
Coaxial (Coax) Cable
Thin coax looks like the copper coaxial cabling that's often used to connect a
Video Recorder to a TV.
It has an inner conductor surrounded by a braided mesh. Both conductors share a
common center axial, hence the term "co-axial". It can support a size of
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bandwidth of up to 400 Mhz and can be used for distances between 300 and 600
meters. Its major advantage is that it is highly resistant to signal interference. Its
major disadvantage is that it is quite bulky and sometimes difficult to install.
The most common type of connector used with coaxial cables is the BNC
(Bayone-Neill-Concelman) connector, which is shown in fig …. below.
There are two types of coaxial cable namely thin coaxial
which is also referred to as thinnet and thick coaxial which
is also referred to as thicknet
.
The 10Base2 is the IEEE standard for Ethernet running on
thin coaxial cable. The 2 refers to the approximate
maximum segment length being 200 meters. This is
popular in school networks, especially linear bus networks.
The IEEE standard for Ethernet running on thick coaxial cable is 10Base5. The 5
refers to the approximate maximum segment length being 500 meters. Thicknet
has an extra protective plastic cover that helps keep moisture away from the
center conductor. Its major disadvantage is that it is difficult to bend and install.
Fibre Optic
Fibre optics consists of a center glass core surrounded by several layers of
protective materials. Fibre optic’s major advantage is that it is immune to
environmental interference and has a greater capacity (bandwidth of up to 2 Gbps)
It is used for distances up to 100 kilometers and carries information at vastly
greater speeds. It is also very small and lighter in weight than other media.
Its major limitation is that it is very expensive. It is difficulty to install, hence
requires highly skilled installers and modifiers. Even with highly skilled personal
adding additional nodes is difficult.
Network media access methods
How computing devices access the network cable and send data is known as the
media access method. There are four commonly used media access methods:
Ethernet, Token Ring, Local Talk, and FDDI.
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Ethernet
Ethernet is the most popular media access method which can allow for linear bus,
star, or tree topologies. It use access method called CSMA/CD (Carrier Sense
Multiple Access/Collision Detection). It is able to transmit data over UTP, thincoaxial, thick-coaxial and fiber optic cables at rates of 10 Mbps. Fast Ethernet
supports 100 Mbps, but requires faster hubs and network interface cards
Token Ring
Token ring was developed by IBM in the mid 1980s. It uses a star-wired ring
topology over shielded and unshielded twisted-pair wiring. A central hub
(referred to as a "MAU" Multi-station Access Unit) is at the center of the ring.
There are two versions of Token Ring, namely 4 Mbps and 16 Mbps. They both
use a token passing process to circulate packets around the ring. These are more
expensive than Ethernet, but are a good option for PC networks.
Local Talk
Local talk was developed by Apple Computer, Inc. for Macintosh computers and
is best suited to small networks of Macs. It allows for linear bus, star, or tree
topologies using twisted pair cable and can connect up to 32 devices (computers,
printers, and file server). Local talk uses the CSMA/CA (Carrier Sense Multiple
Access with Collision Avoidance) process for transmitting data. A single network
can be up to 300 meters. Its major disadvantage is that it is slow, transmits data at
only 230 Kbps.
FDDI (Fiber Distributed Data Interface)
FDDI uses fiber optics for speeds of up to 100 Mbps. The system is used
primarily to interconnect two or more LANs, often over long distances. It
employs the token ring passing process to transmit data; but use a dual counterrotating ring topology, meaning there are two rings of cable with two tokens
circulating in opposite directions.
Wireless
Not all networks are connected with cabling; some networks are wireless. The
term 'wireless network' refers to two or more computers communicating using
standard network rules or protocols, but without the use of cabling to connect the
computers together. Wireless LANs use high frequency radio signals, infrared light
beams, or lasers to communicate between the workstations and the file server or
hubs. Each workstation and file server on a wireless network has some sort of
transceiver/antenna to send and receive the data. Information is relayed between
transceivers as if they were physically connected. For longer distance, wireless
communications can also take place through cellular telephone technology,
microwave transmission, or by satellite.
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Fig 7b: Desktop PC Wireless LAN card
Fig 7c: Laptop PC Wireless LAN card
A wireless local area network (WLAN) consists of two key components: an
access point (also called a base station) and a wireless card. Information can be
transmitted between these two components as long as they are fairly close
together (up to 100 metres indoors or 350 metres outdoors). The types of infrared
communications that we could use in schools are line-of-sight and scattered
broadcast. Line-of-sight communication means that there must be an unblocked
direct line between the workstation and the transceiver. If a person walks within
the line-of-sight while there is a transmission, the information would need to be
sent again. This kind of obstruction can slow down the wireless network.
Scattered infrared communication is a broadcast of infrared transmissions sent out
in multiple directions that bounces off walls and ceilings until it eventually hits
the receiver. Networking communications with laser are virtually the same as
line-of-sight infrared networks.
Wireless LANs have several disadvantages. They provide poor security, and are
susceptible to interference from lights and electronic devices. They are also
slower than LANs using cabling.
Advantages of a Wireless LAN
Wireless LANs have advantages and disadvantages when compared with wired
LANs. A wireless LAN will make it simple to add or move workstations, and to
install access points to provide connectivity in areas where it is difficult to lay
cable. Temporary or semi-permanent buildings that are in range of an access point
can be wirelessly connected to a LAN to give these buildings connectivity. Where
computer labs are used in schools, the computers (laptops) could be put on a
mobile cart and wheeled from classroom to classroom, providing they are in range
of access points. Wired network points would be needed for each of the access
points.
The installation of cables is time consuming and expensive. The advantages of not
doing so are apparent:
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the amount of work required and the time taken to complete it are
significantly reduced
the network is accessible in places where wiring would have been difficult
or impossible
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with no cables linking computers together, cable-related faults and
network downtime are minimised
Where a wireless network is in place, teachers or students can have
continuous access to the network, even as they move with their equipment
from class to class.
The space over which a wireless network operates is not planar but
spherical. Therefore, in a multi-level site, network access is available in
rooms above or below the access point, without the need for additional
infrastructure.
In a location within a school where network access is required
occasionally, desktop computers fitted with wireless network cards can be
placed on trolleys and moved from location to location. They can also be
located in areas where group work is taking place. As they are connected
to the network, documents and files can be shared, and access to the
Internet is available, enhancing group project work.
As the range of the wireless network extends outside the building, students
and teachers can use wireless devices to gather and record data outside,
e.g., as part of a science experiment or individual performance data as part
of a PE class.
Below are some specific advantages of a WLAN:
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It is easier to add or move workstations
It is easier to provide connectivity in areas where it is difficult to lay cable
Installation can be fast and easy and can eliminate the need to pull cable
through walls and ceilings
Access to the network can be from anywhere in the school within range of an
access point
Portable or semi-permanent buildings can be connected using a wireless LAN
Where laptops are used, the ‘computer suite’ can be moved from classroom to
classroom on mobile carts
While the initial investment required for wireless LAN hardware can be
similar to the cost of wired LAN hardware, installation expenses can be
significantly lower
Where a school is located on more than one site (such as on two sides of a
road), it is possible with directional antennae, to avoid digging trenches under
roads to connect the sites
In historic buildings where traditional cabling would compromise the façade,
a wireless LAN can avoid drilling holes in walls
Long-term cost benefits can be found in dynamic environments requiring
frequent moves and changes
They allows the possibility of individual pupil allocation of wireless devices
that move around the school with the pupil.
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Disadvantages of a WLAN
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As the number of computers using the network increases, the data transfer rate to each
computer will decrease accordingly
As standards change, it may be necessary to replace wireless cards and/or access points
Lower wireless bandwidth means some applications such as video streaming will be more
effective on a wired LAN
Security is more difficult to guarantee, and requires configuration
Devices will only operate at a limited distance from an access point, with the distance
determined by the standard used and buildings and other obstacles between the access
point and the user
A wired LAN is most likely to be required to provide a backbone to the wireless LAN; a
wireless LAN should be a supplement to a wired LAN and not a complete solution
Long-term cost benefits are harder to achieve in static environments that require few
moves and changes
It is easier to make a wired network ‘future proof’ for high data transfer.
Network Topologies
Networks have a physical and a logical topology. In this section the physical
topology of a network is discussed. The physical topology of a network refers to
the configuration of cables, computers, and other peripherals. Physical topology
should not be confused with logical topology which is the method used to pass
information between workstations.
Main Types of Physical Topologies
The physical topologies that are commonly found in computer networks are:
 Linear Bus
 Star
 Star-Wired Ring
 Tree
 Considerations When Choosing a Topology
 Summary Chart
Linear Bus (Trunkline)
A linear bus topology consists of a main run of cable with a terminator at each
end (See fig. 4.1). All nodes (file server, workstations, and peripherals) are
connected to the linear cable.
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It is easy to connect a node to a linear bus and less expensive since network
structure requires less cable. Its major disadvantage is that the entire network
shuts down if there is a break in the main cable and it is difficult to identify the
problem if the entire network shuts down.
Advantages of a Linear Bus Topology
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Easy to connect a computer or peripheral to a linear bus.
Requires less cable length than a star topology.
Disadvantages of a Linear Bus Topology
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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.
Not meant to be used as a stand-alone solution in a large building.
Star
A star topology is designed with each node (file server, workstations, and
peripherals) connected directly to a central network hub or concentrator (See fig.
5.2). A separate cable connects to each computer, and if one cable breaks, only a
single computer should be affected. The hub or concentrator manages and controls all
functions of the network. It also acts as a repeater for the data flow.
Data on a star network passes through the hub or concentrator before continuing
to its destination. The hub or concentrator manages and controls all functions of
the network. It also acts as a repeater for the data flow. This configuration is
common with twisted pair cable; however, it can also be used with coaxial cable
or fiber optic cable.
Advantages of a Star Topology
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Easy to install and wire.
No disruptions to the network then connecting or removing devices.
Easy to detect faults and to remove parts.
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Disadvantages of a Star Topology
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Requires more cable length than a linear topology.
If the hub or concentrator fails, nodes attached are disabled.
Star Wired Ring (Token Ring)
Star wired ring (Token ring) network was developed by IBM for IBM-compatible
computers. It employs a special coded message called a token that the operating
software passes in sequence to each computer on the network. It has a bandwidth
capacity of 4 or 16 Mbps using twisted pair cables.
Daisy-Chain
The Daisy-Chain network is similar to a bus, except the electrical signal is routed
through each computer as it moves along the line. Thus it is not practical in multiroom network installations. It is mainly used on the Macintosh network. Its major
advantage is that it is easy to install. The entire network shuts down if there is a
problem on a node. The Daisy-Chain network is very slow.
19
Wireless Network Configurations
Wireless networks can be configured in an ad hoc/peer-to-peer arrangement or as
a local area network.
Ad Hoc/Peer-to-Peer Configuration
This is the most basic wireless network configuration. It relies on the wireless
network adapters installed in the computers that are communicating with each
other. A computer within range of the transmitting computer can connect to it.
However, if a number of computers are networked in this way, they must remain
within range of each other. Even though this configuration has no real
administration overhead, it should only be a consideration for very small
installations.
The Internet
What is the Internet?
The Internet which is also known as the Net is simply a network of networks. It is
a world wide computer network that interconnects computer networks across
countries.
A network is a group of computers that are connected so that they can share
information. The computers are linked together through high speed telephone
wires, satellite and any other telecommunication system such as cable networks.
All computers on the Internet communicate with one another using the
Transmission Control Protocol/Internet Protocol suite, which is commonly
abbreviated to TCP/IP.
As a network of networks, the Internet allows people on one network to share
information with people on another network that may be thousands of miles away.
Through the Internet, one has access to a wide variety of services which
include :
 vast information resources,
 interactive collaboration tools,
 multimedia displays,
 real-time broadcasting,
 shopping opportunities,
 and much more.
These services are available through the:
 World Wide Web,
 electronic mail (email),
 file-transfer between any two computers and,
 remote access to a computer connected to the Internet.
20
What is needed to connect to the Internet
The minimum set of requirements to connect to the Internet is: a computer
attached to an Internet entry point (a service provider) via a telecommunication
link such as the telephone line and a modem. These are discussed in detail below.
Internet Service Providers
An Internet Service Provider (ISP) is a company that gives you access to the
Internet. In Zimbabwe the common ISPs are ComOne, ZARNet, AfricaOnline,
Ecoweb, ZOL , PowerTEL and many others. You sign up for an Internet access
account through your selected ISP. Once you sign up for a dial-up account with
an ISP, you will be able to communicate through the Internet and use the services
offered, such as email and Internet access. Your ISPs can also provide you with
numerous other Internet related services, such as domain name registration and
website hosting.
Modem
When you are connecting through a telephone link, a modem is required. The
modem must be connected to a telephone line to dial up your ISP’s computer
network. A modem (MODulator - DEModulator) is a device that translates
digital (numerical) signals from your computer into analogue signal (sounds) that
are acceptable for an ordinary telephone line. A modem could be internal, that is,
attached on the computer’s motherboard or connected external through a
communication port on your computer.
To connect to the Internet using a dial-up connection you need a modem with a
speed of 56 Kbps modems, which is the maximum for an ordinary telephone line.
The speed at which data circulates through the modem and the telephone line is
called bandwidth. The first modems had very low bandwidth of 300 to 1200 bit
per second (bps). Today, even 14.4 Kbps (kilobit per second) and 28.8 Kbps
modems have become obsolete.
21
Telecommunication link
A telecommunication link such as the telephone, satellite, fibre optics is required
for connecting to the Internet. For a dial-up connection, a telephone link is
required. When you dial to link your computer to the ISP network, your computer
is connected to the Internet. As with ISP, your telephone services provider will
offer many different plans and charging systems from flat rates to blocks of time.
You must find the plan that works best for you according to prices that are offered
and your specific needs.
It is always better to connect to the Internet on a direct telephone line through an
automatic connection system because the quality of the line is very important.
However, some technical solutions can correct mistakes and remove noise and
disturbances. When the Internet entry point is in your local area, you will not need
to pay for an intercity or trunk call, but for a local call. In Zimbabwe we dial 041
as the local call to connect to the Internet. This Internet connection will provide
you with access to the entire world through your local connection. Please note that
you are responsible for paying the telephone bill for the time you will be
connected to the Internet.
Other types of telephone connection are dedicated lines, and the Integrated
Services Digital Network (ISDN)
Dedicated lines
A dedicated line is a telecommunication path between two points that is available
24 hours a day for use by a designated user. A dedicated line is rented from a
telephone company, in which case it is called a leased line. Thus unlike dial-up
lines, it is not shared in common among multiple users. In this type of connection,
you will pay the agreed rate to ISP, but you do not pay additional costs for the
time spent while surfing the Internet. Such lines are ideal for schools and colleges
where the Internet is need throughout the day.
Integrated Services Digital Network (ISDN)
Using an Integrated Services Digital Network (ISDN) adapter, instead of a
conventional modem allows the transmission of data on an ordinary telephone
wire at a much higher speed. When you connect using an ISDN adapter in place
of a modem, you can access highly graphic webpages with easy and at a fast
speed of up to 128 Kbps.
This new technology is not readly available in many developing countries. Since
ISDN requires adapters at both ends of the transmission, your access provider also
needs an ISDN adapter. So before you make the decision to install an ISDN
adaptor you must check if your ISP has one. In some countries, ISDN is available
from phone companies in urban areas.
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The web browser
In addition to the things listed above, there are a number of pieces of software that
works together to connect us to the Internet. One such software is the Internet
browser. The browser helps us to locate websites and allows us to maneuver
around or surf the World Wide Web as we view web pages. The two most
frequently used graphic browsers are Microsoft's Internet Explorer, and America
Online (AOL)'s Netscape Navigator. Before these graphic browsers were in use,
Mosaic and Lynx were the most popular browser and these are still available for
text browsing.
Internet Services
On the Internet we have access to a wide variety of services. In this section were
are going to discuss, a few of these services, namely, the World Wide Web
(WWW), electronic mail (e-mail), file transfer protocol (FTP) and UseNet news.
Electronic Mail
Electronic mail (e-mail) refers to the sending of digitally encoded messages
through the network. Electronic mail is one of the fastest and easiest ways of
sending electronic messages from one person to another or to a group. Email
systems enable us to conveniently and quickly send a message to many people at
one time. Messages sent through e-mail can arrive within a matter of seconds.
Although email is used primarily for sending written messages, we can also send
and receive pictures, sounds and video images as attachments to the text message.
These files are referred to as MIME attachments. MIME stands for Multimedia
Internet Mail Extension. This technique was developed to help e-mail software
handle a variety of file types. For example, a document created in Microsoft Word
can be attached to an e-mail message and retrieved by the recipient with the
appropriate e-mail program.
They are basically two types of e-mail accounts, these are, the one we can be
given by our Internet Service Provider (ISP) and the one we can get free from the
Internet. The email account we can obtain from the ISP is some times called the
computer-based account. Computer based accounts have the advantage that
students can downloads all their messages to read and respond to them offline.
That is when they are not connected to the Internet. Students can only connect to
download or post their messages. This saves on the telephone bill if the
connection is a dial-up connection. The Internet based email account is sometimes
known as web-based account. Web based email accounts are usually free of
charge and they are available from a number of providers on the Internet. These
include yahoo mail, Hotmail, Gmail and many others. The major advantage of
web-based mail is that students can easily gain access from any computer with
Internet access.
The World Wide Web
23
The World Wide Word (WWW) or simply the Web is another commonly used
Internet service. The World Wide Web is a system of Internet servers that
supports hypertext to access several Internet protocols on a single interface. It
provides Internet users with a uniform and convenient means of accessing a wide
variety of resources including pictures, text, sound and video, available on the
Internet. It provides a vast array of experiences including multimedia
presentations, real-time collaboration, interactive pages, radio and television
broadcasts. Both the teacher and the learner can retrieve documents, view images,
animations and videos, listen to sound files, speak and hear voices through the
Web.
The information is found on files called web pages or web sites. A web site is a
set of interlinked files on a web server computer. Each website has an address,
known as a “URL,” that locates it on the internet. Websites are typically
organized around a “home page” that serves as the entry point to other pages.
Websites can present information in words, pictures and sounds, and they can
enable us to exchange information with our students.
A web page is written in a special programming language called hypertext mark
up language (HTML) and its filename ends with file extension html. Hypertext is
basically a document containing words that connect to other documents. The
principle of hypertext is that one text or web page can refer to or point to another
web page, either on the same website or another website somewhere else in the
world. Thus it is easy for the web pages to link to another web page on the same
computer or different computers, anywhere on the Internet. The pages are linked
by special links called a hyperlinks. The hyperlink can be taken as a method of
instant cross-referencing of information on web. A hyperlink is shown by a
coloured and underlined stretch of text or graphic image where the shape of the
cursor changes to a pointing hand. These words are called links and are selectable
by the user. In some cases hyperlinks take the form of buttons, images, or portions
of images that are clickable. A single hypertext document can contain links to
many documents. When you select one of these words or phrases, you will be
transferred to the site or page that is linked by the word or phrase.
How to Access the World Wide Web
For you to access the World Wide Web a Web browser is required. A browser is a
software program that allows users to access and navigate the World Wide Web.
There are two types of browsers, namely graphical and text browsers. These are
explained in detail below.
Text Browsers
Text browsers, such as Lynx provide access to the Web in text-only mode.
Navigation is accomplished by highlighting emphasized words on the screen with
the up and down arrow keys, and then pressing the forward arrow or the Enter key
24
to follow the link. Today, these browsers are fast loosing their popularity due to
the development of more user friendly graphical browsers.
Graphical Browsers
A graphical browser such as Internet explorer, Netscape Navigator, Mozilla and
opera, enable us to retrieve text, images, audio and video. These browsers are
available for Windows, Apple, Linux and other operating systems. Navigation is
accomplished by pointing and clicking with a mouse on highlighted words and
graphics.
Browser buttons
Address bar
Back
Forward
Home
Refresh
Stop
Scroll bar
Homepage
Location on the browser where one enters addresses to web sites. The
address bar is usually located on the top of the screen and it written
“address.”
Clicking this button brings you back to a previous screen. The back button is
located in the upper left hand corner of the screen.
Clicking on the “Forward” button brings you to a page that you viewed
earlier
Clicking on “Home” on the top of the screen brings you to the home location
to which the computer is set. Computers can be and are set to open to
different Web site addresses.
Clicking on “Refresh” reloads an expired page or a page that has timed out.
Clicking this button stops the computer from loading a new page.
The vertical gray space on the right and the horizontal gray space on bottom
of the browser screen allows you to view parts of a Web page that do not fit
inside the screen. When you cannot see the entire Web page, use the small
box or the small arrows to move the page up and down, left and right.
Refers to the beginning page of a Web site. This page will link to other
information found within the Web site as well as outside of the Web site.
A Note on Clicking
Clicking
Double
clicking
Drop down
menu
Link
Use one quick (left) mouse click to open up a link or to darken (highlight) the
address bar to type in a new web address.
Use two quick (left) mouse clicks to open up a program on your screen (such as
Microsoft Word, Internet Explorer, etc.). Programs are usually represented by
symbols known as icons.
Clicking on a drop down menu reveals links. These menus are recognized by a
small downward pointing arrow
Links are found on nearly all Web sites and take you from one part of the Web
site to another (usually referred to as another “page”). Links can also take you
to a completely different Web site. Links may be text (often underlined and
colored blue) or a picture.
When using a mouse, the arrow becomes a hand when it is placed over a link.
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Telnet
Telnet is one of the services available on the Internet. Telnet allows the user to log
onto computers on the Internet and use online databases, library catalogs, chat
services, and more. The major disadvantage of Telnet is that there are no graphics
in Telnet sessions. The most common Internet based resources available through
Telnet are library catalogs, although most catalogs are now migrating to the Web.
As the Web gains more popularity, Telnet is less frequently used as a means of
access to information on the Internet, thus why most library catalogues are now
migrating to the web.
A Telnet program must be installed on your local computer and configured to
your Web browser in order to work. To Telnet to a computer, you must know its
address. The addresses may consist of words (msu.ac.zw) or numbers (10.10.1.8).
File Transfer Protocol (FTP)
FTP stands for File Transfer Protocol. This is both a program and a method used
to transfer files between computers. FTP is used primarily as a tool to efficiently
uploading and downloading files on the Internet. FTP sites contain books, articles,
software, games, images, sounds, multimedia and many other forms of
information. FTP transfers can also be performed on the World Wide Web
without the need for special software. Programs such as WS_FTP for Windows
can be used to conduct a file transfer. FTP files can also be retrieved via search
engines such as FtpFind, with URL http://www.ftpfind.com. This option is easiest
because one does not need to know FTP program commands. The Web browser is
sufficient to carry out the process. In fact every time we download software from
a Web site to our computer, we will be using FTP.
26
StudyUnit
5
THE ROLE OF INFORMATION AND COMMUNICATION
TECHNOLOGIES IN BUSINESS
Introduction
Businesses rely on information because it allows them to make decisions.
Incorrect decisions can be fatal and reliable information is therefore of critical
importance.
The output of information systems consists of information, which is made
available to users who then base their decisions on it .This study unit will look at:
 Who these users are
 And why these users need the information that they need
END USERS OF INFORMATION
 External users
 Internal users
TYPES OF INFORMATION SYSTEMS
 Transaction processing systems
 Management information systems
 Decision support systems
 Executive information systems
 Expert information systems
USES OF INFORMATION SYSTEMS
They help an organisation to maintain an advantage over its competitors by
offering new services to clients before competitors can and by improving the cost
and quality of existing services.
IMPACT OF INFORMATION AND COMMUNICATION TECHNOLOGIES
 Increasing use of the internet, e-mail, and e-commerce
 Has also led to the development of new legislations to govern the use and
conduct of users of these technologies
 In the work environment , computers have led to the following
27

 Reduced need to follow chain of command
 Information overload
 Retraining of staff
 Closer business relationships
 Working from home
 Human computer interface
Effects of technology on the workforce
OPPORTUNITIES, ADVANTAGES AND RISKS OF USING COMPUTERS IN
BUSINESS
 Information technologies have allowed people around the globe to be able
to trade with each other any time of the day and year.
 Business opportunities are now unlimited but they bring with them new
risks and threats.
FURTHER STUDY
Read
from
ISSABE,
Chapter
28
8
(para
8.5.5)
29
 Study unit
Study
Unit
6
1


THE MANAGEMENT OF INFORMATION SYSTEMS
Introduction
Because of the rapid developments in the field of information
technology, it must be managed effectively. Management should be
carefully plan hoe to handle the information systems.
Such a plan is called a strategy. An organisation that does not have an
information systems strategy is like a rowing boat adrift a big ocean.
The information strategy
Information systems are critical for the success of many organisations
and hence the need to have a well organised information management
system in place. This need also stems from the following:
 The high costs involved in acquiring and maintaining information
systems
 The increased levels of customer service due to the use of
information systems
 The achievement of competitive advantage
 The improved quality of information that can impact on the
quality of decisions taken by management.
30
The formulation of an information systems Plan
 Strategic analysis using critical success factors
This involves analysis of small numbers of key and vital goals that
are vital for the success of an organisation.
SWOT Analysis
An organisation must analyse its internal environment
31
Study unit
7
DEVELOPING NEW INFORMATION SYSTEMS
Introduction
This study unit presents an overview of the main stages involved in the
development of information systems. There are a number of ways by
which an information system can be developed. The choice of a
particular method depends on the specific characteristics of the
development project such as
 The size
 Scope
 Limitations
 Time scale
 And the user’s specifications
One of the more popular methods is the systems development life cycle
(SDLC).This model is based on a logical step-by-step approach to
system development
There are other strategies that an organisation could use if it doesn’t
want to develop the new system on its own. These will be discussed later
in the study unit as well.
Reasons why systems get obsolete or become outdated
1. The rapidly changing technological environment
2. Changing output needs of the information system
The Systems Development Life Cycle
32
The phrase “systems development” covers the development of
computer systems from the initial idea through to the eventual
installation of working systems
 The development of particular system is carried out by a
project team which will consist of:
 Users
 Managers
 Data processing staff consisting of systems analysts,
programmers and database analysts
All projects to develop information systems go through a number of
stages known collectively as the Systems Development Life Cycle
(SDLC).The SDLC is an example of a systems development
methodology.
A methodology is simply a collection of stages, procedures and
techniques to assist systems developers in the construction of new
information systems. It is the segmenting of projects which allows
managers to verify the successful completion of project phases before
allocating resources to subsequent phases.
A disadvantage of this model is that it does not guarantee the optimal
use of human resources, because each stage deends on the successful
completion of the previous stage.It alsdo focuses primarily on project
organisation, rather than meeting the users’ needs.
The stages in the SDLC and their respective end products are:
1. Project Definition
The result is statement of scope and objectives
2. Feasibility study
Result is the Feasibility report
3. Systems Analysis
Result is a detailed requirements specifications report
4. Systems Design
Result is Systems specification
5. Programming
Result is a Program specifications and Program code
6. Implementation
Result is a live system
33
FURTHER STUDY
 What is involved at each stage of the SDLC
 Why it is important to involve the user during each stage of the
SDLC
ALTERNATIVE WAYS OF DEVELOPING OR ACQUIRING
INFORMATION SYSTEMS
There are disadvantages in using structured system analysis and design
methods when developing information systems and for this reason one
may choose to use alternative methods. The information system does
not to be developed by the organisation itself.
Please read ISSABE, Chapter 10 ( Para 10.4) paying particular attention to the
following:









Off the shelf software packages
Prototyping (modelling)
Application development tools
Software houses/ bureaus
End-user development
Outsourcing
Re-engineering of business processes
Joint applications development
Rapid applications development
34
Study unit
8
Information System Controls
Introduction
An organisation’s protection of its information-based
assets is now seen as an important and real challenge.
The violation of privacy and the illegal use of
information systems to commit crime or to bring about
economic loss to a third party have a number of legal
and financial implications. Most common threats that
exist include:
 Errors of omission at data input/entry
 Fraud by theft
 Disgruntled employees
 Physical and infrastructure threats
 Malicious hackers
 Industrial espionage
 Unauthorised and inappropriate use of information
systems
 Employee lack of know-how on use of information
technologies.
35
COMPUTER CRIME
Computer crime includes criminal activities of a
traditional nature, such as theft, fraud, forgery and
mischief. In summary the types of Computer Crimes
are:
 Fraud by computer manipulation
 Computer forgery
 Damage to or manifestation of computer data or
programs
 Unauthorised access to computer systems and
services
 Unauthorised reproduction of legally protected
computer programs.
 Introduction of malicious programmes/ viruses
 Computer hacking
DATA SECURITY
This refers to measures that are meant to reduce
unauthorised access to, use and destruction of an
organisation’s data and data resources.
Threats to security come from outside (external) and
inside (internal) the organisation.
Securing data entails making sure that the computers are
in the right environment, there are right software
measures to reduce loss or theft of data.
Security of Equipment
This entails the need to look after the computer
hardware well to avoid loss of data or the computers
themselves. These include
36
 Ventilation
A good room has to be adequately ventilated.
If ventilation is poor the computer may over
heat and thus fail to operate properly.
 Power supply
Should be of the right voltage and supplied
from safe socket outlets
 Use of Uninterrupted Power Supplies (UPS)
 Carpet
These are good dust absorbers. Fust interferes
with the operation of electronic equipment.
 Curtains
They reduce the amount of light an heat
getting to the computer screens.
 Lockable doors
 Metal bars and shutters
This reduces unauthorised access
 An alarm system
This may help warn of an intrusion
 ID badges
They limit access to the room to authorised
individuals only
 Security guards
 Attach computers permanently to the desks using
clamps to avoid theft of the computers
 Have all equipment serial numbers for use if
equipment is stolen.
 Have fire fighting systems in place to deal with any
risks of fire to the equipment.
37
Security of Data
Data itself is at risk of accidental or deliberate loss and
theft.
Accidental loss may occur this way
 Document may be accidentally deleted
 Computer breaks down or power fails
 File or disk becomes corrupted
 File is is destroyed by fire or flood
To reduce the risk of loss there is the use of back-up of
data. Best way to keep backups is to make sure that a
copy is kept on a different medium and in a different
place.
Deliberate damage is loss of data by viruses or hackers.
Computer Virus
A virus is a harmful program that copies itself onto
other programs and destroys them or interferes with
their proper functioning. To reduce the risk of virus
infections, the following may be effective:
 Use anti-virus software
 Use genuine software
 Write protect all software programs
 Make regular back-ups
38
CONTROLS
A security policy should clearly state what controls need
to be implanted to limit computer crime. This policy
should be revised regularly to determine whether the
organisation’s confidentiality and integrity are still
protected.
Controls are usually categorized as:
 Preventative
These are designed to prevent unauthorised
or invalid data entries
 Detective
These help to identify unauthorised or invalid
entries
 Corrective
These assist in recovering from unwanted occurrences
Typical control mechanisms that maybe included in
such a policy are:
APPLICATION CONTROLS and CONTROL STANDARDS
Application controls include policies and procedures
associated with user activities and the automated
controls designed into applications. Application controls
are categorized as follows:
 Input controls
These help ensure employees accurately input
information, systems properly record input,
and systems either reject or accept and record,
input errors for later review and correction.
 Database and file controls
39
 Processing controls
They help ensure systems accurately process
and record information and either reject, or
process and record, errors for later review and
correction. Processing includes merging files,
modifying data, updating master files and
performing file maintenance.
 Output controls
They help ensure that systems securely
maintain and properly distribute processed
information.
Controls should be in place to address both batch and
on-line environments. Standards should address
procedures to ensure management appropriately
approves and control overrides.
OPERATIONAL CONTROLS and STANDARDS
Please read ISSABE Chapter 11 ( Para 11.4- 11.4.3.2.4)
40