Download Chapter 03 - Hailey College of Commerce

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A computer network, often simply referred
to as network, is a collection of computers
and devices connected by communications
channels that facilitates, communications
among users and allows users to share
resources with other users .
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File Sharing
Software Cost & Management
Text Communication
Voice Communication
Secure Data Access (Security)
Resources Sharing such as
◦ scanners, fax machines and printers etc.
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Workgroup Computing
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A path through which data is transmitted from one place to
another place is called transmission media or channel.
◦ Wired / Guided Medium
 In this medium devices are directly connected with each other using
physical media like wires. Such as:
Twisted pair cable, Coaxial Cable, Optical Fiber Cable
◦ Wireless / Unguided Medium
 In this medium devices are directly connected with each other through air
using signals/waves Examples:
 Communications Satellites
 Cellular Systems
 Wireless LANs,
 Bluetooth
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All networks are made up of basic hardware building
blocks to interconnect network nodes, such as:
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NICs Cards
Bridges
Hubs
Switches
Routers
Repeaters
Gateway
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Coaxial Cable - Cable consisting of a single copper conductor in the center surrounded
by a plastic layer for insulation and a braided metal outer shield.
Fiber Optic Cable - A cable, consisting of a center glass core surrounded by layers of
plastic, that transmits data using light rather than electricity. It has the ability to carry
more information over much longer distances.
Twisted Pair - Network cabling that consists of four pairs of wires that are manufactured
with the wires twisted to certain specifications. Available in shielded and unshielded
versions.
Terminator - A device that provides electrical resistance at the end of a transmission
line. Its function is to absorb signals on the line, thereby keeping them from bouncing
back and being received again by the network.
Token - A special packet that contains data and acts as a messenger or carrier between
each computer and device on a ring topology. Each computer must wait for the
messenger to stop at its node before it can send data over the network.
Token Ring - A network protocol developed by IBM in which computers access the
network through token-passing.
Backbone - A cable to which multiple nodes or workstations are attached.
Connector - Standard connectors used to connect coaxial/Fiber Optic / Twisted Pair
cables.
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Local-Area Network
(LAN)
Campus-Area Network
(CAN)
Personal-Area Network
(PAN)
Metropolitan-Area Network
(MAN)
Wide-Area Network
(WAN)
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A LAN (Local Area Network) is a group of
computers and network devices connected
together, usually within the same building.
Data rates are much higher with low error
rates. LANs are designed to share resources
between personal computers or work
stations. LANs are distinguished by their
Sizes, Transmission Media (by twisted-pair
wire, coaxial cables, or fiber optic cables),
Topology (Bus, star, Ring, mesh etc.)
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Networking spanning with multiple LANs but
smaller than a Metropolitan area network,
MAN.
This kind of network mostly used in relatively
large universities or local business offices and
buildings.
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Personal area networks can be constructed
with cables or wirelessly. USB/WI-FI(
Ptcl,wi-tribe, ufone, warid, wateen.) , Broad
Band (Ptcl, World Call, Wateen)
technologies often link together a wired
PAN. While wireless PANs typically use
Bluetooth or sometimes infrared
connections. Personal area networks
generally cover a range of less than 10
meters.
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MAN consists of a medium size geographical
area. The scope of the MAN is always a city
,town or any two or three near by cities.
Common example is Cable TV Network. A
company can use a MAN to connect to all of
its offices/branches throughout a city.
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This is the world-wide network of computers
accessible to anyone who knows their
Internet Protocol (IP) address. The IP address
is a unique set of numbers (such as
207.46.222.30) that defines the computer's
location. Most will have accessed a computer
using a name such
as http://www.hailey.tech.officelive.com.
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Topology refers to the physical or logical
arrangement of a network. A network
topology is how computers, printers, and
other devices are connected over a network.
For example, devices can be arranged in a
ring or in a straight line (bus topology) or
Mesh or Star.
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In a mesh topology, every device has a dedicated
point to point link to every other device.
To connect n devices, we require n(n-1)/2 physical
links .Example: (5 Pc’s) 5(5-1)/2=10 wires .
Advantage & Disadvantages
The use dedicated links guarantees that each
connection can carry its own data load. It provides
privacy and security. The mesh topology is robust.
The main disadvantage is related to the amount of
cabling and the number of Input/output ports
required (For example a pc required more than one
Lan Card (Ethernet Card)).
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In a star topology, each device has a dedicated
point to point link only to a central controller.
A star topology is designed with each node (file
server, workstations, and peripherals) connected
directly to a central network hub or switch.
Data on a star network passes through the hub or
switch before continuing to its destination.
The hub or switch 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.
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Advantages & Disadvantages:
◦ A star topology is less expensive than mesh
topology.
◦ Each device needs only one link and one
Input/output port to connect with other device.
◦ The star topology is robust.
◦ Entire network shuts down if there is a break in the
hub/switch.
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A bus topology is a multipoint topology in which one long
cable acts as a backbone to link all the devices in the
network.
If you need help remembering how the Bus Topology
operates, think of it as the route a bus takes throughout a
city.
It is extremely important to note that both ends of the main
cable need to be terminated.
If there is no terminator, the signal will bounce back when it
reaches the end.
The result: a bunch of collisions and noise that will disrupt
the entire network.
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Advantages & Disadvantages
Easy to connect a computer to a bus topology .
Requires less cable length than a star topology
Ease of installation.
Uses less cabling than mesh or a star.
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
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In a ring topology, each device has a
dedicated point to point connection only
with two devices on either side of it. Note
that since there is no end on a Ring
Topology, no terminators are necessary.
A frame (contain data) travels along the
circle, stopping at each node
(computer/device). If that node wants to
transmit data, it adds destination address
and data information to the frame. The
frame then travels around the ring,
searching for the destination node. When
it’s found, the data is taken out of the
frame and the cycle continues.
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Advantages & Disadvantages:
Easy to install and reconfigure.
Unidirectional traffic can be disadvantages.
Entire network shuts down if there is a break
in the main cable
The five main components of data communication system are:
1. Message - It is the information to be communicated. Popular forms
of information include text, pictures, audio, video etc.
2. Sender - It is the device which sends the data messages. It can be a
computer, workstation, telephone handset etc.
3. Receiver - It is the device which receives the data messages. It can
be a computer, workstation, telephone handset etc.
4. Transmission Medium - It is the physical path by which a message
travels from sender to receiver. Some examples include twisted-pair
wire, coaxial cable, radiowaves etc.
5. Protocol - It is a set of rules that governs the data communications.
It represents an agreement between the communicating devices.
Without a protocol, two devices may be connected but not
communicating. For example a person whose mother language is Urdu
cannot communicate with a person who can speak urdu.
The transmitter(sender) sends the message and the receiver receives the
message. The medium (guided, unguided) is the channel over which the
message is sent and the protocol (for example IP, DHCP etc) is the set of rules
that guides how the data is transmitted. The message of course is central to all
the other components. The message is the data that is being communicated.
Data processing is the sequence of
operations performed on data to convert it
into useful information. These operations
may be arithmetic, statistical or logical
operations. We can
arrange or classify data. We can send and
receive data from one point to another.
In manual data processing data is processed manually. No machine or tool is
used.
All the calculations on data are performed manually. This is a slow method
and errors may occur. This is an old method. It was used before the
invention of calculators. But data is still processed manually in many small
shops.
Example: A book seller ( a small book shop ) records his daily transactions
manually. He prepares bills by pen,paper and carbon paper ( no doubt, brain
is the main data processor in this case ). At the end of day he will use
carbon copies made on a particular date to know how many books he sold
and how much income he got.
In mechanical data processing data is processed with the help of devices or
machines. These machines that help the people in data processing may be
calculators and type writers etc. Obviously, this method is faster easier and
more accurate than manual data processing.
Example: Book seller can use a calculator to speed up his data
processing system. There will be a less chance of errors in calculations.
Bill calculations will be much more faster with a calculator and easier too.
It is the latest and fastest method of data processing. Data is processed with
the help of computer. First of all, data and set of instructions are given to the
computer. Computer gives output results after processing the data according to
instructions. This method of data processing is very fast and accurate.
Electronic data processing is used in banks and business firms, Government
offices, colleges, schools, universities, businesses and other institutes.
Q. DATA PROCESSING CYCLE
1. Origination (Preparation)
The initial capture of raw data on documents as transactions occur is
referred to as origination. This could be in the form of various
documents such as: receipts, time cards, deposit slips, sales orders,
enrollment forms, tickets, to name just a few of the examples
Feedback
2. Input
Source documents are collected and converted into some convenient
form for processing. When editing input data, you should identify and
arrange data with like characteristics into groups or classes. For
example, enrolment forms may be classified according to year level,
courses, and so on
3. Processing
The input data is manipulated to produce data give useful information.
This is the actual operation performed on the input data. This operation
includes classifying, sorting, calculating, recording, storing and
summarizing data.
4. [Output ]or [Storage]
This step yields the results of the data processing in an appropriate
form accepted to the user for analysis or as an input for a second cycle.
Again communication is important in output preparation and
dissemination. Failure to communicate the output clearly, completely,
and accurately to the user is an waste of time and effort.
5. Feedback
Feedback is required for correction of errors from end users (who use
data).
Depend on your business requirements you can choose several
data processing services as follows:
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Survey processing
Order processing
Market research processing
Back office operation
Speed
Accuracy
Number of transactions
Cost
Selectivity (Different Views of same data)
Information
Record Keeping
Customer Service and Support