dc lec 2 (key terminologies)
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DATACOMMUNICATION
Lecture-2
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Recap of Lecture 1
Data Communication
Brief History of Communication
Data Communication System
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Overview of Lecture 2
Key Data Communication Terminology
Data Representation
Data Flow/ Transmission ModesNetworks and Why we need Them?
Distributed Processing
Network Criteria
Network Applications
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Key Data Communication
TerminologySessionCommunication dialog between network users or applications.
Network
Interconnected group of computers and communication devices.Node
Any device that is part of network.
Any device that is capable of sending or receiving data (e.g. computer,
printer etc.)
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Key Data Communication
TerminologyLink
connects adjacent nodes.
e.g. Wires, Cables, any thing that physically connects twonodes, or it can be wireless.
Path
end-to-end route within a network.
Circuitthe conduit or physical path over which data travels.
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Key Data Communication
TerminologyPacketizing
Dividing messages into fixed-length packets prior to
transmission over a networks communication media.Routing
Determining a messages path from sending to receiving nodes.
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Data Representation
Information today comes in different forms such as
Text
NumbersImages
Audio
and Video.
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Text
In data communications, text is represented as a bit pattern, asequence of bits (Os or Is).
Different sets of bit patterns have been designed to representtext symbols. Each set is called a code, and the process of
representing symbols is called coding.Today, the prevalent coding system is called Unicode, which
uses 32 bits to represent a symbol or character used in anylanguage in the world.
The American Standard Code for Information Interchange(ASCII), developed some decades ago in the United States, nowconstitutes the first 127 characters in Unicode and is alsoreferred to as Basic Latin.
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Numbers
Numbers are also represented by bit patterns. However, a codesuch as ASCII is not used to represent numbers;
the number is directly converted to a binary number tosimplify mathematical operations.
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Images
Images are also represented by bit patterns.In its simplest form, an image is composed of a matrix of pixels
(picture elements), where each pixel is a small dot.
The size of the pixel depends on the resolution. For example, an
image can be divided into 1000 pixels or 10,000 pixels.In the second case, there is a better representation of the image
(better resolution), but more memory is needed to store the image.
After an image is divided into pixels, each pixel is assigned a bit
pattern.The size and the value of the pattern depend on the image.
For an image made of only black and white dots (e.g., achessboard), a I-bit pattern is enough to represent a pixel.
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ImagesIf an image is not made of pure white and pure black pixels, you
can increase the size of the bit pattern to include gray scale. Forexample, to show four levels of gray scale, you can use 2-bitpatterns.
A black pixel can be represented by 00, a dark gray pixel by 01, alight gray pixel by 10, and a white pixel by 11.
There are several methods to represent color images. One methodis called RGB, so called because each color is made of acombination of three primary colors: red, green, and blue.
The intensity of each color is measured, and a bit pattern isassigned to it. Another method is called YCM, in which a color ismade of a combination of three other primary colors: yellow, cyan,and magenta.
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Audio
Audio refers to the recording or broadcasting of sound ormusic.
Audio is by nature different from text, numbers, or images. Itis continuous, not discrete.
Even when we use a microphone to change voice or music toan electric signal, we create a continuous signal.
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Video
Video refers to the recording or broadcasting of a picture ormovie.
Video can either be produced as a continuous entity (e.g., by aTV camera),
or it can be a combination of images, each a discrete entity,arranged to convey the idea of motion.
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Data Flow / Transmission
Mode
Communication between two devices can be Simplex
half-duplex
full-duplex
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Transmission Mode
TransmissionMode
Simplex Half-Duplex Full-Duplex
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Simplex
Communication take place only in one direction. Only sender just sends data & receiver just receive data. The simplex mode can use the entire capacity of the
channel to send data in one direction. Called as one-way transmission
i.e. there is no back direction of transmission fromreceiver to sender
e.g.
Radio, TV transmission. Input provided to the computer by keyboard, mouse, or
scanner etc. The flow of data from the computer to monitor, and printer
etc.
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Simplex
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Half-Duplex
Each station can both transmit and receive, but not at the sametime.
When one device is sending, the other can only receive, andvice versa
the entire capacity of a channel is taken over by whichever ofthe two devices is transmitting at the time.
e.g. wireless system walky-talky In computer field a multi-user environment is a best example of
half duplex mode, in which a terminal transmits data to maincomputer and then the computer responds with acknowledgment.
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Half-Duplex
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Full Duplex
Two-way transmission.
Both sender and receiver transmit data simultaneously.
Signals going in either direction share the capacity of thelink.
This sharing can occur in two ways: Either the link must contain two physically separate transmission
paths
Or the capacity of the channel is divided between signalstraveling in both directions.
The best example is telephone communication. Similarlymodem card, NIC, sound card etc are the devices used incomputer technology for full duplex transmission.
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Full Duplex
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Network
When two or more Devices (Nodes) are connected through amedium/cable to share their resources and information, it iscalled a computer network.
A node can be a computer, printer, or any other device
capable of sending and/or receiving data generated by othernodes on the network.
In other words, a group of computers and other devicesconnected together is called computer network, and this
process is called computer networking.
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Networks- Why we need Them?
Point to point communication not usually practical
Devices are too far apart. Large set of devices would need impractical number of connections.
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Networks- Why we need Them?
Solution is to connect all devices to a central system known as aNETWORK
Two Main Classes of Networks Local Area Networks (LANs) Wide Area Network (WANs)
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Benefits Of Networking
Sharing of information.
e.g. sharing information in business environment
Sharing the hardware resources. E.g. Printer, modem, scanner, hard disk, CDRom, floppy
disc, plotter etc.
Sharing Software Resources.
MS Office and Lots of application software.
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Benefits Of Networking
Preserving the information.
Centralized backup.
Protecting the information.
By applying authentication schemes.
E-mail people to communicate.
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Distributed Processing
Instead of a single large machine being responsible for all
aspects of a process, each separate computer handles a subsetof the task
For example a task given by a teacher to group of students.
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Network Criteria
Data Communication
Network Criteria
Performance Reliability Security
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Network Criteria
Performance Can be measured in any ways including Transit and
Response time. Transit time is the amount of time required for a
message to travel from one device to another. Responsetime is the elapsed time between an inquiry and aresponse.
Depends upon these factors
Number of UsersType of Transmission Medium
Hardware
Software
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Network Criteria
Reliability
Depends upon a no. of factors Frequency of failure
Recovery Time of a network after Failure
Network's robustness in a catastrophe.
Fire earthquake or theft
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Network Criteria
Security
Measured by two factors
Unauthorized Access Sensitive data
Protection at multiple Levels
Lower Level: Password and User IDcodes
Upper Level: Encryption
Viruses
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Network Applications
Marketing and Sales
Marketing
Collect, exchange and analyze data relating
to customer needs.Product development cycle.
Sales
Tele shoppingOnline reservation System
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Network Applications
Financial Services
Online Banking
Foreign Exchange transfer
Rates Manufacturing
Computer Aided Design
Computer Assisted manufacturingNetwork Application
Electronic Messaging
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Network Applications
Teleconferencing
Audio/Video Conferencing
Cable Television
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Summary
Key Data Communication Terminology
Data Representation
Data Flow/ Transmission ModeNetworks and Why we need Them?
Distributed Processing
Network CriteriaNetwork Applications
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Suggested Reading
Section1.1,
1.2,
Data Communications and Networking 4th Edition by BehrouzA. Forouzan
Sections
1.3,Data and Computer Communication 6th Edition by
William Stallings