DC Lec 2 (Key Terminologies)

8/3/2019 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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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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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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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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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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Financial Services

Online Banking

Foreign Exchange transfer

Rates Manufacturing

Computer Aided Design

Computer Assisted manufacturingNetwork Application

Electronic Messaging


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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?


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

Documents

DC Lec 2 (Key Terminologies)