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Data Communications

CS 1302 Computer Networks

Unit 1 Topics 1,2,3

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Overview

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Data Communications

Data – facts, concepts, and instructions Data – Information presented in whatever

form is agreed upon by the parties creating and using the data

Represented by binary information units (in the form of 0s and 1s)

Data Communications – exchange of data between two devices via some form of transmission medium such as a wire cable

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Effectiveness of Data Communications Effectiveness of a data communications system

depends on three fundamental characteristics Delivery : The system must deliver data to the correct

destination. Data must be received by the intended device or user and only by that device or user

Accuracy: The system must deliver the data accurately. Data that have been altered in transmission and left uncorrected are unusable

Timeliness: The system must deliver data in a timely manner. Data delivered late are useless. Delivering the data in the same order that they are produced and without significant delay (real time transmission)

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Data Communication

Components

Data Representation

Direction of Data Flow

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Five components of data communicationMessage: Information to be communicated.

Consist of text, numbers, pictures, sound or video - combination

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Five components of data communicationSender: device that sends the data

message- may be computer, workstation. telephone handset, video camera and etc.

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Five components of data communicationReceiver: the device that receives the message. Can be computer, work station, telephone handset, television and so on.

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Five components of data communicationMedium: Physical path by which a message

travels from sender to receiver – twisted pair wire, coaxial cable, fibre optic cable or radio waves

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Five components of data communicationProtocol: Set of rules that governs data

communication. It represents an agreement between the communicating devices. Without a protocol, two devices may be connected but not communicating

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Data Communication

Data Representation

Direction of Data Flow

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Data Representation (1)Information Today comes in different formssuch as text, numbers, images, audio and video Text: Represented as a bit pattern, a

sequence of bits 0s or 1s. Different codes are used ASCII (7 bits per symbol) Extended ASCII (8 bits per symbol) Unicode (16 bits – supports different languages) ISO (32 bits)

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Data Representation (2)

Numbers Converted to a binary number – to simplify the

mathematical operations Images

Represented by bit patterns Each pixel is assigned a bit pattern Black and White Image – 1 bit per pixel Gray scale images – depends on number of levels in gray

scale Colour images: Each pixel has 3 bit patterns (RGB)

Audio / Video Converted in to Analog/Digital

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Data Communication

Direction of Data Flow

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Simplex

Simplex – unidirectional; one transmits, other receives

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Half-duplex

Half-duplex – each can transmit/receive; communication must alternate

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Full-duplex

Full-duplex – both can transmit/receive simultaneously

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Networks

Network Criteria

Physical Structures

Categories of Networks

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Networks

Set of devices (nodes) connected by media Distributed processing Advantages

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Applications (2)

Peer-Peer model: No fixed clients or servers Each host can act as both client & server

Examples: Napster, Gnutella, KaZaA

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Applications (3)

WWW Instant Messaging (Internet chat, text

messaging on cellular phones) Peer-to-Peer Internet Phone Video-on-demand Distributed Games Remote Login (Telnet) File Transfer

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Network Criteria

Performance – can be measured by transit time and response time. Affected by number of users, type of medium, connected HW/SW

Reliability – measured by frequency of failure, recovery time, robustness in a catastrophe

Security – protection from unauthorized access, viruses / worms

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Type of Connections

Line Configuration

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Line Configuration The way two or more communication devices

attach to a link Link – Physical communication pathway that

transfer data from one device to another Two possible line configurations

Point-to-point Multipoint

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Point-to-point connection

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Multipoint connection

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Topology

Physical or logical arrangement Topology of a network is the geometric

representation of the relationship of all the links and linking devices to one another

4 basic types: mesh, star, bus, ring May often see hybrid

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Categories of topology

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Mesh Topology Dedicated point-to-point links

to every other device n(n-1)/2 links an each device

will have n-1 I/O ports Advantages

Dedicated links – no traffic problems

Robust Privacy/Security Easy fault identification and

isolation Disadvantages

more amount of cabling and I/O ports requirement

Installation and reconnection is difficult

Expensive

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Star Topology

Dedicated point-to-point links to central controller (hub)

Controller acts as exchange Advantages

less expensive robustness

Disadvantages More cabling requirement

than ring and bus topologies

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Bus Topology

Multipoint configuration One cable acts as a backbone to link all devices Advantages : Ease of installation, less cabling Disadvantages : Difficult reconnection and fault

isolation, a fault/break in the bus cable stops all transmission

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Ring Topology

Dedicated point-to-point configuration to neighbors Signal is passed from device to device until it

reaches destination Each device functions as a repeater Advantages : easy to install and reconfigure Disadvantages :limited ring length and no: of

devices; break in a ring can disable entire network

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Categories of Networks

Based on size, ownership, distance covered, and physical architecture Local Area Network (LAN) – smaller geographical

area Metropolitan Area Network (MAN) – network

extended over an entire city Wide Area Network (WAN) – large geographical

area

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Categories of networks

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LAN

Privately owned and links the devices in a single office, building or campus

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LAN (Continued)

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MAN

Designed to extend over an entire city – May be a single network such as cable television network – may be a means of connecting a number of LANS into a larger network

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Metropolitan Area Network (MAN)

home

cable headend

cable distributionnetwork (simplified)

Typically 500 to 5,000 homes

A Cable TV Network is an example of a MAN

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WAN

Provides long distance transmission of data, voice, image and video information over large geographic areas – a country/continent/world

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Protocols and StandardsProtocols and Standards

Protocols

Standards

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Protocols and Standards

Protocols Set of rules that governs data communications Defines what is communicated, how it is

communicated, and when it is communicated Key elements

Syntax : Structure/ format of data –order in which it is presented

Semantics : meaning of each section of bits- how pattern to be interpreted – What action to be taken

Timing: When data to be sent and how fast they can be sent

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Protocols and Standards

Standards Essential in creating and maintaining an open and

competitive market for equipment manufacturers and in guaranteeing national and international interoperability of data and telecommunications technology and processes

De facto: Standards that have not been approved by an organized body but have been adopted as standards through widespread use

De jure: legislated by an officially recognized body

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Protocols and Standards

Standards Organizations International organization for Standardization

(ISO) International Telecommunication Union –

Telecommunication Standards Sector (ITU-T) American National Standards Institute (ANSI) Institute of Electrical and Electronics Engineers

(IEEE) Electronic Industries Assoctiation (EIA)

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Protocols and Standards

Regulatory Agencies Federal Communication Commission (FCC)

Internet Standards Internet Draft Request for Comment (RFC)