Comp science notes

INTRODUCTION TO NETWORKING AND

DATA COMMUNICATION

S.N. MBURU - SCI

INTRODUCTION

TO DATA COMMUNICATION & NETWORKS

Introduction to networking data communication

Data communication is the transmission of data and information over a communications channel between two devices

Communications between computers can be as simple as cabling two computers to the same printer. It can be as complex as a computer at NASA sending messages through an elaborate system of relays and satellites as shown by the animation in the next slide.

A network is collection of computing devices connected in order to communicate and share resources. Connections between the devices can be physical using wires or cables or wireless using radio waves or infrared signals

.

Communication systems

Data and data signals Data/ information are entities that convey meaning within

a computer or computer system. In data communication, the two terms means the same.

Data can be transmitted over physical or wireless media. To be transmitted it must first be converted into a signal.

Signals are the electric or electromagnetic encoding of data and are used to transmit data. signals can be analog or digital.

Data Signals can be analog or digital. Analog signals have an infinite number of values in a range represented using sine wave while digital signal is discrete, discontinuous voltage pulses represented using square wave

.

Analog signal

Digital signal

Forms of information

Familiar forms of information carried by data communication are: Text: Alphabetic characters Numeric data: Information in the form of numbers, Graphical data: In the form of pictures or diagram

that can be sent by fax machines or computers. Sound: Video: Pictures accompanied by sound. Multimedia: A combination of the different text,

video and sound.

Channel A communications channel, also called a

communications line or link, is the path that the data follows as it is transmitted from one computer to another

Any communications channel has a direction associated with it as shown below.

Channels types

DTE and DCE

Data Terminal Equipment (DTE): Sources or destinations of information. Comprises of communications equipment such as terminals, host computer, printer etc.

Data Circuit Terminating Equipment (DCE): Made up of interface devices such as the modem, switches, routers etc.

Source

Interface

DTE

DCE

Source

Destination

DCE

DTE

Medium

Data communications interfacing

Illustration of DTE-DCE setup

DTE-computer DCE-modems DTE-computer

Types of networks

LAN (Local Area Network)Network in small geographical Area (Room, Building or a Campus)

MAN (Metropolitan Area Network)Network in a City

WAN (Wide Area Network) Network spread geographically (Country or across Globe)

Benefits of Networks

Resource Sharing Hardware (computing resources, disks, printers) Software (application software)

Information Sharing Easy accessibility from anywhere (files, databases) Search Capability (WWW)

Communication Email Message broadcast

Remote computing

Networks topologies

Computer network Topology refers to the physical layout of the network devices and cabling and how all the components communicate with each other. There are four basic types of computer network topologies: mesh, bus, ring, star

Lesson 3—Networking BASICS 17

Common Topologies

Physical layout of network devices Four types: mesh, bus, ring, and star


Mesh Topology A mesh topology is also called a point-to-

point topology. Each device is connected directly to all

other devices on the network. A mesh topology is sometimes used in a

wide area network (WAN) setting to ensure that all the sites continue to transmit in the event of a cable failure or another similar problem.

Mesh topologies are rarely used in a LAN.


Mesh Topology


Bus Topology The most common type of multipoint

topology is a bus topology. A computer network bus topology is

characterized by one starting point and one ending point.

A bus network topology works well for smaller networks and is inexpensive to install.

However, it can become slow when more devices are added to the network


Bus Topology


Ring Topology

It is a circular with no ends. Packets are sent from one device to the

next. It does not slow down as more devices are

added.


Ring Topology


Star Topology

A star topology describes a network in which all the devices are connected to a central device known as a hub, which is responsible for receiving and forwarding packets to other devices on the network.

Because everything is centralized in a star topology, it is the easiest topology to manage and troubleshoot


Star Topology


Hybrid Topologies

They are variations of two or more topologies. Star bus – used to connect multiple hubs in a

star topology with a bus. Star ring – wired like star, but functions like a

ring.

Transmission Media

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Data transmission• A communication link is established by using

physical or wireless medium. In most cases it is a pair of electric conductors, fiber optic cables or using electromagnetic waves on the free space.

• Thus media are roughly grouped into guided or unguided media.

Classes of transmission media

GUIDED MEDIAGUIDED MEDIA

Guided media, are those that provide a conduit (physical Guided media, are those that provide a conduit (physical connection) from one device to another, include twisted-connection) from one device to another, include twisted-pair cable, coaxial cable, and fiber-optic cable.pair cable, coaxial cable, and fiber-optic cable.

Twisted-Pair CableCoaxial CableFiber-Optic Cable

Three categories of guided mediaThree categories of guided media

Twisted Pair Cables• The oldest and still most common transmission

medium is twisted pair.

• Consists of two insulated copper wires twisted together.

• Can be used for either analog or digital transmission.

• Twisting reduces the effects of the external interferences.

• Common applications are the telephone system and Local Area Network of computers.

Unshielded Twisted Pair (UTP) Cables

• The commonly used UTP cables are categorized as CAT 3, CAT 5 and CAT 5e.

Coaxial Cables• The construction and shielding of the coaxial

cable give it a good combination of high bandwidth and noise immunity.

• The energy loss due to skin effect is also minimized.

Centerconductor

Dielectricmaterial

Braidedouter

conductor

Outercover

Figure 3.39Copyright ©2000 The McGraw Hill Companies Leon-Garcia & Widjaja: Communication Networks

Coaxial Cable

Optical fiber

• A unidirectional optical transmission system has three components ; light source, transmission medium and detector.

• The light source works such that a pulse of light indicates “1” and absence of light indicates “0”.

• The detector at the receiving end generates an electric pulse when light falls on it.

Optical Transmission Ctd.

• Optical Transmission is based on the theoretical principle called Total Internal Reflection in physics.

Light SourceTotal Internal Reflection

• A light ray incident at or above the critical angle is trapped inside the fiber.

Fibre cable structure Core -- a very narrow strand of high quality glass.

Cladding -- again, made from high quality glass, with a slightly different index of refraction of the core.

Buffer/outer jacket -- usually constructed from plastic

Figure 7.14 Fiber construction

Comparison of Fibre Optics & Copper Wire•Fiber has many advantages.

• Higher Bandwidth• Low attenuation• Not affected by electromagnetic

interferences.• Not affected by corrosive chemicals.• Lighter in weight• Secured from wiretappers.•Do not induce high voltages when

lightening takes place.

UNGUIDED MEDIA: WIRELESSUNGUIDED MEDIA: WIRELESS

Unguided media transport electromagnetic waves Unguided media transport electromagnetic waves without using a physical conductor. This type of without using a physical conductor. This type of communication is often referred to as wireless communication is often referred to as wireless communication.communication.

Radio WavesMicrowavesInfrared

Topics discussed in this section:Topics discussed in this section:

Figure 7.19 Wireless transmission waves

Broadcast Radio

Description of broadcast radio antennas Omnidirectional Antennas not required to be dish-shaped Antennas need not be rigidly mounted to a precise

alignment Applications

VHF and part of the UHF band; 30 MHZ to 1GHz Covers FM radio and UHF and VHF television Cellular telephony Wireless LANs

Microwaves• Above 100MHz, the waves travel in straight

lines and can therefore be narrowly focused.

• Parabolic antennas are used.

• Microwaves do not pass through buildings well.

• Used to establish links when laying physical cables are very expensive or impracticable.

• Satellite communications.

Figure 7.21 Unidirectional antennas

Terrestrial Microwave

Parabolic dish Narrow beam – line of sight on towers to avoid obstacles Series of towers for long distance Applications:

Long haul telephone Voice and TV Short point to point between buildings

Main Source of loss Attentuation – especially with rainful Repeaters or amplifiers 10 to 100km Interference with overlapping bands

Satellite Microwave

It is essentially a microwave relay station Uplink

Receives transmission on one frequency Downlink

Transmits on a second frequency Operates on a number of frequency bands known as

transponders Point to Point

Ground station to satellite to ground station Multipoint

Ground station to satellite to multiple receiving stations

Infrared

Description of broadcast radio antennas Transmitters/receivers (transceivers) modulate non-

coherent infrared light Transceivers must be within line-of-sight of each other

either directly or via reflection Unlike microwave, infrared does not penetrate walls

Applications Small LANs Short point-to-point connections

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