Communications Media
•Communications Medium / Media:
–Path over which,
•Messages can be sent for,
•Communication between the source and the receiver.
–2 types:
•Guided Medium / Conducted Medium:
–It is visible.
–The device sends/conducts signals down the wire/cable.
–Example:
»Copper wire.
•Unguided Medium / Radiated Medium:
–It is invisible.
–Signal is sent/radiated through the air by means of a
transmitter and an antenna.
–Example:
»Airwaves.
Communications Media
•Guided Media:
–Visible and are part of the physical portion
of the network.
–3 types of guided media:
•Twisted pair wire.
•Coaxial cable.
•Fiber-optic cable.
Twisted Pair Wire
Cable Jacket
Insulator (Plastic)
Twisted Pair Cable
Conductor
1 pair / 2 pairs / 4 pairs
Single
Communication Line
RJ-11 Connector
RJ-45 Connector
Telephone
Computer
Guided Media
•Twisted Pair Wire:
–Most common transmission medium in use.
–Construction / Composition:
•Has a core that consists of,
–2 separate insulated copper wires,
–Twisted (intertwined) together a specific number of times
per foot where,
–Each pair is considered a single communications line.
•Each wire in a twisted pair is coated with,
–An insulating material such as,
»Plastic.
•Bundles of twisted pair wires can be packed close
together into one large cable.
–The insulation keeps the copper wires from touching,
–So the signal from one pair of wires does not interfere with
the signal from any other pair of wires in the cable.
Guided Media
•Twisted Pair Wire:
–Need / Advantage of Twisting:
•When electricity flows through any wire,
–An electromagnetic field is generated.
•This energy can create interference on
surrounding wires.
•When 2 wires are twisted together,
–The pair generates less energy than a single wire.
–So it makes the pair less susceptible to interference
from neighboring wires.
•Therefore by reducing interference,
–Twisted pair wire provides a better quality media for
transmission than wires without the twists.
Guided Media
•Twisted Pair Wire:
–2 types:
•Unshielded Twisted Pair (UTP)
•Shielded Twisted Pair (STP)
Unshielded Twisted Pair Wire
(UTP)
Shielded Twisted Pair Wire
(STP)
Guided Media
•Twisted Pair Wire:
–Unshielded Twisted Pair (UTP):
•Does not have the extra wire wrapping of shielded twisted
pair (STP) wire and therefore,
–Is more prone (susceptible) to interference.
•However it is sufficient (adequate) in areas with less
chances of noise / interference.
–So often used in residential and office Telephone and
Computer systems.
•Most homes, use 2 pairs (4 UTP wires) to connect their
telephones to the local end office.
–4 wires are used so that if a problem develops in 1 set of
wires, the other set can be used until the problem is
resolved.
•Less expensive than STP wires.
Guided Media
•Twisted Pair Wire:
–Shielded Twisted Pair (STP):
•Each pair of wires is placed into,
–A separate shield to absorb any interference.
•The wires are then put into a plastic outer shell.
•Reliable for transmitting data in,
–High-interference areas because the shielding
prevents interference with the data.
–Example:
»Industry with large electronic equipments.
•More expensive than UTP wires.
Coaxial Cable
Coaxial Cable
Connector
Guided Media
•Coaxial Cable / Coax:
–Construction / Composition:
•Composed of a,
–Single copper wire (Inner conductor),
–Surrounded by an insulating material called,
»Shell
–Shell is surrounded by a second conductor called,
»Copper Mesh / Copper Shield.
»Gives the cable more electromagnetic protection than a
twisted pair wire.
•The entire cable is enclosed in a plastic outer shell called the,
–Jacket.
–Characteristics:
•High-bandwidth medium that can carry thousands of signals at
once.
•Can transmit data over long distances than Twisted Pair wire.
•Less susceptible/prone to interference than Twisted Pair wire.
Guided Media
•Coaxial Cable:
–Allows for 2 types of transmissions:
•Broadband Transmission
–Used by Cable Television Industry
•Baseband Transmission
–Used by Computers in a Local Area Network (LAN)
Broadband Transmission
(Cable Television)
Channel-1
Channel-2
Channel-3
Coaxial Cable
Channel-5
ANALOG Transmission
Channel-4
Baseband Transmission
(Computers)
DIGITAL Transmission
Guided Media
•Coaxial Cable:
–Broadband Transmission:
•Used by cable television industry hence it is,
–Analog Transmission
•Single cable is logically divided by frequency into many
channels,
–Each carrying a different transmission separated by,
–Guardbands to prevent,
»Interference between the signals.
•Using broadband transmission, a cable television
company can,
–Transmit multiple channels to individual homes using only a
single cable.
•Can also be used to transmit,
–Voice, Video, Data and Alarm Signals simultaneously in a
Home security system.
Guided Media
•Coaxial Cable:
–Baseband Transmission:
•Only a single signal is transmitted over the
cable.
•Computers use baseband transmission to,
–Send data to other computers in a local area network
and hence it is,
»Digital Transmission
Guided Media
•Coaxial Cable:
–In spite of high bandwidth offered by
coaxial cable,
•Twisted Pair (and not coaxial cable) is used
more often in Computers and LAN’s because:
–Coaxial cable is more expensive than Twisted Pair
Wire.
–Coaxial cable is difficult to install than Twisted Pair
Wire.
–Coaxial cable is much larger and heavier than
Twisted Pair Wire.
»Space required to store those cables is more.
Fiber-Optic Cable
Fiber-Optic
Cable
Optical
Fiber
Fiber-Optic Cable Principle
Bouncing/Reflection off the walls
Total Internal Reflection
Guided Media
•Fiber-Optic Cable:
–Uses light to transmit data signals.
–Construction / Composition:
•Fiber-Optic Cable is composed of,
–One or more thin strands of glass where,
–Each strand of glass is called:
»Optical Fiber
•Each ‘Optical Fiber’ is as thin as,
–A human hair and is surrounded by a layer called,
–Reflective buffer or Cladding.
•All the Optical Fibers are then enclosed in an
outer covering called:
–Jacket
Guided Media
•Fiber-Optic Cable v/s Copper Wire:
–Fiber-Optic Cable:
•Signals are transmitted by means of light.
•Speed is much faster than copper wire.
–Copper Wire (Twisted Pair / Coaxial
Cable):
•Transmit signals electrically.
•Speed is slower than fiber-optic cable.
Guided Media
•Fiber-Optic Cable:
–2 types of fiber-optic cables based on,
•The method used to transmit light down the
cable.
–Single-Mode Cable (Single Path / Single Signal):
–Multi-Mode Cable (Multiple Paths / Multiple Signals):
»Multimode Step Index
»Multimode Graded Index
Fiber-Optic Cable Principle
Properties
Single-Mode
Transfer less data faster
over long distances.
Diameter Required: Less
MultiMode
Step Index
MultiMode
Graded Index
Transfer more data slower
over short distances.
Signal might suffer:
Loss of Strength
(Attenuation)
So needs to be regenerated
after certain distance.
Diameter Required: More
Guided Media
•Fiber-Optic Cable:
–Advantages:
•Offers high bandwidth.
–Can transmit huge amounts of data at very high speeds.
–Transmission speed starts from 100 Mbps and can go up to
2,500,000 Mbps.
•Much thinner and lighter than,
–Either twisted pair wire or coaxial cables.
•More secure.
–A copper wire is relatively easy to tap which,
»Allows someone to steal data without the owner ever knowing
that the theft is occurring.
–With optical fiber, however, a tap is very difficult to perform.
•More immune (protection) to electrical interference.
–With copper wires, broken insulation can cause interference called:
»Crosstalk.
–Light waves do not interfere with each other even if the cables
touch each other.
Guided Media
•Fiber-Optic Cable:
–Applications:
•Generally used to link together,
–LANs, WANs and other types of networks.
•Are not used to link an individual PC to a LAN
because of,
–The high cost of the network interface cards and the
other electronics needed.
Communications Media
•Unguided Media:
–Also called,
•Wireless Media / Radiated Media which do not
use,
–Hard wires to transmit data.
•Example:
–Air is the best form of unguided media.
Unguided Media
Transmitter Antenna
Receiver Antenna
Nature?
Uni-directional / Omni-directional
Directional / Un-directional
Communications Media
•Unguided Media:
–Question:
•Can any company start sending any signals (through air)
for communication?
–Answer:
•No.
•Company needs to broadcast signals over specific
frequency and,
–Allocation of frequency is regulated / controlled by,
»Some Government Regulatory Agency (such as TRAI)
so that,
»Different forms of communications do not interfere with
one another.
•Example:
–If a new radio station wants to begin broadcasting,
»It must get permission from Government Regulatory
Agency to use the radio frequency over which it wants
to broadcast.
Communications Media
•Unguided Media:
–Forms of transmission that use unguided
media are:
•Broadcast Radio
•Microwave
–Cellular Radio
•Spread Spectrum Radio
•Infrared transmission
Unguided Media
Frequency Spectrum
Unguided Media
Frequency Spectrum
Unguided Media
•Broadcast Radio:
–Nature/Properties:
•Sends signals in a frequency range from,
–540 KHz to 300 MHz
•Term usually is associated with:
–Radio Broadcasting through Radio Stations.
–Shortwave radio.
–CB radio.
–Television Transmission.
•Most forms of Broadcast Radio are,
–Omni-directional.
»‘Omni’ means ‘All / Every’.
–Antenna that is used to receive the broadcast signal and,
»Does not have to be positioned or pointed in a specific
direction.
Broadcast Radio
•Radio Broadcasting through Radio Stations:
–AM Radio:
•Stands for Amplitude Modulation Radio.
•Transmits at a much Lower Frequency than FM Radio
and hence,
–Higher Wavelength than FM Radio and so,
–Can be broadcast farther than FM Radio.
•Interrupted easily by atmospheric changes such as
thunderstorms.
–FM Radio:
•Stands for Frequency Modulation Radio.
•Transmits at a much Higher Frequency than AM Radio
and hence,
–Lower Wavelength than AM Radio and so,
–Cannot be broadcast farther than AM Radio.
•Storm interference will not be noticeable.
Broadcast Radio
•Shortwave Radio:
–Used for communication in:
•Military communications.
•To give news during times of disaster.
•CB Radio:
–Stands for ‘Citizens Band Radio’.
–Uses very low power and cannot transmit over
long distances.
–Was very popular in the 1970s and 1980s with
travelers of all kinds.
•Truck drivers used CB radios to check on road conditions
or get directions to their destinations.
CB Radio
Broadcast Radio
•Television Transmissions:
–Television transmission antenna sends a television signal
out,
•In all the directions.
–Omni-directional.
–However, television receiving antenna (Yagi antenna) is,
•Directional and so,
–Pointing the television antenna more directly at the transmitting
station will produce a better picture.
–Uses higher frequency than AM & FM radio because,
•More data consisting of both ‘Picture’ & ‘Sound’ need to be
transferred.
–2 basic types of television frequencies are used:
•VHF:
–Very High Frequency
–Frequencies from 50 to 225 MHz
•UHF:
–Ultra High Frequency
–Frequencies from about 400 to 900 MHz
Broadcast Radio
•Television Transmissions:
–DTV (Digital Television Technology):
•New technology that is used to transmit,
–Television channels in Digital form rather than Analog
form.
•Decoder / Set-top box is used to decode the
incoming signals.
–HDTV (High-Definition Television):
•Newer technology in DTV which,
–Delivers a higher-quality picture than standard
television.
Unguided Media
•Microwave:
–Nature/Properties:
•Transmits signals between,
–2 or more stations in a frequency range of:
»3 GHz to 30 GHz (3,000 MHz to 30,000 MHz)
•Signals have a high frequency and hence,
–A short wavelength and so it is called,
»Micro.
•High frequency allows,
–Large amounts of data to be transmitted over this
medium.
Unguided Media
•Microwave:
–Nature/Properties (cntd):
•Unlike ‘Broadcast Radio’ signals, which are
omni-directional,
–Microwave transmission is,
»Uni-directional.
•Signals produced by a microwave station,
–Travel in a straight line and so,
»The antennas used for transmission must be
pointed directly at one another.
–Also known as,
»‘LINE OF SIGHT’ transmission.
•They can be affected by,
–Atmospheric changes such as rain and snow and by,
–Obstacles between the microwave stations.
Microwave
Terrestrial Microwave
To prevent obstacles,
Stations (Transmission/Receiving)
are placed on a height.
Earth
Satellite Microwave
Unguided Media
•Microwave:
–2 types:
•Terrestrial Microwave
•Satellite Microwave
Microwave
•Terrestrial Microwave:
–Terrestrial means,
•Related to ground / territory / earth.
•So in terrestrial microwave, transmissions are sent between,
–2 microwave stations on Earth.
–Because microwaves must travel in un-obstructed straight
lines,
•Ground-based microwave stations are placed,
–On top of towers and,
–At very short distances from one another.
•If they were placed too far apart,
–Earth’s curvature blocked the line-of-sight transmission.
–Most common form of long-distance communications today
as,
•Major long-distance telephone companies have microwave
transmission towers placed across the nation where,
•Transmission could take place over 55 miles.
Microwave
•Satellite Microwave:
–Involves sending microwave transmissions
between,
•2 or more Earth-based microwave stations and,
•A satellite.
–Satellite just serves as a,
•Relay (Intermediate/Pass-on) station that
receives signals from,
–One Earth-based station and rebroadcasts it to the
next.
Satellite Microwave
Objectives:
Cover as much area as possible.
Remain in the same place with respect to relative motion of earth.
Geosynchronous
Orbit
GEOS
Geosynchronous Earth Orbiting Satellite
Geostationary Earth Orbiting Satellite
Satellite Footprint
Microwave
•Satellite Microwave:
–Most communications satellites are placed into orbit at a
distance which is,
•22,300 miles above Earth’s surface known as,
–Geosynchronous Orbit / Geostationary Orbit
–At that distance,
•Satellite keeps revolving in orbit at the same rate as that of
Earth’s rotation due to,
•Earth’s gravitational force and so,
•Satellite appears to be in a fixed position over the Earth.
–Such a satellite is called:
•GEOS
–Geo-synchronous Earth Orbiting Satellite
–Geo-stationary Earth Orbiting Satellite
–Part/Region of the earth that 1 satellite can cover is called:
•Footprint.
–Generally covers several countries.
–3 satellites appropriately positioned over the Earth can cover entire
Earth.
Satellite Microwave
Conversion to a different frequency.
Transponder
Amplification is done.
2 different
frequencies
Time wastage
Propagation Delay
Microwave
•Satellite Microwave:
–Propagation Delay:
•Extra/Unnecessary time taken by the signal,
–To travel from an Earth station to a satellite and back plus,
–The time it takes to convert the signal to sending signal of
different frequency.
•Varies from,
–1 second for data transmission to,
–3 seconds for voice or television transmission.
•Example:
–Television:
»When a reporter from one country interviews someone
in another country.
–Telephone:
»Overseas telephone conversation also shows delay.
Microwave
•Satellite Microwave:
–Apart from GEOS satellites, other types of
satellites also exist:
•LEOS.
•MEOS.
Microwave
•Satellite Microwave:
–LEOS:
•Also known as,
–Low Earth Orbiting Satellites.
•Launched at a height of,
–325 to 1,000 miles.
•Do not move at the same speed as that of earth but,
–Travel completely around the earth in 90 to 100 minutes.
•Number of satellites needed to cover the entire earth is,
–12.
•Advantage:
–Decreased propagation delay as they are very close to
earth.
•Example:
–Iridium Project.
Microwave
•Satellite Microwave:
–MEOS:
•Also known as,
–Medium Earth Orbiting Satellites.
•Launched at a height of,
–6,000 to 10,000 miles above Earth.
•Number of satellites needed to cover the entire
earth is,
–6.
•Example:
–Teledisc Project.
GEOS, LEOS, MEOS
Microwave
•Satellite Microwave:
–Applications:
•Telephone Communications
•Computer Networking
•Broadband Internet Access
•Interactive Multimedia
•DirectTV
–Videocon D2H, TataSky, DishTV.
•GPS
Microwave
•Satellite Microwave:
–GPS:
•Also known as,
–Global Positioning System.
•Consists of,
–Satellites and receivers that are used to,
–Determine a location.
•Made possible by,
–US Global Positioning System consisting of,
–A collection of 24 satellites, which are placed in orbit at a
cost of $12 billion.
•Algorithm/Method used to determine exact location on
Earth is called,
–Triangulation.
•Used in,
–Automobiles, airplanes, cell-phones etc.
Microwave
•Satellite Microwave:
–Cost of operation:
•To use satellites, companies need to,
–Rent satellites and transmit their data which could
also be,
»Very costly.
•Cost of repairing a satellite also is very high.
–In the past,
»Satellites that stopped working properly simply
were allowed to fail and were left in orbit.
–Today,
»NASA’s space shuttle program makes it possible
to get a satellite back for repair.
Unguided Media
Cellular Radio
Why it is called ‘Cell Phone’ / ‘Cellular Communication’ ?
Question:
Can these many unique
frequencies be available
at a single time?
No.
So the only solution is:
To reuse one frequency
multiple times.
Question:
But giving the same frequency
in the same area to 2 users
will create Interference.
Entire City
Unguided Media
Cellular Radio
Entire city is divided into
logical hexagonal shaped
structures called:
CELLS
So it is called
Cellular Communication.
Unguided Media
Cellular Radio
As a person moves from one cell to another,
one cell leaves the signal and another cell catches it.
Cell Phone Tower
This is called ‘Hand-Off’.
Unguided Media
•Cellular Radio:
–The genius of the cellular system is:
•The division of a city into small cells where,
•Each cell has its own transmitting antenna which allows,
•Frequency reuse across a city, so that,
•Millions of people can use cell phones simultaneously.
–It is a form of,
•‘Broadcast Radio’ with 1 exception:
–It puts restrictions on how far the signal is transmitted by,
–Operating the transmitters at a very low power so that,
–Transmitters in adjacent cells can broadcast on the same
frequency and not,
»Interfere with one another.
Unguided Media
•Cellular Radio:
–Cellular Telephone:
•Radio device that use cellular radio signals to transmit,
–Voice and Data messages.
–Hand-Off:
•As a person with a mobile phone moves from one cell to
another,
–The signal is transferred from the transmitter in one cell to
the transmitter in the next cell.
•Process of,
–Handing off the signal by one transmitter and,
–Catching off the signal by another transmitter.
•Sometimes, this change in transmitters will cause,
–An interruption or even loss of the signal.
Unguided Media
•Cellular Radio:
–Problems associated:
•Scanner:
–Devices that can intercept (steal / listen to) cell
phone conversations.
–Require more security precautions that are not
needed with standard telephones.
•Cloning:
–The theft of,
»Some unique feature of the cell phone and
duplicating that for,
»Misuse.
Unguided Media
•Spread Spectrum Radio (SSR):
–Transmission of radio signals is,
•Spread over multiple different frequencies rather than,
•A single frequency.
–Developed initially by,
•The military to provide,
–Protection against,
–Eavesdropping (Spying / Listening In) and Jamming of
radio signals.
–2 main methods:
•Frequency-Hopping Spread Spectrum (FHSS)
•Direct-Sequence Spread Spectrum (DSSS)
Spread Spectrum Radio
•Frequency-Hopping Spread Spectrum:
–Signal is broadcast over,
•A large random series of radio frequencies by,
–Transmitting a short time on one frequency and then,
–Hopping to another frequency for another short time and so on.
–So, instead of continuously transmitting on one frequency,
•It switches rapidly from one frequency to the next.
–The choice of the next frequency is,
•Random and so,
–It is very difficult for someone to eavesdrop or jam the signal.
–The challenge is to,
•Keep both the transmitter and receiver synchronized.
•Done by,
–Some precision ‘Clocks’ and ‘PseudoRandom’ (FalseRandom)
generation logics.
–Used in:
•BlueTooth
Spread Spectrum Radio
•Direct Sequence Spread Spectrum:
–Directly add a sequence of,
•A random data bits (Noise) to the transmission so that,
•The signal contains both,
–A useful signal and,
–A signal that appears to be interference (noise).
–These random data bits are called:
•Chips.
–The receiver which is synchronized with the
transmitter tries to,
•Identify the chips / Decode the data and removes them
leaving only,
•The useful signal.
–Used in:
•Wireless LAN / Wi-Fi
Unguided Media
•Infrared Transmission (IR):
–Involves sending electromagnetic signals at a
frequency between:
•Radio Waves & Visible Light
–Used in products such as:
•Television Remote Controls.
•Data transfer.
–Type of transmission is:
•Line-of-sight transmission.
–Maximum coverage of:
•30 to 80 feet.
–Ports which provide IR connectivity are called:
•IrDA ports
–Infrared Data Association
Communications Media
(Classification)
Communications Media
Guided Media
(Conducted Media)
Unguided Media
(Radiated Media)
Types of
Transmissions
Types
Twisted
Pair
UTP
STP
Coaxial
Cable
Fiber-Optic
Cable
Broadcast Microwave Cellular Spread Infrared
Radio
Radio Spectrum
Radio
AM & FM
Single-mode
Shortwave
Multi-mode
CB Radio
Step Index
Broadband Graded Index Television
Terrestrial
Baseband
Satellite
FHSS
DSSS
Communications Media
•Selection of Media:
–Many factors/parameters/criteria are involved in
choosing the medium for a communications
network.
–Parameters might change depending on:
•Existing Network:
–Type of media already in use in an organization.
–How much it would cost to replace the existing media.
•New Network:
–Cost of the medium.
–Speed at which it can transmit.
–Environment in which the medium is used.
–Security of the data transmitted over the medium.
Selection of Media
•Cost:
–What needs to be connected:
•To connect computers in a LAN,
–Least expensive medium for data communications is:
»UTP (Unshielded Twisted Pair) cables.
•To connect 2 or more LANs together between buildings,
–Fiber-optic cable would be cost-effective as,
»It can accept large amounts of data.
–Distance between connections:
•In a city / country:
–Leased telephone lines are the best option.
•Between cities / countries:
–Lease a satellite transponder.
Selection of Media
•Environment:
–High-Interference Area:
•It is better to go for,
–STP (Shielded Twisted Pair) over UTP (Unshielded
Twisted Pair).
•To get the best protection against
Electromagnetic Interference,
–It is good to go with,
»Fiber-Optic Cable
Selection of Media
•Security:
–Guided Media:
•Best security could be provided by:
–Fiber-optic cable instead of copper wire (Twisted pair /
Coaxial Cable) because,
»Copper wire can be easily tapped by,
»Simply breaking the insulation around the wire and,
»Attaching another copper wire to the break.
–Unguided Media:
•Data is transmitted through the air which means,
–Anyone with an antenna that receives the appropriate
frequency can intercept the data.
–One way to secure the data is to:
»Encrypt the data.
Computer / Terminals in a Communication Network
Hotel / Mall
Client /
Terminal
Node
Host /
Server
Marketing Department
Remote Input
Device
Engineering
Industry
Client
Engineering Department
Admin Department
Special
Purpose
Client/Terminal
(POS)
Sales Department
Computers & Terminals in
Communication Network
•Computers & Terminals in a Network:
–Node:
•Device that is connected to the network and,
•Can send and/or receive data on the network.
–Host/Server:
•Computer that provides,
–Storage for files and programs and does,
–Some of the application processing on the network.
Computers & Terminals in
Communication Network
•Computers & Terminals in a Network:
–Terminal/Client:
•Device that is used to,
–Input data to or,
–Receive output from,
»A host/server computer.
•Computer from where,
–User interacts with the network.
•Types:
–Dumb Terminal:
»Does not have its processing power or storage space.
»Asynchronous Transmission to the server.
–Smart Terminal / PC:
»Has its own processing power or storage space.
»Synchronous Transmission to the server.
Computers & Terminals in
Communication Network
•Computers & Terminals in a Network:
–Special Purpose Terminals:
•Also called,
–Transaction Terminals.
•Devices/Terminals that have been designed for,
–Specific tasks and cannot,
–Be used for a variety of functions.
•To address/satisfy the needs of a specific
task/application, it uses,
–Customized hardware and/or specialized software.
•Example:
–Point-of-sale (POS) terminal.
»Includes a monitor, scanner, printer and special
keyboard.
–Credit card authorization device / Smart Card reader.
»To authorize credit card / smart card purchases.
»Sometimes a part of POS terminal.
Computers & Terminals in
Communication Network
•Computers & Terminals in a Network:
–Remote Input Devices:
•Special devices to,
–Automate common, repetitive activities and allow,
–Mobile workers to gather data where networks cannot
reach easily.
•Are not connected to a computer directly.
–Either transmit real-time data over a wireless network or,
–Gather data offline for later transmission to the server
computer.
•Even though they are called ‘Input’ devices,
–They can also output information.
•Example:
–Issue bus tickets.
–Issue electricity bills.
–Issue vehicle parking receipts.
Computers & Terminals in
Communication Network
•Computers & Terminals in a Network:
–Engineering Industry Clients:
•Used to create drawings / blueprints of :
–Layouts of buildings,
–Designs of vehicles etc.
•Special printer to print these drawings on paper,
–Plotter
•Process of drawing designs using computer is
also called:
–CAD / CAM.
»CAD: Computer Aided Design
»CAM: Computer Aided Manufacturing
Computers & Terminals in
Communication Network
•Computers & Terminals in a Network:
–Other important terms:
•Mainframe Computers
•Supercomputers
•Minicomputer
•Microcomputers / Personal Computers
•ATM (Automated Teller Machines)
Network Configurations
•Network Configurations:
–The way in which computers and terminals
are connected in a network.
–Also known as:
•The line configuration.
Network Configurations
Multipoint (Multidrop)
Point-to-Point
Network Configurations
•Network Configurations:
–Based on how data is sent between the
server and clients on the network,
•2 main types of line/network configurations are:
–Point-to-Point
–Multipoint
Network Configurations
•Point-to-Point:
–Direct line exists between a sending device and a receiving
device.
–Each client has its own communications line which is,
•Exclusive to the client and so,
–No other client will ever use it.
•Communication line is also called:
–A circuit.
–A line is always available to the client for sending data to the
server.
–Server does not need to spend time in finding which client
sent the data.
–Each client requires a separate communications line which
increases,
•The line costs.
Network Configurations
•Multipoint:
–Several devices share a single communications
line, so also known as,
•Shared Circuit.
–Each client can transmit to the server only when,
•No other client is transmitting, which can result in,
–Longer wait time to access the communications line for
data transmission.
–Wait time of a client continues to increase if,
•Other client is sending a lot of data or,
•More clients are added to the line.
Network Configurations
•Multipoint:
–What is 2 clients start sending the data at the
same time?
•This situation is called:
–Data Collision / Contention
–Algorithm to resolve Collision / Contention:
•Client can attempt to transmit data at any time.
•If the line is busy (in use by another client),
–A data collision occurs.
•The client stops transmitting and waits for a,
–Random amount of time and then tries to transmit again.
–Solution to resolve collision is only adequate
(sufficient) for,
•Small networks in which the amount of data transmitted is
not very large.
Point-to-Point Line Configuration
Multipoint Line Configuration
Terminal Interfaces
•Terminal Interfaces:
–Interface means,
•A connection that allows interaction between devices.
•Also known as:
–A port.
–Terminal Interface is,
•A connection that allows a client/terminal to be connected
to the network.
–Example:
•Serial Port / Interface
•Parallel Port / Interface
•USB Port / Interface
–Universal Serial Bus
Serial Interface/Port
Parallel Interface/Port
USB Interface/Port
Parallel v/s Serial Transmission
Data ‘01100011’ needs to be sent from Transmitter to Receiver.