Presentation

1. Transmission MediaTransmission Media
Fiona NahFiona Nah
University of Nebraska-LincolnUniversity of Nebraska-Lincoln

2. Transmission: The BasicTransmission: The Basic
Encode data as energy and transmit energyEncode data as energy and transmit energy
Decode energy at destination back into dataDecode energy at destination back into data
Energy can be electrical, light, radio, soundEnergy can be electrical, light, radio, sound
Each form of energy has different propertiesEach form of energy has different properties
and requirements for transmissionand requirements for transmission

3. Transmission MediaTransmission Media
Transmitted energy is carried through someTransmitted energy is carried through some
sort of mediumsort of medium
Transmitter encodes data as energy andTransmitter encodes data as energy and
transmits energy through mediumtransmits energy through medium
Requires special hardware for dataRequires special hardware for data
encodingencoding

4. Copper WiresCopper Wires
Twisted pair uses two wiresTwisted pair uses two wires
Coaxial cable includes shield for improvedCoaxial cable includes shield for improved
performanceperformance

5. Glass FibersGlass Fibers
Thin glass fiber carries light with encodedThin glass fiber carries light with encoded
datadata
Plastic jacket allows fiber to bend (some!)Plastic jacket allows fiber to bend (some!)
without breakingwithout breaking
Fiber is very clear and designed to reflectFiber is very clear and designed to reflect
light internally for efficient transmissionlight internally for efficient transmission

6. Glass FibersGlass Fibers
Light emitting diode (LED) or laser injectsLight emitting diode (LED) or laser injects
light into fiberlight into fiber
Light sensitive receiver at other endLight sensitive receiver at other end
translates light back into datatranslates light back into data

7. RadioRadio
Data transmitted using radio wavesData transmitted using radio waves
Energy travels through the air rather thanEnergy travels through the air rather than
copper or glasscopper or glass
Conceptually similar to radio, TV, cellularConceptually similar to radio, TV, cellular
phonesphones

8. RadioRadio
Can travel through walls and through anCan travel through walls and through an
entire buildingentire building
Can be long distance or short distanceCan be long distance or short distance
Long distanceLong distance
satellite relaysatellite relay
Short distanceShort distance
wireless computer networkwireless computer network

9. SatellitesSatellites
A communication satellite in orbit aroundA communication satellite in orbit around
the earth can provide a network connectionthe earth can provide a network connection
across an oceanacross an ocean

10. SatellitesSatellites
A single satellite usually contains multipleA single satellite usually contains multiple
transponders (typically 6-12)transponders (typically 6-12)
Each transponder consists of a radioEach transponder consists of a radio
receiver and transmitterreceiver and transmitter
Each transponder uses a different radioEach transponder uses a different radio
frequency (I.e., channel)frequency (I.e., channel)
multiple communications can proceedmultiple communications can proceed
simultaneously and independentlysimultaneously and independently

11. Geosynchronous SatellitesGeosynchronous Satellites
Place in an orbit that isPlace in an orbit that is exactlyexactly synchronizedsynchronized
with the rotation of the earthwith the rotation of the earth
Geostationary Earth Orbit (GEO)Geostationary Earth Orbit (GEO)
Distance required for geosynchronous orbitDistance required for geosynchronous orbit
is 36,000 km or 20,000 milesis 36,000 km or 20,000 miles
known as high earth orbitknown as high earth orbit
The entire 360-degree circle above theThe entire 360-degree circle above the
equator can only hold 45-90 satellitesequator can only hold 45-90 satellites
because satellites need to be separated to avoidbecause satellites need to be separated to avoid
interferenceinterference

12. Low Earth Orbit SatellitesLow Earth Orbit Satellites
Orbit a few hundred miles above the earthOrbit a few hundred miles above the earth
(200-400 miles)(200-400 miles)
Period of rotation is faster than the rotationPeriod of rotation is faster than the rotation
of the earthof the earth
DisadvantagesDisadvantages
can only be used during the time its orbit passescan only be used during the time its orbit passes
between two ground stationsbetween two ground stations
continuously moving the ground stations socontinuously moving the ground stations so
they point directly at the satellitesthey point directly at the satellites

13. Low Earth Orbit Satellite ArraysLow Earth Orbit Satellite Arrays
A set of satellites in low earth orbitsA set of satellites in low earth orbits
Allow continuous communications throughAllow continuous communications through
satellites in low earth orbitsatellites in low earth orbit
at least one satellite is available at any timeat least one satellite is available at any time
around 66 satellites are required to providearound 66 satellites are required to provide
service over the entire surface of the earthservice over the entire surface of the earth

14. MicrowaveMicrowave
High frequency radio wavesHigh frequency radio waves
Unidirectional, for point-to-pointUnidirectional, for point-to-point
communicationcommunication
Antennas mounted on towers relayAntennas mounted on towers relay
transmitted datatransmitted data

15. InfraredInfrared
Infrared light transmits data through the airInfrared light transmits data through the air
similar to technology used in TV remotesimilar to technology used in TV remote
controlcontrol
Can propagate throughout a roomCan propagate throughout a room
(bouncing off surfaces)(bouncing off surfaces)
but will not penetrate wallsbut will not penetrate walls
Becoming common in personal digitalBecoming common in personal digital
assistants (PDAs) and portable computersassistants (PDAs) and portable computers

16. LaserLaser
Unidirectional, like microwaveUnidirectional, like microwave
Higher speed than microwaveHigher speed than microwave
Uses laser transmitter and photo-sensitiveUses laser transmitter and photo-sensitive
receiver at each endreceiver at each end
Point-to-point, typically between buildingsPoint-to-point, typically between buildings

17. Choosing a MediumChoosing a Medium
Copper wireCopper wire
mature technologymature technology
rugged and inexpensive;rugged and inexpensive;
maximum transmission speed is limitedmaximum transmission speed is limited
Glass fiberGlass fiber
higher speedhigher speed
spans longer distancesspans longer distances
requires only single fiberrequires only single fiber
more expensive; less ruggedmore expensive; less rugged

18. Choosing a MediumChoosing a Medium
Radio and microwave don't require physicalRadio and microwave don't require physical
connectionconnection
Radio and infrared can be used for mobileRadio and infrared can be used for mobile
connectionsconnections
Laser also does not need physicalLaser also does not need physical
connection and supportsconnection and supports
higher speedshigher speeds