TRANSMISSION MEDIA

SUBJECT INCHARGE,PROF.MERRY K.P PREPARED BY,• SAVALIA DEVANG • 110570116054

WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998

Classes of Transmission MediaClasses of Transmission Media>Conducted or guided media

use a conductor such as a wire or a fiber optic cable to move the signal from sender to receiver

-> The waves are guided along a physical path

>Wireless or unguided media use radio waves of different frequencies and do not

need a wire or cable conductor to transmit signals

-> The medium transmits the waves but does not guide them

WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998

WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998

WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998

S.No.

Guided MediaUnguided media

1. The signal energy propagates within the guided media .i.e. through wires.

The signal energy propagates through air.

2. It is mainly suited for point to point line configurations.

It is mainly used for broadcasting purpose.

3. The signal propagates in the form of voltage, current or photons.

The signal propagates in the form of electromagnetic waves.

4.

Examples of guided media are:-=>Twisted Pair Cable=>Co-axial Cable=>Optical Fiber Cable

Examples are:-=>Microwave or Radio Links=>Infrared

OR

• >Transmission capacity depends on the distance and on whether the medium is point- to-point or multipoint

• Examples >twisted pair wires >coaxial cables >optical fiber

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->Consists of two insulated copper wires arranged in a regular spiral pattern to minimize the electromagnetic interference between adjacent pairs.

->Low frequency transmission medium

->The purpose of twisting the wires is to reduce electrical interference (or noise) from similar pairs close by.

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• >The twisted pair cable can be broadly

categorized into the following two types:

->Unshielded Twisted Pair (UTP) Cable

->Shielded Twisted Pair (STP) Cable

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>UTP (unshielded twisted pair) ->Each wire is insulated with plastic wrap. ->The plastic insulation is color-banded for identification. ->UTP is ordinary telephone wire. ->UTP can transfer data at 1 to 100Mbps over a distance of

100M.

>STP (shielded twisted pair) ->The pair is wrapped with metallic foil or braid to insulate the

pair from electromagnetic interference. ->The metal covering prevents the penetration of

electromagnetic noise. ->t can eliminate the phenomena called crosstalk. ->Provide better performance at lower data rates.

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• ->Most common medium• ->Telephone network

Between house and local exchange (subscriber loop)• ->Within buildings

To private branch exchange (PBX)• ->For local area networks (LAN)

10Mbps or 100Mbps

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• ->Twisted-pair cable is used in telephone lines for voice and data communications.

• ->Inexpensive and readily available• ->Flexible and light weight • ->Easy to work with and install

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• ->Susceptibility to interference and noise• ->Attenuation problem

For analog, repeaters needed every 5-6km For digital, repeaters needed every 2-3km

• ->Relatively low bandwidth (3000Hz)

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• 1 - primarily for voice• 2 – Datarate:4Mbps• 3 - 16MHz of bandwidth: 10Mbps• 4 - 20MHz of bandwidth: 16Mbps• 5- 100MHz of bandwidth; 100Mbps (4

pairs/cable)• 6 - 400MHz of bandwidth; 1Gbps (4

pairs/cable)

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• ->Carries the signal of high frequency ranges than twisted pair cable,

• ->Bandwidth of up to 400 MHz.• ->Coaxial cable has the following layers (starting from

the center): a metallic rod-shaped inner conductor, an insulator covering the rod, a metallic outer conductor (shield), an insulator covering the shield, and a plastic cover.

• ->Both conductors share a common center axial, hence the term “co-axial”.

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WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998

• ->Easy to install• ->Coaxial cable is used in cable TV networks and traditional

Ethernet LANs. • ->Higher bandwidth

400 to 600Mhz• ->Easy to handle and relatively inexpensive as compared to

fiber optic cables.• ->Since it is shielded can span a longer distances at higher

data rates.• ->Excellent noise immunity.• ->Much less susceptible to interference than twisted pair.

• ->High attenuation rate makes it expensive over long distance

• ->Distance is limited.• ->Bulky • ->Higher cost compared to twisted pair• ->Harder to work with & cable easily get

damaged

• ->Fiber-optic cables are composed of a glass or plastic inner core surrounded by cladding, all encased in an outside jacket.

• ->Fiber-optic cables carry data signals in the form of light. The signal is propagated along the inner core by reflection.

• ->Relatively new transmission medium used by telephone companies in place of long-distance trunk lines.

• ->Require a light source with injection laser diode (ILD) or light-emitting diodes (LED).

plastic jacket glass or plasticcladding

fiber core

• ->Consists of three concentric sections

   Frequency

RangeTypical

AttenuationTypical Delay

Repeater Spacing

Twisted pair (with loading)

0 to 3.5 kHz 0.2 dB/km @ 1 kHz

50 µs/km 2 km

Twisted pairs (multi-pair cables)

0 to 1 MHz 0.7 dB/km @ 1 kHz

5 µs/km 2 km

Coaxial cable

0 to 500 MHz

7 dB/km @ 10 MHz

4 µs/km 1 to 9 km

Optical fiber 186 to 370 THz

0.2 to 0.5 dB/km

5 µs/km 40 km

Point-to-point transmission

data rate bandwidthrepeater distance

Twisted pair 4 Mbps 3 MHz 2-10 km

Coaxial cable 500 Mbps 350 MHz 1-10 km

optical fibre 2 Gbps 2 GHz 10-100 km

• 2GHz to 40GHz microwave highly directional point to point satellite

• 30MHz to 1GHz omnidirectional broadcast radio

• 3 x 1011 to 2 x 1014

infrared local

Electromagnetic spectrum for wireless communication

Propagation Methods

Wireless transmission waves

• radio is 3kHz to 300GHz• use broadcast radio, 30MHz - 1GHz, for:

FM radio UHF and VHF television

• is omnidirectional• still need line of sight• suffers from multipath interference

reflections from land, water, other objects

Omnidirectional Antenna

Frequencies between 3 KHz and

1 GHz.

are used for multicasts communications, such as radio and television, and paging system.

• used for long haul telecommunications• and short point-to-point links• requires fewer repeaters but line of sight• use a parabolic dish to focus a narrow beam onto

a receiver antenna• 1-40GHz frequencies• higher frequencies give higher data rates• main source of loss is attenuation

distance, rainfall• also interference

Frequencies between 1 and 300 GHz. Used for unicast communication such as cellular phones, satellite networks and

wireless LANs.

Unidirectional Antenna

• satellite is relay station• receives on one frequency, amplifies or repeats

signal and transmits on another frequency eg. uplink 5.925-6.425 GHz & downlink 3.7-4.2 GHz

• typically requires geo-stationary orbit height of 35,784km spaced at least 3-4° apart

• typical uses television long distance telephone private business networks global positioning

• modulate noncoherent infrared light• end line of sight (or reflection)• are blocked by walls• no licenses required• typical uses

TV remote control IRD port

• electrical conductor used to radiate or collect electromagnetic energy

• transmission antenna radio frequency energy from transmitter converted to electromagnetic energy byy antenna radiated into surrounding environment

• reception antenna electromagnetic energy impinging on antenna converted to radio frequency electrical energy fed to receiver

• same antenna is often used for both purposes

• power radiated in all directions• not same performance in all directions

as seen in a radiation pattern diagram

• an isotropic antenna is a (theoretical) point in space radiates in all directions equally with a spherical radiation pattern

• measure of directionality of antenna• power output in particular direction verses that

produced by an isotropic antenna• measured in decibels (dB)• results in loss in power in another direction• effective area relates to size and shape

related to gain

• velocity of electromagnetic wave is a function of density of material~3 x 108 m/s in vacuum, less in anything else

• speed changes as move between media• Index of refraction (refractive index) is

sin(incidence)/sin(refraction) varies with wavelength

• have gradual bending if medium density varies density of atmosphere decreases with height results in bending towards earth of radio waves hence optical and radio horizons differ

• Free space loss loss of signal with distance

• Atmospheric Absorption from water vapour and oxygen absorption

• Multipath multiple interfering signals from reflections

• Refraction bending signal away from receiver

• Medium Cost Speed Atten Interfere Security• UTP Low 1-100M High High Low• STP Medium 1-150M High Medium Low• Coax Medium 1M–1G Medium Medium Low• Fibre High 10M–2G Low Low High• Radio Medium 1-10M Varies High Low• Microwv High 1M–10G Varies High Medium• Satellite High 1 M–10G Varies High Medium• Cellular High 9.6–19.2K Low Medium Low

Thank you….

WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998