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Module 3.2: Transmission Media

• Electromagnetic Spectrum

• Guided Transmission Media

– Twisted Pair

– Coaxial cable

– Optical fiber

• Unguided Transmission Media

– Terrestrial Microwave

– Satellite

– Radio

– IR

– Cellular Telephony

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Electromagnetic Spectrum

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Guided Transmission Media

• Twisted Pair

• Coaxial cable

• Optical fiber

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Twisted Pair

• 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

• Pros and Cons:– Cheap– Easy to work with– Low data rate– Short range, about 100 meters.

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Unshielded and Shielded TP

• Unshielded Twisted Pair (UTP)– Ordinary telephone wire– Cheapest– Easiest to install– Suffers from external EM interference

• Shielded Twisted Pair (STP)– Metal braid or sheathing that reduces

interference– More expensive– Harder to handle (thick, heavy)– Capacity 10-155 Mbps

UTP Categories

• Cat 3– up to 16MHz– Voice grade found in most

offices

• Cat 4– up to 20 MHz

• Cat 5– up to 100MHz– Commonly pre-installed in

new office buildings

RJ-11 vs. RJ-45

• RJ-11 is a typical UTP phone connector. Has 2 pairs.

• RJ-45 is a UTP connector. Has 4 pairs.

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Coaxial Cable

• Most versatile medium

• Television distribution

– Ariel to TV

– Cable TV

• Long distance telephone transmission

– Can carry 10,000 voice calls simultaneously

– Being replaced by fiber optic

• Short distance computer systems links

• Local area networks

Transmission Characteristics Analog

Amplifiers every few km Closer if higher

frequency Up to 500MHz

Digital Repeater every 1km Closer for higher data

rates

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Optical Fiber

• Greater capacity

– Data rates of hundreds of Gbps

• Smaller size & weight

• Lower attenuation

• Electromagnetic isolation

• Greater repeater spacing

– 10s of km at least

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Transmission Characteristics

Act as wave guide for 1014 to 1015 Hz

Portions of infrared and visible spectrum

Light Emitting Diode (LED) used in MMF

Cheaper Wider

operating temp range

Last longer Injection Laser Diode

(ILD) used in SMF More efficient Greater data

rate Wavelength Division

Multiplexing (WDM) using light prisms.

MMF vs. SMF

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Comparison

Cable Type Cost1 = lowest5 = highest

Typical Capacity

Installation1 = easy5 = hard

Max Cable Length

EMI Resistance1 = low5 = high

Coaxial-Thinnet

2 10 Mbps 2 185 meters 2

Coaxial-Thicknet

4 10 Mbps 3 500 meters 2

UTP 1 10-100 Mbps 1 100 meters 1

STP 3 16-155 Mbps 2 100 meters 2

Fiber-optic 5 100+ Mbps 5 Multiple kilometers

5

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Wireless Transmission

• Unguided media

• Transmission and reception via antenna

• Directional

– Focused beam

– Careful alignment required

• Omnidirectional

– Signal spreads in all directions

– Can be received by many antennae

Frequencies 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 pt-pt confined

area

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Types of Radio Propagation

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Microwave

Terrestrial Microwave

• Parabolic dish

• Focused beam

• Line of sight

• Long haul telecommunications

• Higher frequencies give higher data rates

Satellite Microwave Satellite is relay station Satellite receives on one frequency,

amplifies or repeats signal and transmits on another frequency

Requires geo-stationary orbit Height of 35,784km

GEO vs. LEO Frequency Bands: C, Ku, and Ka Television Long distance telephone Private business networks

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Wide Area: Satellite Systems

• Cover very large areas

• Different orbit heights– GEOs (39000 Km), LEOs (2000 Km), MEOs (9000km)– GEO is stationary. You need 3 to coverwhole planet– LEO and MEO orbit the earth every one hour

• Dish antennas, or bulky handsets

• Optimized for one-way transmission,

location positioning, GPS systems, Satellite Radio– Radio (XM, DAB) and movie (SatTV) broadcasting– Killed MMDS wireless TV offerings. – Future: satTV (eg: directTV) in your car

• Most two-way systems struggling or bankrupt– Expensive alternative to terrestrial cellular system (2G)

• Trucking fleets, journalists in wild areas, Oil rigs

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LEO and MEO

• Used in GPS

• 24 MEOs are need to cover the whole planet

• 54 for LEOs to cover the whole planet

• Could have multiple readings for increased precision and reliability.

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WLAN

• Benefits of Ethernet WLAN– Cheap– Faster to deploy– Mobility– Watch for security

Need for authentication Need for encryption during transmission

• What is an Access Point?

• A typical diameter is a room for one AP about 40 meters

• Frequencies used and data rate– IEEE 802.11b operates at 2.4 GHz range and gives 11Mbps– IEEE 802.11a operates at 5 GHz range and gives 54Mbps– IEEE 802.11g operates at 2.4 GHz range and gives 54Mbps

• Bluetooth gives 1Mbps. Bluetooth networks PDAs or cell phones with PCs. Operates in a short diameter (10 meters).

– Operates at 2.4 - 2.4835 GHz– May have interference with Ethernet WLAN APs

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Others

Broadcast Radio

• Omnidirectional

• FM radio

• UHF and VHF television

• Line of sight

• Suffers from multipath interference

– Reflections

IR (Infrared) Modulate noncoherent

infrared light Line of sight (or reflection) Blocked by walls e.g. TV remote control,

IRD port

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Cellular System

Cellular Bands