Transmission media

Transmission media can be divided into:

- Guided

- Twisted pair cables

- Coaxial cables

- Fiber optic cables

- Unguided- Unguided

- Radio waves

- Microwaves

- Infrared

Twisted Pair

TP Cables

� Cat 1 : telephone lines

� Cat 2 : up to 4 MbpsUTP

� Cat 2 : up to 4 Mbps

� Cat 3 : up to10 Mbps

� Cat 4 : up to 16 Mbps

� Cat 5 : up to 100 Mbps

� Cat 5e : up to 125 Mbps

� Cat 6 : up to 200 Mbps

� Cat 7 : up to 600 MbpsSTP

Unshielded vs Shielded TP

• unshielded Twisted Pair (UTP)

– ordinary telephone wire

– cheapest

– easiest to install

– suffers from external EM interference– suffers from external EM interference

• shielded Twisted Pair (STP)

– metal braid that reduces interference

– more expensive

– harder to handle (thick, heavy)

• in a variety of categories

Coaxial Cable

Up to 600 Mbps

• Standards:

– RG 59 : For TV signals

– RG 58 : For thin Ethernet

– RG 11 : For thick Ethernet

Fiber-Optic

• Glass or plastic core

• Greater capacity

– data rates of hundreds of Gbps

• Smaller size & weight

• Lower attenuation

• Electromagnetic resistance• Can use several different light sources:

• Electromagnetic resistance

• Greater repeater spacing

– 10s of km at least

• Can use several different light sources:- Light Emitting Diode (LED)

cheaper, wider operating temp range, lasts longer

- Injection Laser Diode (ILD)more efficient, has greater data rate

Types of Fiber-Optic

• Multimode Step index (about 50 micron core)

– Earliest fiber-optic systems

– Signal spreads out over short distances (up to ~500m)

– Inexpensive

• Multimode Graded index

– Reduces the spreading problem by changing the refractive

properties of the fiber to refocus the signal

– Can be used over distances of up to about 1000 meters

• Single mode (about 5 micron core)

– Transmits a single direct beam through the cable

– Signal can be sent over many kilometers

– Expensive (requires lasers; difficult to manufacture)

Optical Fiber Transmission Modes

Wavelength range in nm: 820-900, 1280-1350, 1528-1620

Unguided Media: Wireless

Wireless Transmission Frequencies

• 2GHz to 40GHz

– microwave

– highly directional

– point to point

– satellite– satellite

• 30MHz to 1GHz

– omnidirectional

– broadcast radio

•

– infrared

– local

1411 102103 x to x

Propagation Methods

Terrestrial Microwave

• Used for long haul telecommunications and short point-to-point links

• Requires fewer repeaters but line of sight

• Uses a parabolic dish to focus a narrow beam onto a receiver antenna

• 1-40GHz frequencies• 1-40GHz frequencies

• Higher frequencies give higher data rates

• Main source of loss is attenuation

– distance, rainfall

• Loss:

dbd

L2)

4log(10

λ

π=

Satellite Microwave

• 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– height of 35,784km

– spaced at least 3-4° apart

• Typical uses

– television

– long distance telephone

– private business networks

– global positioning

Orbital comparison for satellite communications

applications

Factors Used in Media Selection

• Type of network

– LAN, WAN, or Backbone

• Cost

– Always changing; depends on the distance

• Transmission distance

– Short: up to 300 m; medium: up to 500 m– Short: up to 300 m; medium: up to 500 m

• Security

– Wireless media is less secure

• Error rates

– Wireless media has the highest error rate (interference)

• Transmission speeds

– Constantly improving; Fiber has the highest

Media Summary

Infrared

� Spectrum for infrared virtually unlimited

� Possibility of high data rates

� Infrared spectrum unregulated

� Equipment inexpensive and simple

� Reflected by light-colored objects� Reflected by light-colored objects

� Ceiling reflection for entire room coverage

� Doesn’t penetrate walls

� More easily secured against eavesdropping

� Less interference between different rooms