2 Transmission Media
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Transcript of 2 Transmission Media
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