Magnetic Media
- write to magnetic tape or removable media
- VHS, DVDs
- transmission involves physical delivery to destination
- Due to reduction in cost of data storage, transmission rate, is actually very powerful, a lot of bandwidth is possible
- ultrium tape storage, goes out to 70 Gbps
- however, delivery time uncertain/requires manpower to sort
Twisted Pairs
- twisted pair transmission lines
- consists of two insulated copper wires about 1 mm thick
- helical form, helps limit crosstalk
- can be used to transmit analog or digital information
- Category 5 twisted pair
- two insulated wires twisted together
- different LAN standards use the twisted pairs differently
- Full-duplex
- links that can be used two directions at the same time
- Half-duplex
- links that can only be used one direction at a time but can go both forward and back
- Simplex
- links that can only every be used in one direction
- Category 3 cables
- more twists per meter than cat 5
- Category 6/7
- handle signals with greater bandwidths
- UTP(Unshielded Twisted Pair)
- Only have wires and insulators, no extra shielding
Coaxial Cable
- better shielding and bandwidth than unshielded twisted pairs
- spans longer distances
- 50 ohm cable used for digital transmission
- 75 ohm used for analog transmission and cable tv
Power Lines
- electrical power lines most common wiring
- use for communication X10 standard
- issues
- extremely convenience superimpose low frequency data signal into wiring
- difficult to transmit, not original purpose of grid
- wiring changes from house to house
- signal reflections as appliances turned on/off
- still possible to send 100Mbps over typical household wiring
Fiber Optics
- Moore's Law increase in computer technology
- original IBM PC ran at 4.77 MHz, 28 years later 3 HHz, about factor of 16 per decade
- Fiber technology bandwidth can achieve up to 50,000 Gbps, currently at 100 Gbps
- FttH(Fiber to the Home)
- light pulse is a 1 nothing is a 0
- transmission takes advantage of internal reflection, light ray incidence at or above critical value
- Multimode fiber
- each ray has a different mode, light ray allowed to bounce at different angles
- Single-mode fiber
- light can only propagate in a straight line no bounce
- more expensive, can transmit longer distance
- Transmission of light through Fiber
- made of glass
- no more than 1mm thick
- light attenuation depends on physical property of glass and the wavelength of light
- wavelength bands most commonly used are
- 0.85, 1.30, 1.55 microns
- relatively flat attenuation
- Chromatic Dispersion
- light spreading through propagation
- making pulses in a special shape, called solitons can cancel this effect
- Fiber cables
- construction shown in the following diagram
- fiber connections
- connectors
- when fiber is connected, loses about 10-20% of light
- spliced mechanically
- lay two end to end, and clamp
- about 10% lgith loss
- fused into one
- small attenuation
- light sources
- LED(light emitting diodes) semiconductor lasers
- these light beams can be tuned using Fabry-Perot or Mach-Zhender interferometers
- receiving end is a photodiode
- Comparison of Fiber Optics and Copper wire
- Fiber very advantageous
- more bandwidth
- low attentuation
- distance to amplifier/repeater 50km for fiber
- 5 km for copper
- thin and lightweight
- disadvantages
- less familiar
- unidirectional, can't have two way communication without a separate wire
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