Transmission Media

Guided Media
Unguided Media: Wireless


Transmission Medium & Physical Layer

Classes of Transmission Media





Twisted-pair Cable
UTP and STP Cables
UTP Connector
UTP Performance
Parallel Flat Wire
Coaxial Cable
Optical Fiber

Noise Effect on Twisted-Pair

Cumulative effect of noise is equal on both sides
Twisting does not always eliminate the noise, but does significantly reduce it

Optical Fiber

Optical fiber is made of glass or plastic
It transmits signals in the form of light

The Nature of Light
The speed of light
300,000 Km/sec in a vacuum
Depends on the density of the medium through which it is traveling
Other properties of light
Refraction, Critical angle, Reflection

Bending of Light Ray
Optical Fiber
Propagation Modes
Modes
Fiber Types
Fiber Construction


Fiber-optic Cable Connectors

SC (subscriber channel) connector used for cable TV. It uses push/pull locking system
ST (straight-tip) connector used for connecting cable to networking device. It uses a reliable bayonet locking system
MT-RJ is the same size as RJ45

Advantages/Disadvantages of Optical Fiber

Advantages
Higher bandwidth
Less signal attenuation
Immunity to electromagnetic interference
Resistance to corrosive materials
Light weight
Greater immunity to tapping
Disadvantages
Installation and maintenance
Unidirectional light propagation
Cost

Electromagnetic Spectrum for wireless

Propagation Methods

Bands

Wireless Transmission Waves

Wireless Transmission Waves

Radio waves are used for multicast communications, such as radio and television, and paging systems
Microwaves are used for unicast communication such as cellular telephones, satellite networks, and wireless LANs
Infrared signals can be used for short-range communication in a closed area using line-of-sight propagation

Omnidirectional & Unidirectional Antennas

Infrared

Infrared waves with frequencies from 300 GHz to 400 THz for short-range communication in a closed area using line-of-sight propagation
Having high frequencies, it cannot penetrate walls
IrDA (Infrared Data Association) for standards
Example: IrDA port for wireless keyboard
Originally defined a data rate of 75 kbps for a distance up to 8 m
Recent standard for a data rate of 4 Mbps