Please enable JavaScript.
Coggle requires JavaScript to display documents.
TRANSMISSION MEDIA (CHAPTER6) - Coggle Diagram
TRANSMISSION MEDIA (CHAPTER6)
Guided(wired)
twisted-pair cable
Consists of two conductors (normally copper), each
with its own plastic insulation, twisted together
One of the wires is used to carry signals to the receiver,
and the other is used only as a ground reference
Interference (noise) and crosstalk may affect both wires
and create unwanted signals
both wires are equally effected by internal influences
When the receiver calculates the difference between the
two, receives no unwanted signals
2 types
Unshielded twisted pair (UTP)
Most common
Suitable for transmitting both data and voice
Frequency range for twisted pair wire is between 100 Hz to 5
Mhz
Consists of two conductors (cooper) each with its own
colored plastic insulation
Advantages of UTP are cost and ease to use
Shielded twisted pair (STP)
Has a metal shield that encases each pair of insulated
conductors
The metal casing prevents the penetration of
electromagnetic noise
eliminate phenomenon called crosstalk
More expensive than UTP but uses same connectors
coaxial cable
Carriers signals of higher frequency ranges than
twisted pair wire
Frequency range of coaxial cable is between 100 KHz
to 500 MHz
The whole cable is protected by a plastic cover
Has a central core conductor of solid wire (usually cooper) enclosed with insulator which encased an outer conductor of metal foil (usually cooper)
3 common of coaxial cable
RG-59 used for Cable TV
RG-58 used for Thin Ethernet
RG-11 used for Thick Ethernet
Most commonly type of connectors Bayone-Neill-Concelman (BNC) connector, BNC T connector and BNC terminator
fiber-optic cable
Made of glass or plastic and transmits signals in the
form of light
3 types of connectors
Subscriber channel (SC) connector – used for cable TV
Straight-tip (ST) connector – used for connecting cable
to networking devices
MT-RJ – same size as RJ46
Advantages
Less signal attenuation
Higher bandwidth
Immunity of electromagnetic interference
Light weight
More immune to tapping
Resistance to corrosive materials
Disadvantages
Cost
Installation and maintenance
Fragility
Unidirectional light propagation
introduction
Provide physical conductor from one device to
another
media is directed
and contained by the physical limits of the medium
Twisted pair and coaxial cable use cooper that
transport signal in the form of electrical current
Fiber optic use a glass or plastic that transport signals
in the form of light
Unguided(wireless)
free space
introduction
Transport electromagnetic waves without using
physical conductor
ways signal travel
Ground propagation
Radio waves travel through the lowest portion of the
earth
Greater power , greater distance
Sky propagation
Higher frequency radio waves radiate upward into the
ionosphere where they are reflected back to earth
Line of sight
Very high frequency signal are transmitted in straight
line directly from antenna to antenna
propagation methods
3 groups
Radio waves
Frequency between 3Khz to 1 GHz
Radio waves propagate in the sky can travel in long
distance e.g. AM radio
Function of omnidirectional antenna – radio waves propagated in all direction. Sending antenna and receiving antenna do not have to be aligned
Omni directional Antenna
Send out signals in all directions
Useful for multicasting
Microwaves
Frequencies between 1 to 300 GHz
Microwave are unidirectional(antenna narrowly focused)
Sending and receiving antenna need to be aligned
characteristics
Propagation is line-of-sight
Very high frequency microwaves cannot penetrate wall
The band is relatively wide, almost 299 GHz
Use of certain portions of the band requires permission
from authorities
Undirectional antenna
Send out signals in one direction
2 types of antennas
Parabolic dish antenna
Based on geometry of a parabola
Work as a funnel
Outgoing transmission are broadcast through a horn aimed at the dish
The microwave hit the dish and are deflected outward in a reversal of receipt path
Every line parallel to line of symmetry (line-of-sight) reflects off the curve at angles such that all lines intersect in a common point called the focus
Horn antenna
Like a gigantic scoop
Outgoing transmissions are broadcast up stem (resembling a handle) and deflected outward in a series of narrow parallel beams by the curved head
Received transmission collected by the scooped shape of the horn and deflected down into the stem
Useful in unicast (one-to-one) communication
example=cellular phones, satellite network and wireless LANs
Infrared
Frequencies between 300 GHz to 400 THz
Used for short range communication
example=IrDA port
that allow a wireless keyboard to communicate with PC
Useful for data transmission because use high
frequencies (400 THz)
Cannot penetrate wall or affected by another system
in the next room
