Wireless Basics

Will go over the basic of Wireless Networks.

, is the distance what a wave have to travel one a full 360 degree phase or cycle.
Decibel : dB is a function that use an algorithms to compare the absolute measurement to another.
dB = 10(log10 P2log10 P1)
P2 is the source and P1 is the reference.

The Rules of 3 and 10 :
3dB = *2 Transmit Power
-3dB = /2 Transmit Power
10dB = *10 Transmit Power
-10dB = /10 Transmit Power

Example : AP 100mw with a 7dB antenna = 100*10/2 = 500mw

Modulation :
Data sent across range of frequencies, SS “Spread Spectrum”
FHSS : Frequency Hop ( Divided into 79 channels of 1 MHz wide with a rate of 1-Mbps )
DSSS : Direct Sequence ( fix wide channel of 22mhz more resilient to interference, in 2.4GHz ISM band it use 14 Channel and 1 6 and 11 do not overlap with an 15% overlap acceptance)
OFDM : 5GHz U-NII band or immune to interference by devices using 2.4GHz ( microwave, phone ,tv etc… )

RF Signals :
Interference : Co-Channel, Neighboring Channel and Non-802.11
Co-channel : When devices transmit using the same channel
Neighboring : When devices are too close and overlapping will interfere with each others.
Non-802.11 : Wireless devices, microwave, phone, printers,wireless devices.

Free Space Path Loss ( FSPL ) :
Attenuation of the signal getting weaker further it get.

Physical Object Interference with WLAN :
Reflection : Signal is being reflected back towards any directions.
Absorption : Energy of the signal is being absorbed and attenuated.
Scattering : Signal is being scatter into different directions.
Refraction : Signal get to the destination with different densities.
Diffraction : Signal bend around the object.
Fresnel Zone :

Antennas :

WLAN Topologies :

BSS : “Basic Service Set” Single AP used.
Distribution System : Wireless to wired LAN.
ESS : “Extented Service Set” Multiple AP covering the surface required.
IBSS : AP Cannot communicate with each others.

Frame Type :
Authentication and De authentication
Association, Disassociation and re-association

Frame :
ACK ( unicast )
Block ACK ( Burt )
PS-PoLL ( Power Save Poll – Client to AP )
RTS/CTS ( Request to send / duration value / avoid collision)

Coverage :
BSA : Basic Service Area
The Cell “Area” size determine where service will be available.
Cell size also affect performance of the AP’s as client move around.
Cell control is possible, since it is a share medium the smaller the Cell are the less clients it will support.

Tunning Cells with Transmit Power.
Increase TP or Signal Strength AP’s, will increase the size of the Cell, Gov regulation dont allowed more then 20dBm ( 100mW).

Adding AP’s to ESS :
Site Survey is required
APs configure with different non-overlapping channels or use different frequencies
Monitoring of RSSI SNR , collision and interference.

Design Validate with Site Survey :
Radio Survey : Gather information about the Frequencies, Magnetic Interference and radiate power  from the BSA.
Site Survey : Gather information where devices “APs” can be place physically, safety and security. Then using Heatmaps on Plan or maps to be able to see details of the coverage.

Survey Tools :
Predictive :
Fluke Networks Airmagnet Panner, Exahau Site Servey + WiFi Planner.
Cisco Prime
Cisco Predictive RF Planner
Aerohive Wi-Fi Planner
Passive and Active:
Fluke Networks AirMagnet Survey PRO
Exahau Site Servey + WiFi Planner.

Connected through TUnnel CAPWAP between WLC and  APs.

Radio Resource Management
RRM administer the wireless network by automating the appropriate change for you ( channel, TP levels, RF etc.. )



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