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1089 Cards in this Set
- Front
- Back
Chapter 1 essentials |
1. Know the four industry organizations. 2. Understand core, distribution, and access 3. Understand wavelength, frequency, amplitude, and phase. 4. Understand the concepts of modulation. |
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Responsibilities of ITU-R |
> Global Spectrum management >Ensures interference free communication on land, sea and skies |
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Name Standard Organizations |
1. ITU-R :International Telecommunication Union Radio Sector 2. FCC: Federal Communications Commission 3. IEEE: Institute of Electric & Electronic Engineers 4. IETF: Internet Engineering Task Force 5. ISO: International Organization for Standardization 6: Wi-Fi Alliance |
|
ITU-R responsibilities |
> Global spectrum management > Ensures interference free communications on land, sea and skies |
|
What is FCC and what are their responsibilities |
>Its a communication regulatory domain in US >w.r.t wireless, FCC regulates the usage of radio signals used for communication |
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Name the 6 areas in wireless where FCC regulates on |
1. Frequency 2. Bandwidth 3. Maximum power of Intentional Radiator(IR) 4. Maximum EIRP 5.Use Indoor or Outdoor 6. Spectrum sharing |
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Which organization is responsible for creating WLAN or any standards/protocols? |
IEEE |
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What is RFC stands for? |
>Request For Comments >provided by IETF |
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Responsibilities of IETF |
To make internet better |
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Who created OSI model |
ISO |
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Wi-Fi alliance responsibility |
Ensure interoperability of WLAN devices by certification testing |
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How many layers does OSI model have? |
>Seven Application,Presentation,Session,Transport,Network,Data link(LLC+MAC),Physical |
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WLAN operates in which layer of OSI model? |
Layer 2 |
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Which are the 3 layers in internetworking model? |
Core, Distribution and Access |
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Client node a.k.a end user packet delivery is performed by _____layer |
Access layer |
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Core layer functions are ____ |
>reliable delivery of packets to distribution layer and out the network >high speed switching |
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Packet manipulation is done _____layer |
Distribution layer |
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Out of Core, Distribution & Access which layer is slower and which one is faster |
Access layer is slower Core layer is faster |
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Commonly Wi-Fi is implemented in which layer of internetworking architecture |
Access layer |
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An 802.11 Bridge link is an example for wireless technology being used in ______ layer. |
Distribution layer |
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Which are the different properties of a wave? |
1. Amplitude 2. Wavelength 3. Frequency |
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Distance from rest position to crest is known as ___ of a wave |
Amplitude |
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Distance travelled by wave when it completes one cycle |
Wavelength |
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Frequency is ___ |
Number of occurrence of a wave per second at a specific point |
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____ is used to tell relative displacement between or among waves of same frquency |
Phase |
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Modulation techniques are also known as keying methods. True or False |
True |
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Which are the different keying methods used in WLAN? |
ASK: Amplitude Shift Keying FSK: Frequency Shift Keying PSK: Phase Shift Keying |
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Current State and State Transition are the 2 different techniques used by keying methods to represent data. True or False |
True |
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ASK & FSK uses ____ state technique |
Current State |
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Out of ASK, FSK, PSK which is more effected by noise |
ASK Note: When interference occurs it directly affects amplitude of the signal. A change in amplitude due to noise will lead to misinterpretation of data at the receiver |
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PSK is widely used in 802.11. True or False |
True |
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Current state technique: current state of a signal is used to represent 0s and 1s Analogy: A door can be used to represent 0s and 1s. An opened door represents 0 and closed door represents 1 Eg: ASK(AM/FM), FSK |
Statement: Modulation technique |
|
State transition technique: Change or transition of a state is used to represent 0s and 1s Analogy: A door can be used to represent 0s and 1s. Here moving door(opening or closing) represents 0 and still door(opened or closed) represents 1 Eg: PSK |
Statement: Modulation technique |
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Chapter 2 Essentials |
1. wavelength, frequency, amplitude, and phase 2. RF behaviors Wave propagation, Absorption, Reflection Scattering, Refraction, Diffraction, Loss (attenuation), Free space path loss, Multipath, Gain (amplification) |
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Measure of how effective an antenna is at receiving the power of radio waves is known as____ |
Aperture |
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Higher the frequency, lower the wavelength will be. True or False |
True |
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In real world waves with higher frequency attenuate more than waves with lower frequency. True or False |
True |
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Unit of frequency is ____ |
Hertz(Hz) |
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2.4 GHz WLAN radios, the RF signal is oscillating2.4 billion times per second. True or False |
True |
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Signal strength or power of a signal is known as___ |
Amplitude |
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Amount of initial amplitude that leaves the radio transmitter is known as___ amplitude and received signal strength is known as ___amplitude |
Transmit, Recieve |
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RF signal strength measurements taken during site survey is an example for ____ amplitude. |
Recieve |
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Transmit power range of indoor 802.11 radios range is ____ |
1mW to 100mW |
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Phase can be measured in distance, time or degrees. True or False |
True |
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Name the nine Radio Frequency Behaviours |
1. Absorption 2. Reflection 3. Scattering 4. Refraction 5. Diffraction 6. Free space path loss 7. Multipath 8. Attenuation 9. Gain |
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The manner in which RF signal moves is known as____ |
propogation behaviour |
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Why WLAN Engineer should be aware of RF propagation behaviour? |
For the proper placement of AP, choosing right antenna type and for monitoring wireless performance |
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Which one these will aborb more 1. Dry wall 2. Brick and Concrete 3. Water |
Brick and Concrete |
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When a wave hits a smooth object larger than its wavelength and bounce in a different direction is known as___ |
Reflection |
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Microwave frequency range |
1GHz to 300GHz |
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Two types of RF reflection |
Sky wave and microwave |
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What type of reflection will come across in 802.11 ? |
microwave |
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Sky wave reflection occurs for waves below 1GHz of frequency. True or False |
True |
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Scattering is analogous to multiple reflections. True or False |
True |
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Common reasons for scattering |
Smog in atmosphere, sand in desert Due to uneven surfaces: Chain link fences, wire mesh in stucco walls or old plaster walls, tree foliage, rocky terrains |
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Bending of RF waves when it pasess through medium of different density is known as ___ |
Refraction |
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3 main causes of refraction |
1. Water vapour 2. Changes in air temperature 3. Changes in air pressure |
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Bending of RF signal around an object is known as ___ |
Diffraction |
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Diffraction is caused by partial blockage of RF signal. True or False |
True |
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The place sitting exact behind the RF blockage is known as ___ |
RF shadow |
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Loss of signal strength due to absorption, reflection, negative effects of multipath is known as ___ |
Attenuation |
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Loss in signal strength due to natural broadening of waves is known as |
Free space path loss |
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Unit of attenuation is expressed in |
dB |
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According to 6dB rule,doubling the distance will result in ___dB decrease in amplitude |
6 |
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When a signal encounters an object it may reflect, scatter.refract or diffract resulting same signal travelling multiple maths arriving receiver at nano seconds difference is known as |
Multipath effect |
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____ is the time differential between primary signal and reflected signal |
Delay spread |
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Possible outcomes of multipath are |
1. Upfade 2. Downfade 3. Nulling 4. Intersymbol interference |
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When the primary signal and reflected signal arrives receiver with 0 to 120 degree phase difference it will result in ___ |
Upfade |
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When the primary signal and reflected signal arrives receiver with 121 to 179 degree phase difference it will result in ___ |
Downfade |
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When the primary signal and reflected signal arrives receiver with 180 degree phase difference it will result in ___ |
Nulling |
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Amplification of a signal is known as ___ |
Gain |
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Gain achieved with the help of amplifier is known as ___ |
Active gain |
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Gain achieved without amplifier and only with antenna is known as ___ |
Passive gain |
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Spectrum analyzer is a ___domain tool for measuring amplitude |
Frequency |
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Time domain tool used by WLAN Engineers to measure amplitude |
Oscilloscope |
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Chapter 3 essentials |
1. Components of RF communication: Transmitter, Receiver, Antenna, Isotropic radiator, Intentional radiator, Equivalent isotropically radiated power(EIRP) 2. Units of power and comparison: watt,milliwatt,dB,dBi,dBd,dBm,inverse square law 3. RF Math: Rules of 10s and 3s 4. Noise Floor 5. SNR 6. RSSI 7. Link budget 8. Fade margin/system operating margin |
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Higher the transmit power, higher the transmit amplitude and farther the wave can travel. True or False |
True |
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Transmit power of a wireless transmitter is regulated by ___ |
FCC |
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Functions of antenna |
Transmit and receive signals to and from transceiver |
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Access points, client adapters, wireless bridge links are examples for transreceivers. True or False |
True |
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A point source which radiates signal equally in all directions is known as ___ radiator |
isotropic radiator |
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Transceiver is a single component or device which does two different functions, transmitter and receiver. True or False |
True |
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Transmitter modulates input data/signal and transmit through antenna. The resulting wave after modulation is known as |
Carrier wave |
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Usually carrier wave higher frequency than input signal. True or False |
True |
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The final component in the wireless medium who is responsible for demodulating signal into bits and bytes and fed into computer |
Receiver |
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Anything which generates RF energy is called Intentional Radiator(IR) . True or False |
False |
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A device that intentionally generates and emits RF energy by induction or radiation is called Intentional Radiator |
Statement: Definition of IR by FCC |
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Components of IR |
Everything between transmitter and antenna excluding antenna and including transmitter. components include transmitter,all cables and connectors, amplifiers, attenuators, lightning arrestors, grounding between transmitter and antenna. |
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Power of IR is measured in |
mW or dBm |
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Power of IR is the sum of power of all components including transmitter,cables and connectors. True or False |
True |
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Power of IR is measured at ___ |
connector that provides input to antenna |
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Highest RF signal that is transmitted from antenna is known as ___ |
EIRP |
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Product of power supplied to antenna and antenna gain in a given direction relative to an isotropic antenna |
FCC definition of EIRP |
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Units of transmit and received power measurements are absolute power measurements |
Statement: Absolute power measurement |
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Units of comparison are measurements of change in power |
Statement: Change in power measurement |
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Watt,mW, dBm are ___ |
units of power(absolute) |
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dB,dBi,dBd are units of ___ |
change in power(units of comparison) |
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Antenna gain is expressed in ___ |
dBi |
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Antenna gain is always positive. True or False |
True |
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Antenna power is always expressed in gain not power |
Statement: Antenna facts |
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Decibel gain w.r.t an isotropic antenna is known as ___ |
dBi |
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Antenna radiates equally in all directions. True or False |
False |
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Antenna gain or dBi is measured at the strongest point or focus point of antenna signal |
Statement |
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Antenna with dBi = 0 is also known as ___ |
no gain or unity gain antenna |
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Antenna focus more energy on one side than the other. So the dBi of antenna will be always positive gain and not loss. True or False |
True |
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dBi value of 2.4GHz half-wave dipole antenna is ___ |
2.14 |
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dBd is antenna gain w.r.t dipole antenna |
Statement |
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dBi, dBd relationship |
dBi= 2.14+dBd |
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Both dBi and dBd are used to express antenna gain. True or False |
True |
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dBm is decibel relative to 1mW |
Statement: dBM |
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Since dBm is relative measurement to a known value 1mW, dBm is an absolute measurement.True or False |
True |
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0dBm = __mW |
1mW P(in mw) = 10^(PdB/10) |
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+dBm indicates value is greater than 1mW. True or False |
True |
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-dBm indicates value is less than 1mW. True or Falsse |
True |
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If you double the distance between transmitter and receiver amount of usable signal will ___ by 6dB |
decrease |
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6dB rule |
+6dB doubles the distance of usable signal -6dB halves the distance of usable signal |
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Rules of 3s and 10s |
1. For every 3dB gain, double(x2) the absolute power in mW 2. For every 3dB loss, halve(÷ 2) the absolute power in mW 3. For every 10dB gain, multiply absolute power in mW by 10 4. For every 10 dB loss, divide absolute power in mW by 10 |
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RF Math summary |
dBm=10 log(Power in mW) Power in mW=10^(dBm/10) 3 dB gain = mW x 2 3 dB loss = mW ÷ 2 10 dB gain = mW × 10 10 dB loss = mW ÷ 10 |
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Steps involved in calculating IR and EIRP |
1. Convert mW values in dB 2. Apply rules of 3s and 10s Note: All dB values can be added |
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Ambient or background level of radio energy on a specific channel is called |
Noise floor |
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Noise floor of typical 2.4GHz ISM channel |
-100dBm |
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Noise floor of 5GHz will be higher than 2.4GHz. True or False |
False |
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SNR is the ratio between received signal and noise floor. True or False |
False |
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The difference between received signal and noise floor |
SNR(signal to noise ratio) |
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Low SNR is one of the reason for layer 2 retransmission and low throughput |
Statement: SNR facts |
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Good quality signal will have SNR >= 25dB |
Statement: SNR facts |
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SNR <= 10dB are considered as signal with poor quality |
Statement: SNR facts |
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RSSI is ___ |
recieved signal strength indicator |
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RSSI is expressed in ___ |
dBm |
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Higher the RSSI greater the signal quality |
Statement: RSSI facts |
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power level of RF signal required to be successfully received by the receiver is called as __ |
RSSI |
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Range of RSSI value ___ |
0 to 255 |
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Signal with high data rate are more susceptible to corruption. True or False |
True |
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Device used by WLAN engineers to measure noise floor, SNR |
spectrum analyzer |
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The sum of all planned expected gains and losses from the transmitting radio, through the RF medium, to the receiver radio |
Link budget |
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Purpose of calculating link budget |
To make sure final received signal is above the receiver sensitivity threshold of receiver radio |
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Fade margin = received signal strength - receiver sensitivity of the receiver |
Statement: Fade margin |
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Minimum fade margin required |
10dB |
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For transmissions higher than 5 miles, recommended fade margin for reliable communication will be ___ |
25dB |
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Best practice followed by WLAN engineers for indoor environmentby choosing fade margin ____ , for reliable communication |
5dB greater than receiver's sensitivity amplitude |
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Link budget and Fade margin are the 2 essential things which should be taken care of by WLAN engineers for outdoor deployment. True or False |
True |
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WLAN vendors use RSSI thresholds to trigger which radio card behaviors? |
Roaming and Dynamic Rate Switching(DRS) |
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Chapter 4 essentials |
1. Four antenna types: Omni directional.semi directional,highly directional,sector 2. Azimuth and elevation charts 3. Key concerns while installing point-to-point communication: Visual LOS, RF LOS, Fresnel zone, Earth bulge, Antenna polarization 4. VSWR, antenna mounting issues, antenna accessories and their roles |
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To assist potential buyers, antenna manufactures creates antenna radiation pattern for their antennas known as polar chart or antenna radiation envelopes. |
Statement: Antenna radiation charts |
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Azimuth and elevation charts are example for ___ |
polar charts or antenna radiation pattern charts |
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Which chart will give us top-down-view of antenna radiation pattern? |
Azimuth chart |
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Which chart will give us side view of antenna radiation pattern? |
Elevation chart |
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Radiation charts are drawn by keeping antenna on the center of the chart. True or False |
True |
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Reference plane on which Azimuth chart is drawn. |
H-plane |
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Reference plane on which Elevation chart is drawn. |
E plane |
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E plane gives us the side view of antenna radiation pattern with antenna in the centre of the chart |
Statement: reference plane for antenna radiation pattern |
|
H plane gives us top view of antenna radiation pattern with antenna in the centre of the chart |
Statement: reference plane for antenna radiation pattern |
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Measurement which tells us how broad or narrow is the focus of the antenna is called ____ |
Beamwidth |
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Beamwidth is measured from the centre or at the strongest point of the antenna signal to each points along vertical axis and horizontal axis where signal decreases by half power(-3dB) |
Statement: beamwidth |
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The point at which signal power becomes half the power is called half-power-points |
Statement:Beamwidth |
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The distance between half power points in vertical axis is measured in |
degrees |
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The distance between half power points in horizontal axis is measured in |
degrees |
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3 types of antennas |
1. Omni directional 2. Semi directional 3. Highly directional |
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Which type of antenna gives us 360 degrees of coverage? |
omni directional |
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Type of antenna which provides directional coverage over a large area |
semi directional |
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Type of antenna which is generally preferred in point-to-point communication |
Highly directional antennas |
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Dipole antenna a.k.a rubber duck antenna is an example for ___ |
omni directional antennas |
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Antenna whose RF radiation pattern is similar to that of isotropic radiator |
Dipole antenna |
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Higher the dBi or dBd value of antenna higher will be the focus of the signal. True or False |
True |
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Omnidirectional antennas have great horizontal coverage and less vertical coverage |
Statement: Omni directional antenna |
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Vertical beamwidth of omni directional antenna ranges from |
7 to 80 degrees |
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Patch, Panel, Yagi are examples for ____ type of antennas |
semi directional |
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Type of antennas suitable for short to medium distance communications |
Semi directional |
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Type of antennas preferred in libraries with large corridors and shelves,hallways where omni directional antennas are ineffective to provide proper coverage |
Planar antennas |
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Patch and Panel antennas are commonly referred as ___ antennas |
Planar antennas |
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Horizontal beamwidth of patch/panel antennas |
30 to 180 degrees |
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Vertical beamwidth of patch panel antennas |
6 to 90 degrees |
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Antennas ideal for high density environment like gymnasium, schools, hallways when 802.11n or 11ac is deployed |
MIMO patch antennas |
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MIMO patch antennas are mounted from the ceiling downward to provide coverage on tight sectors |
Statement: MIMO patch antenna |
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What type of antenna is shown in pic |
Yagi uda antenna(Semi directional) |
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Type of antenna shown in pic |
Panel antenna (semi directional) |
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Name the antenna |
rubber duck or half wave dipole antenna |
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Antenna type shown in pic |
parabolic dish(highly directional) |
|
Antenna type shown in pic |
Grid antenna(highly directional) |
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The spacing of wires in grid antenna is determined by the wavelength of the frequencies that antenna is designed for |
Statement: Grid antenna |
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Out of 2 antenna types parabolic dish and grid, which one is more susceptible to high wind environment? |
parabolic dish Note: Because the spacing between the wires, grid antennas are less affected by high wind environment |
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Sector antennas are high gain semi directional antennas which has pie shaped coverage area. |
Statement: Sector antennas |
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Sector antennas are placed in the centre, where RF coverage area is required, by keeping antennas back to back |
Statement: Sector antennas |
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Combining sector antennas, so that each coverage pie area of each antenna forms a 360 degree coverage is called sector array |
Statement: Sector antennas |
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The main disadvantage in a sector array is, back lobes of each antenna's radiation pattern interfere with each other. True or False |
False Note: Radiation formed at back side of sector antenna are minimal and doesn't cause any interference or have least impact |
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Sector antennas typically have a gain of ___dBi |
10 dBi |
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Horizontal beamwidth of sector antennas |
60 to 180 degrees |
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Vertical beamwidth of sector antennas |
7 to 17 degrees |
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Name the antenna type used in picture |
Sector antenna |
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To provide RF coverage in outdoor areas, stadium ____ antennas are preferred |
Sector |
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A group of two or more antennas that are integrated together to provide coverage is generally known as ___ |
antenna arrays |
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3 types of beamforming |
1. Static beamforming 2. Dynamic beamforming 3. Transmit beamforming |
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Beamforming is method of concentrating RF energy by focusing the RF transmission from antenna to receiver |
Statements: Beamforming |
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Beamforming achieved by clustering multiple directional antennas to provide a fixed radiation pattern,aimed away from centre or location |
Static beamforming |
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Indoor sectorized array is an example for ___ |
static beamforming |
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smart antenna or beam steering is a technology used in ___ beamforming |
dynamic |
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In dynamic beamforming adaptive antenna arrays maneuvers radiation pattern in the direction of the receiver. |
Statements: Dynamic beamforming |
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Unlike static beamforming whose radiation patterns are fixed, radiation pattern varies frame-by-frame in dynamic beamforming. True or False |
True |
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Wi-Fi vendor Xirrus is an example for manufacturing indoor sectorized array solution |
Statement: Static beamforming |
|
Ruckus wireless is an example for Wi-Fi vendors who is capable of providing dynamic beamforming solutions |
Statement: Dynamic beamforming |
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Transmit Beamforming: By carefully adjusting phase of signals transmitted from each antenna so that, when signals arrive at receiver are in phase. |
Statement: TxBf |
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2 types of beamforming |
implicit and explicit |
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802.11n uses what type of beamforming |
Both implicit and explicit |
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802.11 ac uses what type of beamforming |
explicit |
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Light travels from one to another point in an unobstructed straight line called ___ |
Visual line of sight(LOS) |
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RF line of sight is also known as ___ |
Fresnel zone |
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Imaginary elongated football shaped area around visual line of sight is called ___ |
Fresnel zone |
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Fresnel exists both above and below visual los. True or False |
True |
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It is recommended practice while mounting outdoor point-to-point communication that 1st fresnel zone is not obstructed by buildings, trees or any other obstacles. |
Statement: Fresnel zone |
|
Size of fresnel zone is a function of distance between points and frequency being used |
Statement: Fresnel zone |
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Multiple fresnel zone exists around the primary or first fresnel zones. |
Statement: Fresnel zone |
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RF signal at first fresnel zone is in phase with point source signal |
Statement: Fresnel zone |
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All the odd fresnel zones are in phase with point source and all the even fresnel zones are out of phase with the point source signal. True or False |
True |
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Earth bulge is earth's curvature. |
Statement: Earth bulge |
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Earth bulge should be considered when distance between point to point communication are greater than 7 miles |
Statement: Earth bulge |
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Which all factors are considered when calculating antenna height in feet |
Fresnel zone, Earth bulge, Height of obstacle Note: H = obstacle height + earth bulge + Fresnel zone |
|
Antenna diversity is also known as ___ |
spatial diversity |
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Antenna diversity works only if receiver has multiple antennas. True or False |
True |
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Antenna diversity is introduced to avoid/minimize negative effects of ___ |
multipath |
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When transceiver receives multiple copies of same signal from multiple antennas, it choose signal from those antenna which has the best signal quality. This technique is commonly used in pre-802.11n and known as ___ |
switched diversity |
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switched diversity is also known as |
receive diversity |
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While using receive diversity signal with best amplitude is chosen by the receiver. True or False |
True |
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While using switched diversity during transmission, same signal is sent across all the antennas. True or False |
False Note: Only one antenna is used. The antenna in which last best received signal was heard is used. |
|
switched diversity used in transmission is known as ___ |
transmit diversity |
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If implemented, access point when making use of antenna diversity, all the antennas should have same gain, same orientation and distance between antennas should be a factor of wavelength(1/4, 1/2,1,2) |
Statement: antenna diversity |
|
MIMO stands for |
Multiple Input Multiple Output |
|
MIMO took positive effects of ___ to increase throughput |
multipath |
|
MIMO was first introduced in |
802.11n |
|
While transmitting using antenna diversity out of all antennas only one antenna is used. But in MIMO all the antennas are used concurrently |
Statement: MIMO Vs Antenna diversity |
|
3 key components associated with antenna installation |
1. Voltage Standing Wave Ratio(VSWR) 2. Signal loss 3. Mounting of antenna |
|
Voltage standing wave ratio is a measurement of change in impedance of an AC signal. True or False |
True |
|
Voltage standing waves are generated due to impedance mismatch between transmitter,cable and antenna |
Statement: VSWR |
|
Numerical expression for VSWR |
VSWR = Vmax/Vmin Maximum voltage across the line /Min voltage across the line |
|
Ideal value for VSWR |
1:1 |
|
Typically VSWR value ranges from |
1.1:1 to 1.5:1 |
|
The ratio between voltage of reflected wave and incident wave is known as |
reflection coefficient |
|
reflection coefficient is denoted by |
greek letter rho (ρ). |
|
Difference between power sent to antenna and power reflected back is known as |
return loss |
|
Return loss is expressed in |
dB |
|
VSWR may cause decreased signal strength, erratic signal strength , transmitter failure if not protected |
Statement: VSWR |
|
Resulting signal reaching the antenna will be larger if VSWR is larger. True or False |
False |
|
Key areas to be concerned while installing antennas |
1. Placement 2. Mounting 3. Appropriate use and environment 4. Orientation and alignment 5. Safety 6. Maintenance |
|
2 standards that designates how device can stand up against harsh environments |
1. IP Rating(Ingress Protection Rating) 2. NEMA Rating(National Electrical Manufacturers Association) |
|
IP rating is denoted by IP followed by two digits or a digit and one or two letters Example: IP66 |
Statement: IP rating |
|
You have been provided an antenna with IP rating IP66. What does it indicates? |
First digit indicates how far the antenna can withstand intrusion against solid particles like dust on a scale of 0 to 6 Second digit indicates water resistance capability on a scale of 0 to 8 |
|
You have been provided an antenna with IP rating IPX. What does it indicates? |
It means no protection is provided against intrusion of solid particles and water |
|
Rating of NEMA is in the form of number or number followed by a letter |
Statement : NEMA |
|
Which are the features included in Nema ratings that are not present in IP rating? |
Corrosion resistance Gasket aging Construction practices |
|
Atex directive pertains to equipment and protective systems that are intended to be usedin potentially explosive atmospheres. |
ATEX 95 |
|
Atex directive pertains to the workplace and is intended to protect and improve thesafety and health of workers at risk from explosive atmospheres. |
ATEX 137 |
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NEC is __ |
National Electrical Code |
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__ is a standard for safe installation of electrical equipment and wiring |
NEC |
|
NEC classifies hazardous location by type condition and nature. Name them those classifications |
1. Class I gas or vapor 2. Class II dust 3. Class III fibers and flyings |
|
To prevent from water damage cold shrink tubing is used rather than hot shrink tubing. The reason is __ |
cable can be damaged by the heat that is necessary to shrink the wrapping. |
|
Silicone is not used to prevent the cable from water damage. The reason is __ |
air bubbles can form inside silicone and moisture can be formed |
|
Cable manufacturers will list range of frequencies that cable can support and is generally known as ___ |
Frequency response |
|
LMR 900 cable is generally used for __GHz |
5 |
|
LMR 1200 is used for ___GHz |
2.4 |
|
Higher the frequency of signal, higher will be attenuation caused by the cable. True or False |
True |
|
RF connectors generally add __dB of insertion loss |
1/2 |
|
Antenna accessory which takes a RF signal and divides into two or more seperate signals is known as |
splitter |
|
The increase in gain by applying electrical power to signals by an amplifier is known as |
active gain |
|
It is a recommended practice to install amplifier as close to antenna to prevent cable loss. |
Statement: amplifier |
|
Antenna accessory which is used to decrease the amount of signal radiating from antenna |
attenuator |
|
Two different type of attenuator |
1. Fixed loss attenuator 2. Variable loss attenuator with a dial to control dB loss |
|
__ is used to calculate fade margin in outdoor site surveys. |
variable attenuator |
|
Lightning arrestors are not capable of direct lightning strike. True or False |
True |
|
Lightning arrestors protect against surges from 5000amps to 50 volts |
Statement: Lightning arrestor |
|
As per IEEE, a lightning arrestor should be capable of redirecting transient current within 8micro seconds |
Statement: Lightning arrestor |
|
Lightning arrestor should be placed close to antenna with all other communication devices like amplifiers, attenuators installed between transceiver and lightning arrestor . True or False |
True |
|
Antenna accesories |
1. Cables 2. Connectors 3. Splitter 4. Amplifier 5. Attenuator 6. Lightning arrestor 7. Grounding rods and wires |
|
Azimuth chart is prepared in reference with H-plane. What is this H denotes? |
Horizontal |
|
Semi directional antennas reduce reflection and thereby reduces negative effects of multipath. True or False |
True |
|
Chapter 5 essentials |
1. Know different types of spread spectrum technologies used in each PHY 2. Required rates and supported rates of each PHY 3. Frequency band of each PHY 4. TPC and DFS 5. Pre-RSN and RSN security standards |
|
The original 802.11 standard was first published in June 1997 as IEEE 802.11-1997 standard and is often referred as 802.11 prime. |
Statement: 802.11 standard |
|
The most recent iteration of 802.11 standard is __ |
IEEE 802.11-2012 Note: As per cwna 106 exam latest 802.11 is 2012. But the most recent version is IEEE 802.11-2016 which incorporates 11ac into it. |
|
Data rate is number of bits leaving physical layer during single transmission. |
Statement: Data rate |
|
Data rate is expressed in ___ |
Mbps |
|
Due to medium contention overhead, MAC layer overhead and interference, throughput will be always 30 to 40 lesser than bandwidth. True or False |
True |
|
Data rate supported by 802.11 b radios |
1, 2, 5.5, 11Mbps |
|
PHY techniques introduced in 802.11 b to achieve high data rate |
HR-DSSS |
|
Complementary code keying and Barker code are modulation schemes used in ___ |
802.11 b |
|
Optional modulation scheme introduced in 802.11 b |
PBCC |
|
802.11 a operates in ___GHz band |
5GHz |
|
RF technology introduced in 802.11 a |
OFDM |
|
5GHz band in which WLAN operates is known as |
UNII bands |
|
UNII stands for __ |
Unlicensed National Information Infrastructure |
|
What are the supported rates of 802.11 a |
6, 9, 12, 18, 24, 36, 48, 54Mbps |
|
Mandatory rates for 802.11 a |
6, 12 ,24 |
|
PHY technology introduced in 802.11 g |
ERP-DSSS/CCK, ERP-OFDM |
|
802.11g works in __ frequency band |
2.4 to 2.4835 GHz ISM |
|
Supported rates of 802.11 g |
6, 9, 12, 18, 24, 36, 48, 54 |
|
Higher rates in 802.11 g is acheived due to ___ |
ERP-OFDM |
|
Backward compatibility of 802.11 g with legacy DSS and 802.11b radios is achieved with the help of __PHY technology |
ERP-DSSS/CCK |
|
Two optional PHYs defined in 802.11 g spec |
ERP-PBCC, DSSS-OFDM |
|
802.11 a/g work sin 2.4GHz ISM band. ISM stands for ___ |
Industrial Scientific Medical |
|
Country code information is included in Beacons and probe response as a part of ___ amendment |
802.11 d |
|
Radar detection and avoidance technology is introduced in ___ ammendment |
802.11 h |
|
Mechanisms implemented in 802.11 h to avoid radar detection and interference |
DFS(Dynamic Frequency Selection) and TPC(Transmit Power Control) |
|
Frequency band introduced as part of 802.11 h |
UNII-2 extended |
|
RSN stands for __ |
Robust security network |
|
Security enhancements addressed in 802.11 i are__ |
1. Data privacy: CCMP,TKIP 2. Data Integrity: MIC 3. Authentication : PSK and 802.1x |
|
Wi-Fi alliance certification based on 802.11 i |
Wi-Fi protected access 2 certification(WPA2) |
|
Amendment which allows WLAN operation in 4.9 to 5.091GHz band to conform to the Japanese regulatory authorities |
802.11 j |
|
Available data rates while operating in Japan |
3, 4.5, 6, 9, 12,18, 24, 27 |
|
Which are mandatory data rates when using 10MHz channel spacing in Japan |
3,6,12 |
|
QoS is defined in which amendment |
802.11e |
|
EDCA and HCCA are the two channel methods defined in 802.11 e |
Statement: 802.11e |
|
EDCA is an extension of DCF and HCCA is an extension of PCF |
Statement: 802.11e |
|
Certification provided by Wi-Fi alliance for QoS |
WMM certification |
|
Fast secure roaming or Fast Basic Service Set Transition(FT) is defined in ___ amendment |
802.11 r |
|
802.11 r is introduced to reduce the delay in roaming while stronger encryption like 802.1x is in use. |
Statement: 802.11 r |
|
RRM or Radio Resource Management was defined in 802.11__ amendment |
802.11 k |
|
Key areas where 802.11 k focus on |
1. Transmit power control 2. Client statistics 3. Channel statistics 4. Neighbor reports |
|
Name the Wi-Fi alliance certification in which 802.11 r and 802.11 k are tested |
Voice Enterprise |
|
802.11 y allows WLAN usage at higher power than the regular 802.11 in the licensed frequency range 3650 MHz- 3700MHz |
Statement: 802.11 y |
|
To avoid interference 802.11 y uses CSMA/CA along with Dynamic STA enablement(DSE) procedures |
Statement: 802.11 y |
|
Amendment 802.11 __ provides unicast,multicast,broadcast management frame protection |
802.11 w |
|
In 802.11 w unicast management frames are protected using ___ |
CCMP |
|
In 802.11 w broadcast/multicast management frames are protected using |
BIP-Broadcast/Multicast Integrity Protocol |
|
802.11 p is also known as WAVE. WAVE stands for ___ |
Wireless Access in Vehicular Environments |
|
802.11 p operates in 5.850-5.925 GHz frequency |
Statement: 802.11p |
|
802.11 p is introduced for inert vehicular communication |
Statement: 802.11p |
|
STA to STA communication or Direct Link setup is introduced in 802.11 __ |
802.11 z Note: DLS allows client stations to bypassthe access point and communicate with direct frame exchanges |
|
Wireless Interworking with External Network or WIEN is defined in __amendment |
802.11 u |
|
Wi-Fi alliance certification based on 802.11 u |
passpoint certification |
|
Wireless Network Management is introduced in ___ amendment |
802.11 v |
|
802.11 s introduced ___ |
mesh networking |
|
802.11-ae -2012 introduced Quality Management Frames 802.11-aa-2012 introducedGroup Cast Retries 802.11-ad-2012 introduced WiGig 802.11-ac-2013 introduced VHT 802.11-af-2013 introduced wlan operation in TV white space 54MHz-790 MHz |
Post 2012 ratified amendments |
|
802.11 m Task group is intended for__ |
internal maintenance of 802.11 documentation |
|
Chapter 6 essentials |
1. Know all the specs about ISM and UNII bands 2. Know about different spread spectrum technologies like DSSS, FHSS, OFDM 3. Channels 2.4/5GHz, adjacent, non adjacent, overlapping channels 4. Throughput vs bandwidth |
|
Frequency ranges of ISM band |
902-928 MHz: 26 MHz wider. a,k,a Industrial band 2.4-2.5 GHz: 100 MHz wide, a.k.a Scientific band 5.725-5.875 GHz: 150MHz wide, a.k.a Medical band |
|
Out of ISM band frequency range , GSM uses which frequency |
900MHz |
|
Baby monitors, wireless telephones, wireless headphones uses ___ frequency range of ISM band |
900MHz |
|
Cordless home telephones, microwaves, baby monitors, wireless video cameras use ___ frequency range of ISM band |
2.4GHz |
|
One of the major disadvantage of using 2.4GHz for wlan is this band is heavily used and there is a huge potential for interference. True or False |
True |
|
IEEE allows 2.4GHz wlan transmission across 14 channels. However local regulatory authority determines which channels can be used. True or False |
True |
|
ISM band which shares the same frequency range with UNII-3 |
5.725 - 5.875 GHz(150 MHz wider) Note: UNII-3 band 5.725 - 5.850(125 MHz wider) |
|
Consumer devices which operates in 5.8GHz cause interference to wlan operating in ___ frequency band |
UNII -3 |
|
Wi-Fi radios that operates in UNII frequency bands |
802.11a 802.11n(HT) 802.11 ac(VHT) |
|
UNII bands |
UNII 1: 5.150 - 5.250, 4 channels of 20MHz width, total 100MHz wide UNII 2: 5.250 - 5.350, 4 channels of 20MHz width, total 100MHz wide UNII 2 Extended: 5.47 - 5.725, 12 channels of 20MHz width, total 255 MHz wide, 144 channel introduced UNII 3: 5.725 - 5.850, 5 channels of 20MHz width, total 125 MHZ wide, 165 channel introduced |
|
Devices operate sin UNII2 and UNII2 extended should support ___ to avoid radar interference |
DFS |
|
FCC approved 195 MHz of frequency in UNII bands. These new bands are__ |
UNII 2B: 5.35 - 5.47, 120 MHz wide UNII 4: 5.85 - 5.925, 75 MHz wide |
|
Future UNII bands |
UNII 1 : 5.150 - 5.250 (100 MHz), 4 channels UNII 2A: 5.250 - 5.350 (100 MHz), 5 channels UNII 2B: 5.350 - 5.470 (120 MHz), 6 channels UNII 2C: 5.470 - 5.725 (255 MHz), 13 channels UNII 3 : 5.725 - 5.850 (125 MHz), 5 channels UNII 4 : 5.850 - 5.925 (75MHz), 4 channels |
|
UNII 2A and UNII 2c would gain extra one channel if FCC approves the future UNII proposal |
Statement: UNII bands UNII 2A: 5 channels UNII 2C: 13 channels |
|
The band licensed exclusively for public safety |
4.94 - 4.99 GHz |
|
WiGig operates in __GHz frequency |
60GHz |
|
Maximum theoretical bandwidth of WiGig |
7Gbps |
|
Radios which supports 2.4,5,60 GHz are called __ |
triband radios |
|
2 types of RF transmission methods |
1. Narrow band 2. Spread spectrum |
|
Out of two transmission methods narrowband and spread spectrum, which one ill use more bandwidth |
spread spectrum |
|
Out of two transmission methods narrowband and spread spectrum, which one ill use more power |
narrow band |
|
Out of two transmission methods narrowband and spread spectrum, which one is more intended to be affected by RF jammers, interferences |
narrow band |
|
AM and FM are examples of ___ type of transmisson |
narrow band |
|
The phenomenon in which same signal arrives the signal at different times is called |
multipath |
|
A typical delay spread in an indoor wlan environment |
30 - 270ns |
|
Spread spectrum spread their signals across a range of frequencies.Because of this reason they are less affected by multipath. True or False |
True |
|
According 802.11 vendors, required delay spread for 802.11 b is |
65ns |
|
According 802.11 vendors, required delay spread for 802.11 g is |
150ns |
|
802.11 FHSS would use 79 MHz of frequency from __GHz to __GHz |
2.402 to 2.480 |
|
Terms used in FHSS 1. Dwell time 2. Hop time 3. Hop sequence |
Statement: FHSS |
|
FHSS transmits data using specific set of frequency for sometime and then switches to another set of frequency. This specific set of frequency is known as |
Dwell time |
|
Time required by the FHSS transmitter to change from one frequency to another is known as |
Hop time |
|
FHSS radio transmits data on a sequence of subchannelscalled hops instead of sending in a finite channel. These set of hops will be repeated and is known as |
hopping sequence |
|
802.11 standard defines hoping sequence can be configured in AP and can be delivered to client using Beacon frames |
Statement: FHSS |
|
As per 802.11 standard hopping sequence must consist of at least 75 frequencies, 1 MHz wide |
Statement: FHSS |
|
Longer the dwell time shorter will be the throughput. True or False |
False Note: If dwell time is lesser transmitter as to hop more and thereby decrease throughput. So longer the dwell time, the greater the throughput. |
|
FHSS hop sequence consisting of 75 hops and dwell time of 400ms it would take 30s to complete a hop sequence |
Statement: FHSS |
|
Modulation used by FHSS |
GFSK Gaussian frequency shift keying |
|
The process of converting single data bit into series of bits is known as |
chipping or spreading |
|
802.11 b uses Barker code and CCK for encoding |
Statement: 802.11 b Barker code uses 8 bit PN CCK can encode 4 bits of data with 8 chips which results in 5.5 Mbps CCK can encode 8 bits of data with 8 chips which results in 11 Mbps |
|
Modulation used in 802.11 b |
DBPSK DQPSK |
|
Data rates supported by PBCC |
5.5, 11, 22, 33 |
|
OFDM is a frequency-division multiplexing (FDM) scheme used as a digital multi-carrier modulation method. A large number of closely spaced orthogonal sub-carrier signals are used to carry data on several parallel data streams or channels. Each subcarrier is modulated with a conventional modulation scheme (such as quadrature amplitude modulation or phase-shift keying) at a low symbol rate, maintaining total data rates similar to conventional single-carrier modulation schemes in the same bandwidth |
Statement: OFDM |
|
Out of OFDM, FHSS, DSSS which one is more resistant to negative effects of multipath |
OFDM |
|
Frequency of subcarrier in OFDM |
312.5KHz |
|
Modulation schemes used by OFDM |
BPSK, QPSK, 16QAM, 64QAM, 256QAM |
|
Number of channels available in 2.4GHz band |
14 For US 1-11 |
|
Each channel in 2.4GHz ISM band is ___MHz wide |
22 |
|
In 2.4GHz what is the conditions to be met if two channels are nonoverlapping |
Difference between their center frequency should be at least 25 MHz or separated by 5 channels |
|
Non overlapping channels in 2.4GHz ISM band |
1, 6 and 11 |
|
Access points should be kep 5 to 10 feet separate, so that interference from sideband frequencies does not occur |
Statement: 2.4GHz Interference |
|
Terminal Doppler weather radar(TDWR) operates in which channel |
120, 124, 128 of UNII 2 extended |
|
Non overlapping channels requirement: 1. DSSS- 30 MHz separation between center freq 2. OFDM(a/g)- 25 MHz separation between center freq 3. OFDM(n/ac)- 20 MHz separation between center freq |
Statement: Non overlapping channels |
|
When using 11n/ac aggregate throughput = 65% of data rate. Medium contention eats up 35% of bandwidth |
Statement: Throughput vs bandwidth |
|
When using a/b/g aggregate throughput = 50% of data rate. Medium contention eats up 50% of bandwidth |
Statement: Throughput vs bandwidth |
|
Chapter 7 essentials |
1. Wireless topologies: WWAN, WLAN, WPAN, WMAN 2. Four types of 802.11 service sets: BSS, ESS,IBSS,MBSS 3. Various way in which 802.11 radios can be used: Indoor/outdoor 4. Purpose of DS: WDS, Distribution system services, Distribution system medium 5. Know about SSID, BSSID, ESSID 6. Various way in which ESS can be designed and their purpose 7. Different configuration modes of AP and client |
|
4 types of wireless networking topologies |
1. WWAN 2. WMAN 3. WLAN 4. WPAN |
|
Internet is an example for which networking topology |
WAN |
|
Wi-max is an example for which wireless networking topology |
WMAN |
|
Apple air drop, wifi p2p connections are examples for ___ wireless networking topology |
WPAN |
|
Four 802.11 topologies defined by IEEE standard |
BSS, ESS, IBSS, MBSS |
|
802.11 wireless networks are half-duplex communications |
Statement: 802.11 communication nature |
|
IEEE 802.3 networks are full-duplex communication |
Statement: 802.3 communication nature |
|
Standalone APs are called autonomous APs and controller based APs are called ___ |
lightweight APs or thin APs |
|
when a client successfully establish a layer 2 connection with an AP, it is said to be associated with that AP. True or False |
True |
|
Two components of a DS |
1. Distribution system medium 2. Distribution system services |
|
Logical physical medium used to connect AP is called __ |
Distribution system medium |
|
802.3 ethernet is an example for ___ |
Distribution system medium |
|
Software inside AP which provide switch like intelligence |
Statement: Distribution system services |
|
Wireless bridge, repeaters, mesh networks are examples for ___ |
WDS |
|
The 802.11 communications betweenthe repeater and the access point is a WDS. True or False |
True |
|
1. AP and Repeater must be on the same channel 2. There must be 50% cell overlap so that AP and repeater can communicate each other |
Statement: Repeater requirements |
|
Throughput degrades in repeater environment because 1. In a repeater environment, same frame has to be sent twice. client->repeater->AP and vice versa. 2. AP and repeater cell are on the same channel all radios should contend for the medium. |
Statement: Repeater |
|
SSID can be 32 characters long and are case sensitive |
Statement: SSID |
|
SSID stands for |
Service Set Identifier |
|
In a BSS if client stations want to communicate with each other, communication has to go thru AP |
Statement: BSS Note: If client stations support Wi-Fi direct they can directly connect and communicate without the need of an AP |
|
BSSID is the MAC address of the radio network interface card of the access point |
Statement: BSSID |
|
BSSID stands for |
Basic service set identifier |
|
Physical coverage provided by an AP in BSS is called ___ |
Basic service area |
|
a collection of multiple access points and their associated clients united by single DSM(Distribution system medium) is called |
ESS |
|
In an ESS all APs will have same ssid with overlapping coverage cells to provide seamless roaming. This ssid in an ESS is called |
ESSID |
|
IBSS is also known as peer-to-peer network or adhoc network |
Statement: IBSS |
|
1. In an IBSS first all the client stations should be on the same channel 2. Entire group will have a single SSID WLAN name 3. BSSID will be a virtual mac address generated by first client station which initiates IBSS |
Statement: IBSS |
|
Mesh functions are used to provide wireless distribution of network traffic when wired network is not a good option. The set of APs that provide mesh distribution forms a MBSS |
Statement: MBSS |
|
One or more mesh AP will be connected to wired infrastructure. These mesh Aps are known as |
mpp(mesh point portal) or mesh root or gateway |
|
The other APs which are not connected to wired network will form wireless backhaul connections to MPP to reach wired network. These APs are known as |
MPs or mesh points |
|
Client stations will associate with MPs and the MPs forward their traffic to wired network thru backhaul connections |
Statement: Mesh networks |
|
Generally MBSS uses __GHz for backhaul connections |
5GHz |
|
Mesh routing is based on hardware address and not ip address. |
Statement: Mesh networks |
|
Default path selection protocol to MBSS |
Hybrid Wireless Mesh Protocol(HWMP) |
|
AP configuration modes |
1. Root 2. Bridge 3. Workgroup bridge 4. Repeater 5. Scanner 6.Mesh |
|
Client station modes |
1. Infrastructure mode 2. Adhoc mode |
|
Chapter 8 essentials |
1. CSMA/CA, physical carrier sense, virtual carrier sense, random backoff timer, IFS, 2. DCF,PCF,HCF 3. WMM, Block Ack 4. Airtime fairness |
|
Name the 2 commonly used contention methods used in networks |
CSMA/CA, CSMA/CD |
|
Medium contention used in 802.3 networks |
CSMA/CD |
|
Medium contention used in 802.11 networks |
CSMA/CA |
|
Wired network is duplex communication. It can transmit/receive at same time. If collision occurs wired medium can detect collision and prevent that node from transmitting. Wireless network is half duplex communication. It can either transmit or receive at that given time. If collision occurs, wireless clients cannot detect it during transmission |
Statement: why CSMA/CA over CSMA/CD |
|
CSMA CA: CS- determines whether medium is busy or not MA-ensures every radio gets fair amount of time to transmit CA-ensures only one radio transmit at any given time |
Statement: CSMA CA overview |
|
In 802.11 communications, every unicast frame is acknowledged |
Statement: Ack |
|
Delivery of aggregated unicast frames is verified using Block Ack |
Statement: Block Ack |
|
Broadcast and multicast frames are never acknowledged |
Statement: BC/MC frame delivery verification |
|
Out of DCF, PCF, HCF which one is mandatory access method for 802.11 communication |
DCF Distributed coordination function |
|
Which channel access method got introduced as part of 802.11e |
HCF hybrid coordination function |
|
Optional channel access method defined in 802.11 standard |
PCF point coordination function |
|
Every 802.11 radio will stay idle for sometime after each transmission to avoid interference and to add/control prioritize frame transmission . This idle period is known as |
Interframe space a.k.a IFS |
|
Six different types of IFS |
RIFS |
|
IFS used for corrupted frames |
EIFS |
|
IFS used for QoS transmission |
AIFS |
|
DIFS = SIFS + 2 * SLOT TIME SIFS = 10μS for 2.4GHz b/g/n 16μS for 5GHz a/n/ac SLOT TIME 9μS for OFDM 20μS for 2.4GHz legacy and 2.4GHz b/g/n with long preamble |
Statement: DIFS |
|
Value of Duration/ID field ranges from |
0 to 32767 Length of Duration/ID field is 2 bytes. 2 bytes = 16bits = 2^15 = 32768 |
|
Duration/ID of an ACK frame |
zero |
|
Special occasion in which Duration field represents client association id (AID ) instead of transmission time. |
PS-Poll frame during legacy power management |
|
Two collision avoidance defense mechanism used by CSMA/CA |
Virtual carrier sense physical carrier sense |
|
Layer 1 defense mechanism used by CSMA/CA |
physical carrier sense |
|
Layer 2 defense mechanism used by CSMA/CA |
Virtual carrier sense |
|
PCF will not work for ad hoc networks and will only work in BSS . True or False |
True Note: PCF requires a point coordinator to poll the clients. Since there is no AP present in ad hoc networks PCF will not work |
|
For PCF to work only AP is required to support PCF. True or False |
False Note: Both AP and client should support PCF |
|
HCF combines DCF and PCF and add enhancements to create two new channel access methods called |
EDCA, Enhanced distributed channel access HCCA, HCF controlled channel access |
|
TXOP stands for |
Transmit opportunity |
|
IFS used in TXOP |
SIFS |
|
In DCF 802.11 radios can send a single frame after contention and to send another frame they have to contend again. In HCF 802.11 radios can send multiple frames in an allotted time called TXOP |
Statement:HCF vs DCF |
|
Four access categories defined in EDCA |
Voice AC_VO Video AC_VI Best effort AC_BE Background AC_BK |
|
Block Ack is first introduced in ___ amendment |
802.11 e |
|
Two types of Block Ack |
Immediated and Delayed |
|
After sending a block of unicast QoS data frames, transmitter will send a BlockAckReq frame to the receiver. Once the reciever recieves BlockAckreq frame it replies back with BlockAck frame containing delivery status of all the unicast QoS frames . This type of Block Ack is called |
Immediate Block ACK |
|
WMM uses which channel access method of 802.11 e amendment |
EDCA |
|
AC_VO :7,6 AC_VI :5,4 AC_BE :0,3 AC_BK :1,2 |
Statement: Access categories and their priority number |
|
Certifications provided by Wi-Fi alliance for testing QoS |
WMM WMM-POWER SAVE WMM ADMISSION CONTROL |
|
Airtime fairness is introduced to prevent slower devices from bogging down the rest ofthe network. True or False |
True |
|
Chapter 9 essentials |
1. 802.11 MAC architecture 2. MSDU, MPDU, PSDU, PPDU 3. Differences and similarities b/w 802.3 and 802.11 frames 4. Control,Management, Data frames 5. Active scanning/Passive scanning 6. Authentication,DeAuthentication Association,ReAssociation,DisAssociation,Roaming,Ack Frame 7. Fragmentation 8. Protection mechanisms RTS/CTS, CTS-to_Self 9. Power management : TIM, DTIM, ATIM, WMM-PS, UAPSD, Legacy PS, 802.11n PS |
|
Two sublayers of Data link layer |
1. Logical Link Control(LLC) sublayer 2. Media Access Control(MAC) sublayer |
|
MSDU contains payload from layers __ |
3 to 7 |
|
Datagram n MAC sublayer is known as |
MPDU(MAC Protocol Data Unit) |
|
Contents of MPDU |
MAC header + Frame body + FCS |
|
Sublayers in PHY layer |
1. PLCP(Physical Layer Convergence Procedure) sublayer 2. PMD(Physical Medium Dependent) sublayer |
|
When MPDU reaches PLCP sublayer, it is known as |
PSDU PLCP Service Data Unit |
|
PLCP sublayer adds PHY header and preamble to PSDU. The resulting datagram is called |
PPDU PLCP Protocol Data Unit |
|
Preamble in PPDU is used for |
synchronization b/w transmitting and receiving 802.11 radios |
|
PMD sublayer takes the PPDU, modulates and transmit the bits |
Statement: PMD function |
|
Maximum size of 802.3 frame |
1518 bytes with data payload 1500 bytes 1522 bytes with data payload 1504 if VLAN information is present |
|
Maximum size of IP packets based on MTUs |
1500 bytes |
|
802.11 MAC header has 4 address fields |
Statement: 802.11 address |
|
Size of MAC address is |
6 bytes = 6 octets = 48 bits |
|
First 3 octets of MAC address represent ___ |
OUI Organizationally Unique Identifier in other words vendor name like Intel, Broadcom, Marvell |
|
Last 3 octets of MAC address represent |
NIC specific information |
|
3 major 802.11 frame types |
1. Control 2. Management 3. Data |
|
Out of 3 frame types, control management and data, which frame type is used by 802.11 radios to join or leave a BSS |
Management frames |
|
Management frames are also known as |
MMPDU MAC Protocol Data Unit |
|
Management frames does not carry any upper layer data. True or False |
True |
|
(Re)Assoc req/res Auth re/res DeAuth Probe req/res Beacon ATIM ACTION ACTION No ACK Timing advertisement |
Management frames |
|
Control frames responsible for clear the channel, acquire the channel and provide unicast frame acknowledgement |
Statement: Control frames |
|
RTS/CTS,CTS-to-SELF ACK,Block Ack, Block Ack Req PS-POLL, Control wrapper |
Control frames |
|
Any data frames that does not carry upper layer information are unencrypted. True or False |
True |
|
Information present in Beacon frames |
time stamp, spread spectrum parameter, channel information, data rates, service set capabilities,ssid, tim, rsn information, wmm, vendor info |
|
2 types of scanning |
active and passive |
|
In __ client listens to beacons sent by the AP |
passive |
|
In __ client sents probe request in all the available channels and collect APs in the vicnity |
active |
|
A probe request with null ssid length is called |
null probe request |
|
A probe request with a specic ssid name is called |
directed probe req |
|
2 types of authentication |
Open system authentication Shared key authentication |
|
AID is present in which frame |
Association response |
|
In order for a client station to successfully associate to an AP basic rates of AP and STA should match |
Statement: Basic rates |
|
Basic rates are required rates for a STA who wants to join the BSS. If client station does not support all the basic rates of AP , it won't be able to associate to that AP Supported rates are data rates that AP offers to a client station, but the client does not have to support all of them |
Statement: Basic vs Supported rates |
|
Ability for the client station to transition from one Ap to another by maintaining upper layer connectivity is called __ |
Roaming |
|
Roaming decision is made by __ |
client station |
|
1. DisAssociation and DeAuthentication are notification and not request 2. Client or AP any device can send DisAssoc and DeAuth 3. Both DisAssoc and DeAuth cannot be refused by either party except 802.11w in negotiated and MIC fails |
Statement: DisAssoc and DeAuth |
|
1.In 802.11 every unicast frame is acknowledged 2. Ack is used for successful delivery verification 3. Receiving STA copies MAC address of transmitting STA from the data frame and places in the RA field of ACK frame. When the transmitting STA receives ACK frame with its MAC address in RA field it confirms successful delivery of frame |
Statement: ACK |
|
Size of ACK frame |
14 bytes = 14 octets 2 byte FC +2 byte Duration+6 byte RA + 4 byte FCS |
|
Fragmentation is used increase network performance when there is increased data corruption. True or False |
True |
|
Suppose an AP is configured in 802.11b mode. What types of client devices can associate the the AP |
802.11 DSSS, 802.11b HR-DSSS, 802.11g ERP-DSSS, 802.11n using the data rates 1, 2, 5.5, 11 |
|
802.11 g mode is also known as |
Pure G network |
|
Suppose an AP is configured in 802.11g mode. What types of client devices can associate the the AP |
802.11 g ERP-OFDM, 802.11n using data rates 6,9,12,18,24,36,48,54 |
|
Suppose an AP is configured in 802.11bg mixed mode. What types of client devices can associate the the AP |
802.11 DSSS,802.11 b, 802.11g, 802.11n |
|
In a BG mixed mode environment, the transmitting 802.11 radio will send a RTS/CTS or CTS-to-Self before transmission. Out of legacy/b/g radios which STA will will send RTS before transmission and at what rate? |
802.11g STA will send RTS/CTS or CTS-to-Self at basic rates in which other clients like 802.11 DSSS/802.11b devices understand |
|
ERP protection is triggered when |
1. When an non-ERP STA associate to ERP AP 2. When ERP AP hears a beacon frame from another AP whose supported data rates contain only 802.11 b or 802.11 DSSS rates 3. When ERP AP hears a management frame (other than probe req)where the supported rates include only 802.11 b or 802.11 DSS rates |
|
802.11g radios revert to 802.11b data rates when the protection mechanism is used. True or False |
False Note: 802.11 g radios transmit at higher 802.11 ERP OFDM rates itself |
|
Duration of RTS |
CTS+DATA+ACK+3SIFS |
|
Duration of CTS |
DATA+ACK+2SIFS |
|
CTS-to-Self is commonly used by AP. True or False |
True |
|
NULL function frame or NULL Data frame is commonly used |
power management |
|
Beacons are transmitted at consistent predetermined interval known as |
Target Beacon Transmission Time(TBTT) |
|
A DTIM is used to ensure all the client stations in power saving mode are awake during multicast/broadcast transmission |
Statement: DTIM |
|
A DTIM interval o f 3 means every 3rd beacon will be a DTIM beacon A DTIM interval o f 1 means every beacon is a DTIM beacon |
Statement: DTIM |
|
A DTIM value of 0 indicates current TIM is a DTIM |
Statement: DTIM |
|
ATIM is a frame used for power management by adhoc clients. TIM is field in Beacon |
Statement: TIM vs ATIm |
|
Disadvantages of legacy powersave |
1. Amount of client station dozing is determined by client driver not application traffic 2. Client has to wait for a Beacon frame with its TIM field set to download unicast buffered frames intended to it 3. Client has to send PS-POLL frame to retrieve every single buffered frame These caused time sensitive application like voip to decreased performance |
|
Advantages of WMM-PS |
1. Application sets client dozing behaviour and not client's driver 2. Client can download buffered frame by sending a trigger frame and does not have to wait for Beacon frame 3. Trigger frame can be any frame, can be a data frame also thereby avoiding PS-POLL frame 4. All the buffered frames are send in frame burst during the allocated TXOP |
|
2 types of Automatic powersave delivery |
Static A-PSD S-APSD Unscheduled A-PSD U-APSD |
|
Powersave feature introduced in 802.11n |
SM power save, PSMP |
|
Chapter 10 essentials |
1. 802.11 radio form factors, radio chipsets, client utilities: enterprise, integrated and third party 2. Logical network planes of operation and where they are used: Management, control , data planes 3. WLAN architecture: Autonomous, Centralized and Distributed 4. WLAN specialty architecture |
|
Different types of 802.11 radio formafactors |
external: PCMCIA, Express card, USB Internal: mini PCIE, PCIE Express, Embedded |
|
3 types of client utilities |
1. Integrated operating system client utilities 2. Vendor specific eg: Intel PROSet wireless client interface 3. Third party |
|
Juniper Networks Odyssey Access Client is an example for ___ type of client utility |
third party |
|
3 logical planes of operation in networking |
1. Management plane 2. Control plane 3. Data plane |
|
Management plane: N/w monitoring Control plane: N/w intelligence Data plane: location where user traffic forwarded |
Statement: planes of operation |
|
Network management solution to monitor routers and switches is an example __ plane |
Management |
|
Dynamic layer 3 protocols like OSPF, BGP used in routers and CAM tables , Spanning tree protocol used in switches to forward packets is an example for ___ plane |
control |
|
In an Autonomous AP, all the three planes exist in AP itself. True or False |
True |
|
Functions of Management plane |
1. WLAN configuration: SSID, security, power settings, wmm 2. WLAN monitoring and reporting: Statistics like number of clients (re)associated, ACKS ,data rates 3. WLAN firmware management: firmware upgrade Inshort all the administrative activities :-) |
|
Functions of Control plane |
1. Dynamic RF or Radio resource Management(RRM): Coordinated channel and power setting for multiple APs 2. Roaming mechanism 3. Client load balancing:collecting and sharing client load and performance metrics b/w multiple APs to improve overall WLAN operation 4. Mesh protocols |
|
3 types of WLAN architecture |
1. Autonomous 2. Centralized 3. Distributed |
|
Standalone APs are also known as |
Autonomous APs or fat APs |
|
BVI is |
Bridged virtual interface |
|
BVI is the management interface for an AP |
Statement: BVI |
|
SNMP,CAPWAP are mostly used management protocol to manage and monitor network in NMS. True or False |
True |
|
Autonomous APs are deployed at access layer and typically powered by PoE. The integration service in Autonomous AP translates 802.11 frame to 802. 3 frame |
Statement: Autonomous AP |
|
NMS is a management plane solution. No control plane and data plane mechanisms exist in NMS. |
Statement : NMS |
|
3 layers in hierarchical internetworking model |
1. Access layer 2. Distribution layer 3. Core layer |
|
NMS solutions deployed at company data center are referred as on premise NMS NMS solutions are available in cloud as software subscription service |
Statement : NMS |
|
2 types of cloud networking models |
1. Cloud-Enabled networking(CEN) 2. Cloud-Based networking(CBN) |
|
In Cloud-Enabled networking(CEN), management plane resides in the cloud . Data plane mechanisms will be present locally in hardware |
Statement: CEN |
|
In Cloud-Based networking(CBN), both management and data plane resides in the cloud |
Statement: CBN |
|
In centralized WLAN architecture all the logical planes management, control, data resides in WLAN Controller. True or False |
True |
|
CAPWAP is |
Control and Provisioning of Wireless Access Points |
|
CAPWAP is a WLAN ___ protocol |
management Note: CAPWAP protocol can also be used for tunneling user traffic |
|
In centralized wlan architecture integration service resides in |
WLAN controller |
|
Controller based access points are also known as |
lightweight APs or thin Aps |
|
WLAN controller is deployed at __ layer of internetworking model |
core |
|
Lightweight APs are deployed at __ layer of internetworking model |
access |
|
Lightweight APs are powered using __ |
PoE provided |
|
Lightweight APs tunnel all the traffic to WLAN controller. Integration service inside the controller converts 802.11 frame into 802.3 format and Distribution System Service(DSS) directs the traffic to wired destination |
Statement: WLAN controller |
|
AP group profile: Channel, Supported data rates, txpower configurations |
Statement: AP group profile |
|
WLAN group profile: SSID, security, VLAN, QoS configurations |
Statement: WLAN group profile |
|
An AP can be only in one AP group profile but can be in multiple WLAN profile. True or False |
True |
|
SSID is logical name and BSSID is MAC address of the 802.11 radio |
Statement: SSID vs BSSID |
|
WLAN can create multiple SSIDs and BSSIDs. True or False |
False |
|
WLAN Controller features |
1. AP management 2. 802.11 traffic tunneling 3. AP group profile 4. WLAN group profile 5. Multiple BSSIDs 6. VLAN 7. User management 8. Layer 2 security 9. Layer 3 VPN concentrator 10. Captive portal 11. Automatic failover recovery and load balancing 12. Internal WIDS 13. Firewall capabilities 14. Bandwidth management 15. PoE 16. Layer3 roaming 17. Management interface 18. Dynamic RF |
|
In split mac architecture, control and management frames are not tunneled to wlan controller since they doesn't have any upper layer payloads and DSS doesn't have to translate to 802.3 frames. |
Statement: split mac architecture |
|
CAPWAP protocol define split mac architecture. True or False |
True |
|
CAPWAP is proposed by |
Internet Engineering Task Force(IETF) |
|
2 types of controller data forwarding models |
1. Centralized data forwarding 2. Distributed data forwarding |
|
In centralized data forwarding AP tunnels every 802.11 user data traffic to controller or come from controller. AP plays a passive role in data handling |
Statement: Centralized data forwarding |
|
In Distributed data forwarding AP solely determines where and how to forward user data traffic. Controller plays a passive role in Distributed data forwarding. |
Statement: Distributed data forwarding |
|
One major disadvantage of Distributed data forwarding is control plane mechanisms like Dynamic RF, Layer 3 roaming, Firewall policy enforcement, Fast secure roaming will not be available |
Statement: Distributed data forwarding |
|
Remote office wlan controller less powerful and less expensive than core wlan controller. True or False |
True |
|
Remote office wlan controller is used to manage local APs in remote office branches. True or False |
True |
|
Remote office wlan controller connects with core wlan controller thru a secure WAN link using VPN and download all the configuration data to manage local APs |
Statement: Remote office wlan controller |
|
Distributed WLAN Architecture: No WLAN Controller present. All control plane and data forwarding intelligence resides in AP APs share control plane info b/w them using proprietary protocols Management plane is centralized usually a local or cloud NMS server |
Statement: Distributed WLAN Architecture |
|
VLANs will be configured at the core layer s/w in wlan controller based architecture and APs will be connected to the accessport of access layer s/w VLANS will be configured at the access layer s/w , and APs will be connected to 802.1Q trunk port of the access layer s/w |
Statement: VLAN config in controller based vs distributed |
|
WLAN architecture in which wlan controller capabilities are integrated into wired devices like routers, switches is known as |
Unified WLAN Architecture |
|
A device which provides wireless connectivity to the wired infrastructure devices which do not have radio cards is called ___ |
Workgroup Bridge(WBG) |
|
All the wired infrastructure devices will be connected to WGB. WGB connects to an AP and provide wireless connectivity to these wired devices which do not have a radio card small desktop workgroups, cash registers, network printers are few devices which we can connect ot WGB |
Statement: WGB |
|
Wired devices connected to WGB can contend the half-duplex medium. True or False |
False |
|
WGB can also provide wireless connectivity just like AP to other wireless client stations. True or False |
False |
|
A device used to connect one or more wired devices together wirelessly wired device----wireless bridge---wired device |
wireless bridge |
|
Wireless bridge posess all the features that an Autonomous Ap has. True or False |
True |
|
A wireless bridge is usually used as redundant backup to T1 or fiber connections between buildings |
Statement: Wireless bridge |
|
A wireless bridge link that connects only 2 wired networks using 2 bridges are known as |
point-to-point bridge(PtP) |
|
In PtP bridge, one bridge will be root bridge and other will be non root bridge |
Statement: point-to-point bridge(PtP) |
|
A bridge link that connects multiple wired networks are known as |
point to multipoint bridge(PtMP) |
|
In PtMP bridge link, one bridge will be root bridge and all other bridge will be non root bridge. All the non root bridge connects to root bridge |
Statement: point to multipoint bridge(PtMP) |
|
In PtMP bridge link, for redundancy there can be more than one root bridge. True or False |
False Note: Only one root bridge is possibel |
|
Root bridge will have high gain omni directional antenna and non root bridges will have uni directional antenna pointing back to root bridge. True or False |
True |
|
Vendor bridge configuration modes |
1. WGB 2. Root with clients 3. Root without clients 4. Non root with clients 5. Non root without clients |
|
Associating clients to bridge will reduce throughput. True or False |
True |
|
Its is a recommended bridge deployment practice to use two bridge links as opposed to repeating the link of a root bridge to non root bridge. True or False |
True |
|
Things to be considered while deploying a bridge link |
Fresnel zone Earth bulge Free space path loss Fade margin IR and EIRP values by regulatory authority |
|
In long distance link, ACK timeout setting are adjusted so that delayed arrival of ACK for unicast frame can be accommodated thereby preventing retransmission of a frame that does not need to be resent and improving network performance. |
Statement: long distance bridge link |
|
Retransmission of a frame that does not need to be resent due to ACK timeout degrade throughput by 50%. True or False |
True |
|
WLAN routers are almost like home routers but with a better hardware quality and few extra features Access points have bridged virtual interface whereas WLAN routers have separate routed interface. Radio card of WLAN routers exists in one subnet and WAN port exists on a different subnet |
APs Vs WLAN routers |
|
Wireless Mesh APs communicate with each other using proprietary layer 2 protocols and create self forming and self healing wireless infrastructure over which edge devices can communicate |
Statement: Mesh |
|
Routing of data traffic in Mesh networks are based on measurement of traffic, signal strength, data rates hops |
Statement: Mesh |
|
Mesh n/w use 5GHz to communicate with each other and 2.4GHz to provide client connections |
Statement: Mesh |
|
WLAN array is an all in one device, which combines multiple APs, wlan controller with sectorized antennas to provide 360 degree coverage |
Statement: WLAN array |
|
Vendor which provides WLAN array solution |
Xirrus |
|
WLAN arrays can be deployed where less hardware is needed,high density areas |
Statement: WLAN array |
|
WLAN array can combine upto 16APs |
Statement: WLAN array |
|
A 16 access-point WLANarray would consist of four 2.4 GHz radios and twelve 5 GHz radios.One of the radios can beused as a full-time sensor device for the WIDS that is embedded with the controller |
Statement: WLAN array |
|
WLAN solution in which multiple access points share a single BSSID |
Virtual AP system |
|
In Virtual AP system, BSSID is same for all the APs.When client roams , they think they are connected to same single access point resulting zero roaming handoff time and latency issues will be solved |
Statement: Virtual AP system |
|
All the APs in Virtual AP system uses single channel architecture(only one channel) and contend for the medium in coordinated manner handled by WLAN controller |
Statement: Virtual AP system |
|
Real-Time Location Systems are used to locate devices accurately with Wi-Fi RFID tags |
Statement: Real-Time Location Systems |
|
Infrastructure required for Real-Time Location Systems to function |
pre-existing WLAN infrastructure, pre-existing WLAN clients,wlan rfid tags, rtls server, rtls sensor |
|
Vendors which produce RTLS solutions |
Aeroscout, Ekahau |
|
Essential requirements for VoWiFi setup |
VoWiFi phone WMM support PBX to route the calls to telephone cables |
|
In centralized wlan controller model, all the 802.11 user frames are tunnelled to WLAN controller. WLAN controller are deployed close to core layer An extra WLAN controller is also placed for redundancy so that if one fails whole WiFi network will not go down |
Statement: Centralized WLAN architecture |
|
Chapter 11 essentials |
1. WLAN vertical markets 2. FMC Fixed mobile convergence |
|
VoWiFi phones have low transmission power to decrease battery usage and increase battery longevity. True or False |
True |
|
Choppy audio in video conference will be highly disruptive, causing participants to ask speaker to repeat whereas if audio is clear and video is choppy participants can understand what speaker has said. This means video has higher loss tolerance than voice. True or False |
True |
|
In most of the use cases video streaming devices are stationary not moving or mobile. Eg: Video streaming of tv,music,wireless security cameras, video conference |
Statement: Video |
|
Healthcare is biggest users of RTLS technology |
Statement: RTLS users |
|
1. undergroundcable or fiber between the two buildings, 2. high-speed leased data circuit 3. building-to-building wireless bridge Out of these which one is more cost effective |
building-to-building wireless bridge Note: clear RF line of sight and a technician to setup wireless bridge is all that required |
|
School wall are usually made up of cinder block which attenuates 2.4 and 5GHZ RF signals .To provide better coverage, more access points are required while deploying wireless in school environment. |
Statement: Deploying wireless in school environment |
|
Wireless networks deployed in warehouses are designed to provide more coverage than bandwidth. True or False |
True |
|
Most commonly used wireless devices in warehouses are barcode scanners |
Statement: warehouse wlan deployment |
|
Key uses of WLAN in retail environment |
1. support to operations of the store and retails transactions 2. location tracking of items 3. customer analytics 4. supplementary internet access |
|
WLAN vendor who specialize in providing customer analytics |
Euclid analytics |
|
Advantages of using WLAN over wired |
end user mobility quick and secure data access |
|
Key uses of WLAN in hospital/healthcare environment |
1. quick,secure access to clinical data, patient or hospital data 2. VoWiFI 3. RTLS |
|
Companies recommend their employees to use VPN while they connect to public hotspot or network. The reason behind this |
hotspots are not secured no matter its free or paid |
|
Key uses of WLAN in stadium environment |
1. high speed internet access to press box 2. video surveillance 3. ticketing 4. point of sale transaction processing |
|
Automatic uploading of video surveillance datas to central server is a common use case in WLAN deployment in law enforcement environment |
Statement: WLAN deployment in law enforcement environment |
|
WLAN networks are used a first responder networks during disasters/crisis when regular cellular network fails. |
Statement: First responder networks |
|
Mobile devices which can communicate using either cellular network or wlan network by switching between them are called |
Fixed mobile convergence(FMC)devices |
|
Consideration to be taken while integrating mobile devices into wlan infrastructure |
1. ensure devices are capable of connecting to network with proper authentication 2. ensure device support encryption protocols and roam smoothly 3. ensure network access not only based on user identity but also considering device id and connection characteristics |
|
When mobile devices with low tx power are integrated to wlan infrastructure, coverage areas are made small to avoid RF dead zones. |
Statement: Integration of mobile device into WLAN infrastructure |
|
Wireless connectivity is least recommended in distribution and core layers. True or False |
True |
|
WLAN is an end user access technology |
Statement: wireless lan |
|
WLAN vertical markets |
1. Corporate data access and end user mobility 2. Network extension to remote areas 3. Bridging: building to building connectivity 4. Wireless ISP: last mile data delivery 5. SOHO 6. Mobile office networking 7. Branch offices 8. Education/classroom use 9. Industrial: warehouse and manufacturing 10. Retail 11. Healthcare 12. Municipal networks 13. Hotspots 14. Stadium networks 15. Transportation networks 16. Law enforcement networks 17. First responder networks 18. Fixed mobile convergence |
|
The goal of fixed mobile convergence is to enable the user to have a singledevice with a single phone number and to enable the user to roam between differentnetworks, taking advantage of the least expensive and best performing network that isavailable. |
Statement: FMC goal |
|
Last mile internet service is provided by |
1. Cable provider 2. Telecom company 3. WISP |
|
PtMP network design is also known as |
Star or bub and spoke |
|
To provide higher throughput and prevent single point of failure, multiple PtP bridges b/w the same locations are usually installed |
Statement: advantage of multiple PtP bridges |
|
key concerns of healthcare providers when installing a wirelessnetwork |
1. Fast, secure and accurate access to patient data 2. RF interference from other healthcare devices |
|
Chapter 18 essentials |
1. Difference b/w MIMO vs SISO 2. Spatial multiplexing 3. MIMO diversity 4. TxBf 5. 20MHz/40MHz channels 6. Guard interval 7. MCS 8. HT-PPDU formats: non-HT legacy, HT Mixed, HT Greenfield 9. HT MAC Enhancements 10. HT protection modes |
|
Maximum theoretical data rate of 802.11n |
600 Mbps |
|
propagation phenomenon in which same signal arriving at receiver at same time or nano second difference by travelling different paths is known as __ |
multipath |
|
MIMO is |
Multiple Input Multiple Output |
|
MIMO makes use of positive affects of multipath |
Statement: MIMO |
|
All wifi alliance certified n products must also support WMM and WPA/WPA2 security |
Statement: wifi certified n |
|
Features tested in wifi alliance certification of 802.11 n |
1. two spatial streams for AP and 1 spatial stream for STA 2. support of 3SS if implemented 3. AMSDU,AMPDU in receive mode. AMPDU in transmit mode 4. BlockACK 5.2.4GHz operation 6. 5GHz operation 7. concurrent operation of 2.4/5 GHz 8. 40 MHz channels on 5GHz 9. 20/40 coexistence 10.SGI for 20/40 MHz 11.Greenfield preamble 12. STBC 13. HT Duplicate mode |
|
STBC and CSD are transmit diversity techniques implemented using MIMO. True or False |
True |
|
MRC is ___ diversity techique |
receive |
|
Necessary hardware required to transmit and receive signal processing is called __ |
radio chain Note: all of the supporting architecture including mixtures, amplifiers, analog/digital converters |
|
Tx X Rx:SS Eg: 2x3:2 Total 3 radio chains, 2 transmitter, 3 receiver, 2 spatial streams Eg: 3x3:2 Total 3 radio chains, 3 transmitter, 3 receiver, 2 spatial streams |
Statement: radio chain denotation |
|
Maximum supported radio chain for 802.11n |
4x4:4 |
|
Sending multiple streams of uniques data using multiple antennas is known as |
Spatial multiplexing Note: These unique data streams are also known as spatial streams(SS) |
|
Most of handheld devices uses 1x1:1 MIMO because increasing radio chain will increase drainage of battery |
Statement: MIMO radio in handheld devices |
|
Antenna diversity(both receive and transmit) is method of using multiple antennas to survive negative effects of multipath |
Statement: Antenna diversity |
|
pre-802.11n devices used __ diversity |
switched |
|
Multiple copies of same signal are received at multiple antennas and signals with best amplitude is choosen and other are ignored. |
Statement: switched diversity |
|
When switched diversity used in transmitting only one antenna will be used out of multiple antennas. The transmitting antenna will be that antenna where best amplitude signal is last heard |
Statement: switched diversity |
|
combining multiple signals by uniquely looking at each signal and adding them in an optimal way using MRC algorithms to raise SNR is known as |
MRC |
|
Sending multiple copies of same data through multiple antennas is known as |
STBC |
|
STBC can be used when number of radio chains exceeds number of spatial stream. |
Statement: STBC |
|
STBC is a transmit diversity. True or False |
True |
|
STBC works with both 11n and legacy devices. True or False |
False |
|
Cyclic shift diversity is a transmit antenna diversity. True or False |
Statement: True |
|
CSD works with both 11n and legacy devices. True or False |
True |
|
TxBF increases SNR and throughput by carefully adjusting phase of the transmitted signals |
Statement: TxBF |
|
TxBF is used when number of radio chains are greater than spatial streams |
Statement:TxBF |
|
TxBF increases range . True or False |
True |
|
In TxBF transmitter will not be sending multiple streams of unique data. Instead it will send multiple copies of same data phase adjusted for each RF signal |
Statement: TxBF |
|
Transmitters while using TxBF will use a implement a feedback mechanism to learn about receiver location using ___ frames |
sounding |
|
TxBF transmitter: Beamformer TxBF receiver: Beamformee |
Statement:TxBF |
|
2 types of beamforming |
Implicit feedback Explicit feedback |
|
Implicit feedback: beamformer creates steering matrix Explicit feedback: beamformee creates steering matrix |
Statement: TxBF |
|
Transmitter send sounding frames and then receives long training symbols send by receiver which allows transmitter to learn about the MIMO channel b/w transmitter and receiver. |
Statement: Implicit feedback |
|
Receiver learns about the channel from the long training symbols sent by the transmitter, calculate steering matrix and send back to the transmitter |
Statement: Explicit feedback |
|
Sonar is an analogy for which type of beamforming |
Implicit |
|
Beamforming is not practically implemented in 802.11n. True or False |
True |
|
|
Statement: subcarriers |
|
2.4GHz 40MHz channels are not used in multichannel architecture because two 2.4GHz 40MHz channels overlap. |
Statement: 40MHz channels |
|
2.4GHz 802.11n APs use 20MHz channels by default |
Statement: 2.4GHz channels |
|
An AP using 40MHz channel will be forced to used 20MHz channel if it hears a AP with 40MHz intolerant bit set. |
Statement: 2.4GHz channels |
|
40MHz intolerant is only applicable for 2.4GHz. True or False |
True |
|
Time between symbols that accommodates late arrival of symbols over long paths is known as |
Guard interval |
|
Guard interval prevents __ |
Intersymbol interference |
|
Guard interval is 4x times delay spread |
Statement: Guard interval |
|
Delay spread is the time difference b/w multipaths of the same signal |
Statement: Delay spread |
|
Normal delay spread value |
200ns |
|
Legacy GI value |
800ns |
|
802.11n GI value |
400ns |
|
SGI increases throughput by 10% |
Statement: SGI |
|
MCS is |
Modulation and coding scheme |
|
Total MCS rates in 802.11n |
77 |
|
Mandatory MCS rates in 802.11n |
0-7 |
|
Data rates are based on channel bandwidth, guard interval, spatial streams, modulation, coding method |
Statement: MCS rates |
|
Maximum data rate in 1x1:1 with 800ns GI |
65Mbps |
|
Maximum data rate in 1x1:1 with 400ns GI |
72Mbps |
|
Main purpose of PHY header |
use signal field 1. to indicate how long it will take to transmit 802.11 frame 2. to notify receiver MCS rates used |
|
3 Preambles introduced in 802.11n |
Snon-HT legacy HT-mixed HT-Greenfield |
|
Support for non-HT legacy is mandatory in 802.11n and can occur in 20 MHz |
Statement: Preamble |
|
Support for HT-mixed is mandatory in 802.11n |
Statement: Preamble |
|
The length field in the legacy section of HT-mixed header indicate legacy STAs how long medium will be busy. |
Statement: Preamble |
|
Support for HT-Greenfield is optional in 802.11n |
Statement: Preamble |
|
Legacy STA cannot decode HT-Greenfield PPDUs and will interpret as noise |
Statement: Preamble |
|
2 aggregation methods |
A-MSDU A-MPDU |
|
Frame aggregation is a method of combining multiple frames into a single frame for transmission |
Statement: aggregation |
|
All aggregated frames will have a single MAC header Individual MSDUs are of same QoS category All MSDUs will have a single destination Whole A-MSDU is encrypted by treating it as a single frame |
Statement: A-MSDU |
|
Individual MPDUs will have separate MAC header Individual MPDUs should be of same Qos category Individual MPDUs are encrypted seperately All MPDUs should have same receiver address |
Statement: A-MPDU |
|
AMPDU uses BLOCK ACK and AMSDU uses normal ack |
Statement: aggregation ack |
|
RIFS only works with HT-greenfield Value of RIFS is 2ms |
Statement: RIFS |
|
Power save supported by 802.11n devices |
legacy wmm-ps SM power save: Static, Dynamic PSMP: ScheduledPSMP. Unscheduled PSMP |
|
802.11n devices power down all the radio chains except one. 802.11n device inform this by sending SM powersave action frames 802.11n device will use the SM powersave action frames to inform AP it powered up all the radio chains |
Statement: Static SM powersave |
|
802.11n devices power down all the radio chains except one after frame exchange. AP sends an RTS frame when client receives it, it power up all radio chains and respond with CTS |
Statement: DynamicSM powersave |
|
HT protection modes |
4 modes, 0-3 |
|
Mode 0-Greenfield (No protection) mode Mode 1-HT non member protection mode Mode2-HT 20MHZ protection mode Mode3-non-HT mixed mode |
Statement: HT protection modes |
|
1. Only associated STA are HT capable 2. If HT BSS is 20MHz all the STA must be 20 MHz capable 3. If the BSS is 20/40MHz , all the STA must be 20/40 capable |
Statement: Mode 0-Greenfield (No protection) mode |
|
1. All the STAs must be HT STAs 2. Protection kicks in when a non member legacy STA or AP is heard by AP Eg: 802.11 a STA or AP transmitting in 20 MHz space interferes with primary or secondary channel of 40 MHz HT AP |
Statement: Mode 1-non-member protection mode |
|
1. BSS is 20/40 and all STAs are 20/40 2. Protection must be used by 20/40 capable STAs while transmitting at 40MHz when a 20MHz only STA associates to 20/40 BSS |
Statement: Mode2-HT 20MHz protection mode |
|
1. BSS is 20 MHz or 20/40 2. protection kicks in when a legacy STA associates to BSS 3. All the HT STAs uses protection mechanisms before transmitting |
Statemnt: Mode3 non-HT mixed mode |
|
Protection mechanism in which two identical 20 MHz non-HT control frames to be transferredsimultaneously on both the primary and secondary channels |
Statement :Non HT duplicate mode |
|
Non-HT duplicate transmissions will be sent using 802.11a data rates in the 5 GHz bandor 802.11g data rates in the 2.4 GHz band |
Statement: Non HT duplicate mode |
|
MRC and TxBF will result in greater range. True or False |
True |
|
Chapter 19 essentials |
1. Difference b/w 11n vs 11ac 2. 20,40,80,160MHZ channels 3. 64QAM and 256QAM 4. MCS in 11ac 5. Explicit beamforming 6. SU-MIMO vs MU-MIMO 7. 11ac data rates 8. Infrastructure requirements for 11ac 9. concerns when deploying 11ac in any environment |
|
Maximum theoretical data rate of 802.11 ac |
6.93Gbps |
|
Reason for increased data rate/bandwidth in 802.11 ac |
1. increased channel bandwidth 80MHz,160MHz 2. more radio chains and spatial streams (upto 8SS) 3. enhanced modulation and coding schemes (upto 256QAM) |
|
1st wave of 802.11ac supports data rates upto |
1.3Gbps |
|
802.11 ac operates in 5GHz UNII band |
Statement: 802.11 ac |
|
|
802.11n vs 802.11 ac |
|
802.11 ac is backward compatible with PHYs |
a/n |
|
Each subcarrier in a channel is 312.5KHz wide |
Statement: Subcarrier |
|
Total usable subcarriers in 80MHz is slight higher than two 40 MHz channels combined (2x 114 )because some unused subcarriers between the adjacent channels can be used |
Statement: Subcarrier in 80 MHz |
|
160MHz channels are made of two 80 MHz channels. It is not necessary these two 80 MHz channels should be adjacent. Since two 80 MHz channels are not adjacent unused subcarriers between adjacent channels can't be used Total subcarriers in 160MHz channels will be 2x subcarriers in 80MHz |
Statement: Subcarrier in 160 MHz |
|
Subcarriers in 80MHz |
Total 256 Data subcarriers: 234 Pilot: 8 Unused:14 |
|
Subcarriers in 160MHz |
Total :512 Data subcarriers: 468 Pilot: 16 Unused:28 |
|
Number of primary channel in 160 MHz |
3 one 20MHz primary one 40 MHz primary one 80MHz primary |
|
160MHz channels are deployed in low density high throughput requirements |
Statement: 160MHz deployement |
|
64QAM can modulates __bits per second |
2^6 =64 6bits |
|
256QAM can modulates __bits per second |
2^8 = 256 8 bits |
|
33 percent of bandwidth increase is achieved by the introduction of 256 QAM modulation. True or False |
True |
|
256 QAM implemented in 2.4GHz is known as |
Turbo-QAM Note: implemented by Broadcom |
|
Number of MCS in 802.11ac |
10 MCS 0-9 |
|
Mandatory MCS rate for 802.11ac |
MCS 0-7 |
|
MCS 8 and 9 are optional. True or False |
True |
|
Unlike previous PHYs 802.11 ac does not allow us to disable individual data rates instead it supports 3 ranges MCS 0-7, MCS 0-8, MCS0-9 |
Statement: MCS rates in 11ac |
|
MCS rates which support 256 QAM modulation |
MCS 8,9 |
|
code rate representation: number of user bits = ------------------------------------- number of bits in channel |
code rate representation |
|
Higher the code rate,higher the data is transmitted and greater chance for corruption |
Statement: code rate |
|
Code rate 5/6 means, out of 6 bits in channel 5 are user bit and 1 is redundant bit. True or False |
True |
|
Maximum number of spatial stream supported in 11ac |
8 |
|
Maximum number of spatial stream supported in 11n |
4 |
|
Due to technical reasons there are ___ instances certain MCS rates are not applicable |
10 |
|
10 instances in which MCS rates are not applicable |
MCS 6, 80 MHz channel, SS 3,7 MCS 9, 20 MHz channel, SS 1,2,4,5,7,8 MCS 9, 80 MHz channel, SS 6 MCS 9, 160 MHz channel,SS 3 |
|
MCS 9 is not supported for 20MHz channels |
Statement: MCS 9 |
|
Data rate= 20MHz data rate x SS multiplier x channel width multiplier |
SS multiplier: x number of SS Channel width multiplier: x1.0 for 20MHz x2.1 for 40 MHz x4.5 for 80 MHz x9 for 160 MHz Eg: AP using MCS3, 4 SS, 80MHz 28.9 x 4 x 4.5 = 520.2 Mbps |
|
Total number of available data rates in 11ac |
310 Note: (10 x 8 x4) -10 = 310 Total 10 MCS rates Total 8 SS Total 4 channel width Total 10 invalid MCS rates |
|
Notification frame send my transmitting station to notify other stations that it is changing the channel width and number of SS it can receive/transmit |
Operating mode notification frame |
|
In 802.11ac all frames are transmitted as A-MPDU even if it is a single frame. |
Statement: 802.11ac |
|
Aggregation shifts some of the frame information from PLCP header to MPDU header. PLCP information are transmitted at lowest rate and MPDU information are transmitted at highest rate This improves performance. |
Statement: Aggregation |
|
RIFS is introduced in 802.11n to reduce the time of transmission of multiple frames In 11ac all frames are sent as aggregated frames at higher data rate followed by block ack. Aggregation reduces per frame overhead and requirement of RIFS is no longer required |
Statement: no RIFS in 11ac |
|
If an AP wants to transmit using 80 MHz, it will make sure all the four 20MHz channel is available by sending RTS in 11a rates to the client across all the available four channels(non-HT Duplicate mode). If all the channels are clear or idle, client will be able receive all the RTS and respond back with CTS When AP receives all the four CTS, it assumes all the 4 channels are available If AP doesn't receive CTS in any of the channel, it will assume that channel is busy and do the transmission in 40MHz or 20MHz channel in which it received CTS |
Statement: 11ac channel assessment before transmission |
|
Beamforming can occur from AP to client and vice versa. True or False |
True |
|
Beamforming results in 3dB increase in signal |
Statement: Beamforming |
|
Beamforming allows transmitter to focus RF energy to a particular client. AP sends same information across multiple radio chains by correctly adjusting the phase so that the waves reach the receiver in phase |
Statement: Beamforming |
|
Beamforming can be adjusted frame-by-frame basis. One frame AP can be beamformer and next client can become beamformer |
Statement: Beamforming |
|
Type of beamforming used in 11ac |
Explicit beamforming |
|
Beamformer sends a NDP announcement frame to notifying beamformee its intent to send a beamformed transmission. AP then sends a NDP frame Beamformee process each each OFDM subcarrier and creates feedback information. Feedback information contains regarding power and phase shift between each pair of transmit and receive antennas This information is used to create feedback and matrix that is then compressed and sent to beamformer Beamformer use this feedback matrix to create steering matrix that is used to direct data transmission to the beamformee |
Statement: beamforming process |
|
With MU-MIMO 802.11ac APs can can communicate upto ___ clients simultaneously |
4 |
|
The goal of MU-MIMO is to use as many spatial streams as possible whether transmission is with one client with 4 SS or with 4 clients with 1SS |
Statement: MU-MIMO |
|
MU-MIMO is supported only in APs due to requirement of advanced signal processing |
Statement: MU-MIMO |
|
AP sends a NDP announcement frame notifying multiple beamformeess to notigy its intend to send a beamformed transmission. AP then sends a NDP frame Each beaformee process each OFDM subcarrier and creates feedback information then creates a compressed feedback matrix First beamformee responds AP with a feedback matrix AP then polls rest of the beamformees to send the feedback matrix, by sending Beamforming Report Poll frames to them AP uses these feedback matrix to create a single steering matrix steering matrix defines transmit parameters between each of the antennas on the AP and each of the antennas on each of the client devices After MUMIMO transmission, AP sends BAR to each clients sequentially and collects BlockAck to verify frame delivery |
Statement: MU-MIMO process |
|
If beamformees are close together they may experience inter-user interference. They will receive signals beamed towards other clients |
Statement: MU-MIMO |
|
The AP will initiate a transmission from whichever access category is next in line. This is known as the primary access category, and all others are known as secondaryaccess categories. The AP can transmit additional frames (one or more) from primary or secondary access categories, providing that the frames are shorter thanthe primary frame. AP transmit using a multi user frame During transmission of each multiuser frame, low priority frames are added along with high priority frames as long as they don't increase the transmission time of primary data and clients they are being sent are spatially distinct AP verifies the successful transmission with Block ACK |
Statement: MU-MIMO Access category |
|
Mandatory features tested Wifi alliance 11ac certification |
WMM WPA2 20,40,80MHz MCS 0-7 one SS for clients and 2 SS for APs Long guard interval 800ns |
|
VHT radios use modulation and coding schemes to define data rates based on |
Modulation and code rate |
|
|
Statement: Subcarriers legacy/HT/VHT |
|
Power required for 802.11 ac APs |
PoE+ |
|
Normal enterprise APs are powered by 802.3 af compliant PoE |
Statement: power supply to APs |
|
|
FHSS |
|
|
Installation of lightning protectors |
|
|
Indoor sectorized array Eg for static beamforming |
|
|
Beamwidth calculated at half power points |
|
|
Fresnel zone |
|
Chapter 12 essentials |
1. Causes of layer 2 retransmissions: multipath, hidden nodes, mismatched power settings,RF interference, low SNR, near/far problems, and adjacent channel interference. Layer 2retransmissions affect throughput, latency, and jitter 2. Dynamic rate switching 3. Various aspects of roaming 4. adjacent channel vs co-channel interference 5. MCA vs SCA wireless design 6. various types of interference 7. hidden node problem 8. importance of channel reuse 9. aspects of band steering, load balancing and high density wlans 10. consequences of weather conditions |
|
Tool used by WLAN engineers to troubleshoot layer 1 issues |
Spectrum analyzer |
|
Tool used by WLAN engineers to troubleshoot layer 2 issues |
Protocol analyzer |
|
Possible results of excessive layer 2 transmission |
1. decrease in throughput 2. latency and jitter to time sensitive applications like voice and video |
|
Latency Vs Jitter |
Latency is time taken to deliver the packet from source to destination Jitter is variation in latency. Sometimes packet delivery takes less time sometimes more time. Jitter measures latency of each packet on an average. |
|
If all packets are delivered at same time in network, value of jitter will be __ |
zero |
|
Jitter will result in |
1. choppy audio transmission 2. battery drainage of voip phones due to increased layer 2 transmission |
|
Data applications in WiFi network can handle layer 2 transmissions upto __ percent without any noticeable performance degredance |
10 |
|
VoWifi networks has to limit layer 2 transmission upto __ percent to ensure timely and consistent delivery of voip packets |
Statement:vowifi networks layer 2 transmission |
|
time sensitive applications like voip requires higher lay IP packet loss be no greater than 2 percent |
statement: voip ip packet |
|
How can we measure layer 2 retransmissons |
layer 2 retry statistics thru a protocol analyzer WLAN controller NMS server |
|
Layer 2 retransmissions are mainly used caused by |
layer 1 issues: RF interference result of an improper wlan design |
|
Different types of RF interferences that causes layer 2 retransmissions |
1. Narrow band interference 2. Wide band interference 3. all band interference |
|
Narrow band signals are very high amplitude signals which occupies smaller and finite frequency space can completely disrupt 802.11 communications in the frequency it is transmitting will not cause denial of service of entire band like complete 2.4GHz ISM band but few channels can be affected |
Statement: Narrow band signals |
|
If the transmitting signal has a capability to disrupt communication in entire band it is considered as wide band interference can cause denial of service in entire band |
Statement: wide band interference |
|
All band interference are caused by devices using FHSS device like bluetooth, medical telemetry units, Home RF are sources of all band interference while hopping and dwelling FHSS devices will transmit sections of frequency where 802.11 devices are transmitting |
Statement: all band interference |
|
Narrow band,Wide band and all band interference sources can be located and removed using __ |
spectrum analyzer |
|
Majority of RF interference occur in 2.4GHz band |
Statement: RF interference |
|
Layer 2 retransmission caused by multipath are affected only to older a/b/g radios Multipath cause intersymbol interference(ISI) antenna diversity, using semi directional antennas are few workarounds to survive multipath when a/b/g radios are used radios using MIMO are not affected due to multipath instead they make use of multipath to achieve greater wlan performance |
Statement: multipath |
|
If there is no RF interference is found in RF site survey and there is layer 2 retransmission possible cause can be __ |
multipath |
|
multipath in indoor cannot be avoided because some reflections will always occur. True or False |
True |
|
WLAN vendor which provides wlan troubleshooting tools that can detect and visualize occurance of multipath and delay spread into a useful graphical display |
Berkeley Varitronics Systems |
|
Indoor MIMO patch antennas are used in high density environments like gymnasium |
Statement: usecase of MIMO patch antennas |
|
a channel is considered adjacent channel if it is immediately above or below the current numbered channel eg: for channel 3 , 4 and 2 are adjacent channels |
Statement: adjacent channel |
|
while designing wlan, for seamless roaming overlapping coverage cells are required These overlapping cells should not have overlapping frequencies In 2.4GHz we have only 3 non overlapping channels overlapping coverage cells with overlapping frequencies will cause adjacent channel interference adjacent channel interference will corrupt the frames and causes layer 2 retransmission |
adjacent channel interference |
|
In 5GHz all the 25 channels are non overlapping channels because |
20 MHz of separation between the center frequencies |
|
Signal to noise ratio is not a ratio It is the difference in decibels between received signal and noise floor |
SNR |
|
A wlan with SNR 25 dB or above is considered good signal quality |
Statement:SNR |
|
A wlan with SNR 10 dB or below is considered good signal quality |
Statement:SNR |
|
A low SNR will casue layer 2 retransmissions |
Statement:SNR |
|
When designing coverage during site survey, the normal recommended best practiceis to provide for a –70 dBm or stronger received signal that is well above the noise floor. |
Statement:SNR |
|
When designing for WLANs with VoWiFi clients, a –67 dBm or stronger signal that is evenhigher above the noise is recommended. |
Statement:SNR |
|
Recommended SNR for wifi data network |
20dB |
|
Recommended SNR for vowifi network |
25dB |
|
Wlan troubleshooting tool used to measure SNR |
spectrum analyzer |
|
Mismatched power setting: Tx power of AP should match lowest powered client station. majority of clients are mobile devices with lowest txpower. If Ap increase txpower it might increase range but the transmission from client cannot reach AP due to its low tx power. To increase range, instead of increasing tx power use a high gain antenna. Antenna will amplify outgoing signal and received signal |
Mismatched power setting |
|
Use a protocol analyzer to identify layer 2 retransmission are caused due to mismatched power setting An AP/client power problem exists if the frame transmissions of the clientstation are corrupted when you listen near the access point but are not corrupted whenyou listen near the client station |
Mismatched power setting troubleshooting |
|
Near/Far problem: occurs due to tx power mismatch b/w multiple clients in same BSS if there a client with high tx power near Ap, it will increase the noise floor of AP . So transmission from client far from Ap with low tx power will be unheard. The problem is often caused by AP's inability to distinguish high amplitude signal and low amplitude signal subsequently can troubleshoot using the same way we troubleshooted mismatched txpower settings |
Near/Far problem |
|
How to negate near/far issues: CSMA/CA usually averts the near/far problem. well plannedWLAN that provides for –70 dBm or stronger coverage |
Near/Far problem |
|
Hidden node problem: 2 clients of a rf coverage cell cannot hear each other and both trying to send at same time |
hidden node |
|
Overcome hidden node by |
RTS/CTS in hidden node remove obstacles increase power of all stations move hidden station if possible add another AP |
|
Layer 2 retransmission reasons |
RF interference: Narrow band,wide band, all band Multipath Adjacent channel interference Low SNR Mismatched power setting Near/Far problem Hidden node |
|
When client move away from the AP, it will downshift to less complex modulation with low data rates and when it move closer it up shifts to higher data rates to improve wlan performance. This mechanism is known as |
Dynamic rate switching |
|
DRS is also known as |
Dynamic rate shifting Adaptive rate selection Automatic rate selection |
|
|
DRS |
|
Threshold used for DRS are vendor proprietary It can be based on RSSI, packet error rates, retransmissions |
DRS |
|
Why lower data rates of AP are disabled by WLAN admins |
1. to decrease coverage area 2. to avoid hidden node issue 3. sticky roaming client 4. to avoid medium contention overhead caused by clients using low data rates. If airtime fairness is introduced no need to disable lower data rates |
|
Roaming is transition of client from one AP to another AP within the saem ESS without losing upper layer connectivity. Roaming decision is made by client and its proprietary For seamless roaming there should be 15-30 percent coverage overlap of -70dBm cells |
Roaming |
|
802.1x takes an average of __ milliseconds for authentication during roaming |
700 |
|
VoWifi networks requires a roaming handoff of__miliseconds |
150 |
|
Non standard method of fast secure roaming implemented by most vendors |
OKC |
|
IEEE standard for fast secure roaming |
FT |
|
For troubleshooting roaming issues wlan engineers require protocol analyzers which support multi channel monitoring capabilities with multiple wlan cards with monitoring capabilities each on different channel 1,6,11. |
|
|
IEEE standards which enhance roaming perfomance |
802.11k, 802.11 r |
|
Roaming is a layer 2 process while roaming, client has to maintain layer 3 connectivity. When it roams from one AP to another in different subnet, client must acquire new IP address which means it has to reestablish layer3 connectivity IETF introduced Mobile IP solution which allows client to maintain original IP address when it roams from one layer 3 network to another |
Layer 3 roaming |
|
Mobile IP is defined in RFC 3344 |
Statement: Mobile IP |
|
IP address of roaming client is Home address Controller to which client originally connected is known as Home Agent(HA) Controller present in network to which client roams is known as Foreign Agent(FA) HA shares Home Address Table with FA, which contains client's MAC/IP information When client roams to a network in FA resides, FA uses HAT to locate HA of the roaming client FA contacts HA and setup a Mobile IP tunnel to FA FA then delivers all the traffic to the client thru this tunnel and client can maintain its original IP address WLAN architecture in which there is no controller, tunnelling occurs between APs that assumes role of HA and FA |
|
|
The unnecessary medium contention overhead that occursbecause all the APs are on the same channel is called __ |
co-channel interference (CCI). |
|
Reason for co-channel interference |
when overlapping coverage cells are on the same channel |
|
|
co-channel interfernce |
|
|
Adjacent channel interference occurs when overlapping coverage cells have overlapping channels resulting in data corruption and layer 2 retransmission |
|
|
2.4GHz channel reuse multi channel architecture |
|
|
5GHz channel reuse multi channel architecture |
|
In 5GHz channel 120,124,128 are not used for channel reuse because they are used TDWR and FCC defines (DFS) regulations that restrict use of the5600 MHz–5650 MHz frequency band |
Statement: 5GHz channel reuse |
|
|
Three-dimensional channel reuse When APs are mounted on multiple floor, make sure their channels don't overlap as shown in fig 5 GHz, and the signal will attenuate faster than the signalthat is being transmitted at 2.4 GHz from the 802.11b/g/n radio when performinga site survey for deploying dual-frequency WLANs, you should perform the 5 GHzsite survey first and determine the placement of the access points. After those locations areidentified, channel reuse patterns will have to be used for each respective frequency |
|
|
Channel reuse/Channel bonding 1. 2.4GHz 40MHz is not used 2. In 5Ghz we have 25 , 20MHz channels, when channel bonded =12 40MHz channels 3. Channels in DFS range are not used , so channels in UNII 1 and UNII 3 are only used 36,40,44,48 and 149,153, 157, 161 |
|
|
Current UNII channels |
|
|
All the APs will be connected to a single wlan controller Each APs will have its own radio and its own mac address but all will have same virtual BSSID that is broadcast from all APs the multiple access points advertise only one single virtual MAC address(BSSID), client stations believe they are connected to only a single access point, althoughthey may be roaming across multiple physical APs the clients think theyare associated to only one AP, so they never initiate a layer 2 roaming exchange. All of theroaming handoffs are handled by a central WLAN controller |
|
Main advantage of virtual AP SCA |
zero handoff time while roaming no adjacent channel interference |
|
Disadvantage of SCA |
co-location of multiple APs for capacity a.k.a channel stacking multiple APs maybe co-located by using 3 channels and 3 BSSIDs each layer of multiple APs on a single channel and using same virtual BSSID is known as channel blanket or channel span |
|
802.11 coverage consideration |
1. Dynamic rate switching DRS 2. Roaming 3. Layer 3 roaming 4. Co-channel interference 5. Channel reuse/ multi-channel architecture MCA 6. Channel reuse/ channel bonding 7. Single channel architecture SCA |
|
Capacity Vs Coverage |
client stations connected to access point share the throughput capabilities of that access point as a wlan engineer it is important to design and decide number of client stations that can connect to a single AP simultaneously In MCA environment , determine the cell size and limit the coverage cell size by adjusting tx power to get desired cell size Adjusting the transmit power to limit the coverage area is known as cell sizingand is the most common method of meeting capacity needs in an MCA environment |
|
Band Steering |
a technology to encourage dual band client radios to connect to 5GHz AP radio instead of 2.4GHz AP radio Client sends probe request in both 2.4 and 5GHz band When AP sees probe request in both 2.4 and 5 GHZ from same MAC address it responds back with probe response only in 5GHZ So client connects with 5GHz AP radio Band steering is used in environment where high density of clientdevices exists, band steering to both frequencies can be used to balance an almost equalnumber of clients to both of the radios in the AP. |
|
When client wants to connect to an AP it sends an assoc req to that AP If that AP has already overloaded with clients it will defer from sending assoc response assuming client will send another assoc req to neighboring AP with less client connected load balancing information is shared among all the APs |
Load balancing |
|
Load balancing is __plane mechanism |
control |
|
Load balancing works for centralized wlan architecture as well as distributed wlan architecture. True or False |
True |
|
Load balancing is implemented in high density client environments where roaming is not a priority. True or False |
True |
|
Load balancing is detrimental to roaming process. True or False |
True |
|
General rules for high density wlans |
1. deploy 11n or 11ac APs as opposed to legacy 2. disable 11b rates 3. deploy only 11n or 11ac clients and select high minimum data rates such as 18MBps 4. lower AP tx power for cell sizing and avoid co-channel interference 5. For stability use static channel and power settings instead of dynamic RF 6. enable load mechanism b/w multiple APs 7. In 5GHz if DFS channels are supported cut down to 20MHz. if client devices support DFS and channel bonding go for 40MHz 8. consider using sectorized MIMO patch antennas to provide sectorized coverage 9. disable few 2.4 GHz radios to avoid co-channel interference |
|
Number of devices per AP radio = B.W used by application 80 ÷ ------------------------------------------------------------ Throughput of single device using that app |
Statement: Number of devices per AP radio Note: airtime consumption = B.W used by application ------------------------------------------------------------ Throughput of single device using that app |
|
An 802.11 access point is considered to be fully burdened at about 80 percentof airtime utilization |
Statement: airtime consumption |
|
Possible side effects of over sized coverage cells |
1. CCI 2. hidden node 3. AP may not hear transmission of client with low tx power |
|
recommended power setting for higher density environment |
1mW |
|
Increasing of tx power is not a recommended option to increase coverage . To increase coverage use a high gain antenna |
Statement: coverage |
|
WLAN performance considerations |
1. Tx power rates 2. Antenna gain 3. Antenna type 4. Wavelength 5. Free space path loss 6. physical environment 7. CSMA/CA 8. ENcryption overhead 9. Application used 10. Number of clients 11. Layer 2 transmissions |
|
Consequences of weather conditions in wlan |
1. Lightning 2. Wind 3. Water 4. Air stratification 5. UV/Sun |
|
Chapter 13 essentials |
1. AAA concepts 2. legacy 802.11 security 3. EAP framework 4. requirements for RSN n/w 5. TKIP/RC4, AES/CCMP 6. VLANS and VPNs 7. Guest WLAN security |
|
802.11 security basics |
1. Data privacy and integrity 2. Authentication, Authorization, Accounting 3. Segmentation 4. Monitoring and policy |
|
Data privacy and integrity |
privacy is achieved by encrypting upper layer data (MSDUs) using encryption algorithms like RC4, AES RC4 is streaming cipher used in WEP and TKIP AES is block cipher used in CCMP Integrity is achieved by: ICV in WEP MIC in TKIP, CCMP MIC in CCMP is stronger than MIC in TKIP ICV in WEP is considered as weaker |
|
Authentication, Authorization, Accounting |
Authentication: Whether user have right credentials to join the n/w Authorization: privileges given to authenticated user to access n/w resources based on group,device,time of the day, locations Accounting: keeping track of access details of n/w resource by authenticated user |
|
Segmentation |
Separating user traffic in a network based on device type, roles Achieved using VLANs, firewall, routers, VPNs |
|
Monitoring and Policy |
Monitoring WLAN networks for n/w attacks Achieved using WIDS |
|
Legacy Security |
provide 2 types of authentication: Open, Shared used in WEP |
|
WEP |
Wired Equivalent Privacy uses RC4 algorithm for encryption and ICV for integrity check WEP supports 64 bit and 128 bit WEP supports 4 static keys either in 64bit or 128 bit . Uses any one of it for data encryption |
|
64 bit WEP key contains |
24 bit IV and 40 bit static key |
|
128 bit WEP key contains |
24 bit IV and 128 bit static key |
|
40 bit static key can be ascii or hex. How many characters will it have |
ascii: 5 characters hex: 10 characters |
|
128 bit static key can be ascii or hex. How many characters will it have |
ascii: 13 characters hex: 26 characters |
|
|
Static WEP key |
|
|
WEP encryption |
|
WEP weakness |
IV collision attack: 24bit IV is driver generated It is limited and will be reused. IV is send as cleartect with encrypted frame Weak key attack: coz weak RC4 scheduling algorithm weak IVs are generated and with theses IV secret keys can be recovered Reinjection attack: used in n/w with less traffic packets are injected to recover weak IVs Bit flipping attack: tampering wep encrypted frames |
|
MAC filtering |
Using MAC address to allow or deny access to network MAC address can be easily spoofed and mac filtering is considered weak |
|
SSID cloaking |
making ssid hidden can make connection by sending directed probe req SSID cloaking is considered weak coz anyone with a protocol analyzer can capture these packets and can start attacks |
|
Robust security network |
A robust security network is one which allows only rsn associations 2 STAs should authenticate each other and create dynamic encryption keys using 4 way handshake RSN capability is present in RSN IE in beacons,prob req/res, (re)assoc req/res WPA/TKIP, WPA enterprise WPA2/AES, WPA2 enterprise creates dynamic encryption keys |
|
PSK is ideal for ___ environment |
SOHO |
|
802.1x is ideal for __environment |
enterprise |
|
802.1x is ideal for enterprise environment because it requires RADIUS server and advanced skills are required to support it |
Statement: 802.1x |
|
Passphrase size used in wpa2-psk |
8 to 63 |
|
WPA personal vs WPA2 personal |
both uses PSK WPA uses TKIP/RC4 WP2 uses AES/CCMP |
|
Wi-Fi Alliance name for PSK authentication is |
WPA-Personal or WPA2-Personal. |
|
Wlan vendors which provides uniques psk for each client dynamically |
Aerohive Networks’ Private PSK and Ruckus WirelessDynamic PSK |
|
A database of unique PSKs mapped to usernames or client stations must be stored on allaccess points or on a centralized WLAN controller. Individual users are then assigned aunique PSK that is created either dynamically or manually theauthenticator maintains a database of each individual PSK for each individual client. ThePSKs that are generated can also have an expiration date. Unique time-based PSKs can alsobe used in a guest WLAN environment as a replacement for more traditional username/password credentials |
Dynamic psk generation |
|
Advantages os proprietary psk solution |
no need of complex configuration like 802.1x |
|
|
Proprietary PSK |
|
802.1X/EAP Framework |
3 components 1. Supplicant: client who want to access n/w resources 2. Authenticator: usually an AP. Maintains two virtual port blocked and unblocked will not allow any n/w traffic to pass thru blocked port until client credential are verified unblocked port allows only EAP packets for authentication purpose 3. Authentication server: usually a RADIUS server. verifies credentials of supplicant and if verified inform AP to open blocked port to allow client to access n/w resources |
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RADIUS is |
Remote Dial in User service |
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802.1X security solution is used with a WLAN controller solution, theWLAN controller is typically the authenticator and not the controller-based access points |
Statement: 802.1x Authenticator |
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802.1X comparison—standalone vs. controller-based access points |
|
|
the root bridge would be the authenticator and the nonrootbridge would be the supplicant if 802.1X security is used in a WLAN bridged network |
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802.1X/EAP authentication |
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4 way handshake |
method for creating dynamic encryption keys PTK and GTK PTK for unicast and GTK for group traffic The 4-Way Handshake will always be the final four frames exchangedduring either an 802.1X/EAP authentication or a PSK authentication |
|
TKIP rectify the problems that were inherent in WEP which are |
TKIP starts with a 128-bit temporal key that is combined with a 48-bit initializationvector (IV) and source and destination MAC addresses in a complicated process known asper-packet key mixing. (TK+PN+SMAC+DMAC) This key-mixing process mitigates the known IV collision and weakkey attacks used against WEP. TKIP also uses a sequencing method to mitigate the reinjectionattacks used against WEP. TKIP uses a stronger data integrity checkknown as the message integrity check (MIC) to mitigate known bit-flipping attacks againstWEP. The MIC is sometimes referred to by the nickname Michael. All TKIP encryptionkeys are dynamically generated as a final result of the 4-Way Handshake. |
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11n and 11ac doesn't permit use of TKIP or WEP. True or False |
True |
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CCMP is |
CTR with CBC MAC Counter mode with cipher block chaining message authentication code protocol |
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CCMP/AES uses a 128-bit encryption-key size and encrypts in 128-bit fixed-length blocks. |
CCMP |
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CCMP uses __alogorithm |
AES(Rijndael algorithm) |
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By upgrading the firmware older wlan devices can support CCMP. True or False |
False AES cipher is processor intensive, older legacy 802.11 devices donot have the processing power necessary to perform AES calculations |
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Traffic segmentation is achieved by |
VLAN RBAC |
|
VLAN |
create separate broadcast domains in alayer 2 network and are often used to restrict access to network resources without regardto physical topology of the network Guest VLAN, Voice VLAN, Enterprise VLAN are the VLANS usually created by enterprise In enterprise environment, VLAN assignment done with the help of Attribute value pairs present in Radius_accept packet |
|
RBAC |
Role Based access control approach is users, roles , permissions, once user is authenticated depending on their roles they have given permission to access n/w resources Permissions can be defined as layer 2permissions (VLANS or MAC filters), layer 3 permissions (access control lists), layers 4–7permissions (stateful firewall rules), and bandwidth permissions |
|
Infrastructure security |
1. physical security 2. interface security |
|
physical security |
enterprise wlan products are expensive and has to prevent it from theft by locking them in enclosures it also prevents unwanted users from gaining access to AP using serial cables or console cables |
|
interface security |
telnet should be disabled use only ssh change default passwords disable interface which are not using CLI or Web based configure wireless devices from wired side |
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It is recommended practice to configure infrastructure device from wired side. Reason behind this |
If devices are configuredfrom the wireless side, an intruder might be able to capture your wireless packets and beable to watch what you are doing When performing administration through a wireless connection, there is also a chance thatyou will accidentally lock yourself out of the device while configuring Wi-Fi hardware thatyou are connecting through. |
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VPN |
Virtual private network provides layer 3 security 2 types : router-to-router, client server based VPN create a secure tunnel between two networks encapsulates original IP packets and securely send to destination Commonly used VPN is IPsec which supports ciphers 3DES, DES, AES IPSec requires client to be installed on remote machine that connects to VPN server IPsec VPNS are NAT-transversal any firewalls at a remote site require (at a minimum) that UDP ports 4500 and 500 beopen. A |
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SSL VPN |
no need to install client software user connects to ssl vpn server using web browser traffic b/w browser and vpn server are encrypted using SSL or TLS uses asymmetric cryptography for privacy and a keyed message authentication code formessage reliability. |
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SSL VPn is chosen over IPSec because |
NAT issues, firewall policy at remote locations |
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common use of VPN technology is to provide site-to-site connectivity betweena remote office and a corporate office. |
VPN |
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VPN Deployment |
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Site-to-site VPN |
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Guest WLAN |
to provide internet access to visitors, contractors,sales people |
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Guest WLAN security |
to provide internet access to visitors with less hurdles and sametime prevent them from accessing corporate n/w security components : Guest VLAN, Guest SSID, Firewall policy, Captive portal, Guest management solution |
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A captive portal is essentiallythe integration of a firewall with an authentication web page. |
captive portal |
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Chapter 14 essentials |
1. Different types of wireless attacks 2. Intrusion monitoring 3. Wireless security policy |
|
components that should be mandatory in every remote access wireless securitypolicy |
Encrypted VPN Personal firewall |
|
attacks which wireless users susceptible to at a public-access hotspot |
1. Wi-Fi phishing 2. Peer-to-peer attack 3. Malicious eavesdropping 4. Man-in-middle 5. Wireless hijacking |
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actions should be taken after the WIPS detects the rogue AP |
1. Enable the layer 2 rogue containment feature that his WIPS provides. 2. Unplug the rogue AP from the data port upon discovery. |
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two solutions that can help mitigate peer-to-peer attacks from other clients associatedto the same 802.11 access point |
Personal firewall Client isolation |
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unintentional RF jamming attacks against an 802.11 wireless network |
1. Microwave oven 2. 2.4 GHz cordless phones |
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when attacker compromises psk he can decrypt the packets and access n/w resources |
Statement: PSK compromised |
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The only way to prevent a wireless hijacking, man-in-the-middle, and/orWi-Fi phishing attack is to use a __ |
mutual authentication solution Note: 802.1X/EAP authenticationsolutions require that mutual authentication credentials be exchanged before auser can be authorized |
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Examples for malicious eavesdropping |
Packet reconstruction Protocol analyzer capture |
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Different types of wireless attacks |
1. Rogue wireless devices 2. peer-to-peer attacks 3. Eavesdropping 4. Encryption cracking 5. Authentication attacks 6. Mac spoofing 7. Management interface exploits 8. Wireless hijacking 9. Denial of service(Dos) 10. Vendor-specific attacks 11. Social engineering |
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Intrusion monitoring |
1. WIDS 2. WIPS 3. Mobile WIDS 4. Spectrum analyzer |
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A rogue accesspoint is any unauthorized Wi-Fi device that is not under the management of the propernetwork administrators. |
Statement: Rogue AP |
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2 types of eaves dropping |
Casual eavesdropping Malicious eavesdropping |
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Offline dictionary attack is an example for __ |
Authentication attack |
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How can we prevent authentication attacks |
802.1X solution which provide mutual authentication and dynamic keys proprietary PSK solutions which provides unique PSK to each client |
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How to avoid management interface exploits |
use only SSH or HTTPS enabled encrypted login strong passwords should be used disable unused management interfaces change default passwords use wired network while configuring infrastructure device |
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Wireless Hijacking is also known as |
evil twin attack |
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2 types of RF jamming |
Intentional jamming Unintentional jamming |
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Jamming caused by microwave ovens, cordlessphones is ___ jamming |
unintentional |
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Jamming casued by signal generator to cause interference in unlicensed frequency space is a an example for ___ jamming |
intentional |
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Tool used to detect RF jamming |
spectrum analyzer |
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DoS |
RF jamming Deauthentication and Dissociation by spoofing MAC address Association floods Authentication floods PS-POLL floods virtual carrier attacks |
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Tools to detect DoS attack |
Spectrum analyzer Protocol analyzer or WIDS Physical security |
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802.11 w protects from DoS attacks by spoofing management frames like disassoc,deauth, action frames |
Statement:Management frame protection |
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WIDS components |
typical WIDS is client server model consists of 3 components 1. WIDS server: can be s/w or h/w server server uses signature analysis, behavioural analysis, protocol analysis, RF spectrum analysis, performance analysis to detect potential threats 2. Management consoles: portal to connect to wids server 3. Sensors: are 802.11 radios in monitoring mode |
|
|
WIDS |
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3 different types of WIDS |
1. Overlay: Expensive and more features Dedicated WIDS server and sensors which are not part of WLAN solution that provides access to clients 2. Integrated: less expensive less features as compared to overlay model comes along with wlan controller, NMS or AP 3. Integration Enabled: integrate APs with WIDS vendors APs are turned into sensors and communicate info to third party WIDS server |
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Overlay WIDS are mostly used in defense, finance, retail vertical markets |
Statement: Overlay WIDS |
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Most commonly used WIDS model |
Integrated WIDS |
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WIDS vs WIPS |
WIDS: detects potential threats WIPS: detects and mitigate the threats |
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WIPS classifies client radios into 4 |
1. Infrastructure device: any client station or AP that is an authorizedmember of the company’s wireless network 2. Unknown device: any new802.11 radios that have been detected but not classified as a rogue or infrastructure device 3. Known device: device whose identity is known 4. Rogue device: device which is a potential threat |
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WIPS also use a wired-side termination process to effectively mitigate roguedevices The wired-side termination method of rogue mitigation uses the Simple NetworkManagement Protocol (SNMP) for port suppression. Many WIPSs can determine that the rogue AP is connected to the wired infrastructure and may be able to use SNMP to disablethe managed switch port that is connected to the rogue AP. If the switch port is closed, theattacker cannot access network resources that are behind the rogue AP. |
Statement: WIPS action on Rogue devices |
|
Mobile WIDS |
essentially a protocol analyzer with layer 1 decoding capabilities uses 802.11 radios as sensors advantage: Mobility The mobile WIDS locks ontothe RF signal of the rogue device, and then an administrator can locate the transmittingrogue by using a directional antenna |
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A spectrum analyzer is a ___ domain tool that can detect any RF signal in the frequencyrange that is being scanned. |
frequency |
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Two major areas that should be addressed while designing a wireless policy document |
1. General policy 2. Functional policy |
|
General Policy |
depicts why wireless policy is required for the organization It defines: Statement of Authority: The statement of authority defines who put the wireless policy inplace and the executive management that backs the policy. Applicable Audience: The applicable audience is the audience to whom the policy applies,such as employees, visitors, and contractors. Violation Reporting Procedures: Violation reporting procedures define how the wirelesssecurity policy will be enforced, including what actions should be taken and who is incharge of enforcement. Risk Assessment and Threat Analysis: The risk assessment and threat analysis defines thepotential wireless security risks and threats and what the financial impact will be on thecompany if a successful attack occurs. Security Auditing: Internal auditing procedures, as well as the need for independent outsideaudits, should also be defined |
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Functional Security Policy |
Defines technical aspects of wireless security tells how to secure wireless network in terms of what solution and actions needed It defines: Policy Essentials: Basic security procedures, such as password policies, training, andproper usage of the wireless network, are policy essentials and should be defined. Baseline Practices: Baseline practices define minimum wireless security practices such asconfiguration checklists, staging and testing procedures, and so on. Design and Implementation:The actual authentication, encryption, and segmentationsolutions that are to be put in place are defined. Monitoring and Response: All wireless intrusion detection procedures and the appropriateresponse to alarms are defined. |
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Legislative Compliance |
NIST: FIPS 140-2 HIPAA:The Health Insurance Portability and Accountability Act The goal is to protect patient information andmaintain privacy Sarbanes-Oxley: The Sarbanes-Oxley Act of 2002 GLBA:The Gramm-Leach-Bliley Act goal is to protect personal information such as credit card numbers, Social Security numbers from |
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PCI compliance |
Payment card industry data security standard regulations for organizations processing and storing cardholder information |
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802.11 policy recommendation |
1. BYOD policy 2. Remote-Access wlan policy 3. Rogue AP policy 4. Ad Hoc Policy 5. WLAN proper use policy 6. IDS policy |
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Chapter 15 essentials |
1. WLAN site survey interview 2. Documentation and forms: identify all the documents required before and after the site survey 3. Vertical market considerations: requirements will change depending on verticals we choose like healthcare,retails etc. |
|
Why site survey is required? |
to educate the customer and properly determine their requirement |
|
Wlan site survey interview |
1. Customer briefing 2. Business requirements 3. Capacity and coverage requirements 4. Existing wireless network 5. Infrastructure connectivity 6. Security expectations 7. Guest access |
|
Customer briefing |
Brief him on advantages of choosing wifi over wired(about mobility) Educate customer why a RF site survey is required Brief him on: difference b/w throughput vs bandwidth. Throughput will be always 50 percent less than advertised data rate RF propagation behavior. How RF waves propagate and attenuate and how site survey helps to ensure proper coverage,capacity and performance of wlan difference b/w 2.4 and 5GHz |
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Business requirements |
1. What is the purpose of WLAN is it for internet gateway, infrastructure connectivity 2. What applications will be used data or voice or bandwidth intensive or less bandwidth intensive 3. Who will be using WLAN what kinda users will be using wlan 4. What types of devices will be connecting to WLAN personal devices,infrastructure devices, barcode scanners, BYOD, MDM solutions needed? |
|
Capacity and coverage requirements |
Coverage: Get the floor plan and enquire about locations in which coverage is required. Barcode scanner doesn't need coverage till front office other than warehouse, laptops doesn't need coverage in courtyard or storage area etc Capacity: 1. Data applications used what kinda data application will be used and how many user will be using it How many simultaneous client will be connected to single AP radio 2. Users and device density how many users need wireless access and how many devices they will be using how many users and devices need wireless access in future Where are the users located. Is it 1 or 2 members in a room or 30 members in a common area separated by cubicle plan to conduct site survey during office hours and non office hours 3: Peak hours of usage 4: Existing wireless transmitters like microwave,BT mouse 5: Portability/Mobility 6: Backward compatibility with legacy devices |
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Existing wireless network |
5 factors: 1: What is the issue with existing WLAN n/w? 2: Are there any known source of interference? 3: Is there any coverage dead zones? 4: Does previous site survey data exists? 5: What equipment is currently installed? |
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Infrastructure connectivity |
10 factors 1: Roaming 2: Wiring closet->100 feet 3: Antenna structure-> for roof/outdoor 4: Switches->managed/unmanaged 5: PoE-> CAT5e 6: Segmentation of WLAN from wired n/w 7: Naming convention 8: User management->RADIUS,RBAC 9: Device management->BYOD,MDM 10: Infrastructure management->NMS |
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A comprehensive site interview that provides detailed feedback about infrastructureconnectivity requirements will result in a more thorough site survey and a well-designed wireless network. Seventy-five percent of the work for a good wireless network is in the pre-engineering. It creates the road map for all the other pieces |
Statement: Infrastructure connectivity |
|
Security expectations |
Consult network management personnel of the organization and enquire about data privacy and encryption which need to be implemented installing WIDS or WIPS to safegaurd against wireless attacks Industry specific regulations need to be taken into account like HIPAA, GLB, PCI Taking all these into consideration check whether existing h/w s/w support these requirements if not recommend purchasing new one which does support |
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Guest access |
whether guest access need to enabled Firewall rules and bandwidth throttling for guest users |
|
Documents and reports |
proper document about facility and network should be obtained create site survey checklist and adhere the checklist during physical site survey After physical survey a professional comprehensive final report will be submitted to customer . The report should contain detailed information on how to install and configure proposed network so that anyone could read our report and understand our intent |
|
Documents which need to collected from customer before site survey interview |
1. Blue print 2. Topographic map or contour map 3. Network topology map 4. Security credentials 5. Survey checklist: Interview checklist Installation checklist Equipment checklist |
|
Blue print |
to record RF measurements taken during site survey , location of h/w placement if not available with customer, check with original architect, govt offices like city hall,fire dept. use predictive analysis s/w which takes blueprints in vector graphic format like .dwf or .dwg to create capacity and coverage simulations |
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Topographic map |
a.ka. contour map necessary when using bridging calculations like Fresnel zone display info like elevations, forest cover, streams and other water bodies |
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Network topology map |
get necessary approval and obtain network topology map to understand customers wired n/w infrastructure for seamless integration WLAN into existing wired n/w provides necessary info like location of wiring closet, layer 3 boundaries |
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Security credentials |
meet with facility manager and get necessary approval for badge . As part of survey we may have to move around most of the places |
|
Survey Checklists |
Interview checklist: detailed checklist on questions to be asked to customer Installation checklist: checklist on installation h/w like AP, antenna type, antenna orientation, mounting devices,power sources Equipment checklist: checklist of all necessary h/w and s/w tools required during site survey |
|
Site survey report |
final comprehensive report submitted to customer after physical site survey Contains: 1. Purpose statement: stipulates customer requirements and business justification for the wlan 2. Spectrum analysis: identify potential source of interference 3. RF cell boundaries: define cell boundaries 4. H/w placement and configuration: recommend AP/antenna placement/antenna orientation, channel/channel reuse pattern/power settings 5: Capacity and performance analysis: application throughput test results |
|
Additional reports gave along with site survey report |
1. Vendor recommendations 2. Implementation diagrams: Wireless topology diagram tells how wlan is integrated into wired n/w AP placement, VLANS, layer 3 boundaries all will be defined 3. Bill of Materials(BOM): every single item both s/w and h/w required for the final installation of the wireless network. includes model number and quantity of each item includes access points, bridges, wireless switches, antennas,cabling, connectors, and lightning arrestors 4. Project schedule and cost: equipment cost, labour costs, schedule timelines. 5. Security solution recommendations 6. Wireless policy recommendation: assist the customer to create if they don't have one 7. Training recommendations: training session for customer's network personnel and brief training for all end users |
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Vertical market considerations |
1. Outdoor surveys 2. Aesthetics 3. Government 4. Education 5. Healthcare 6. Hotspots 7. Retail 8. Warehouses 9.Manufacturing 10 Multi Tenant buildings |
|
Outdoor Surveys |
calculations like Fresnel zone, earth bulge, free space path loss, link budget, and fade margin are required equipments should be kept in NEMA-rated enclosure units to protect from weather conditions like lightning, snow and ice, heat, and wind if tower mount antennas are using get approval from regulatory authorities if tower is 200 ft above ground level or its a roof mount with 20 ft above high roof level get approval from FCC and Federal Aviation Agency FAA |
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Aesthetics |
conceal access points from sight. extremely important in retail and hospitality industry |
|
Government |
security is the major concern get proper approval for identification badge or pass before conducting site survey |
|
Education |
high density environment h/w must be properly locked to prevent from theft and hampering class room wall attenuate RF signals fast. Proper coverage consideration has to be taken care of |
|
Healthcare |
interference from medical equipments is a major concern A thorough spectrum analysis survey using a spectrum analyzer is extremely important VoWifi, RTLS are commonly used in hospitals Healthcare applications used in handheld devices like smartphones, ipad should also be considered Long hallway, multiple floors, fire safety doors, reflective materials, concrete construction, lead-lined x-ray rooms, wire mesh safety glass are some of the physicalconditions that you will encounter during the survey. |
|
Hotspots |
wireless Internet access for their customers captive portal solution is required |
|
Retail |
interference sources: baby monitors, cordless phones operating in ISM band kept in display Multipath sources: storage rack, bins ,inventory coverage is more important than capacity retail analytics, wireless connectivity to barcode scanners, pcs |
|
Warehouses |
coverage is more important than capacity seamless roaming is mandatory bcoz devices are mobile metal racks, inventory, indoor chain like fences causes reflection and multipath directional antennas may be required if legacy a/b/g are deployed |
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Manufacturing |
same like warehouse in interference and coverage design heavy machines and robotics might be present. Surveyor should be cautious some manufacturing plants works with hazardous chemicals proper gear should be worn. AP should be kept in ruggedized enclosures |
|
Multi Tenant Buildings |
major challenge is interference from neighboring office wlan and tenants whose APs are configured at high power and non standard channels less crowded 5GHz is recommended for deploying |
|
hardware may be necessary when installing APs to be used for outdoor wirelesscoverage |
NEMA enclosure Patch antenna Outdoor ruggedized core switch |
|
biggest concerns when planning for a WLAN in a warehouse environment |
coverage, roaming, security |
|
possible causes of issues while roaming |
Clients stations can only hear a –70 dBm signal from one access point. Clients stations can only hear a –70 dBm signal from multiple access point. interference from 2.4 GHz portable phones. |
|
What roaming issues should be discussed during an interview for a future VoWiFi network? |
Layer 3 boundaries Latency |
|
Chapter 16 essentials |
1. Site survey defined 2. Site survey tools 3. Coverage analysis |
|
Potential source of interference in 2.4GHz band |
1. Microwave ovens 2. 2.4 GHz cordless phones, DSSS and FHSS 3. Fluorescent bulbs 4. 2.4 GHz video cameras 5. Elevator motors 6. Cauterizing devices 7. Plasma cutters 8. Bluetooth radios 9 .Nearby 802.11, 802.11b, 802.11g, or 802.11n (2.4 GHz) WLANs |
|
potential sources of interference in5 GHz U-NII bands |
1. 5 GHz cordless phones 2. Radar 3. Perimeter sensors 4. Digital satellite 5. Nearby 5GHz WLANs 6. Outdoor wireless 5 GHz bridges |
|
When you are designing for coverage during a site survey, the normalrecommended best practice is to provide for a –70 dBm or strongerreceived signal, which is well above the noise floor. |
Statement: signal strength for normal wlan deployment |
|
When you are designing for WLANs with VoWiFi clients, a –67 dBm or stronger signal that is even higher above the noise is recommended. |
Statement: signal strength for voWifi deployment |
|
excessive coverage overlap because it can cause frequent roaming andperformance degradation |
Statement: coverage overlap |
|
recommended coverage cell overlap for roaming purposes |
15 percent to 30 percent |
|
1st AP placement |
2nd AP placement |
|
SNR |
The SNR is simply the difference in decibels between thereceived signal and the background noise |
|
The recommended SNR for a VoWiFi network is |
25 dB or higher |
|
|
VoWiFi cell recommendation |
|
AP Placement and Configuration |
1. Cell edge measurements -RSSI(dBm), SNR(dB), Noise level(dBm) 2. AP location and tx power when survey was conducted 3. Location of all wiring closets 4. carry variety of antennas both omnidirectional and semi directional |
|
Application Analysis |
done at the end of survey Use simulators which provides real world environment such vowifi clients, roaming, bidirectional traffic etc and calculate wlan performance |
|
|
Using a unidirectional antenna in areas where there aremetal racks, file cabinets, and metal lockers can be advantageous at times because you cancut down on reflections in legacy environment |
|
|
provide coverage in abuilding by using a combination of both low-gain omnidirectional antennas and indoorsemidirectional antennas, |
|
When conducting a site survey, you should use the same 802.11 access point hardwarethat you plan on deploying. True or False |
True |
|
Indoor Site Survey Tools |
1. Spectrum analyzer 2. Blueprints 3. Signal strength measurement s/w 4. 802.11 client card 5. AP: both autonomous and lightweight 6. WLAN controller 7. Battery pack 8. Binoculars 9. Flashlight 10. Walkie-Talkies or cellphones 11. Antennas 12. Temporary mounting gear: Bungee cords and plastic ties, mast or tripod which can be moved within the building 13. Digital camera 14. Measuring Wheel or Laser Measuring Meter 15. Colored electrical tape: Stick a small piece of colored tape in location where you mounted AP during site survey so that person who install can easily find the spot and fix AP 16. Ladder or forklift |
|
Calculations needed while performing Outdoor Site Survey |
1. Fresnel zone 2. Link budget 3. Fade margin 4. Free space path loss 5. Earth bulging 6. IR & EIRP limitations by the regulatory body of country 7. Weather conditions |
|
Outdoor Site Survey Tools |
1. Topographic map 2. Link analysis s/w : predictive modelling tool used with topographic map to calculate fresnel zone, EIRP etc 3. Calculators 4. Maximum tree growth data 5. Binoculars 6. Walkie-talkies or cellphones 7. Signal generator and Wattmeter: to to test cabling, connectors, and accessories for signalloss and VSWR before deployment 8. Variable loss attenuator 9. Inclinometer: to measure height of the obstruction 10. GPS 11. Digital camera 12. Spectrum analyzer 13. High-power spotlight or sunlight reflector |
|
2 types of Coverage Analysis |
1. Manual 2. Predictive |
|
Manual coverage analysis |
2 types :active and passive passive: all the measurements like rssi, snr, noise level are collected without connecting client adapter to AP during survey active: measurements are taken by connecting client adapter to AP during survey. Ping is used to connect low level data and check layer 3 connectivity Vendors recommend both active and passive coverage analysis Commercial RF survey application can record RF measurements in a building floor plan. They can perform both active and passive coverage analysis |
|
Acommon mistake that surveyors make is to hold the VoWiFi phone in a horizontal positionwhen measuring RF signals during a manual site survey.Reason behind this is |
The internal antenna of the VoWiFi phone is typically vertically polarized, and holdingthe phone in a horizontal position results in misleading signal measurements holding the phone as it will be used, not holding it in a way that creates the best signalreadings. |
|
Predictive coverage analysis |
a predictive s/w is used to predict coverage it takes blueprints and floor plans in .dwf,.dwg,.bmp,.jpg,.tif formats wlan engineer indicate materials used in floor and s/w have pre programmed attenuation values for various materials like dry wall, concrete, glass using predictive algorithms and attenuation information it creates forecast models which contains info on : Number of APs, AP placement, AP power settings, Data rates, channel reuse patterns, coverage cell boundaries |
|
A forecast model isfirst created with the predictive application, and then the site survey engineer conducts amanual site survey to validate the projected design. |
Predictive and Manual coverage analysis |
|
Dynamic RF |
a.k.a Radio Resource Management(RRM) it's a self organizing wlan used in post-deployment environment to make necessary channel and power settings in real time environment RF information gathered in AP radios are reported back to WLAN controller to perform dynamic RF It can perform automatic cell sizing, automatic monitoring,troubleshooting and optimization of RF n/w |
|
Wireless Network Validation |
to validate Rf coverage and data rates of installed n/w and compare it with values proposed in site survey Performed by walking through the floor and recording the RF measurements in a floor map most of the site survey tools can be used but handheld devices provided by vendors like FLuke networks are preferred |
|
Dew point, cloud cover, and thunder have no effect on an 802.11 outdoordeployment |
Statement: effect of weather on outdoor deployment |
|
parameters should be validatedduring the manual site survey |
1. AP placement and power settings 2. Throughput 3. Coverage boundaries 4. Roaming parameters |
|
Chapter 17 essentials |
1. History of PoE 2. PoE devices 3. Planning and deploying PoE |
|
Ethernet has __ pair of wires |
4 |
|
Out of the 4 pairs 10 and 100 MBps ethernet uses __ pairs to transmit data and __ pairs are unused |
2 pairs, 2 pairs |
|
Gigabit ethernet uses all the 4 pairs to transmit data. |
Statement: Gigabit ethernet |
|
PoE comes in ___ IEEE standard |
IEEE 802.3 af |
|
PoE+ comes in ___ IEEE standard |
IEEE 802.3 at |
|
802.3 at |
provides 30 watts using 2 pairs of ethernet supports older devices(Type 1) which requires less power and newer devices (Type 2) which requires more power |
|
PoE components |
2 components Power Sourcing Equipment(PSE) and Powered Device(PD) |
|
Powered Device |
device which draws power like AP they are capable of accepting upto 57v in either polarity from PSE known as Mode A or Mode B PD will reply with Detection signature to PSE, which indicates whether it is in a state to accept power or not and it's 802.3 2012 compliant If the device is in state in which it will accept power, PD will sent a Classification signature to PSE indication how much power the device need If the PD doesn't sent classification signature or PSE couldn't identify the device, PSE doesn't how much power is required for the device. At this time device is classified as Class 0 device and PSE provides full power to the device Type 2 device perform two event physical layer classification or Data link layer classification which allows Type 2 devices to identify whether it is connected to Type1 or Type 2 PSE |
|
Mode A |
1,2,3,6 |
|
Mode B |
4,5,7,8 |
|
Power Class 0-3 are considered as Type 1 devices, 802.3 af compliant PoE |
Statement: PD classes |
|
Power class 4 is considered as Type 2 device. 802.3 at compliant PoE+ |
Statement: PD classes |
|
Maximum power of 802.3 af compliant device(PD) |
12.95 watts |
|
Maximum power of 802.3 at compliant device(PD) |
25.5 watts |
|
PSE |
provides power to PD power supplies is nominal 48 v(44-57 v) PSE searches for the devices using a Detection signal and PDs has to respond back with a Detection signature If PSE doesn't receive any response it will withhold power preventing non compliance device from damaging Amount of power supplied by the PSE is greater than required by PD to accommodate loses from cables.connectors PSE will continuously monitor connection status with PD to check electrical conditions like short circuit. If the power is no longer required PSE will terminate the power supply to PD Type 2 devices will perform a two-event Physical layer classification or Data- Link Layer classification, which allows a Type 2 PD to identify whether it is connected to a Type 1 or a Type 2 PSE. If mutual identification cannot be completed, then the device can only operate as a Type 1 device |
|
|
PSE power class |
|
2 types of PSE |
1. Endpoint 2. Midspan |
|
Endpoint PSE |
device that provides ethernet data and power from same device. Normally a 48 port switch with PoE enabled provides power using 2 methods Alternative A: PSE places power on data pair Alternative B: initially used to provide power to 10/100M Ethernet using unused pairs now Gigabit ethernet ethernet also can be powered putting power on data pairs |
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Midspan PSE |
a.k.a power injector or PoE hub placed b/w ethernet s/w and PD acts as a ethernet repeater while adding power to the Ethernet cable enables us to provide power to existing networks without replacing existing switches |
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multiport midspan PSE is a.k.a |
inline power patch panel |
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single port midspan PSE is a.k.a |
single-port power injector |
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Maximum distance of Ethernet cable |
100 meters or 328 feet |
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Three PSE solutions |
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If an AP cannot get the power that it needs, the AP will reboot and try again |
Statement: Reboot issue in AP due to inadequate power supply |
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It is a recommended practice to wait 5-10s after unplugging a PoE enabled device and connecting a non PoE device to prevent it from damaging |
Statement:PoE power at Ethernet plug |
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What will happen in 11n and 11ac capable APs are not provided adequate power |
Aps will: downgrade MIMO capabilities like 3x3:3 will be made to use 1 or 2 transmitter disable power intensive transmissions like 80MHz and complex modulations |
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The PD must be able to accept power over either the data pairs or theunused pairs if it is a 10BaseT or 100BaseTX device and over the 1-2, 3-6 data pairs,or the 4-5, 7-8 data pairs if it is a 1000BaseT device. The PD must also reply to the PSEwith a detection signature. The PD must accept power with either polarity. Replying tothe PSE with a classification signature is optional. |
PD |
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The maximum power used by a Class 0 PD is |
12.95 W |
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The maximum power used by a Class 1PD is |
3.84 W |
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The maximum power used by a Class 2 PD is |
6.49 W |
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class and range values |
Class 0: 0 to 4 mA Class 1: 9 to 12 mA Class 2: 17 to 20 mA Class 3: 26 to 30 mA Class 4: 36 to 44 mA |
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PD power class |
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Maximum power from PSE |
30W |
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Minimum power from PSE |
15.4W |
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Chapter 20 essentials |
1. Mobile Device Management 2. Guest WLAN access 3. Network access control (NAC) |
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BYOD is |
Bring Your Own Device |
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BYOD refers to the policy of permitting employees tobring personally owned mobile devices such as smartphones, tablets, and laptops to theirworkplace. |
Statement: BYOD |
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MDM Architecture |
1. Mobile device 2. WLAN controller 3. MDM server 4. Push notification servers |
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TCP ports which need to be open in firewall to allow for communications between all of the various componentsof the MDM architecture |
AP-MDM: 443 MOBILE-MDM:443 MOBILE-APN: 5223 MOBILE-GCM:443,5223,5229,5330 MDM-APN: 2195,2196 MDM-GCM:443 |
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APN is |
Apple Push Notification Service |
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GCM is |
Google Cloud Messaging |
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MDM Enrollment process |
1. Mobile device connects with the AP: AP quarantines device in walled garden where device has access to only few services like DHCP,DNS, push notification service and MDM server 2. AP checks if the device is enrolled: AP queries MDM server for device's enrollment status. If device is already enrolled MDM server notify AP to release the mobile device if not kept in walled garden 3. MDM server queries LDAP: for user authentication 4. Device is redirected to MDM server: User can open only MDM captive portal for enrollment and cannot proceed further without enrolling 5. Device installs certificate and MDM profile 6. MDM server releases mobile device from walled garden 7. Mobile device exists walled garden |
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MDM enrollment—initial steps |
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MDM server—enrollment captive web portal—step 4 |
Certificate and MDM profile installation—step 5 |
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Mobile device exits the walled garden–final steps |
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MDM agent application |
Used in android device Apple devices doesn't need MDM agents they have inbuilt MDM agents MDM agent application from mobile device communicates with MDM server via the Google Cloud Messaging(GCM) service |
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Information that can be read by MDM server |
Device name serial number capacity battery life apps installed on device |
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Information that cannot be read by MDM server |
SMS Personal emails Calendars Browser history |
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Mobile device which are enrolled with MDM server can be managed remotely through push notification service like APN or GCM even though they are not connected to corporate WLAN |
Statement: MDM server-Mobile device communication |
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Over the air management |
1. Admin make changes to MDM configuration in MDM server 2.MDM server contacts push notification server 3. Push notification server contacts enrolled mobile device and sends a message to contact MDM server over the internet 4. Mobile device contacts the MDM server 5. MDM server sends configuration changes to mobile device |
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Remote actions that a MDM admin can perform |
1. Configuration changes 2. Changes in device restrictions 3. Deliver a message to device 4. Lock the device 5. Wipe the device 6. Make application management changes: Application can be purchased and pushed to devices silently , eBooks can also be managed and distributed to mobiledevices via an MDM platform. |
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Wi-Fi Client Onboarding |
give the customer an inexpensive and simple way toprovision mobile devices onto the secure corporate SSID Over-the-air provisioning is used to install Wi-Fi client profiles configured with the corporateSSID and security settings |
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Guest WLAN access |
1. Guest SSID
2. Guest VLAN: a unique VLAN for segmenting guest traffic from corporate network 3. Guest firewall policy: to route all guest traffic away from the corporate network infrastructure Some ports need to be enabled for availing services like DHCP(UDP 67), DNS(UDP 53), HTTP(TCP 80), HTTPS(TCP 443), IPSec IKE(UDP 500), IPSec NAT-T(UDP 4500) 4. Captive web portal: a webportal to register a guest |
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One of the most important aspects of the captive web portal pageis the legal disclaimer. True or False |
True |
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Guest access moderating |
Client Isolation Rate Limiting, Web Content Filtering using web filter |
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Guest credential delivery methods |
Text, email, print copy |
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The parameters within DHCP option 55 create a fi ngerprint that can be used to identifythe operating system of the client |
Statement: OS fingerprinting |
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RADIUS Change of Authorization is defined in RFC |
5176 |
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MDM, WLANguest management, and NAC can be deployed as separate components or can be deployedin unison to provide mobile device security management, guest user security, and networkaccess security |
Statement:MDM,Guest,NAC |
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NAC is |
Network Access Control |
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NAC |
evaluates capability or state of a computer to determine the potential risk of the computer on the network and to determine level of access to allow |
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NAC and BYOD NAC uses various monitoring and fingerprinting techniques to identify different devices so that access can be controlled |
A NAC server will use system health information, as reported by a posture agent, to identify if the device is healthy. DHCP fingerprinting is used to help identify the hardware and operating system. RADIUS attributes can be used to identify if the client is connected wirelessly or wired, along with other connection parameters. RADIUS CoA is used to disconnect or change the privileges of a client connection. |
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methods that can be used to provision a root certificate onto Wi-Fi clientsthat function as 802.1X supplicants |
1. GPO 2. MDM |
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resources can a mobile client reach while quarantinedinside a walled garden |
1. DHCP 2. DNS 3. MDM server |
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methods that can be used by a captive web portal to redirect a user tothe captive portal logon page |
1. HTTP redirection 2. IP redirection 3. DNS redirection |
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In order to initially identify, set his permission and calculate the capability of a user should have on the network, the NAC server uses |
1. Posture 2. DHCP fingerprinting 3. RADIUS attributes |