6943327
Description
Flashcards by Dustin Sanders, updated more than 1 year ago
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Created by Dustin Sanders
over 7 years ago
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| Question | Answer |
| What is amplitude? | the height/force/power of a wave |
| What is frequency? | how many waves in a 1 second period |
| What is wavelength? | distance between 2 similar back to back parts of a wave λ lamba |
| What is phase? | relative term, describes 2 waves of the same frequency and how they are positioned in relation to one another. Usually talked about in terms of degrees. |
| How does a signal differ from a carrier signal? | KEYING keying transforms a signal from just noise into something that can encode data |
| What are three popular forms of signal keying? | ASK - Amplitude Shift Keying FSK - Frequency Shift Keying PSK - Phase Shift Keying |
| How does ASK alter a signal? | Changes the height or amplitude of a wave to represent 1 or 0 |
| How does FSK alter a signal? | Changes the frequency to represent 1 or 0 |
| How does PSK alter a signal? | Changes the phase to represent 1 or 0 - state change |
| What are the two different techniques used by keying to distinguish between a 1 and a 0? | Current State (checks signal at regular intervals to see if it is one state or another) State transition (checks signal at regular intervals to see if there is a difference in phase) |
| What is MPSK? | Multi-Phase Shift Keying Uses multiple different phases to send more bits per signal |
| What is oscillation? | The ups and downs of a wave |
| What is the rough speed of light? | 300 million meters a second |
| What is the relationship between wavelength and frequency? | Inverse. The higher the f the shorter λ. The longer the λ the lower the f |
| What is the main cause of signal attenuation? | Distance |
| Do higher f and lower f signals travel the same distance? | Yes, higher f signal more prone to attenuation when passing through mediums. (makes aperture for "hearing" them smaller) |
| What is the λ of a 2.4GHz wave? | 12cm |
| What is the λ of a 5GHz wave? | 5cm |
| What is a radio aperture? | the effective receiving area of a signal |
| What is transmit amplitude? | initial amplitude a signal is sent at |
| What is receive amplitude? | amplitude a signal is received at |
| What is phase? | relationship between 2 waves, can either work together to amplify a signal, or work against each other to cancel out a signal. |
| what is wave propagation? | the way RF waves move and spread out |
| what is Absorption? | a signal loses amplitude as it passes through an object and is absorbed. |
| what is Reflection? | when a wave hits a surface larger than itself, it can bounce off of the surface and change direction. (This is why AM radio can hit the sky and bounce back to earth) |
| what is Scattering | like light hitting a disco ball, RF can sometimes scatter into multiple directions |
| What is multipath? | a signal can take multiple paths to a client station, sometimes getting there after another copy of the signal has already gotten there. This used to be an major issue, but with Multiple Input, Multiple Output, this can now be useful. |
| what is Refraction? | when a wave changes direction passing through a medium. (Think light going through water) |
| what is Diffraction? | bends a wave going around an object, like water going around a stone in the river |
| what is an RF Shadow? | a dead zone behind an obstruction like a concrete pillar |
| What is FSPL? | FREE SPACE PATH LOSS Just like ripples in water spread out and lose energy, FSPL is when RF waves fan out over a space and slowly lose amplitude |
| What is the distance/6dB rule? | Double the distance, -6dB Cut the distance in half, +6dB |
| What is delay speed? | time (in nano seconds) between when one signal arrives and when another arrives |
| What are the 4 possibilities when multipath occurs? | upfade downfade nulling data corruption |
| Between what degrees difference between two signals does upfade occur? | between 0-120 |
| Between what degrees difference between two signals does downfade occur? | between 121-179 |
| At what degree phase do two signals cancel each other out? (Nulling) | 180 degrees |
| what is data corruption or Inter Symbol Interference? | ISI happens when a client has trouble demodulating a symbol |
| What is active gain | an amplifier is used to increase outbound and inbound power |
| What is passive gain? | focusing RF with an antenna |
| What is the transmitter? | generates the oscillation /signal with AC, also responsible for power level |
| what is the antenna | When connected to a transmitter it collects the signal and radiates it away, when connected to a receiver it collects the RF signal and directs the AC to the receiver |
| what is an Isotropic Radiator | point source that radiates equally in all directions The SUN is a perfect example. No antenna can be like this |
| What is EIRP? | Equivalent Isotropically Radiated Power, basically, how much light would a flashlight bulb without a lens and focuser bit have to produce to match the amount of light output of a flashlight WITH a lens and focuser bit? |
| What are two way to increase the output from an antenna? | MOAR POWAR!!!! Focus the signal |
| What is an Intentional Radiator? (IR) | Something that purposely generates RF. (All the bits before an antenna focuses it) |
| Is a Watt a relative or absolute measurement of power? | Absolute |
| Is a milliwatt a relative or absolute measurement of power? | Absolute |
| What is dBm? Is it absolute or relative? | Decibels in relation to 1mW Absolute |
| Is a dB a relative or absolute | Relative (unit of comparison) |
| What is dBi and is it absolute or relative? | decibels in relation to an isotropic radiator (Relative) (How much stronger is the signal gain compared to if there was no antenna to focus it?) |
| What is dBd and is it absolute or relative? | decibels in relation to a half-wave dipole antenna (Relative) (gain increase compared to dipole antenna) |
| What is a Watt | Watts = Volts x Amps It's like pressure washer where Volts are the pressure, Amps are water flow, and Watts are resulting blast of water |
| How many milliwatts do indoor WAPs usually operate at? | 1-100mWs |
| What does a dB compare? | Loss in signal strength between EIRP and received signal |
| What is a dipole antenna? | omni-directional antenna |
| What is the standard dBi of a dipole antenna? | 2.14 |
| How do you convert dBd to dBi? | add 2.14 to dBd to get dBi |
| 1mW is = to how many dBm? | 0dBm |
| 100mW is = to how many dBm? | 20dBm |
| What is the inverse square law? | change in power is equal to 1 divided by the square of the change in distance (As distance doubles, energy spreads over 4x the area, thus losing 1/4th original intensity) |
| What is the Rule of 10s & 3s? | +3dB = (absolute power x2) -3dB = (absolute power / 1/2) +10dB = (absolute power x10) -10dB = (absolute power / 10) |
| What is the noise floor? | ambient or background RF level on a specific channel |
| What is SNR? | Signal to Noise ratio Difference in strength between signal and background RF |
| What is RSSI | Received Signal Strength Indicator (Relative measurement) How loud do you have to speak in a crowded bar in order for your friend to hear you? That's you RSSI in the bar. |
| What is DRS? | Dynamic Rate Switching As a client gets farther away from an AP, AP will dynamically adjust data rate to accomidate |
| What is BER? | Bit Error Rate Measurement of data corruption, usually from low SNR |
| Why aren't NICs in laptops good spectrum analyzers? | They can't see raw RF, only RF that's been encoded that they can then decode |
| What is a link budget? | The sum of all planned and expected gains and losses from transmitting data through RF |
| What is Tx and Rx? | Tx=transmit power Rx=received power |
| What is a fade margin? | difference in dB between RSSI and the receiver sensitivity (25dBm good to have as a fade margin buffer) |
| What has the greatest impact on whether or not communication is successful? | The proper installation of antennas |
| What is the name of the type of charts used to displace antenna radiation patterns from top down? | AzimutH (H for high above/top down) |
| What are the three main types of antennas? | Omnidirectional Semidirectional Highly directional |
| What is a Yagi-Uda antenna (Yagi antenna) | short to medium distance p2p communications |
| What is a parabolic dish antenna? | Think satellite dish antenna Highly directional |
| What is a grid antenna? | Highly directional, spacing on grill determined by wavelength used |
| What is the name of the protective cover over an antenna? | Radome |
| What are sector antennas? | High gain, semidirectional antennas that can work together to cover an area like a pie |
| What is beamforming? | A method of concentrating RF energy in a given direction |
| What are three different types of beamforming? | Static beamforming Dynamic beamforming Transmit beamforming |
| How is static beamforming performed? | Directional antennas provide a fixed radiation pattern |
| How is dynamic beamforming performed? | Focuses RF in a particular direction like static, but radiation pattern can change on frame by frame basis |
| How is Transmit beamforming performed? TxBf | Multiple antennas transmitting at different phases so the waves collide and amplify at a given location |
| What are the two types of TxBf? | Implicit and Explicit |
| How does Implicit TxBf work? | Implicit TxBF uses an implicit channel-sounding process to optimize the phase differentials between the transmit chains. |
| How does explicit TxBf work? | Explicit TxBF requires feedback from the stations in order to determine the amount of phase-shift required for each signal. |
| Does Line of Sight dictate if RF communication will be successful? | No. |
| What is the Fresnel Zone? | Fruh-nel Zone an imaginary, elongated, football-shaped area (American football) that surrounds the path of the visual LOS between two point-to-point antennas. |
| At what point do you need to think about earth bulge when dealing with outdoor RF communications | distances over 7 miles |
| What is antenna polarization? | The direction in which waves radiate from an antenna. Important to get right when mounting WAP. Vertically or horizontally polarized |
| What is antenna diversity? | When APs have 2 or more antennas to reduce negative effects of multipath |
| Is RF a half duplex of full duplex medium? | Half-Duplex. Can either send or receive on a given channel at any given time, not both |
| What is MIMO? | Multiple In, Multiple Out radio architecture that allows an AP to use different antennas to send and receive while operating both antennas at the same time. |
| What are the three components associated with proper antenna installation? | voltage standing wave ratio (VSWR) signal loss actual mounting of the antenna. |
| What is Voltage standing wave ratio (VSWR) | a measurement of the change in impedance to an AC signal. (Inside an the IR leading up to the antenna) |
| What is Signal Loss? | loss of signal between transmitter and antenna |
| What are three important factors to consider when mounting an antenna? | Placement Physical mounting Appropriate for use/environment? |
| What is 802.11 prime? | original standard passed in 1997 |
| What is FHSS? | Frequency Hopping Spread Spectrum |
| What is DSSS | Direct sequence spread spectrum |
| What is OFDM | Orthogonal Frequency Division Multiplexing |
| What is DFS | dynamic frequency selection |
| What is TPC | transmit power control |
| What is DFS used for? | To check for radar, to change to another channel if there is too much interference, can alter transmit power per environmental conditions |
| What two protocols can be used to manage and configure AP or LAN controllers? | HTTPS, SSH |
| When doing a site survey, which measurement best indicates the clients ability to maintain connection with the WLAN? | SNR |
| What are two 802.11-2012 authentication mechanisms? | Preshared key 802.1X port-based access control |
| What is CIA? | Confidentiality, Integrity, and Availability Confidentiality ensures the privacy of communications. Integrity ensures that the communication received is the communication sent. Availability ensures that the system functions and is there when the user needs it. |
| What is the minimum acceptable backhaul bandwidth for 802.11ac? | 1Gbps |
| What kind of antenna can help with capacity issues? | Semi-directional, so the cell is more focused. (You'll need more APs, but you'll have fewer clients per AP so the service is better) |
| What PoE method uses power over the two unused pairs | Alternative B |
| What PoE method uses power over the data pairs? | Alternative A |
| What kind of WLAN architecture has all the features inside the AP? | Autonomous |
| What is 40 MHz intolerant? | allows an AP to advertise in its beacon that it prohibits 40 MHz operation in adjacent or overlapping cells |
| What is a Near/Far situation? | a type of hidden node problem where a nearby AP operating at high power increases the noise floor at the AP causing the low level signals from far away client stations to become corrupted. |
| What new feature of 802.11ac uses changes to the PHY framing format to improve power management? | VHT TxOP |
| What are three benefits of using WLAN controllers? | Rogue AP/Client detection HTTPS device management Local or remote data bridging |
| What are the three most used features in a client OS wifi utility? | Channel selection tool for Ad Hoc networking Scan tool for locating and displaying information about APs Protection mechanism configuration options |
| Name three things that cause excessive CRC errors | Multipath Co-channel interference RF interference |
| What does an AP do if a transmitted A-MPDU is too large for an 802.3 network? | The access point de-aggregates the frame's payload (MPDU) and puts each MPDU into a separate Ethernet frame for transmission onto the Ethernet segment |
| What 802.11 amendment provides for more 22.5 watts of PoE? | 802.11at |
| What mechanism allows you to tell if a collision occurred? | ACK (if you didn't get an ACK, there was probably a collision) |
| When considering the DCF operations of a WLAN, what value is used in most cases to establish the NAV timer in a STA? | The Duration field of the 802.11 frame is used to set the network allocation vector (NAV) |
| When using active scanning, what two frames, unique to this process, are used? | Probe request frame Probe response frame |
| What is the maximum data rate of an ERP-OFDM WLAN | 54 Mbps |
| When operating in the 2.4 GHz frequency band at a data rate of 5.5 Mbps, what coding method is used? | CCK |
| How many channels are available in the 5.150 to 5.875 frequency range as specified for use with 802.11 devices in the IEEE standard including 802.11ac? | 25 |
| The 802.11-2012 standard (as amended with 802.11ac) supports eight common physical layer specifications. Which two of the following are rarely used today? | Infrared FHSS |
| You are running an HT network in the 2.4 GHz frequency band. You use the HT-Greenfield PLCP format only on the AP. What device types can communicate with this AP? | 802.11n |
| What are valid power management modes for 802.11-2012 WLAN devices? | Power save mode WMM-PS Active mode |
| What mechanisms or components are used to notify an 802.11g client that the 802.11n AP has frames buffered for it? | The Delivery Traffic Indication Map (DTIM) and the TIM are used to notify STAs that a frame is buffered in the AP during power management operations. The TIM is included in each Beacon frame. The DTIM is included in regularly scheduled Beacon frames. The AID is the association ID of the STAs |
| You plan to implement an 802.11n WLAN in the 5 GHz frequency band. You will only use channels available in the UNII-1 and UNII-2 bands. How many 40 MHz channels can be implemented assuming all channels in these bands are available in your regulatory domain? | 4 |
| What can significantly affect the data throughput available to each client station connected to the same AP when all the stations are actively transmitting and receiving in the BSS? | Enabling RTS/CTS on APs and client stations Data frame retransmissions due to narrowband RF interference |
| You have been hired by ABC Office Solutions in North America as a consultant to implement a wireless network in a multi-tenant office building. The building currently has two HR/DSSS autonomous APs that are set to channels 2 and 7. What type of AP should you implement at this site that is legal and will not have overlapping adjacent channel interference from the two existing APs? | A dual-band HT AP that supports 20/40 MHz channels and is configured to use channel 36, 40 (36, +1) |
| Which standardized wireless PHYs support frame aggregation? | HT VHT |
| When calculating the data rates for 802.11n and 802.11ac links, the guard interval (GI) impacts the final calculation. What is the length of the short GI in nanoseconds? | 400 |
| You have an AP that transmits at 30 mW. It is connected to an antenna that provides 11 dBi of gain; however, a cable is used to connect the antenna and it causes 5 dB of loss. What is the output power at the antenna in the intended direction of propagation? | The correct answer is 120 mW. Here is the math: 11 dBi gain + 5 dB loss = 6 dB gain 30 mW + 6 dB gain = 30 mW * 2 * 2 30 mW * 2 * 2 = 120 mW |
| You have studied the rules of 10s and 3s for simple calculations in RF math. What is the power ratio of 10 dB loss? | 10:1 |
| What amendment standardized OFDM | 802.11a-1999 |
| What is the difference between the cellular spectrum vs spectrum used by wifi | licensed vs unlicensed bands 3G, 4G are 3GHz and 4GHz. Wifi uses 2.4G and 5G. |
| What is the max Mbps of 802.11b | 11 |
| What is the max Mbps of 802.11a | 54 |
| What is the max Mbps of 802.11g | 54 |
| What is similar and different between 802.11a and 802.11b | Both standardized in 1999 a is 5GHz max 54Mbps b is 2.4GHz max 11 Mbps |
| What is max Mbps of 802.11n | 100Mbps |
| What's the difference between a BSS and an ESS? | BSS is just one service set. ESS is a collection of multiple service sets working together to allow things like roaming. (Think home wifi vs work wifi) |
| What's the difference between a backhaul and access network? | Backhaul connects APs to the Access network, access network provides access to internet |
| What is the primary metric a client uses to determine which AP to connect to? | SIR Signal to Interference Ration not just signal strength, but how much or little interference there is with that signal |
| What happens in CSMA after a collision? | Backoff, wait, listen |
| How does backoff timer work? | window size minus 1, then pick random number in that range to transmit at. window size 32 range 0-31 transmit again somewhere between 0 and 31 |
| What can cause a High Voltage Standing Wave Ratio in an RF chain? | An impedance mismatch in the RF cables and connector |
| What are the 4 things to calculate into a link budget? | The link budget must factor in the transmit power, cable and connector losses, antenna gain and free space path loss. |
| A WLAN transmitter that emits a 100 mW signal is connected to a cable with 3 dB of loss. The cable is connected to an antenna with 7 dBi gain. What is the EIRP at the antenna element? | 250mW 100 mW + -3 dB + 7 dBi = 100 mW + 4 dB To get to 4 dB, we can multiple by 10 and then divide by 2 twice (+10 -3 -3 is equal to 4) 100 mW * 10 / 2 / 2 = 250 mW |
| What is a Fade Margin | Fade margin is an addition signal padding designed into the RF system to allow for unpredictable signal fading |
| What term describes the effect of increasing the intensity of an RF wave by placing an RF amplifier in-line between the transmitter and the Tx antenna? | Active gain |
| What determines the amount of spacial streams that can be used? | the lowest number supported on either side of the link. If one device (doesn't matter if AP or client) supports 3 spatial streams and the other device only supports 2, then only 2 can be used |
| What is the channel number for the new 20MHz 802.11ac channel? | 144 |
| What is through loss and what type of antenna usually has it? | When implementing sector antennas, an RF splitter is sometimes used such that the same signal is transmitted out all antennas simultaneously. Such a design incurs loss and this loss is often called through loss. |
| What f band does DSSS function in? | 2.4GHz |
| What IEEE 802.11 physical layer (PHY) specifications include support for both 64-QAM and multiple spatial streams? | HT VHT |
| What channels are non-overlapping in 2.4Ghz? | 1 and 6 2 and 7 3 and 8 4 and 9 5 and 10 6 and 1 Think 6 and 6. 1st column ends in 6, 2nd column starts in 6! |
| How many MHz apart are each 2.4GHz channels? | 5MHz |
| What is the MHz of channel 1 in the 2.4GHz spectrum? | 2412 MHZ |
| How many channels in 2.4GHz? | 14 |
| What interconnects the APs that form an ESS in a large WLAN? | Distribution System |
| What kind of traffic announcement frames are used in BSS, what kind are used in IBSS? | BSS = TIM and DTIM IBSS = ATIM |
| What data payload is received by the MAC sublayer to be processed and transmitted onto the wireless network? | MSDU (MAC Service Data Unit) gets turned into a frame and sent across physical layer 1 as a MPDU. |
| What are the two method specified in the 802.11n and 802.11ac amendments for frame aggregation? | A-MSDU A-MPDU |
| What does a STA listen for when passively scanning for a BSS to join? | Beacon frames |
| What is EDCA | Enhanced Distributed Channel Access different types of traffic get different tags and priorities |
| What is DCF | Distributed Coordination Function uses csma/ca to to send |
| When EDCA is used in a wireless LAN, to what are the priority tags identical? | 802.1D priority tags |
| Does the AP or client STA decide what data rate is used? | Both STAs decide on the data rate when they transmit based on proprietary algorithms specified by the vendor |
| Why is it important to disable the lowest data rates when designing an AP configuration set? | Sticky client roaming issues Hidden node problems Excessive medium contention |
| 802.11n APs transmit information about the HT Protection mode and Non-ERP Present field. Why do they transmit this information? | To indicate to the BSS backward compatibility options with older PHYs |
| How many queues are supported based on the 802.11e specification now included in the 802.11-2012 standard rollup? | 4 AC_VO - voice AC_VI - video AC_BE - best effort AC_BK - background. |
| What is WMM? | The Wi-Fi Multi-Media (WMM) certification is based on the IEEE 802.11 standard implementation of the Hybrid Coordination Function (HCF) and contention-based QoS priority. That is, it uses EDCA and the four priority queues specified in the standard to increase the probability that higher priority traffic will win access to the medium over lower priority traffic. |
| What kind of interference is created when non-overlapping channels are configured with output power settings that are too high? | Adjacent channel interference occurs when non-overlapping channel APs are configured with very high output power settings. This can occur because the side bands interfere with one another. Co-channel interference occurs when multiple BSSs use the same channel in the same area or very near each other in relation to output power settings. Adjacent channel interference can also occur if APs are placed to close to one another. |
| According to the 802.11 standard, what is considered an overlapping channel with ERP? | Less than 25 MHz apart |
| What is RBAC? | Role-based access control (RBAC) is supported by some WLAN systems and can be used to control access to network resources based on departments, job functions or roles or other categories. |
| What can not be detected by WIPS | Packet Capturing since it doesn't generate anything on the medium |
| What kind of device may generate incidental energy that can interfere with WLANs? | Electric motor Incidental energy can also be defined as unintended energy. |
| What physical layer medium is defined by 802.11b? | High-Rate DSSS (HR-DSSS) |
| What is U-NII ? | Unlicensed National Information Infrastructure (U-NII) |
| What is the difference between ISM bands and U-NII bands? | ISM bands 900MHz to 2.45 GHz U-NII bands 5.15-5.35 & 5.725-5.825GHz |
| What 802.11 amendment introduced ERPs, DFS, TPC | 802.11g-2003 |
| What is ERP? | Extended Rate Physicals |
| What are he four layer options defined in the 802.11g specification? | ERP-DSSS ERP-OFDM ERP-PBCC DSSS-OFDM |
| What does DFS do? | checks for radar and interference When interference is detected, the AP may choose a different channel to transmit on and inform all the associated stations. |
| What does TPC do? | transmit power control ■ Designation of the maximum transmit power levels permitted on a channel, as permitted by regulations. ■ An AP can specify the transmit power of any or all stations that are associated with the AP. ■ An AP can change transmission power on stations based on factors of the physical RF |
| What are the 3 components of any wireless security solution? | data privacy (encryption), data integrity (protection from modification) authentication (identity verification). |
| What is RSN | RSN-Robust security network: the entire method of establishing authentication, negotiating security associations, and dynamically generating encryption keys for client stations and access points. |
| What security amendment to the original 802.11 standard provided for AES, TKIP, CCMP? | 802.11i |
| What is AES | Advanced Encryption Standard (AES) supports 128, 192, 256 bit keys |
| What is TKIP | Temporal Key Integrity Protocol (TKIP) Stop-gap solution to WEP, depreciated in 2012. |
| What is MIC | Message Integrity Check (MIC) MIC is designed to protect both the data payload and header on a WEP encrypted network. |
| What is FCS | frame check sequence (FCS) a hash to check data integrity |
| How is PSK different from EAP? | PSK are pre-shared keys. EAP is a framework for authentication with different flavors |
| How does WPA2 relate to 802.11i? | WPA2 (by wifi alliance) is pretty much a mirror of IEEE 802.11i |
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