Reflected direct current (DC) voltage on the main RF signal line
An impedance mismatch in the RF cables and connectors
Attenuation of the RF signal as it travels along the main signal path
Crosstalk (inductance) between adjacent RF conductors
MAC layer encryption
Transmitting station’s power source
Free Space Path Loss
Transmitting station’s output power
Temperature in the Fresnel zone
Receiving station’s radio sensitivity
Inverse square law
Path spread phenomenon
Fresnel zone thinning
A Voltage Standing Wave Ratio (VSWR) of 1:1
Cross-polarization of the RF signal as it passes through the RF system
An impedance mismatch between components in the RF system
The use of cables longer than one meter in the RF system
High output power at the transmitter and use of a low-gain antenna
Transmit antenna gain
The Fade Margin of a long-distance radio link should be equivalent to the receiver’s antenna gain.
A Fade Margin is unnecessary on a long-distance RF link if more than 80% of the first Fresnel zone is clear of obstructions
Fade Margin is an additional pad of signal strength designed into the RF system to compensate for unpredictable signal fading.
The Fade Margin is a measurement of signal loss through free space, and is a function of frequency and distance.
Accurate Earth Bulge calculations
Minimum output power level of 2 W
Grid antennas at each endpoint
A Fresnel Zone that is at least 60% clear of obstructions
A minimum antenna gain of 11 dBi at both endpoints
Reflected power due to an impedance mismatch in the signal path
The power output from the radio into the RF cable
The highest RF signal strength that is transmitted from a given antenna
Power supplied from the transmission line to the antenna input
The power output from the radio into the RF cable
Alternates between awake and dozing, depending on its need to transmit and receive information
Enters a low-power radio state until it receives a WMM PS-Poll frame from the AP
Experiences higher throughput and lower latency than when operating in Active mode
Powers down a subset of MIMO radio chains and transmits information at a slower data rate
Buffers frames destined to the low-power AP until the AP wakes its radio and begins beaconing again
Fresnel Zone size
Fresnel Zone size
The lower the gain of an antenna, the more narrow one or both beamwidths become
The beamwidth patterns on an antenna polar chart indicate the point at which the RF signal stops propagating
Horizontal and vertical beamwidth are calculated at the points in which the main lobe decreases power by 3 dB.
Horizontal beamwidth is displayed (in degrees) on the antenna’s Azimuth Chart.
Short guard intervals
Maximal ratio combining
Orthogonal Frequency Division Multiplexing
Fresnel Zone size
Maximum input power
One spatial stream, because the definition of the AP indicates that it is capable of only one spatial stream.
Three spatial streams, because the definition of the client indicates that it is capable of only three spatial streams.
Two spatial streams, because the definition of the AP indicates that it is capable of only two spatial streams
Three spatial streams, because the definition of the AP indicates that it is capable of only three spatial streams.
Impedance in Ohms
Return Loss Rating
Mounting a lightning arrestor to a grounding rod
Mounting an omnidirectional antenna to a mast
Mounting an RF amplifier to a dipole antenna
Mounting a PoE injector to a perforated radome
Mounting an access point to a site survey tripod
The data throughput rate will increase because VSWR will decrease.
The Equivalent Isotropically Radiated Power (EIRP) will decrease.
The antenna’s azimuth beamwidth will decrease.
The size of the Fresnel zone will increase.
The likelihood of a direct lightning strike will increase.
RF cables have upper and lower frequency range specifications.
75 and 125 ohms are the typical impedances of 802.11 WLAN connectors.
Two RF connectors of the same type (e.g. SMA), manufactured by different companies, may vary in specifications.
Every RF connector causes insertion loss.
Large diameter RF cables cause greater loss than small diameter cables.
802.11a and 11n use six (6) “pilot” subcarriers as a reference for the receiver to detect frequency and phase shifts of the signal.
802.11a/g/n OFDM includes several combinations of modulation and coding to achieve data rates from 1-600 Mbps.
With 802.11a OFDM, 16-QAM provides either 48 or 54 Mbps data rates, depending upon coding rates.
802.11ac VHT-OFDM utilizes 256-QAM, which increases the data rate significantly over 64- QAM available in HT-OFDM.
In 802.11a OFDM, fifty-six (56) subcarriers are used as parallel symbol transmission paths to carry data.
802.11n OFDM is more susceptible to high-power, narrowband interference than 802.11a
In order to earn Wi-Fi Alliance certification, 802.11n clients stations are required to support both 2.4 and 5 GHz frequencies
802.11ac devices support the features of the VHT PHY only in the 5 GHz frequency band.
802.11ac is not backwardly compatible with 802.11n or 802.11a.
When HR/DSSS devices are present, VHT MCS rates are disabled for the entire BSS.
Introduces “fast transition” roaming protocols for VoWiFi phones
Better link reliability between 802.11a/b/g client devices and 802.11ac APs
Improves service quality for real-time applications at greater distances
Increases in receive sensitivity enhance RTLS location accuracy
Stronger security with more robust encryption modes.
Stronger security with more robust encryption modes.
Use of WEP or TKIP for encryption instead of CCMP
Use of passphrase authentication instead of 802.1X/EAP authentication
Increasing the beacon interval from 100 to 200 (TUs)
RF interference from more than 10 nearby Bluetooth transmitters
Increasing or decreasing the number of spatial streams in use by the client station and AP
The number of client stations associated to the BSS
The power management settings in the access point’s beacons
The presence of co-located (10m away) access points on non-overlapping channels
The data rates at which nearby client stations are transmitting and receiving data
The layer 3 protocol used by each station to transmit data over the wireless link
Channels 5 and 10
Channels 1 and 5
Channels 3 and 7
Channels 2 and 8
Channels 8 and 11
Channels 10 and 13
An IP tunnel is established between the AP and controller for AP management and control functions.
Using centralized data forwarding, APs never tag Ethernet frames with VLAN identifiers or 802.1p CoS.
With 802.1X/EAP security, the AP acts as the supplicant and the controller acts as the authenticator.
Management and data frame types must be processed locally by the AP, while control frame types must be sent to the controller.
In a distributed data forwarding model, the AP handles frame encryption and decryption.
Radio receiver hardware cannot process data as quickly as it can be transmitted.
Half of the bandwidth is allocated to uplink traffic and half to downlink traffic.
The DCF and EDCA coordination functions require backoff algorithms
WLAN devices cannot detect collisions and must receive positive frame acknowledgment.
APs do not have sufficient wired connection speeds to the LAN.
After waiting a SIFS, all APs reply at the same time with a probe response.
After waiting a SIFS, a designated AP sends an ACK, and then replies with a probe response.
Each AP checks with the DHCP server to see if it can respond and then acts accordingly.
For each probe request frame, only one AP may reply with a probe response.
Each AP responds in turn after preparing a probe response and winning contention.
14 channels are available worldwide
11 channels are available worldwide.
Regulatory domains worldwide require DFS and TPC in all these channels.
DFS may be required in some regulatory domains on some channels.
802.11 channels are separated by 5 Mhz
Distributed Coordination Function (DCF)
Phase Shift Keying (PSK)
Transmit Power Control (TPC)
Radio Resource Management (RRM)
Dynamic Frequency Selection (DFS)
902 - 928 MHz
2.4000 – 2.4835 GHz
5.15 – 5.25 GHz
5.470 – 5.725 GHz
5.725 – 5.875 GHz
This client device supports protection mechanisms such as RTS/CTS and/or CTS-to-Self.
This client device supports both TKIP and CCMP cipher suites.
300 Mbps is the maximum supported data rate for this device.
This client device supports the ERP, OFDM, and HT physical layer specifications.
This client device supports X.509 certificates for EAP authentication
The client station transmits a Reassociation Request frame to its current access point.
The current access point informs the IP gateway of the reassociation.
The current access point triggers the client’s reassociation service.
The new access point transmits a Reassociation Response to the client station with a status value.
The client and new access point create unicast encryption keys.
The client station transmits a deauthentication frame to the current access point
The current AP is using channel 1 and the new AP is using channel 40.
The SSID of the current AP does not match the SSID of the new AP.
The current AP supports only HT and the new AP is VHT capable.
The access points are hiding the SSID in Beacons and Probe Response frames
The SSID is a security session identifier used in RSNs.
The SSID must be included in an association request frame.
The SSID is an alphanumeric value assigned to device manufacturers by the IEEE.
The SSID is a pseudo-random number assigned to each client by an AP.
The SSID is an alphanumeric value with a maximum length of 32 octets.
When configuring a new network, creating an SSID is optional.
An IBSS does not have a distribution system (DS), but a BSS does.
An IBSS does not require beacon frames, but a BSS does.
An IBSS does not support 802.11 authentication or association, but a BSS does.
An IBSS does not support any 802.11ac enhancements, but a BSS does.
A single AP supports multiple BSSs with different SSIDs
A virtual cell single channel network has been implemented
The beacons are from an IBSS instead of a BSS
Three APs still share the same default configuration.
VHT TXOP power save allows stations to enter sleep mode and legacy Power Save does not.
VHT TXOP power save uses the partial AID in the preamble to allow clients to identify frames targeted for them.
Legacy Power Save mode was removed in the 802.11ac amendment.
VHT TXOP power save allows the WLAN transceiver to disable more components when in a low power state.
Client devices ignore the TIM field and automatically send PS-Poll frames after every beacon.
After each beacon, the AP attempts to empty its frame buffer by sending Wake-on-WLAN frames to wake each dozing client.
Request-to-Send and Clear-to-Send frame exchanges are used to trigger the delivery of buffered data.
The Beacon interval is changed from the default 100 time units to 10 or less time units.
Clients send null data frames to the AP and switch the power management bit from 1 to 0 to receive queued data.
Stations send a CTS-to-self frame to the AP with a very long duration period so they can receive all of their buffered data at once.
MAC Service Data Unit (MSDU)
MAC Protocol Data Unit (MPDU)
PLCP Service Data Unit (PSDU)
PLCP Protocol Data Unit (PPDU)
Signal strength of access point beacons received
Proximity to potential access points
Retry rate of probe request and response frames
Average round trip time to reach the Internet DNS server
Average round trip time to reach the IP router
Access points broadcast Beacons on all channels of each radio within the regulatory domain. Nearby client stations record information found in the Beacons for use in the association process.
Client stations broadcast Probe Request frames on all supported channels in the regulatory domain. Nearby access points respond with Probe Response frames. Client stations record information in the Probe Response frames for use in the association process.
Client stations broadcast Probe Request frames on the single channel for which they are programmed. Nearby access points respond on that channel with Probe Response frames. Client stations record information found in the Probe Response frames for use in the association process.
Access points broadcast Beacons on a single channel for which they are programmed. Nearby client stations listen for Beacon frames and record information found in the Beacons for use in the association process.
During the association, the client and AP agree to use the same transmit rate, but either station can request a change at any time after the association.
The client and AP each choose the optimal data rate to use independently of one another, based on their own measurements related to the RF link.
The client and AP may use different transmit rates, but the AP determines the data rate that will be used by each client station in the BSS.
The client and AP may use different transmit rates, but the client determines the data rate that it will use and the data rate that the AP will use when communicating to the client.
The client and AP may use a different transmit rates, but the transmit rate is determined by the peer station, based on the peer’s experience of the RF link.
Dynamic Rate Switching
Modulation and Coding Selection
Rate Set Selectivity
Adaptive Rate Management
802.11 QoS is achieved by giving high priority queues a statistical advantage at winning contention.
Four 802.1p user priorities are mapped to eight 802.11 transmit queues.
When the Voice queue has frames awaiting transmission, no data will be transmitted from the Best Effort queue.
To improve efficiency, Block Acknowledgments are required for Voice and Video WMM queues
802.11 control frames are assigned to the 802.11 EF priority queue.
Short guard intervals
Probe Request frames
RTS or CTS frames
Use of larger frame sizes results in greater throughput in low interference environments
BSS support for 65 KB A-MPDUs will increase the maximum data rate available to client devices.
In 802.11ac, changing the security mechanism from WPA2-Personal to WPA2-Enterprise will enable the VHT MCS rates.
Compared to an Independent BSS, an Infrastructure BSS can provide almost twice the throughput between wireless nodes.
Use of short guard intervals improves reliability and throughput in high multipath environments
Random backoff timer
Clear channel assessment
Network allocation vector
Slot assessment value
When the client sends a probe request in the 2.4 GHz band, the AP may reply with information about the 5 GHz BSS.
The AP may ignore the initial probe requests or 802.11 authentication requests sent in the 2.4 GHz band by dual-band clients
The AP may allow an 802.11 association with the client in the 2.4 GHz band, then send unicast channel switch announcements to the client announcing the 5 GHz channel as the new channel.
After receiving probe request frames from the same client in both bands, the AP may send an association request frame to the client in the 5 GHz band.
The AP may allow an 802.11 association with the client in the 2.4 GHz band, then the AP may perform a transparent client handoff by transferring the client’s MAC address to the 5 GHz radio
HT Protection mode
Non-ERP Present field
Secondary channel offset
Power save mode of clients
Link aggregation / port trunking
802.1p and DSCP QoS
BGP and Frame Relay
Captive web portals
RF pre-deployment planning and post-deployment reporting of access point locations on a floor plan
Performance and security monitoring of WLAN controllers with alarms and notifications for
Radio management, fast roaming, key caching, and other centralized control plane operations
Centralized bridging of guest data traffic and application of firewall and QoS policies to data
Management of WLAN controller configuration and provisioning of firmware updates
Generating, encrypting, and decrypting 802.11 frames and collecting RF radio data.
Mode 0: No protection mode (Greenfield)
Mode 1: Nonmember protection mode
Mode 2: 20 MHz protection mode
Mode 3: Non-HT mixed mode