1
Q
802.11 Security Basics
A
Five major security components are required:
- Data privacy and integrity
- AAA (Authentication, Authorization, and Accounting)
- Segmentation
- Monitoring
- Policy
AAA is a key computer security concept that defines the protection of network resources
2
Q
What are the two data forwarding methods when using a WLAN controller?
A
- Centralized Data Forwarding
This process is where all data is forwarded from the AP to the WLAN controller for processing - Distributed Data Forwarding
This is where the AP performs data forwarding locally. Distributed local data forwarding is also used to avoid high latency WAN links
3
Q
All Band Interference
A
- The term “All Band Interference” is typically associated with FHSS
- This interference occurred on the 2.4GHz range
4
Q
Adjacent Channel Interference
A
Most WiFi vendors use this term to refer to degradation of performance resulting from overlapping frequency space
5
Q
Channel Bonding
A
- Channel bonding is a recent type of technology
- With channel bonding you can take 2 20MHz channels and create 1 40MHz channel to double the amount of data you can send across that channel
6
Q
Load Balancing
A
This is the method to manipulate MAC sublayer to balance clients between multiple access points
7
Q
Telecommunication networks are defined as what?
A
Telecommunication networks are defined as 3 logical planes of operations:
- Management Plane
- Control Plane
- Data Plane (User Plane)
8
Q
Data Plane
A
- The data plane is where administrators focus on forwarding data
- The data plane is the decision maker on how to move traffic it receives
- The data plane can be handled within an access point or WLAN controller
9
Q
Band Steering
A
- This is the process of directing wireless devices to connect to 5GHz over 2.4Ghz
- 5GHz offers more channels & faster throughput rates
10
Q
802.11 Coverage Considerations
A
When designing an 802.11 WLAN, most vendors recommend 15%-30% overlap of -70 dBm coverage cells
11
Q
Layer 2 Retransmissions
A
- Unicast 802.11 frames MUST be acknowledged
- If a collision occurs or any portion of a unicast frame is corrupted, the CRC will fail
- Retransmissions cause more overhead and less throughput
12
Q
Last-Mile Delivery
A
- The term “last-mile” is often used by ISP companies to refer to the last segment of their service that connect a subscriber to their network
- Typically can be the most difficult and costly to run due to a cable needs to be run individually to the subscriber
13
Q
Control Plane
A
- Control plane is defined by protocols that provide the intelligence and interaction between equipment in a network
- Examples of Control plane intelligence
Dynamic RF
Roaming Mechanisms
Client Load Balancing
Mesh Protocols
14
Q
What considerations should you have in mind when deploying WLAN solutions?
A
- Always remember business needs are first
- Always look at the protocols that are being implemented
- Have awareness of what applications would be supported
15
Q
Management Plane
A
The functions of the management plane are as follows:
- WLAN configuration of SSIDs, security, WMM, channel and power settings
- WLAN monitoring & reporting of Layer 2 statistics like ACKs, client associations, re-associations, and data rates occurring in the management plane
16
Q
Wavelength
A
- Wavelength is the distance between similar points (peaks) on two back-to-back waves
- Typically measured from the peaks of the two back-to-back waves
- Wavelength is measured in meters
17
Q
Amplitude
A
- Amplitude is the height, force, or power of the wave
- Amplitude is also referred to as either Transmit amplitude or Received amplitude
18
Q
Reflection
A
- A wave that can bounce off a flat smooth surface that is larger than the wave
- Reflection will change the direction of the wave
- There are two major types of reflection:
Skywave reflection
Microwave reflection
19
Q
Frequency
A
- Frequency describes the behavior of waves
- Can also be described as how many waves are generated over a 1 second period of time
- Frequency has an inverse relationship to wavelength
20
Q
WiFi Direct
A
- WiFi Direct enabled WiFi devices to connect directly without the use of an AP
- WiFi Direct is ideal for mobile phones, cameras, printer, and PCs
- Uses WPA2 security
21
Q
The WiFi Alliance is responsible for what certification program?
A
- WiFi Multimedia (WMM)
- Voice Personal
22
Q
Which organization’s website would be best to use for research to a document titled “RFC 3935”?
A
Internet Engineer Task Force (IETF)
23
Q
IBSS with WiFi Protected Setup
A
- IBSS w/ protected setup provides easy configuration and strong security for ad-hoc (peer-to-peer) WiFi networks
- This would be used with devices that have a limited user interface
- WiFi Vendors refer to IBSS as either peer-to-peer or an ad hoc network
24
Q
Modulation
A
The method of adjusting the signal to create the carrier signal
25
What two components make a WAVE?
- Wavelength
| - Amplitude
26
WiFi Multimedia
- WMM
- Based on the QoS mechanisms that were defined in the 802.11e amendment
- WMM enables WiFi networks to prioritize traffic generated by different applications
27
Phase
- Phase is known as a relation term
- Its the relationship between two waves with the same frequency
- To determine phase, a wavelength is divided into 360 pieces referred to as degrees
- Phase can be measured in distance, time, or degrees
28
Watt
- A watt (W) is the basic unit of power
- Example
Instead of the pressure generated by the machine, electrical systems have voltage
Instead of water flow, electrical systems have current, which is measured in amps
29
Absorption
- If a signal doesn't bounce off, or move around an object, and it can't move through the object then you'd have 100% absorption
- Example
A 2.4GHz signal will be 1/16 the original power after propagating through a brick wall
30
The Unit Bel
- The unit bel is defined as a ratio of 10 to 1 between the power of two sounds
- Example
AP1 transmits data at 100mW, Laptop 1 receives the signal from the AP1 at 10mW. The ratio of what was sent by AP1 and what was received by Laptop 1 is 10 to 1, which is equal to 1 bel
31
Decibel
- Decibel (dB) is a unit of comparison and not a unit of power
- With finding the comparison of dB, we're trying to find a way to compare two different sets of power to each other
- Decibel is the measurement in change of power
32
Milliwatt
- A milliwatt (mW) is a unit of power
- A milliwatt is 1/1000 of watt
- Most indoor 802.11 equipment transmits at power levels between 1mW and 100mW
33
Units of Comparison (Relative)
- Decibel (dB)
- Decibel relative to an isotropic radiator (dBi)
- Decibels relative to a half-wave dipole antenna (dBd)
34
Tunneled Direct Link Setup
TDLS enabled devices that establish secure links directly with other devices after they joined a WiFi network
35
Intentional Radiator
- IR, by the FCC, is defined as something that is specifically designed to generate RF
- The FCC regulates the power level, the levels are typically measured in milliwatts (mW) or decibels relative to 1 milliwatt (dBm)
36
Receiver
- The receiver is the final component in the wireless medium
- The receiver takes the carrier signal that is received from the antenna and translates the modulated signals into 1s and 0s
37
Multipath
- Multipath is a propagation phenomenon that results in two or more paths of a signal arriving at a receiving atenna at the same time or within nano-seconds of each other
- Multipath is often caused by reflection
- There are 4 possible results of Multipath
Upfade
Downfade
Nulling
Data Corruption
38
Diffraction
Similar to refraction, a signal is bent, but in this case around an object, not passing through a different medium
39
Scattering
- With scattering, it can be considered as multiple reflections at once
- When the electromagnetic signal's wavelength is larger than pieces of whatever medium the signal is reflecting from or passing through
40
Gain
- Gain is known as amplification and is best described as increased of amplitude, or signal strength
- There are 2 types of Gain
Passive Gain
Active Gain
41
Microwave Reflection
- Microwave signals that exist between 1GHz and 300Ghz
| - Microwave signals can bounce off smaller objects like a metal door
42
WMM Admission Control
Allows WiFi networks to manage network traffic based upon channel conditions, network load, and type of traffic
43
The FCC regulates which two categories of wireless communications?
- Licensed spectrum
| - Unlicensed spectrum
44
Licensed & Unlicensed communications are regulated in what five areas?
- Frequency
- Bandwidth
- Maximum power of the intentional radiator (IR)
- Maximum equivalent isotropically radiated power (EIRP)
- Use case (Indoor/Outdoor)
45
State each WiFi technology and its frequency band and maximum data rate
- WiFi Tech
802. 11a
802. 11b
802. 11g
802. 11n (HT)
802. 11ac (VHT)
- Frequency Band
802. 11a - 5GHz
802. 11b - 2.4GHz
802. 11g - 2.4GHz
802. 11n (HT) - 2.4/5GHz
802. 11ac (VHT) - 5GHz
- Max Data Rates
802. 11a - 54Mbps
802. 11b - 11Mbps
802. 11g - 54Mbps
802. 11n (HT) - 450Mbps
802. 11ac (VHT) - 1.3Gbps
46
IETF
- Internet Engineer Task Force
- Has 8 subjects matter areas:
Applications, General
Internet, Operations & Management
Real Time Applications & Infrastructure, Routing
Security, Transport
47
WMM Power Save
- WMM Power Save helps conserve battery power for devices using WiFi radios
- It does this by managing the time the client device spends in sleep mode
48
Components of a wave that can fluctuate or be modified to create a carrier signal
- Amplitude
- Frequency
- Phase
49
What organization ensures the interoperability of WLAN products?
WiFi Alliance
50
Multiple Phase Shift Keying
- MPSK is an advance version of PSK
- MPSK can encode multiple bits per symbol
- Instead of using 2 phases like PSK, MPSK uses 4 phases, which is capable of representing 2 binary values instead of 1
51
Phase Shift Keying
- PSK varies the phase of the signal to represent the binary data
- PSK is a state transition technique
- PSK can also be used as a current state technique
- The degree of difference, or differential, is used to determine the bit value
52
Keying Method
- The method of changing a signal into a carrier signal which represents multiple pieces of data
- There's 3 methods of keying (modulation techniques)
ASK (Amplitude Shift Keying)
FSK (Frequency Shift Keying)
PSK (Phase Shift Keying)
53
RSSI
- Received Signal Strength Indicator
- RSSI is the sensitivity, the received sensitivity to the power level of the RF signal that we need at a minimum to successfully hear and receive the transmission
54
dBi
- dBi is the process of calculating the radiating power of the antenna so that you can determine how strong a signal is at a certain distance from the antenna
- The measurement is decibels isotropic (dBi)
- Comparing measurements from an IR (Isotropic Radiator)
- The dBi value is measured at the strongest point
55
dBd
- The antenna industry uses two dB scales to describe the gain of antennas
First scale is dBi
Second scale is dipole (dBd), decibel gain relative to a dipole antenna
- The dBd value is the increase in gain of an antenna when its compared to the signal of a dipole antenna
56
Frequency Shift Keying
- Varies the frequency of the signal to represent the binary data
- FSK is a current state technique
- FSK shifting determines that data is being transmitted
- used in legacy deployments of 802.11 networks
57
The 6dB Rule
- The 6dB Rule is also known as the "Inverse Square Law"
- By doubling the distance from the RF source, the signal will decrease by about 6 dB
- The 6dB rule is useful comparing cell sizes or estimating the coverage of a transmitter
- The 6dB rule estimates free space path loss
58
dBm
- dBm provides a comparison of signal to 1mW of power
- dBm means decibels relative to 1 mW
- 0 dBm is equal to 1mW
- Formula
dBm = 10x log10 (PmW)
- With this formula we can determine that 100mW of power is equal to +20 dBm
59
Amplitude Shift Keying
- ASK varies the amplitude, or height, of a signal to represent the binary data
- ASK is a current state technique
60
DCF
Distributed Coordination Function is a fundamental access method of 802.11 communications
61
CSMA/CA
- Carrier Sense Multiple Access w/ Collision Avoidance is the process used to ensure that only one 802.11 radio transmitting at a time
62
BSS
- Basic Service Set is the cornerstone topology of an 802.11 network
- What makes up BSS are communicating devices that consist of 1 AP radio w/ 1 or more client stations
63
WMAN
- Wireless Metropolitan Area Network (WMAN) provides RF coverage to a metropolitan area such as a city and the surrounding suburbs
- 802.16 is associated w/ WMAN
- 802.16 standard defines broadband wireless access and sometimes referred to as Worldwide Interoperability for Microwave Access (WiMAX)
64
WWAN
- Wireless Wide Area Network provides RF coverage over a vast geographical area
- WWAN uses a wireless medium instead of a wired medium
65
IFS
- The Interframe Space is a period of time that exists between transmissions of wireless frames
- There's 10 types of IFS, to name partial:
Reduced Interframe Space (RIFS) - Highest priority
Short Interframe Space (SIFS) - Second highest priority
PCF Interframe Space (PIFS) - Middle priority
DCF Interframe Space (DIFS) - lowest priority
Arbitration Interframce Space (AIFS) - Used by QoS STAs
Extended Interframe Space (EIFS) - Used after receipt of corrupted frames
66
PCF
- Point Coordination Function is an access method form of polling
- The AP performs the function of the Point Coordinator (PC) because the AP is taking on this role
- PCF only works in a BSS, and is considered obsolete
67
802.11 Topologies
```
- 802.11 topologies are known as service sets
Basic Service Set (BSS)
Extended Service Set (ESS)
Independent Basic Service Set (IBSS)
*This service set does NOT need an AP*
Mesh Basic Service Set
- Everything operates in half-duplex
```
68
Management Frames
```
- There are 12 management frame sub types used by the 802.11 standard
Beacon
Probe request
Probe response
Authentication
Deauthentication
Association request
Association response
Reassociation request
Reassociation response
Announcement (ATIM)
Disassociation
Action
```
69
Control Frames
```
- There are 9 control frame sub-types by the 802.11 standard
Power Save Poll (PS-Poll)
Request To Send (RTS)
Clear To Send (CTS)
Acknowledgment (Ack)
Contention Free-End (CF-End)
CF-End + CF Ack
Block Ack Request
Block Ack
Control Wrapper
```
70
Dwell Time
- Dwell time w/ FHSS is defined as the amount of time that a system transmits on a specific frequency before it switches to the next frequency
- Typical dwell times are considered around 100-200ms
71
5.0GHz
The 5GHz ISM band is 160MHz wide and spans from 5.0GHz to 5.875GHz
72
OFDM
- Orthogonal Frequency Division Multiplexing is not Spread Spectrum technology, but it has similar properties to it. Such as low transmit power & using more bandwidth than is required to transmit data
- OFDM uses binary phase shift keying (BPSK) and quadrature phase shift keying (QPSK) phase modulation for the lower OFDM data rates
73
2.4GHz
- The 2.4GHz ISM band is the most common band for wireless communications
- 2.4GHz ISM band is 100MHz wide and spans from 2.4GHz to 2.5GHz
- 802.11 (FHSS or DSSS radios), 802.11b, 802.11g, 802.11n use this band
74
802.11w
- 802.11w was defined by the IEEE Task Group to provide a way of delivering management frames security
- Prevents management frames from being spoofed
- 802.11w frames are known as robust management frames
75
900MHz
- The 900MHz ISM band is 26MHz wide and spans from 902MHz to 928MHz
- Part of the 900MHz frequency range is allocated to GSM for communication
76
Hop Time
- Hop time is a measurement of the amount of time it would take the transmitter to change from one frequency to the other
- Typical hop time rates are 200-300 microseconds
77
802.11r-2008
- 802.11r is often referred to as fast secure roaming
| - 802.11r defines faster handoffs when roaming occurs between cells in a WLAN
78
U-NII Review
```
- Band
U-NII-1
U-NII-2
U-NII-2 Extended
U-NII-3
- Frequency
U-NII-1 - 5.15GHz - 5.25GHz
U-NII-2 - 5.25GHz - 5.35GHz
U-NII-2 Extended 5.47GHz - 5.725GHz
U-NII-3 - 5.725GHz - 5.85GHz
- Channels
U-NII-1 - 4 channels
U-NII-2 - 4 channels
U-NII-2 Extended - 12 channels
U-NII-3 - 5 channels
```
79
Units of Power (Absolute)
- Watt (W)
- Milliwatt (mW) 1/1000
- Decibels relative to milliwatt (dBm)
- Things that we can measure
80
WiFi Protected Setup
WiFi Protected Setup defines simplified and automatic WPA and WPA2 security configurations
81
Example of The Rule of 10s and 3s (Gain)
- An AP is configured to transmit at 100mW & the antenna is rated for 3 dBi of passive gain, the amount of power that will radiate out of the antenna (EIRP) will be 200mW
- The 3dB of gain from the antenna caused the 100mW signal from the access point to double
82
Example of The Rule of 10s and 3s (Loss)
- If your AP is configured to transmit at 100mW and is attached to a cable that introduces 3dB of loss, the amount of absolute amplitude at the end of the cable will be 50mW
- The 3dB of loss from the cable caused the 100mW signal from the AP to be halved
83
Transmitter
- The transmitter is the initial component in the creation of the wireless medium
- The endpoint hands the data off to the transmitter, and its the transmitter's job to begin the RF communication
- When a transmitter receives data, it then generates the AC current to start this transmission
84
Skywave Reflection
- Skywave reflection is a signal that bounces off the ionosphere
- Skywave frequencies are frequencies below 1GHz
85
Equivalent Isotropically Radiated Power
- EIRP is regulated by the FCC
- EIRP is the product of transmitter power and the antenna gain in a given direction relative to an isotropic antenna of a radio transmitter
86
The Rule of 10s and 3s
-3s
For every 3dB of gain (relative measurement) you'll double the absolute power by 2 (multiply). The answer will be in mW
For every 3dB of loss, then you'll take 1/2 of the absolute power by 2 (division)
- 10s
For every 10dB of gain, you'll multiple the absolute power by a factor of 10
For every 10dB of loss, you'll divide the absolute power by a facotr of 10
87
Beamwidth
- Measurement of how broad or narrow the focus of an antenna
| - Beamwidth is measured both horizontally and vertically
88
What is an RF signal?
- An RF signal is a spectrum range of all possible electromagnetic radiation, which is the radio frequency signal
- An RF signal starts out as AC signal that originated from a power source (transmitter)
89
802.11i
- 802.11i is focused on wireless security
- There's 3 key components of any wireless security solution:
Data privacy - Confidentiality
Data integrity - Integrity
Authentication - Authentication
- 802.11i is defined as Robust Security Network (RSN) to hide data flying through the air
90
Yagi Antenna
- Yagi antennas are typically used for short-to-medium distance point-to-point communications of up to about 2 miles, although high-gain Yagi antennas can be used for longer distances
- Horizontal Beamwidth = 30 to 78 degrees
- Vertical Beamwidth = 14 to 64 degrees
91
Highly Directional Antenna
- Highly directional antennas are strictly used for point-to-point communications
- Typically to provide network bridging between two buildings
- Highly directional antennas are the most focused, narrow beamwidth of any of the antenna types
92
Parabolic Dish Antenna
- The parabolic dish antenna is similar in appearance to the small digital satellite TV antennas
- This is a type of a highly directional antenna
- Horizontal Beamwidth = 4 to 25 degrees
- Vertical Beamwidth = 4 to 21 degrees
93
Grid Antenna
- The spacing of the wires on a grid antenna is determined by the wavelength of the frequencies that the antenna is designed for
- This is a type of a highly directional antenna
- If a wider beam grid antenna is used, less gain will be experienced
94
Antenna Arrays
- Antenna arrays are considered as a group of two or more antennas that integrated together to provide coverage
- The group operates together to perform beamforming
95
Noise Floor
- Noise floor is an ambient or background level of radio energy on a specific channel
- This can happen due to another transmitter using the same channel or devices that emit radio frequency unintentionally like a microwave oven
- We have to have a measurement of noise floor to see if it'll be an interferer w/ the signal we're broadcasting
96
Semi-Directional Antenna
- Semi-directional antennas are designed to direct a signal in a specific direction
- Semi-directional is typically used for short-to-medium distance communications
- Three types of antennas that fall in the category:
Patch, Panel, Yagi
97
Patch Antenna
- Patch antennas are used for outdoor point-to-point communications up to a mile
- More commonly used as a central device to provide unidirectional coverage from the AP to the clients in an indoor environment
- Horizontal Beamwidth = 30 to 180 degrees
- Vertical Beamwidth = 6 to 90 degrees
98
Omnidirectional Antenna
- An omnidirectional antenna radiates RF signal horizontally in all directions
- Typically consists of small, rubber-coated dipole antenna, often referred to as a rubber duck antenna
- The higher the dBi or dBd value of an Omni antenna, the more focused the signal is, causing the vertical signal to decrease and horizontal signal to increase
- Horizontal Beamwidth = 360 degrees
- Vertical Beamwidth = 7 to 80 degrees
99
Planar Antenna
- Planar antennas are often used to provide coverage for long hallways with offices on each side
100
Static Beamforming
- Static beamforming is performed by using directional antennas to provide a fixed radiation pattern
- Static beamforming uses multiple directional antennas (clustered)
101
Dynamic Beamforming
- Dynamic beamforming focuses the RF energy in a specific direction and in a particular shape
- Similar to Static Beamforming the direction and shape of the signal is focused
- With dynamic beamforming the radiation pattern of the signal can change on a frame by frame basis
102
Transmit Beamforming
- Transmit beamforming (TxBF) is performed by transmitting multiple phase-shifted signals w/ the hope that they will arrive in-phase at the location where the transmitter believes that the receiver is located
- With TxBF, the idea is that if you have two or more Tx antennas, then one of the extra antennas can assist with the distance and strength of the signal
- TxBF relies on implicit or explicit feedback from the transmitter and receiver
103
FHSS
- Frequency Hopping Spread Spectrum
- FHSS is the process of using narrowband signals to spread information across multiple different channels, but not at the same time
104
DSSS
- Direct Sequence Spread Spectrum
- Its different from FHSS, but uses fixed channels
- DSSS was specified as the primary/root method of being able to give you 1 to 2Mbps of RF communication in the 2.4GHz band
- DSSS 802.11 radios are known as Clause 15 devices
105
IEEE 802.11-2007 Ratified Amendments
- In 2007, the IEEE consolidated 8 ratified amendments along w/ the original standard and published the single document as IEEE standard 802.11-2007
- The document included:
802. 11 (1999)
802. 11a (1999)
802. 11b (1999)
802. 11g (2003)
802. 11i (2004)
106
802.11b
- 802.11b is also known as high-rate DSSS
| - The frequency space in which 802.11b radio cards can operate is the unlicensed 2.4GHz to 2.4835GHz ISM band
107
802.11a
- 802.11 technology would operate in the 5GHz frequency space using an RF technology called Orthogonal Frequency Division Multiplexing (OFDM)
- The bands used in 802.11a are unlicensed and we called those bands Unlicensed National Information Infrastructure (U-NII) frequency bands w/ a total of 12 available channels
108
802.11g
- 802.11g used a new technology called Extended Rate Physical (ERP) but were still meant to transmit in the 2.4- - 2.4835GHz ISM frequency band
- Supported data rates of up to 54Mbps
109
SNR
- Signal to Noise Ratio
- Example
If a radio receives a signal of -85 dBm and the noise floor is measured at -100 dBm, the difference between the received signal and the background noise if 15 dB. The SNR is 15 dB
110
Spectrum Analysis
Before conducting the coverage analysis survey, locating sources of possible interference is a MUST
111
Passive Coverage Analysis
A passive coverage survey collects RF measurements, including received signal strength (dBm) noise level (dBm) and signal-to-noise ratio (dB)
112
Active Coverage Analysis
- An active coverage survey utilizes a radio that's associated with the access point and has layer 2 connectivity allowing for low-level frame transmission
- If layer 3 connectivity is established, then ICMP pings are sent in 802.11 data frame transmissions
113
802.3af
- This standard was officially referred to as the amendment for data terminal equipment power via the media-dependent interface
- The standard was approved in 2003
- This is provided over copper wire
114
Powered Device
- A powered device (PD) either requests or draws power from the source equipment
- PDs must be capable of accepting up to 57 volts from either data lines or unused pairs of the ethernet cable
115
802.11n-2009 Amendment
- This amendment defines HT (High Throughput)
- HT Clause: 20 radios that use multiple-input, multiple-output (MIMO) technology in unison with Orthogonal Frequency Division Multiplexing (OFDM) technology
- The benefits of MIMO are increased throughput and greater range
116
Space-Time Block Coding
- STBC is a method where the same information is transmitted on two or more antennas
- It's known as a transmit type of diversity
- STBC can be used when the number of radio chains exceeds the number of spatial streams
117
Cyclic Shift Diversity
- CSD is another transmit diversity technique specified in 802.11n
- Unlike STBC, a signal from a transmitter that uses CSD can be received by legacy 802.11a/g devices
118
Four Components of MDM Solution
```
- Mobile device
Requires access to the corporate WLAN
- AP/WLAN Controller
All communications are between the mobile devices and APs
- MDM Server
Responsible for enrolling client devices
- Push Notification Servers
```
119
MDM Agent Software
- MDM Agent Software is similar to spyware
- The end user has to approve of the software being installed
- Analytics and reporting information are sent back to the MDM device
120
802.11d
- The 802.11d amendment was published as IEEE standard 802.11d-2001
- 802.11d added requirements and definitions necessary to allow 802.11 WLAN equipment to operate in non-areas served by the original standard
- Country code information is delivered within the wireless frames
121
802.11e
- The 802.11e amendment defines the layer 2 MAC methods needed to meet the QoS requirements for time-sensitive applications over IEEE 802.11 WLANs
- HCF (Hybrid Coordinated Function) is an additional coordination function used in 802.11e WLANs
122
Hybrid Coordinated Function
- HCF has two access mechanisms to provide QoS
- Enhanced Distributed Channel Access (EDCA)
This mechanism is an extension of DCF, EDCA provides the prioritization of frames based on upper-layer protocols
- Hybrid Coordination Function Controlled Channel Access (HCCA)
This mechanism is an extenstion of PCF
HCCA gives the access point the ability to provide for "prioritization of stations"
123
802.11h
- 802.11h defined mechanisms for DFS (Dynamic Frequency Selection) and TPC (Transmit Power Control)
- The main purpose of DFS and TPC is to provide services where 5GHz wireless transmissions will not cause interference with 5GHz satellite and radar transmissions
- U-NII-2 Extended was introduced which offered 11 more channels
124
802.11k
- 802.11k defined mechanisms in which client station(s) resource(s) data is gathered and processed by either an AP or WLAN Controller
- 802.11k called for measurable client stat information in the form of requests and reports
Transmit Power Control (TPC)
Client Stats
Channel Stats
Neighbor Report(s)
125
802.11p
- 802.11p is known as Wireless Access in Vehicular Environments (WAVE)
- Speeds may be possible of up to 200 kilometers per hour and within a range of 1000 meters
- 802.11p defined a method to support Intelligent Transportation System (ITS) applications
126
802.11s
- 802.11s defined access points acting as a portal device(s) to a Wireless Distribution System (WDS)
- 802.11s also defined the use of Mesh Points (MPs)
127
802.11ac
- 802.11ac defines Very High Throughput (VHT) enhancements below 6GHz
- 802.11ac takes advantage of greater spectrum space that 5GHz U-NII bands can provide
- 4 Enhancements
Wider Channels
New Modulation (256-QAM Modulation)
More Spatial Streams
Improved MIMO and Beamforming
128
802.11ah-2016
- 802.11ah defines the use of WiFi in frequencies below 1GHz
- 802.11ah has lower data rates but longer distance
- IoT devices primarily utilize this standard for wireless communications
129
802.11ai-2016
- 802.11ai provides a Fast Initial Link Setup (FILS)
| - This standard was implemented to combat challenges that exist in high-density environments
130
Aperture
The effective area for receiving power of an antenna
131
Refraction
An RF signal being bent as it passes through a medium is also known as refraction
132
Loss (Attenuation)
- Loss is also known as attenuation
| - Loss is defined as the decrease of amplitude or signal strength
133
Free Space Path Loss
- Free Space Path Loss (FSPL) is the loss of signal strength caused by the natural broadening of the waves, also known as beam divergence
- RF signal energy spreads over larger areas as the signal travels farther away from an antenna, and as a result, the strength of the signal attenuates
134
Multipath - Upfade
- Upfade is considered as increased signal strength
- This is the process of multiple signals arriving at the receiver at the same time and the signals are in-phase
- The final received signal can never be stronger than the original transmitted signal because of free space path loss
- Phase differences of between 0 and 120 degrees will cause upfade
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Multipath - Downfade
- Downfade is considered as decreased signal strength
- When multiple signal paths arrive at the receiver at the same time and are out-of-phase with the primary wave, the result is a decrease in signal strength
- Phase differences of between 121 and 179 degrees will cause downfade
136
Multipath - Nulling
- Nulling is considered as signal cancellation
- This is the process of multiple signals arriving at the receiver at the same time and are 180 degrees out-of-phase with the primary wave
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Multipath - Data Corruption
- This is the process of a receiving antenna having problems demodulating an RF signal's information
- The delay spread time differential typically causes bits to overlap with each other, and the end result is data corruption
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Gain - Active
- Active Gain is usually caused by the transceiver or the use of an amplifier on the wire that connects the transceiver to the antenna
- The amplifier is usually bi-directional, meaning that it increases the AC voltage on both inbound and outbound
- Active gain devices require the use of an external power source
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Gain - Passive
- Passive gain is accomplished by focusing the RF signal with the use of an antenna
- Antennas are passive devices that don't require an external power source
- An increase of signal amplitude results in either, active gain prior to the signal reaching the antenna, or passive gain focusing the signal radiating from the antenna
140
SINR
- Signal to Interference Plus Noise is a term used by vendors
- SINR is the difference between the power of the primary RF signal, compared against the sum of the power of the RF interference and background noise
- SINR is measured in decibels
141
Link Budget
The link budget is the sum of all the planned and expected gains and losses from the transmitting radio, through the RF medium, to the receiver radio
142
Sector Antenna
- Sector antennas are a special type of high-gain, a semi-directional antenna that provides a pie-shaped coverage pattern
- These antennas are typically installed in the middle of the area where RF coverage is desired and placed back-to-back with other sector antennas
- Horizontal beamwidth = 60 to 180 degrees
- Vertical beamwidth = 7 to 17 degrees
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Fresnel Zone
- Pronounced (FRUH-nel) zone
- The Fresnel zone is an imaginary, elongated, football-shaped area that surrounds the path of the visual line of sight (LOS) between two point-to-point antennas
144
Transmit Diversity
This is the method of transmitting out of the antenna where the last best-received signal was heard
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Receive Diversity
This is the method of listening for the best-received signal
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Switched Diversity
- 802.11n radios used switched diversity
| - When receiving incoming transmissions, switched diversity listens with multiple antennas
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Voltage Standing Wave Ratio
- VSWR is a measurement of the change in impedances to an AC signal
148
Azimuth and Elevation Charts
- Azimuth and Elevation charts are commonly known as radiation patterns, for antennas
- These charts assist potential buyers with their purchasing decision on an antenna
- Azimuth Charts are labeled as H-plane and show the top-down view of the radiation pattern of the antenna
- Elevation Charts are labeled as E-plane and shows the side view of the radiation pattern on the antenna
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Maximal Ratio Combining
- MRC is a type of receive diversity technique
| - MRC is the process of where multiple received signals are combined, thus improving received sensitivity
150
Radio Chain
A radio chain is defined as a single radio and all is supporting architecture (including mixers, amplifiers, and analog/digital converters)
151
Delay Spread
- The delay spread is the time differential between multiple paths of the same signal
152
Error Vector Magnitude
- EVM is a measure used to quantify the performance of a radio receiver or transmitter in regards to modulation accuracy
153
Frame Aggregation
- Frame aggregation is a method of combining multiple frames into a single frame transmission
154
PBSS
- Personal Basic Service Set is an 802.11 WLAN topology in which 802.11ad stations communicate with each other
- PBSS can be established only by DMG (Directional Multi-Gigabit) radios that transmit the 60GHz frequency band
- Similar to an IBSS, no access point is needed
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NAV
- Virtual carrier sense uses a timer mechanism also known as Network Allocation Vector (NAV)
- The NAV timer maintains a prediction of future traffic on the medium based on Duration value information seen in a previous transmission
156
MSDU
- MAC Service Data Unit contains data from the LLC (Logical Link Control) and layers 3 - 7
- When the Network layer (Layer 3) sends data to the Data-Link layer, that data is handed off to the LLC and becomes a MSDU
157
MPDU
- MAC Protocol Data Unit occurs when the LLC sublayer sends the MSDU to the MAC sublayer, the MAC header information is added to the MSDU to identify it
- An 802.11 MPDU is considered as an 802.11 frame
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Physical Layer
- Similar to the Data-Link layer being divided into two sublayers, the Physical layer (PHY) is also divided into two sublayers:
Physical Layer Convergence Procedure (PLCP)
Physical Medium Dependent (PMD)
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Physical Layer Convergence Procedure
- The PLCP prepares the frame for transmission by taking the frame from the MAC sublayer and creating the PLCP protocol data unit (PPDU)
160
Physical Medium Dependent
- The PMD sublayer modulates the received transmission from the PLCP and transmits the data as bits
CWNA
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