221 Midterm Flashcards
(117 cards)
1
Q
What company standardized WLAN technologies?
Lect 1
A
IEEE began standardizing WLAN tech in 1991.
In 1992, IEE created the original 802.11 standard which is the foundation for most WLAN tech.
2
Q
What is Wi-Fi?
Lect 1
A
Wi-Fi is the brand name used to market 802.11 technology. Doesn’t actually stand for anything.
3
Q
Name some Technical Standards organizations.
Lect 1
A
- ITU-R
- IEEE
- IETF
- ISO
- 3GPP
4
Q
Name some Regulation Comissions
Lect 1
A
The FCC and CRTC / IC are both regulation commissions.
5
Q
Name and define the 2 categories of wireless communications.
Lect 1
A
Licenced Spectrum - Have to be subjected to the licence application procedure (no diea what that is) before they can install wireless systems.
Unlicenced Spectrum - These do not have to apply for a licence before operating, and include the ISM Band (industrial, scientific, medical)
6
Q
What are the 6 areas that define communications regulations?
Lect 1
A
- Frequency
- Bandwidth
- Maximum of the Intentional radiator (IR)
- MAximum equivalent isotopically radiated power (EIRP)
- Use (Indoor or outdoor)
- Spectrum Sharing Rules
7
Q
What network types does the IEEE create standards for?
Lect 1
A
LANs, PANs, and MANs
8
Q
What is the most recent standard published by IEEE?
Lect 1
A
The WLAN standard 802.11-2020 is the newest standard published by IEEE.
9
Q
What are the main goals of the Wi-Fi alliance?
Lect 1
A
- Marketing the Wi-Fi brand and raising consumer awareness of new 802.11 developments
- Providing interoperability between different WLAN products using a certification process.
10
Q
What are the different generations of Wi-Fi?
A
Wi-Fi 7 is currently being developed and should be implemented by 2024. 7 will use the 802.11be standard and will support:
* 2.4, 5, and 6GHz
* Up to 48GBps
11
Q
What are the 3 enterprise network layers? What layer does Wi-Fi reside in?
Lect 1
A
The 3 layers are Core, Distribution, and Access.
While Wi-Fi is typically an access layer technology, some devices operate on the distribution layer such as bridge links.
12
Q
What kind of transmission does Wi-Fi use?
Lect 2
A
Wi-Fi is a Half-Duplex technology. This meanas that both ends of a communication are capable of transmitting and receiving, however only one device can be communicating at a time.
Other transmission types are Simplex, which is only one way, and full duplex, where both sides of a communication can transmit and receive similtaniously.
13
Q
Describe data modulation
Lect 2
A
Modulation is the process of converting data into radio waves by adding information to a carrier signal.
14
Q
What are the 4 components of waves used in modulated carrier signals?
Lect 2
A
- Amplitude - The Height, force, or power of the wave.
- Wavelength - The disance between similar points on two back-to-back waves.
- Frequency - The number of electromagnetic waves put out in one second.
- Phase - A relative term used to describe the relationship between two waves with the same frequency.
15
Q
What are Keying Methods?
Lect 2
A
Keying methods are the manipulation of a signal to represent multiple pieces of data as 1s and 0s. Using a keying method changes a regular signal into a carrier signal. Allows a signal to encode data sop it can be communicated / transported. There are 3 types of keying methods:
* Amplitude-Shift Keying (ASK)
* Frequency-Shift keying (FSK)
* Phase-shift keying (PSK)
16
Q
Describe the attributes of Amplitue-Shift Keying (ASK)
Lect 2
A
ASK varies the height (amplitude) of a signal to represent the binary data.
One level of amplitude is used to represent a 0 bit, while another level of amplitude can represent a 1. The receiving station samples the wave during the initial period of transmission to determine the amplitude of the wave.
17
Q
Describe the attributes of Frequency-Shift Keying (FSK)
Lect 2
A
FSK uses the frequency of the wave to represent 0s and 1s.
18
Q
Describe the attributes of Phase-Shift Keying (PSK)
Lect 2
A
PSK uses the change of phase to represent 1s and 0s. If the phase changes, it can represent a 1, and then a lack of change represents a 0. PSK is used extensively for radio transmissions defined in 802.11-2020 standards.
19
Q
What is an RF Signal?
Lect 3
A
RF Signals reside in the heart of the physical layer, and they are electromagnetic waves used in wireless communication.
20
Q
Describe how RF Signals are created
Lect 3
A
- Start out as electrical alternating current (AC) signals that are generated by a transmitter
- Sent through a copper coax cable and radiated out of an antenna element in the form of an electromagnetic wave
- Changes of electron flow into an antenna produce changes in the electromagnetic field surrounding the antenna.
- This wave that leaves the antenna is known as the RF signal.
21
Q
What is a sine wave?
Lect 3
A
A sine wave is the shape and form of the AC signal leaving an antenna.
22
Q
What are the properties of a RF signal?
lect 3
A
- Wavelength
- Frequency
- Amplitude
- Phase
23
Q
Name some properties of a sine wave.
Lect 3
A
- Oscillation - The fluctuation of voltage in an AC current.
- Cycle - The complete wave oscillation from one point that returns to the same point it started from.
- Period - the time it takes for one cycle to be completed.
24
Q
Define RF Signal wavelengths.
Lect 3
A
A wavelength is the distance between two successive peaks or valleys in a wave pattern (or the distance that a single cycle of an RF travels)
Wavelength calculation formula:
λ (in.) = 11.811/Frequency (GHz)
λ (cm) = 30/Frequency (GHz)
25
How are wavelengths and frequency related?
| Lect 3
Wavelengths and frequency have an inverse relationship This means that a higher frequency signal with a smaller wavelength will not travel as far as a lower frequency signal with a larger wavelength. This relationship has 3 components:
1. Frequency (f, measured in hz )
2. Wavelength (λ measured in metres (m)
3. The speed of light (a constant of 300,00,000m/sec)
## Footnote
λ = c/f, f = c/λ
26
Describe RF Signal Frequency
| Lect 3
Frequency is the numnber of times a specified event occurs within a specified time interval.
Frequency is measured in Hz.
An event that occurs once in 1 second has a frequency of 1 hz.
27
Describe RF Signal Amplitude
| Lect 3
Amplitude is characterized as the signal's strength, or power.
Amplitude in terms of wireless signals is reference as how long / strong the signal is.
This can be defined as the maximum displacement of a continuous wave.
In terms of RF signals, amplitude corresponds with the electrical field of the wave.
Transmit amplitude is defined as the initial amplitude of a signal that leavs a transmitter.
Recieved amplitude is the recieved signal strength.
28
Define RF Signal phase
| Lect 3
Phase describes the relationship between multiple signals that share the same frequency.
Phase describes the comparison between the positions of the amplitude valleys and peaks of 2 or more seperate wave forms.
29
What is RF wave propagation?
| Lect 3
RF wave propagation is the way RF waves move around or through certian materials.
Propagation has 5 different behavior types:
* Absorption - How much a material absorbs a RF wave travelling through it. The missing piece when comparing total reflected and transmitted energy.
* Reflection - The waves behavior after it hits a smooth object larger than the wave itself.
* Refraction - The bending of a RF signal as it passes through a medium with a different density.
* Diffraction - The bending of an RF signal as it travels around an object.
* Scattering - Multiple reflections coming off of a single signal.
30
Describe RF signal attenuation and Free Space Path Loss (FSPL)
| Lect 3
Loss or attenuation (measured in db) is the gradual weakening of an RF signal as it travels.
Free Space Path Loss is the attenuation of a signal even without any other propogation affecting the signal.
31
What is the 6DB rule of Free Space Path Loss?
| Lect 3
The 6 DB Rule is an easy way to calculate FSPL. If the distance doubles, the approximate loss is 6db.
32
What is the multipath propagation phoenomenon?
| Lect 3
Multipath is the result of two or more paths of a signal arriving at a receiving antenna at the same time.
The effects of multipath can be either constructive or destructive, and are categorized in 4 different results:
* Upfade
* Downfade
* Nulling
* Data Corruption
33
What is upfade?
| Lect 3
Upfade is the constructive multipath result where the combined signals result in increased strength. While the received signal is stronger than the primary signal, it can never be stronger than the transmitted signal.
Upfade occurs when multiple RF signal paths arrive at the receiver at the same time and are ***in*** phase with the primary wave.
Upfade requires smaller phase differences between 0 and 120 degrees.
34
What is downfade?
| Lect 3
Downfade is the destructive multipath result where the signal strength is decreased at the receiver.
Downfade is the result of phase differences between 121 and 179 degrees.
35
What is nulling?
| Lect 3
Nulling is the destructive multipath result where the signal is completely cancelled.
Both RF signal paths arrive at the receiver with exactly a 180 degree phase difference.
36
What is multipath data corruption?
| Lect 3
The difference in time between primary signals and reflected isgnals is known as delay spread.
Delay spread along with multiple reflected signals can result in issues with demodulating the RF signal's information.
This can result in corrupted data.
Most common occurence of destructive multipath.
37
What are the 3 main RF components?
| Lect 4
Transmitters, antenna, and receivers.
38
What is the main function of an RF transmitter?
| Lect 4
A transmitter is the initial components in the creation of a wireless medium. Data is sent to the transmitter from the osurce, and the transmitter begins the transition to the destination.
Transmitters assist in communication by:
* Encoding data
* Modulating the signal
* Sending the signal to the antenna
39
What is the main function of an RF Antenna?
| Lect 4
Antenna provide 2 functions in a communication system:
1. When connected to a transmitter, it collects the AC signal from the transmitter and directs or radiates the signal in a pattern specific to the type of antenna.
2. When connected to a receiver, the antenna takes in the RF waves from the air, and directs the AC signal to the receiver.
40
What is the main function of an RF receiver?
| Lect 4
The receiver is the final component of the wireless medium. The main functions of the receiver are to:
* Translate the modulated signal into binary bits.
* Passes the translated data to the end host machine.
41
What are units of power used for?
| Lect 4
Units of power are used to measure transmission amplitude and received amplitude. These are also known as Absolute Power MEasurements
Absolute power measurements include watts(W), milliwatts(mW), and decibels related to 1 mW(dBm)
42
What are units of comparison used for?
| Lect 4
Units of comparison are often used to measure how much gain or loss occurs because of the introduction of cabling or an antenna.
Units of comparison are also used to represent a difference in power from point A to point B.
Units of comparison are also knwn as relative power measurements.
dBs are units of comparison.
43
decibel formula sheet for RF math
| Lect 4
decibels = 10 × log10(P1/P2)
dBm = 10 × log10(P1/1mW)
0 dBm = 1 mW
44
Explain the rule of 10s and 3s.
| Lect 4
The rule of 10s and 3s is used to easily calculate RF signal strength values.
▪ For every 10 dB of gain you multiply signal strength by 10.
▪ If calculating loss, for every 10 dB of loss you divide signal strength by
10.
▪ For every 3 dB of gain multiply the signal strength by 2.
▪ If calculating loss, for every 3 dB of loss divide the signal strength by 2.
45
For WLAN design, name some received power recommendations.
| Lect 4
-70dBm for High Data rate connectivty
-65 dBm: for Voice over Wi-Fi.
46
What is the noise floor?
| Lect 4
The noise floor is the ambient background level of radio energy in a specific channel.
This background energy can include modulated or encoded bits being transmitted fro other newarby 802.11 transmitting devices, as well as unmodulated 802.11 devices.
Anything electromagnetic has the potential to rais the amplitude of the noise floor.
47
What is SNR?
| Lect 4
SNR stands for the Signal-to-Noise ratio.
The lower the SNR, the higher chance of corruption. If the amplitude of the noise floor is too close to the amplitude of the received signal, corruption will occur.
-70 dBm is reccomended for coverage because it is usually well above the noise floor.
48
What is SINR?
| Lect 4
Signal-to-Interface-Plus-Noise (SINR) is the standard measurement system for Wi-Fi networks.
SINR is the difference between the power of the primary RF signal and the sum of the power of the interference and background noise.
Measured in dB.
49
What are RSSIs used for?
| Lect 4
Recieved Signal Strength Indicators (RSSI) are used to measure the signal strength of received transmissions.
Used to measure a signal strength with a value between 0 and 255.
Atheros: 0-127 and Cisco 0-11 are examples of manufactuer RSSIs.
50
What is receive sensitivity?
| Lect 4
Recieve sensitivity refers to the power level of an RF signal required to be successfully received by the receiver radio.
The receive sensitivity is dependant on the device that is receiving the signal.
The more complex the modulation and coding, the stronger the received signal needs to be.
51
Describe dynamic rate switching.
| Lect 4
Dynamic rate switching is the process of APs and radios upshifting and downshifting their data rates based on the receive sensitivity thresholds of connected devices.
52
What is the purpose of a link budget?
| Lect 4
When radio communications are deployed, link budgets are the sum of all planned and expected gains and losses from the transmited radio, through the medium, to the receiver radio.
Link budget calculations guarentee that the final received signal amplitude is above the receiver sensitivity threshold of the receiver radio.
53
What are the components of link budget calculations?
| Lect 4
Original Transmit gain, passive antenna gain, and active gain from RF amplifiers are all components of link budget calcluations.
All gain and losses must be accounted for. Any hardware device installed in a system adds attenuation known as insertion loss.
Calculation is rated for dB loss per 100 feet, and connectors typically add about .5dB of insertion loss.
54
What different types of antennas exist?
| Lect 5
* Omnidirectional - Designed to provide general coverage horizontally in all directions.
* Semidirectional - Radiate RF similar to how a wall sconse radiates light. Directional coverage across a large area.
* Highly directional - Radiate like a spotlight which focuses on a specific point.
55
How can indoor antennas be used?
| Lect 5
Usually indoor patch antenna provide directional coverage within a building.
In cluttered warehouse environments, coverage is the main concern.
In high density environments, using directional patch antennas can reduce interference.
56
What kind of antennas are used in outdoor environments?
| Lect 5
Sector Semidirectional antenna are used for building to building communication.
Dishes and grid antenna are used for long distance point-to-point bridge links.
57
What should be taken into consideration when designing an antenna?
| Lect 5
* Polarization - The antenna structure or the orientation of an antenna's wave oscillations
* Earth Buldge - The curvature of the earth needs to be taken into consideration when setting up long range point-to-point RF communications.
* Tilt - Determined by the height of the antennas at both locations to point both antenna in the correct directions.
58
Describe different methods of simple antenna diversity.
| Lect 5
Switched Antenna Diversity - Legacy method. Includes:
* Recieve diversity - Taking in multiple transmit signals using multiple antenna, and choosing the signal with the best amplitude while discarding the weaker connections.
* Transmit Diversity - Used when transmitting through a single antenna. Transmits out of the diversity antenna where the best amplitude signal was last heard.
MIMO Antenna diversity - More sophisticated
* Multiple Input, Multiple Output allows for receiving and transmitting using multiple antennas concurrently.
59
What is the Spread Spectrum?
| Lect 6
Spread Spectrum is a technology that spreads the RF signal across more bandwidth than necessary for the size of the data.
Spread spectrum technologies include:
* FHSS (Frequency Hopping Spread Spectrum)
* DSSS ( Direct-Sequence Spread Spectrum)
* HR-DSSS (High Rate DSSS)
* OFDM (Othogonal Frequency-Division Multiplexing)
60
What are the advantages of Spread Spectrum technology?
| Lect 6
* More resistant to interference
* Harder for threat actors to pick up transmissions
* Resistant to fading
61
How does frequency hopping work?
| Lect 6
Frequency hopping break up full bandwidth communication into a number of channels. The signal hops between these established chanels in a random sequence only shared between the transmitter and the receiver.
62
Modulation Examples
| Lect 6
63
What Modulation methods does WiFI use?
| Lect 6
*** PSK (Phase Shift Key)**
* Quadrature PSK (QPSK)
* Binary PSK (BPSK)
*** QAM (Quadrature Amplitude Modulation)**
* 16-QAM
* 64-QAM
* 256-QAM introduced with 802.11ac radios
* 1024-QAM introduced with 802.11ax (Wi-Fi 6)radios
64
What is coding?
| Lect 6
Coding is the conversion of data bits into a series of symbol bits.
Adds redundancy to the bit stream to minimize errors and maximize data recovery.
65
What are ISM Bands?
| Lect 6
ISM Bands are portions of the radio spectrum reserved internationally for industrial, scientific, and medical purposes.
ISM Bands are licence free.
Devices and services that operate inside of ISM bands include:
* Bluetooth devices
* Cordless phones
* Garage Door openers
* Microwaves
* Wi-Fi
* Baby Monitors
66
What hz levels do ISM bands operate on?
| Lect 6
ISM Bands use
* 902MHz to 928mhz
* 2.4GHz to 2.5GHz
* 5.725GHz to 5.875GHz
* 6GHz (WIfi 6)
* 60GHz (not widely supported)
67
Compare and contrast different Wireless Networking Topologies.
| Lect 7
* WWAN (Wireless Wide Area network) - Covers large geographical areas using wireless medium. Used by cellphone companies.
* WMAN (Wireless Metropolitan Area Network) provides RF coverage to a smaller metropolitan area.
* WPAN (Wireless Personal Area Network) Wireless network used for communication between devices within a close proximity to a user. (bluetooth and infared)
* WLAN (Wireless Local Area Network) Wireless netowrking for a building / campus environment.
68
What are 802.11 Stations?
| Lect 7
Stations are the main components of a wireless network , also known as radios.
Stations can either reside inside of a wireless access point (AP Station) or on a client device (client station)
Client stations refer to any radio that is not used in an access point. They must contend for the half-duplex RF medium in the same way that an AP does. If a client station has a layer 2 connection, they are known as associated stations.
AP stations function as a wireless portal for other client stations to communicate over. The portal functionality is what differentiates clients and AP sations.
69
What are 802.11 Service Sets?
| Lect 7
802.11 topologies are also known as service sets. They describe how radios can be used to communicate wityh each other.
802.11 topologies include:
* basic service set (BSS)
* extended service set (ESS)
* independent basic service set (IBSS)
* personal basic service set (PBSS)
* mesh basic service set (MBSS)
* QoS basic service set (QBSS)
70
What are SSIDs?
| Lect 7
SSIDs (Service Set Identifiers) are logical names used to identify a wireless network.
The SSID network name is comparable to a workgroup name.
SSIDs can have up to 32 characters and are case sensitive.
71
Describe the Basic Service Set and Basic Service Area.
| Lect 7
The Basic Service Set is the cornerstone topology of an 802.11 network.
Topology consists of one AP with one or more client stations. Stations that are members of the BSS are associated ( have a layer 2 connection)
The physical area of coverage provided by an AP in a BSS is known as the Basic Service Area. client stations can move throughout the BSA and maintain communications with the AP as long as communications remain above RSSI thresholds.
The MAC address of an AP is known as the Basic Service Set Identifier (BSSID).
72
Describe Extended Service Sets.
| Lect 7
Extended Service sets are 2 or more identically configured BSDs connected by a distribution system medium (DSM)
ESS are usually a collection of multiple access points united by a single DSM (which is usually an ethernet connection)
73
What are Distribution Systems?
| Lect 7
Distribution Systems are used to interconnect sets of BSS via integrated LANs to create an ESS.
Usually connected with physical media, but Wireless Distribution Systems exist too.
74
Compare and contrast ESS Seamless and Nomadic roaming.
| Lect 7
Seamless roaming exists when ESS accesspoints have overlapping coverage. This allows devices to freely move between coverage areas without an interruption in service.
Nomadic roaming exists when coverage areas are disjointed. In between coverage areas your devices will lose connectivity.
75
Compare and contrast different Service Sets (topologies)
| Lect 7
* Independent BSS - No AP, only client stations. Connected using crossover cables.
* Personal BSS - Same as an Independent BSS but uses wireless technology.
* Mesh BSS - Used to provide wireless distribution of network traffic, and APs provide mesh distribution to devices. Devices connected to the distribution frame are known as mesh gates, and provide access to the networok.
* QoS BSS - QoS additions can be included in service sets.
76
Compare and contrast different AP configuration modes.
| Lect 7
Root Mode - AP is set up as a gateway portal to a wired network.
Mesh Mode - AP is used as a wireless backhaul station for a mesh environment.
Sensor Mode - AP is integrated into a wireless intrusion detection system. Set to a continuous listening state while scanning multiple channels.
Bridge Mode - Used as a wireless bridge, which adds MAC layer intelligence to the AP.
Workgroup Bridge Mode - Used to assist 802.3 wired clients.
Client Mode - Functions as a client device that can associate to other APs. Used for troubleshooting.
77
What are the two client configuration modes?
| Lect 7
1. Infrastructure Mode - Allows for communication via an AP. allows for the client station to participate in a BSS or an ESS
2. Ad Hoc / Peer-To-Peer Mode - Participate in an IBSS topology and do not communicate via an Access Point.
78
What are the 2 sublayers of the 802.11 Data-Link Layer?
| Lect 9
The upper section of the Data-Link layer is the Logical Link Control (LLC) sublayer.
The Lower section is the Media Access Control (MAC) layer.
79
Describe MSDUs and MPDUs
| Lect 9
MAC Service Data Units (MSDUs) are data sent up from the LLC layer to the MAC layer. Contains the IP packet and some data from the LLC.
Mact Protocol Data Units (MPDUs) are MSDUs with the MAC header information attached to them. Also known as 802.11 frames.
80
What the the main components of MPDUs?
| Lect 9
* MAC Header - contains Frame Control Information, duration information, MAC addressing, sequence control, QoS control information, and HT information.
* Frame Body - Contains the MDSU Payload, and different information depending on the frame.
* Trailer - Contains the frame check sequence, as well as the 32 bit cyclic redundancy check. Used for frame validation.
| `
81
What different types of 802.11 frames exist?
| Lect 9
82
What different types of MAC addresses can be found in 802.11 frames?
| Lect 9
* Source Addresses (SA) MAC of the original sending station.
* Destination Address (DA) MAC of the final destination of the Layer 2 frame.
* Transmitter Address (TA) - MAC address of the 802.11 radio that is transmitting the frame.
* Reciever Address (RA) - MAC address of the 802.11 radio that is intended to recieve the incoming transmission.
83
What are the 14 management frame subtypes?
| Lect 9
* Association request
* Association response
* Reassociation request
* Reassociation response
* Probe request
* Probe response
* Beacon
* ATIM
* Disassociation
* Authentication
* Deauthentication
* Action
* Action No ACK
* Timing advertisement
84
How do different frame type bodies differ from each other?
| Lect 9
* Data frames are the only frames that carry an upper layer MSDU
* Management frames are used by wireless stations to join and leave a BSS, however they do not carry the upper-layer information.
* Control frames are used to clear and acquire the channel, while also providing unicast frame acks. Because of this, there is no body in a control frame.
85
What is the difference between active and passive scanning?
| Lect 9
Scanning is the process of a station discovering APs.
A station can discover APs by either listening for an AP (passive) or searching for an AP (active)
Passive scanning is the process of listening for becon frames being transmitted by APs .
Actie scanning involves transmitting management probe frames out for APs to accept.
86
What are the components of beacon frames?
| lect 9
Beacon frames contain information for a client station to learn about the parameters of a BSS before joining.
They are transmitted to APs 10 times per second.
87
How does active scanning work?
| Lect 9
Active scanning enhances the discovery process by using probe requests.
The two types of probe requests that exist are null and directed.
Null probe requests contain no SSID information, and look for any open AP accepting devices without authentication.
Directed probe requests contain SSID information for connecting to a specific BSS.
88
What is the process of Authentication and Association?
| Lect 9.
Both authentication and association need to ocur before an 802.11 client can pass traffic through the AP to another device.
Authentication is the first step in this process, and occurs using SSIDs.
After authentication, the station needs to be associated with an AP. When association occurs, a client device becomes a memeber of the BSS, and has established Layer 2 connectivity with the AP.
89
What is the difference between basic and supported rates?
| Lect 9
Basic rates are the minimum required data rate that an AP needs to be able to communicate using.
Supported rates are all rates that an AP is able to use, which can either be above or below the basic rate.
however, if a client station is not capable of communicating with all of the basic rates, association with the AP will not occur.
90
What are the 12 Control frame subtypes?
| Lect 9
* Beamforming report poll
* HT NDP announcement
* Control frame extension
* Control wrapper
* Block ACK request (BAR)
* Block ACK (BlockAck)
* Power save-poll (PS-Poll)
* Request-to-send (RTS)
* Clear-to-send (CTS)
* Acknowledgment (ACK)
* Contention Free-End (CFEnd) CF-End + CF-ACK
91
What two forms of medium contention are heavily used today?
| Lect 8
*** Carrier Sense Multiple Access with Collision Detection (CSMA/CD)**
CSMA/CD is used mainly in Ethernet networks due to the ability to hear collisions in Ethernet cable.
* Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA)
Used in Wifi, it is not capable of detecting colissions. Used by 802.11 for wireless connection.
92
What are some characteristics of CSMA/CA?
| Lect 8
* Carrier sense determines whether the medium is busy.
* Multiple access ensures that every radio gets a fair shot at the medium (but only oneat a time).
* Collision avoidance means only one radio gets access to the medium at any given time, hopefully avoiding collisions.
93
What is the benefit of using PoE in a wireless network?
| Lect 12
Using PoE (Power Over ethernet) in a wireless network reduces the cost and increses the flexibility of installing APs and other network devices.
By not requiring seperate electrical and network cabling to be installed, installation of APs in different locations can be done. Also does not require electricians and network technicians to be called for AP installations.
94
Compare and describe some different PoE Standards.
| Lect 12
95
What are the 2 types of devices defined by PoE standards?
| Lect 12
1. Powered Devices
Powered devices are systems that require power from the Power Sourcing Endpoints. This is achieved either through data lines, or unused pairs.
2. Power Sourcing Endpoints (PSE)
A PSE proivdes power and ethernet connections from the same device. These are typically PoE enabled switches, but can also be WLAN controllers, branch routers, or wall plate APs.
96
What are the 8 classes and 4 types of PoE devices?
| Lect 12
## Footnote
When no class is detected, a device is considered Class 0
97
What are the three typical ways of providing power to a PD?
| Lect 12
1. The device is directly conneted to an PoE enabled switch which is providing both Ethernet and power.
2. The device is connected to a multi-port PSE referred to as an inline patch panel which provides power, and through the patch panel is connected to the switch.
3. A single port power injector is used to provide power in between a device and a switch. This power injector is then plugged directly into a wall outlet.
98
What are the functions of the management plane within an 802,11 WLAN?
| Lect 11
The management plane governs:
* WLAN configuration
* WLAN monitoring and reporting
* WLAN firmware management
99
What are the functions of the control plane in an 802.11 WLAN?
| Lect 11
Some functions of the control plane in a WLAN include:
* Adaptive RF
* Roaming mechanisms
* Load balancing between APs
* Mesh Protocols for Layer 2 routing.
100
What are the functions of the data plane in an 802.11 WLAN?
| Lect 11
The data plane governs forwarding user data.
* A standalone AP handles all data forwarding aplications locallly.
* If a WLAN controller exists in the BSS, data is normally forwarded from the WLAN controller, but can also be forwarded from APs.
101
What are the 4 types of WLAN architectures?
| Lect 11
* Autonomous
* Centralized
* Distributed
* Hybrid
102
Describe autonomous WLAN architecture.
| Lect 11
Autonomous WLAN architecture uses legacy autonomous APs.
Management, control, and data planes are all at the edge of the network.
* Management - All devices have to be managed individually.
* Control - No shared intelligence between APs. Control plane mechanisms were limited.
* Data - Forwarded at the edge of the network despite the lack of widespread support for VLANs at the time.
103
Described Centralized WLAN architecture.
| Lect 11
This architecture uses WLAN controllers and controller based APs
Management, control and data planes are all centralized on a WLAN controller.
* Management - All devices managed and monitored from the central controller.
* Intelligence centralized within the WLAN controller. Controle plane mechanisms exist within the controller as well.
* Data - The WLAN controller acts as a data distrobution point for user traffic. APs tunnel all user traffic to the central controller.All 802.11 user traffic is encapuslated in an IP tunnel between APs and the controller.
104
Describe Distributed WLAN architecture.
| Lect 11
This is the growing standard for WLAN architecture. Multiple access points are combined with a suite of cooperative protocols without needing to use a centralized WLAN controller.
The management plane remains centralized, while the control and data planes reside on the edge of the network.
* Management - All APs and clients are managed and monitored through a NEtowkr Management Server (NMS), and could be cloud / web based.
* Control - Cooperative protocols allow multiple APs to share control plane information and provide control mechanisms.
* Data - All data is forwarded locally by APs. Only management traffic exists between APs and the NMS. all VLANs reside at the edge of the network, and .1Q trunks may be required between access points and access layer switches.
105
What are Enterprise WLAN Branch Routers used for?
| Lect 11
Very similar to consumer grade Wi-Fi routers.
Enterprise routers are just bgetter quality and offer more robust security features as well. as 4g security and VPNs.
106
What are WLAN Mesh access points used for?
| Lect 11
WLAN Mesh APs are able to communicate with other APs using Layer 2 routing protocols to create a self healing infrastructure.
THe main purpose of mesh WLANs is to provide wireless client access in areas where ethernet cables can't be connected to APs.
107
How are different GHz radios used in a WLAN mesh network?
| Lect 11
When a mesh network is using Dual-band APs, the different GHz radios are used for different purposes.
The 5Ghz radio is used for the mesh backhaul, which allows the connection to other meshed APs.
The 2.4GHz radio is used for client access.
108
How are WLAN bridges used?
| Lect 11
WLAN bridges exist to connect 2 wired networks over long distances when no cabling infrastructure can be placed between them.
109
Compare root and nonroot WLAN bridge configuration methods.
| Lect 11
Root bridges establish the channel and beacons for the nonroot bridge to join.
The nonroot bridge associates with the root bridge to establish the link.
Point to Point bridge links are links between 2 wires networks only.
Point to Multipoint bridge links exist with a central root bridge, and multiple non-root bridges.
110
What are the components of a VoWiFi solution?
| Lect 11
VoWiFi consists of:
* VoWiFi telephones - use 802.11 connections instead of cellular or wired connections.
* APs and Controlllers
* PBX - Private Brance Exchanges (PBX) are telephone exchange servers used in a particular area. The PBX provides common telephony features sucha s dial tone and voice mail. Can also facilitate connections to a PSTN.
* WMM Support
111
Compare and contrast 802.11n and 802.11ac (High throughput vs Very High throughput)
| Lect 12
112
Compare and contrast basic communication modes.
| Lect 12
113
How does MIMO Spatial Stream work?
| Lect 12
MIMO radios are capable of sending unique independent streams of modulated data.
Each stream of data is known as a spatial stream, and each stream can contain different data than the other independent streams.
Each stream also travels down it's own path due to the need for at least half a wavelength of space between multiple transmitting antenna.
This allows for higher throughput due to the use spatial multiplexing.
114
What is the syntax for MIMO capabilities?
| Lect 12
MIMO uses a 3 number syntax, with each number standing for a different portion of MIMO's capabilities.
The first number always references transmitters, and the second references recievers. The last number represents how many spacial streams of data can be sent and recieved.
115
Describe Multi User MIMO technology.
| Lect 12
Multi user MIMO allows for downstream communications from an AP to multiple clients.
This changes the MIMO syntax to append 2 new numbers, one for the Multi-user Group, and one for the Multi-user streams.
The benefits of MU-MIMO include:
* INcrease network capacity and throughput
* Reduced latency
* Increased spectral efficiency
* Simpler, and cheaper clients.
116
Throwing in the 802.11ac modulation table for ref
| lect 12
117
Throwing in the 802.11ac data rate table for ref
| Lect 12
