2.3 Compare & contrast protocols for wireless networking

Question 1

2 main RF bands used by 802.11 standards?

Answer 1

• 2.4GHz
• 5GHz

Question 2

What benefit does 2.4GHz RF band have over 5GHz?

Answer 2

Better signal penetration, giving it longer signal range

Signal penetration = ability of a signal to pass through obstacles like walls, floors, or building

Question 3

3 Downsides to 2.4GHz RF band?

Answer 3

• Limited channels
• Prone to congestion & interference
• Lower max data rates than 5GHz

Question 4

3 examples of wireless technologies that congest the 2.4GHz RF band?

Answer 4

• Wi-Fi networks
• Bluetooth
• Microwaves

Along with many others

You’ll likely need to memorize these specific examples for the exam

Question 5

Downside of 5GHz RF band compared to 2.4GHz?

Answer 5

Worse signal penetration, giving it less signal range

Question 6

What is the tradeoff with 5GHz?

Answer 6

Supports higher data rates at shorter ranges

Question 7

Why does 5GHz have higher data rates than 2.4GHz?

Answer 7

Supports more individual channels & is less congested

less congestion = less interference

Question 8

Nominal indoor range for Wi-Fi over 2.4GHz?

Answer 8

45m (150 feet)

Question 9

Nominal indoor range for Wi-Fi over 5GHz?

Answer 9

30m (100 feet)

Question 10

At what distances are clients able to connect to Wi-Fi at full speed?

This applies to both 2.4GHz & 5GHz

Answer 10

At 1/3 to a 1/2 of a RF’s max range

This depends on the wireless standard, building features, and interference from other radio sources.

Question 11

6 IEEE 802.11 standards?

Answer 11

• a
• b
• g
• n
• ac (Wi-Fi 5)
• ax (Wi-Fi 6)

Question 12

What RF band does 802.11a use?

Answer 12

5GHz

Question 13

Data rate of 802.11a?

Answer 13

Up to 54Mbps

Question 14

How many non-overlapping channels does 5GHz RF band have?

Answer 14

23

Question 15

How wide is each channel in 5GHz RF band?

Answer 15

20MHz

Question 16

What do regulatory requirements dictate for the use of 5GHz?

Answer 16

• Channels permitted for Wi-Fi & other purposes
• Power output of Wi-Fi devices operating in the band

The limites on power output may impace the range of Wi-Fi devices

Question 17

Why must devices in the 5GHz RF band implement DFS?

DFS = Dynamic Frequency Selection

DFS is a mechanism & is a regulatory requirement in many countries for Wi-Fi devices operating in 5GHz & other certain RF bands

Answer 17

It requires Wi-Fi devices to detect & avoid using frequencies used by radar systems

This ensures Wi-Fi coexistence with critical communication systems.

Question 18

When does a Wi-Fi device with DFS disable a Wi-Fi channel?

Answer 18

If it detects radar signals on that channel

Question 19

What RF band does 802.11b use?

Answer 19

2.4GHz

Question 20

Data rate of 802.11b?

Answer 20

Up to 11Mbps

Question 21

How many channels does 2.4GHz RF band have?

Answer 21

14 channels

Question 22

How are each channels in the 2.4GHz RF band spaced at?

Answer 22

5MHz

Meaning each channel would be 5MHz higher in frequency than the previous one (it starts from a base frequency of 2,412MHz , so the next channel would be at 2,417MHz, & so on)

Question 23

What is the 2.4GHz RF band’s frequency range?

Answer 23

2,412-2,484MHz

Question 24

Why do 802.11b channels overlap quite considerabely?

Answer 24

Spacing is only 5MHz & Wi-Fi needs 20MHz channel bandwidth

If you use Channel 2 (2,417MHz to 2,437MHz) in the 2.4GHz band, it overlaps with both Channel 1 (2,412MHz to 2,432MHz) and Channel 3 (2,422MHz to 2,442MHz). Interference can occur if nearby Wi-Fi networks are on Channels 1 or 3.

Question 25

Which channels in the 2.4GHz RF band has the least overlap?

Answer 25

1, 6, & 11 | These will suffer the least with interference

Question 26

What 2.4GHz RF brand channels are permitted in the Americas?

Answer 26

1-11

Question 27

What 2.4GHz RF band channels are permitted in Europe?

Answer 27

1-13

Question 28

What 2.4GHz RF band channels are permitted in Japan?

Answer 28

14 (All channels)

Question 29

What RF band does 802.11g use?

Answer 29

2.4GHz

Question 30

Data rate of 802.11g?

Answer 30

Up to 54Mbps

Question 31

What RF band does 802.11n use?

Answer 31

2.4GHz & 5GHz

Question 32

How is each RF band in 802.11n (2.4 & 5GHz) implemented?

Answer 32

By 2 distinct radio transceivers

Question 33

When is an AP or adapter considered "dual-band"

Answer 33

When it can support simultaneous 2.4GHz & 5GHz operations ## Footnote Cheaper client adapters & many smartphone adapters support only a 2.4GHz radio

Question 34

Which 802.11 standard introduced channel bonding? ## Footnote Channel bonding allows more data to be transmitted at once, potentially increasing the overall throughput of the Wi-Fi network

Answer 34

802.11n

Question 35

How does channel bonding in 802.11n work? ## Footnote Channel bonding allows more data to be transmitted at once, potentially increasing the overall throughput of the Wi-Fi network

Answer 35

Combining 2 adjacent 20MHz channels into a single 40MHz channel

Question 36

Which RF band is better suited for channel bonding?

Answer 36

5GHz ## Footnote 2.4GHz should not be used for channel bonding due to its restricted channel layout

Question 37

Which 802.11 standard introduced MIMO? | MIMO = Multiple Input Multiple Output

Answer 37

802.11n

Question 38

What does MIMO do? | MIMO = Multiple Input Multiple Output

Answer 38

Increases reliability & bandwidth by merging signal streams from 2-3 antennas

Question 39

3 common MIMO notations?

Answer 39

- 1x1 - 2x2 - 3x3

Question 40

What do MIMO notations describe?

Answer 40

The number of transmit & receive anteannas ## Footnote **1x1** means there is 1 transmit antenna & 1 receive antenna **3x3** means there are 3 transmit antennas & 3 receive antennas

Question 41

Data rate of 802.11n?

Answer 41

Up to 72Mbps per stream or 150Mbps per stream for a 40MHz bonded channel

Question 42

What naming convention is used to market 802.11n APs?

Answer 42

Nxxx | The ***N*** represents 802.11n ## Footnote i.e. N600

Question 43

What does ***xxx*** signify in the 802.11 AP naming convention? ## Footnote i.e. Nxxx, ACxxx, AXxxx

Answer 43

Combined throughput of all radios

Question 44

What does it mean if an 802.11n AP is marketed as an N600 2x2?

Answer 44

It can allocate a bonded channel & 2 streams for a data rate of 300Mbps ## Footnote If it does this simultaneously on both its 2.4GHz & 5GHz radios, the bandwidth of the AP could be described as 600Mbps

Question 45

What is 802.11n aka?

Answer 45

Wi-Fi 4

Question 46

What is 802.11ac aka?

Answer 46

Wi-Fi 5

Question 47

What is 802.11ax aka?

Answer 47

Wi-Fi 6

Question 48

What RF band does 802.11ac (Wi-Fi 5) use?

Answer 48

5GHz

Question 49

How many radios does a tri band AP have?

Answer 49

1 2.4GHz radio & 2 5GHz radios

Question 50

How many streams does 802.11ac (Wi-Fi 5) support?

Answer 50

Up to 8 streams

Question 51

What MIMO notation do most 802.11ac (Wi-Fi 5) APs support?

Answer 51

4x4 streams ## Footnote (or lower). Most APs dont support the amount of streams that Wi-Fi 5 can support (Wi-Fi 5 supports up to 8 streams)

Question 52

Data rate for Wi-Fi 5 (802.11ac) with a single stream over an 80MHz channel?

Answer 52

Up to 433Mbps

Question 53

What are the bonded channel options for Wi-Fi 5?

Answer 53

80 & 160MHz ## Footnote You can bond 2 adjacent 40MHz channels for an 80MHz channel, or 4 adjacent 40MHz channels for a 160MHz channel. However, not all devices or environments may support or benefit from 160MHz channels due to interference and compatibility issues.

Question 54

What does it mean when 802.11 operations have shared bandwidth?

Answer 54

APs can only communicate with 1 station (device) at a time | Multiple station requests go into a queue (just like a hub)

Question 55

What 802.11 standard introduced MU-MIMO? | MU-MIMO = MultiUser MIMO (Multiple Input Multiple Output)

Answer 55

802.11ac (Wi-Fi 5)

Question 56

How does DL MU-MIMO partially address the problem of shared bandwidth? | DL MU-MIMO = DownLink MultiUser MIMO (Multiple Input Multiple Output)

Answer 56

Allows AP to send data to up to 4 clients simultaneously using multiple antennas

Question 57

Data rate for 802.11ax (Wi-Fi 6) over an 80MHz channel?

Answer 57

Up to 600Mbps

Question 58

What RF band does 802.11ax use?

Answer 58

2.4 & 5GHz

Question 59

How does Wi-Fi 6e differ from Wi-Fi 6?

Answer 59

Adding support for 6GHz RF band

Question 60

What is the tradeoff with Wi-Fi 6e's 6GHz RF band?

Answer 60

Has less range but more frequency space | This makes it easier to use 80 & 160 MHz channels

Question 61

How many clients can Wi-Fi 5 (802.11ac) serve simultaneously?

Answer 61

Up to 4 | (using MU-MIMO in the downlink direction)

Question 62

How many clients can Wi-Fi 6 (802.11ax) serve simultaneously?

Answer 62

Up to 8

Question 63

Which 802.11 standard adds support for uplink MU-MIMO?

Answer 63

802.11ax (Wi-Fi 6)

Question 64

What does uplink MU-MIMO do?

Answer 64

Allows MU-MIMO-capable clients to send data to the AP simultaneously

Question 65

Which 802.11 standard introduced OFDMA? | Orthogonal Frequency Division Multiple Access

Answer 65

802.11ax (Wi-Fi 6)

Question 66

Why does 802.11ax use MU-MIMO & OFDMA? ## Footnote (MU-MIMO = Multiuser Multiple Input Multiple Output) (OFDMA = Orthogonal Frequency Division Multiple Access)

Answer 66

To improve client density ## Footnote This means sustatining high data rates when more stations are connected to the same AP

Question 67

Meaning of SSID?

Answer 67

Service Set Identifier

Question 68

How long can SSIDs be?

Answer 68

32 bytes

Question 69

What ASCII characters should be used for SSIDs?

Answer 69

- Numbers - Letters - `+` (Plus) - `-` (Minus) - `_` (Underscore) | These should be used to avoid compatibility issues

Question 70

What happens if the same SSID is used for both RF bands in AP configuration?

Answer 70

The AP and client device search for the band with the strongest signal

Question 71

What happens if different names are configured for both RF bands in AP configuration? | (2.4GHz & 5GHz)

Answer 71

User can choose which network & band to use

Question 72

What is long-range fixed wireless?

Answer 72

Wireless technology commonly used to bridge 2 networks

Question 73

How does P2P LoS fixed wireless create a direct link between 2 locations? | (P2P = Point to Point) (LoS = Line of Sight) ## Footnote This is a specific type of fixed wireless communications

Answer 73

Using precisely aligned high-gain microwave antennas | "high-gain" means the antenna is strongly directional

Question 74

What is the max range for a P2P LoS fixed wireless link? | WITHOUT OBSTRUCTION BY PHYSICAL OBJECTS!

Answer 74

30 miles

Question 75

Where are antennas in a P2P LoS fixed wireless link typically placed?

Answer 75

Top of tall building/poll | This reduces the risk from obstructions

Question 76

How can long-range fixed wireless be implemented?

Answer 76

Using licensed or unlicened frequency spectrum

Question 77

What does a Licensed frequency spectrum mean?

Answer 77

Network operator buys exclusive RF band rights from regulator | Network operator means entity/org managing a telecom network. i.e. ISP ## Footnote The US regulator is the Federal Communications Commision (FCC). If any interferense sources are discovered, the network operator has the legal right to get them shut down

Question 78

What does an Unlicensed frequency spectrum mean?

Answer 78

Operator uses a public RF band | Network operator means entity/org managing a telecom network. i.e. ISP

Question 79

What must operators adhere to when operating in unlicensed spectrum?

Answer 79

Regulatroy power limitations

Question 80

Data rate of bluetooth?

Answer 80

Up to 3Mbps | Depending on Bluetooth version

Question 81

What speeds can Bluetooth adapters supporting version 3 or 4 achieve?

Answer 81

Up to 24Mbps

Question 82

How do Bluetooth adapters supporting version 3/4 achieve a 24Mbps data rate?

Answer 82

They can negotiate an 802.11 radio link for large file transfers

Question 83

What variant did Bluetooth 4 introduce?

Answer 83

Bluetooth Low Energy (BLE)

Question 84

What is Bluetooth Low Energy (BLE) designed for?

Answer 84

Small low-power devices transmitting small data infrequently | i.e. Fitness trackers, smart locks, asset tracking tags, etc.

Question 85

is BLE backwards compatible with "classic" Bluetooth? | BLE = Bluetooth Low Energy

Answer 85

No

Question 86

Can a device support Bluetooth & BLE simultaneously? | BLE = Bluetooth Low Energy

Answer 86

Yes

Question 87

Meaning of RFID?

Answer 87

Radio Frequency ID

Question 88

What is RFID?

Answer 88

Means of identifying & tracking objects using encoded tags

Question 89

What happens when a RFID reader scans a tag?

Answer 89

Tag responds with the information programmed into it

Question 90

What does it mean when an RFID tag is passive?

Answer 90

It only responds when scanned at close range | Up to about 25m

Question 91

How far can an active RFID tag be read from? | (powered)

Answer 91

100m (328 feet)

Question 92

What type of RFID tags can be embedded in stickers/labels?

Answer 92

Passive RFID tags ## Footnote RFID is also used to implement some types of access badge to operate electronic locks

Question 93

Meaning of NFC?

Answer 93

Near-Field Communication

Question 94

What does it mean that NFC is a P2P version of RFID?

Answer 94

NFC devices can function as tags & as readers | Allowing them to exchange data with other NFC-enabled devices

Question 95

What are the data rates of NFC?

Answer 95

- 106 Kbps - 212 Kbps - 424 Kbps