Gjermunds WiFI Quizzle 1

I made a Kahoot challenge last week. But because of different subscription models only 20 could attend. The winner in that challenge had 8 correct answers out of 10 questions.

I make this blog with the same challenge so everyone who wishes can test themself.

First is the 10 question, each with 4 options.
Then the same 10 questions with the correct answers, and some explanation

Question 1
What is the center frequency of channel 64?

a- 5300 MHz
b- 5320 MHz
c- 5400 MHz
d- 5360 MHz

Question 2
How many data subcarriers is there on a 20MHz HT or VHT data transmission?

a- 48
b- 64
c- 52
d- 56

Question 3
In which frame in the 4-way handshake is the S-Nounce been transferred?

a- 1
b- 2
c- 3
d- 4

Question 4
What is the duration of the SIFS in the 5 GHz band?

a- 9 microsecond
b- 43 microsecond
c- 10 microsecond
d- 16 microsecond

Question 5
What is the spacing between each subcarrier with OFDM, HT and VHT

a- 312,5 KHz
b- 78,125 KHz
c- 312 KHz
d- 320 KHz

Question 6
With 256-QAM modulation, how many bits does each data subcarrier transfer?

a- 4
b- 6
c- 8
d- 10

Question 7
In a Beacons RSN IE, under Authentication Key Management (AKM), the value is 00-0F-AC-03. What is the authentication method?

a- 802.1X
b- PSK
c- FT over 802.1X
d- Open

Question 8
When receiving a Compressed Block Acknowledgment, what is the usual size of the Bitmap?

a- 24 bytes
b- 10 bytes
c- 128 bytes
d- 8 bytes

Question 9
A VHT dataframe is sent in 20 MHZ, 64-QAM, 5/6 coding and 1 spatial stream. Aka MCS7. What is the throughput?

a- 72,2 Mb/s
b- 144,4 Mb/s
c- 86,7 Mb/s
d- Impossible to predict

Question 10
A transmitter sends two spatial streams. On a 2×2;2 receiver, how many spatial streams are received on each antenna chain?

a- 0
b- 1
c- 2
d-3

################################################################

With correct answers and some explanation

Question 1
What is the center frequency of channel 64?

a- 5300 MHz
b- 5320 MHz
c- 5400 MHz
d- 5360 MHz

My rules of tumb: The channel number multiplied with 5 + 5000 (in MHz)
64×5 = 320. 320+5000= 5320 MHz, or 5,32 GHz

Question 2
How many data subcarriers is there on a 20MHz HT or VHT data transmission?

a- 48
b- 64
c- 52
d- 56

It is 52 data subcarriers in a HT and VHT transmission at 20 MHz.
It is 48 data subcarriers in a OFDM (and ERP) transmission
It is 64 subcarriers on the full 20MHz OFDM, HT and VHT (and ERP) channel

Question 3
In which frame in the 4-way handshake is the S-Nounce been transferred?

a- 1
b- 2
c- 3
d- 4

The Supplicant Nounce is been transferred to the AP in frame number 2 in the 4-way handshake

Question 4
What is the duration of the SIFS in the 5 GHz band?

a- 9 microsecond
b- 43 microsecond
c- 10 microsecond
d- 16 microsecond

The SIFS (short Interframe Space) in the 5GHz band is 16 microsecond
The slot time in the 5GHz band is 9 microsecond. It can also be the slot time in the 2.4GHz band
The SIFS in the 2.4GHz band is 10 microsecond
The AIFS (Arbitration Inter-Frame Spacing) for access category Best Effort is, by the standard, 43 microsecond

Question 5
What is the spacing between each subcarrier with OFDM, HT and VHT

a- 312,5 KHz
b- 78,125 KHz
c- 312 KHz
d- 320 KHz

The subcarrier spacing with OFDM, HT and VHT (and ERP) is 312,5 Khz
The subcarrier spacing with HE (802.11ax) is 78,125 KHz

Question 6
With 256-QAM modulation, how many bits does each data subcarrier transfer?

a- 4
b- 6
c- 8
d- 10

With QAM the transferred bits value is expressed with a mathematical vector. With 256-QAM we have 16 values (4 bits) to express the real part (X-axis) and 16 values (4 bits) to express the imaginary part (Y-axis). Therefore 8 bits

Question 7
In a Beacons RSN IE, under Authentication Key Management (AKM), the value is 00-0F-AC-03. What is the authentication method?

a- 802.1X
b- PSK
c- FT over 802.1X
d- Open

00-0F-AC-03 is the value for FT over 802.1X authentication
00-0F-AC-01 is the value for 802.1X authentication
00-0F-AC-02 is the value for PSK authentication
With Open Authentication there is no RSN IE in the Beacon

Question 8
When receiving a Compressed Block Acknowledgment, what is the usual size of the Bitmap?

a- 24 bytes
b- 10 bytes
c- 128 bytes
d- 8 bytes

With Compressed Block Ack the Bitmap is 8 bytes, 64 bits
Normal Block Ack has a bitmap of of 128 bytes (64×16 bits)

Question 9
A VHT dataframe is sent in 20 MHZ, 64-QAM, 5/6 coding and 1 spatial stream. Aka MCS7. What is the throughput?

a- 72,2 Mb/s
b- 144,4 Mb/s
c- 86,7 Mb/s
d- Impossible to predict

If I had asked about the data rate, the correct answer would have been 72,2 Mb/s
But I asked about the throughput and it is impossible to predict

Question 10
A transmitter sends two spatial streams. On a 2×2;2 receiver, how many spatial streams are received on each antenna chain?

a- 0
b- 1
c- 2
d-3

Even if the different spatial streams is sent from different antenna chains at the transmitter, each and every antenna chain on the reciever will receive everything in the air. And the receiver uses mathematics to separate the different spatial streams

One thought on “Gjermunds WiFI Quizzle 1

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s