A Wireless LAN Cisco engineer is troubleshooting 802. 11ac WLAN at customer site Doe to interferences with neighboring 802 11n networks the engineer must determine the current primary secondary channel allocation to enhance the current configuration. Channel 60 has been chosen by the customer as primary 20 MHz channel. Which combination determines the resulting primary 40 MHz and primary 80 MHZ channels?
A. primary 40 MHz channel 62, primary 80 MM: channel 58
B. primary 40 MHz channel 54, primary 80 MHz channel 58
C. primary 40 MHz channel 64, primary 80 MHz channel 60
D. primary 40 MHz channel 60, primary 80 MHz channel 56
All HT/VHT would be on same primary channel. So:
A&B: wrong. ch58,ch62 – not available channels,overlapping. Available – ch52,ch56,ch60,ch64 – and mixture, they are not overlapping in 20Mhz.
C: wrong, while primary channel for 20Mhz and 40Mhz – the same, ch60
D: that’s most possible but still ambiguous. Primary 40 channel should be 60(secondary 40 = ch64), that’s correct. I can’t figure out exactly why is Primary 80 it ch 56 – it’s either typo and shall be same 60, then secondary 40 will be ch52 & ch56, or it’s an inverted channel with primary 20 ch 56, secondary 20 ch 52 and secondary 40 ch 60 & ch 64.
The best coexistance is primary misaligned P20 on S40, so it fit somehow… But still doesn’t fit to same primary 20 for HT and VHT.
Refer to: https://www.cisco.com/c/en/us/td/docs/wireless/controller/technotes/8-3/b_RRM_White_Paper/b_RRM_White_Paper_chapter_0100.html#id_15165
So, I think D is the closest to be “correct”.
If we use another article (NON-Cisco), there are such channels as 58,62 for 40MHz and 80 MHz channels. So I thimk I’m wrong about D. Let it be A.
http://www.revolutionwifi.net/revolutionwifi/2013/03/80211ac-channel-planning.html
A. Its correct!
Search on google images “5 GHz channel width” to see the full channels numbers and understand the allocations of the 40 MHz, 80 MHz and 160 MHz.
Width 20 = Channel 60
Width 40 = Use channels 60 and 64 => Channel 62
Width 80 = Use channels 54 and 62 => Channel 58
Width 160 = Use channels 42 and 58 => Channel 50