While analyzing wireless packet capture traces using wireshark, bandwidth was represented as 20 MHz, channel 1/4. On searching about this, I found this means 20 LL(lower lower) and total bandwidth of 20 LL is 80 MHz. The trace was taken on channel 36, so how were lower channels used for channel aggregation to 80 MHz?
I had searched the links mentioned below for the same :
The first link mentions that meaning of 20 MHz, channel 1/4 is IEEE80211_RADIOTAP_VHT_BW_20LL. The second link gives the meaning of 20 LL, mentioning that the total bandwidth in 20 LL is 80 MHz.
Can anyone tell me the correct meaning of this vht bandwidth representation in wireshark : 20 MHz, channel 1/4 ?
asked 29 Oct '16, 00:30
edited 29 Oct '16, 02:38
I see this too:
Since the 802.11ac channel is 80MHz, that is four bonded channels. We can usually choose which is the primary. In my case, I have chosen (for test) to set primary to channel 157, which would be 3 / 4:
149 153 157 161
When I migrate the primary channel to 149, I get slightly different results:
So this is representing the primary channel from the channel bonded set. This is the channel beacons come out on, as well as other control traffic.
To manipulate yourself, see if you can change the primary channel in the 802.11ac configuration like I did. This is a Ruckus Wireless AP, standalone, that allows me to change this. Also note that I expect 80MHz communications in both direction, but for whatever reason, right after association, the FromDS frames are 802.11ac 20MHz for a while, then comms goes 80MHz in both directions. I don't know why - signal strength is good. If I get 80MHz frames, you don't see the information you are looking for.
answered 29 Oct '16, 02:53
Please see here: https://crnetpackets.com/2015/06/23/basics-facts-about-wlan-standards-in-north-america-and-europe/ 1/4 meant 36 is the first 40,44and 48 are the other ones to achieve 80MHz .
answered 29 Oct '16, 02:55
edited 29 Oct '16, 06:31