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Hello,

Does anybody have a reference for how wlan_radio.11ac.bandwidth is defined in Wireshark?  I tried a web search but have not found any useful references. 

There is some CWNP reference material that says

wlan_radio.11ac.bandwidth  == 11 means 160 MHz channel width

and

wlan_radio.11ac.bandwidth == 4 is 80 MHz channel width.

I have some doubts as to if this if correct.  The value according to one CWNP document is 0(20MHz), 1(40MHz), 4(40MHz), 11 (80 Mhz).

This does seem like the nice binary sequence  we would ordinarily expect to see.  I would expect the sequence  of values for wlan_radio.11ac.bandwidth to be 0, 1, 2, 4.  Instead the progression of values is 0, 1, 4, 11.

Does anyone know why the numbers are like this or have a reference where this is defined?

Regards,

  David

The IEEE /ac standard states that the VHT Operational Information Element has a one byte field that represents the width.

0 = 20 or 40 MHz

1 = 80 MHz

2 = 160 MHz

3 = 80+80 MHz

All other values are reserved.

These are also described in Matthew Gast's 802.11ac book, under Management Frames.

Although I know Wireshark is not always up-to-date, I would hope that in this case it is getting the width information from the same place.

Hi Howard,

Thanks for the reference.  I looked in Matthew Gast's book and found it.  For a small book, it does have a lot of material.  BTW I did find this also in table Table 10-19—VHT BSS operating channel width of IEEE Std 802.11ac™-2013.  It turns out it was not enough to look in the 2012 version of the standard.  There is still the question of how this matches up with wireshark, but regardless one more step on the path to wireless understanding.

Thanks,

  David

With wlan_radio.11ac.bandwidth:

20 = 0

40 = 1

80 = 4

160 = 11

There are many combinations of channelization in between 40 and 80, 80 and 160 and methods for 160. Seems to be built from the options originating in Table 22-7 in 802.11ac-2013. All the options can be seen in the Wireshark Expression Builder. Just search for wlan_radio.11ac.bandwidth to see the options.

Tom,

I just downloaded the latest /ac spec, and I don't see how table 22-7 relates to the values used in Wireshark.

Could you explain that part a little better?

Thanks. 

If you look at the wireshark filters, you will see they are for 20, then 40, then 20-1, then 20+1, etc. This is the representation of the channel combinations available in the referenced table it appears. The operating bandwidth, defined elsewhere in 802.11ac, indicates the maximum bandwidth of the channel (for example 80 MHz). The CBW## indicates the channel for this frame. It appears wireshark can capture these uniquely with these filters. So when, CBW20 is in use, but operating bandwidth is 80, the frame is on the primary 20 MHz channel within the four used for the 80 MHz channel. That's the best linkage I can come up with to the wireshark filters. Would love to know if I've missed the head of the nail :)

Tom

Thanks.

.

WARNING:

Chrome, Firefox, and IE all say the site "theengineeringprojects.com", has an invalid SSL secutity certificate.

Try it without the s, that is http://www.theengineeringprojects.com/.  This is not really wireless however.  Someone is advertising.