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Wireshark-users: Re: [Wireshark-users] [wireshark-user] GUI and radiotap.datarate

From: Guy Harris <guy@xxxxxxxxxxxx>
Date: Thu, 23 Jul 2009 02:38:51 -0700

On Jul 15, 2009, at 8:07 AM, iodavide@xxxxxxxxx wrote:

I'm using Version 1.2.0 (SVN Rev 28753)
From "preference --> column" menu
I've selected to display a custom column with parameter "radiotap.datarate" but the displayed column shows values exactly double than value shown in "packet
details" pane inside "Radiotap Header".
For example if "Datarate" value shown
in the "packet details" pane inside "Radiotap Header" is 3.0Mb/s I can see 6 in
the column

I don't know which value is reliable!

Both values are reliable.

However, the value in the packet details pane is in units of Mb/s (as indicated), while the value in the column - which is the actual value in the radiotap header - is in units of .5 Mb/s, as that's the way rates are indicated in various places in the 802.11 specifications. (And, yes, I have at least one radiotap capture with a packet with a data rate of 5.5 Mb/s, so that the raw rate value is 11.)

We should probably either

1) make radiotap.datarate an FT_FLOAT or FT_DOUBLE, and store the raw value times .5

or

2) have some way of associating a "raw value to display" function with fields, and have that handle the multiplication by .5.