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Wireshark-users: Re: [Wireshark-users] radiotap RSSI v.s. IEEE802.11 RSSI

From: Guy Harris <guy@xxxxxxxxxxxx>
Date: Fri, 26 Jun 2009 13:25:48 -0700

On Jun 26, 2009, at 7:42 AM, iodavide@xxxxxxxxx wrote:

I'm using Atheros device and I'm capturing data from monitor interface
using Radiotap
To better understand link quality I've selected two columns:
IEEE 802.11 RSSI

At least as I read IEEE 802.11-2007, RSSI is just some positive number such that

	1) it's between 0 and some maximum;

2) the greater the value, the more power is being received at the antenna;

with no indication of what it means other than that.

What Wireshark displays in the "RSSI" column depends on the type of capture; at least in the top-of-SVN-tree version:

for captures from AiroPeek, it's a percentage - RSSI/max_RSSI*100 (as that's what AiroPeek saves to the file, at least as I read one of WildPackets' documents);

for captures from CommView, it's a percentage - probably the same as AiroPeek, but I didn't find anything obvious in their document to indicate what it is;

for captures from Windows Sniffer, I *suspect* it's a percentage, probably the same as AiroPeek;

for captures from Shomiti's wireless version of Surveyor (Finisar no longer seem to offer it), I don't know what it is;

for pcap captures with Prism headers, it's whatever the heck the particular driver puts there - a quick look at the drivers didn't indicate that they put anything there;

	for pcap captures with AVS headers, it's signal strength as either:

"Normalized RSSI" - integers in the range [0-1000] where higher numbers indicate stronger signal, with no particular mapping to an actual signal strength;

		dBm - an actual received signal strength, in dBm;

		a raw RSSI value, which is probably the raw IEEE RSSI value;

	with the column indicating which it is;

for pcap captures with Radiotap headers, it's radiotap.dbm.antsignal, shown as dBm.


and a custom colums radiotap.dbm.antsignal
I'm very surprise
to see different values for those columns

Given that the Radiotap code, at least in the top-of-tree version of Wireshark just puts up the radiotap.dbm.antsignal value, I'd be *extremely* susprised to see different values.

The 1.2.0 code should behave the same as the top-of-SVN-tree version; what version of Wireshark are you using?