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Why do Tshark gives two data_rate?

asked 2019-07-19 11:53:15 +0000

updated 2019-07-19 12:08:43 +0000

grahamb gravatar image

Hi, Using tshark -2 -r Dump2.pcapng -T fields -e wlan_radio.data_rateon a OTA dump ( https://remy.grunblatt.org/Dump2.pcapng ), I get values such as "6.5,6.5" or "526.5,526.5".

From the documentation, the values are supposed to be Floating point (single-precision). Is there a problem with the pcap? Or is that a problem with tshark?

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answered 2019-07-19 12:31:11 +0000

grahamb gravatar image

There are two reports of the rate as the field appears twice in the wlan_radio block, once under the wlan_radio.11ac.user (User 1:) block and once under the main block. I'm not familiar enough with WLAN captures to say if this is a dissector error or not, but I would think that there should either be one entry, or there should be different field names. Please raise an issue on the Wireshark Bugzilla for this.

The "single-precision" part of the definition is that the field is an IEEE 754 single precision float with a range of ± 2-126 to (2-2-23)×2127

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This is bug 15928. See further discussion there.

Guy Harris gravatar imageGuy Harris ( 2019-07-19 17:50:09 +0000 )edit

A fix has been checked in. In a VHT frame, there will now be exactly one data rate field instance per user.

Guy Harris gravatar imageGuy Harris ( 2019-07-19 19:10:47 +0000 )edit

And note that the documentation to which you refer does not state that there will be only one instance of the field in question, so the fact that it says the values are floating-point does not mean that there will be only one value, it just means that the values - possibly more than one - will be floating-point values.

Guy Harris gravatar imageGuy Harris ( 2019-07-19 19:12:20 +0000 )edit

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Asked: 2019-07-19 11:53:15 +0000

Seen: 68 times

Last updated: Jul 19