802.11 wlan_radio.duration wlan_radio.preamble

Question

I am using wireshark in linux to capture 802.11 packet. When I see the resolution result, I see the durationt, preamble, then I find it is actually wlan_radio.duration, wlan_radio.preamble. wlan_radio.preamble is matched with the 802.11 protocol, and its meaning is obvious. But what does wlan_radio.duration mean? When I use (frame length - radiotaoheader length)*8/data rate, then plus preamble time, it is not equal to duration? So, what does wlan_radio.duration mean in wireshark? How/where can I find its definition?

Answer 1

There's the following comment in epan/dissectors/packet-ieee80211-radio.c:

  /* durations in microseconds */
  guint preamble = 0; /* duration of plcp */
  guint duration = 0; /* duration of whole frame (plcp + mac data + any trailing parts) */

further down the duration for the different types (a, b, g, ...) are calculated and yes, it's different for different types. Also, you need to be aware that the frame will usually change its symbol speed after the first few header (not preamble) bytes.