Mahesh Krishnan wrote:
I read somewhere on the internet that the MAC time is the time when the packet
was seen by the network card. If that is true, How do I interpret the value
that is printed in Hex.
You ask whoever maintains the driver for the card what that particular
card supplies as the "MAC time". I think the driver is just supplying
whateve data the card supplies, and passing that up to the application.
The Prism header is, umm, woefully underspecified; there's no
documentation for it that I know of.
The AVS header used to be documented, but it appears that Solomon
Peachy's replaced his old Web site with his blog; I don't know where the
AVS spec went.
The radiotap header is reasonably well documented in its header file:
http://www.freebsd.org/cgi/cvsweb.cgi/src/sys/net80211/ieee80211_radiotap.h?rev=1.5&content-type=text/x-cvsweb-markup
http://cvsweb.netbsd.org/bsdweb.cgi/src/sys/net80211/ieee80211_radiotap.h?rev=1.10&content-type=text/x-cvsweb-markup
http://www.openbsd.org/cgi-bin/cvsweb/src/sys/net80211/ieee80211_radiotap.h?rev=1.5&content-type=text/x-cvsweb-markup
(hopefully DragonFly BSD will adopt it as well, if they haven't done so
already, and once the one other major remaining BSD changes IOKit to
support 802.11 as a network interface type, rather than forcing 802.11
drivers to pretend their interfaces are Ethernet interfaces, it'll adopt
it as well).
That header speaks of
* IEEE80211_RADIOTAP_TSFT u_int64_t microseconds
*
* Value in microseconds of the MAC's 64-bit 802.11 Time
* Synchronization Function timer when the first bit of the
* MPDU arrived at the MAC. For received frames, only.
*
so that *MIGHT* be what the time in question is in the Prism headers, as
the reference to it as an "802.11" Time Synchronizaton Function timer
suggests that it's part of the 802.11 standard - but, at least from my
quick reading of the 802.11 spec, there's no notion that it's an
absolute time with a fixed reference point.
