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Comment: Typo
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Comment: typo #2
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== Discussion ==  == Discussion ==

Timestamps

Ethereal just gets its timestamp from libpcap/WinPcap, and libpcap/WinPcap gets it from the packet capture mechanism it uses; Ethereal itself doesn't generate the time stamp, so there's nothing Ethereal can do about it.

How the time stamp works is OS dependent. In some UNIXes, that code is in the network drivers; it's higher up in the networking code path in other UNIXes. In Windows, with WinPcap, it's done by the WinPcap driver.

Note also that the time stamp on a packet isn't a high-accuracy measurement of the instant the first bit, or the last bit, of the packet arrived at the network adapter; there's a delay between the arrival of that last bit and the interrupt for the packet, and a delay between the interrupt handling starting and the point in the code path where the time stamp is attached to the packet.

Resolution

It's the resolution of whatever clock is being used. It might not be the "PC clock" because it might not be running on a "PC", either in the sense of machines sold as "personal computers" or in the sense of "IBM-compatible personal computer". Some of those machines might have better high-resolution timers than IBM-compatible PCs do - at least some OSes on more modern IBM-compatible PC's use the RDTSC instruction, if present on the processor, to get higher-precision time stamps.

There's precision and accuracy; a clock with picosecond resolution, set to a time that's 1 1/2 hours off, is very precise and very inaccurate.

Discussion

That's the usualy discussion about this might me / this could be / this will be / and so on.

Please put some hard facts here ...

Just simply add measurement values (and the hard facts on the environment) on a specific platform so others can participate ...

Timestamps (last edited 2008-04-12 17:51:23 by localhost)