Re: where does PCAP timestamp before or after the MAC scheduler?

[David Young <dyoung () pobox com>]

On Thu, Mar 30, 2006 at 12:17:47PM +0200, Debrei Gabor wrote:
> Hello!
>
> We want to compare 802.11 MAC schedulers performance, to decide 
> how much the Media Access takes.

Many 802.11 MACs put a microsecond timestamp on received frames.
Some wireless drivers in *BSD will load that timestamp into the radiotap
capture header.  In principle (maybe in fact), Linux can do the same.

Sadly, 802.11 MACs do not stamp transmitted frames.  That would be
very useful!

Dave

> We want to know where/when does PCAP put the timestamp (from not 
> so accurate kernel time) on to the packets. I already know,  it does 
> when the kernel "sees" the packet. The question is: Is it after or before 
> the MAC scheduler? I mean, does it in TR or RX buffers or at higher 
> protocol layers take place?
> (If it takes place in the buffers the use of HW monitoring devices the 
> only way of measuring? )
>
> Thanks, I am looking forwad to Your answers.
>
>
> Gabor
>
>
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-- 
David Young             OJC Technologies
dyoung () ojctech com      Urbana, IL * (217) 278-3933
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