[Winpcap-users] timestamping and huge latency

[Helmut Vaupotitsch]

Hi Gianluca and all others,

I am facing a major latency problem on *long lasting* capture sessions 
which maybe
has to do with timestamping by the driver, every hint to solve it is 
appreciated:

We developed a proprietary protocol to configure, manage and monitor
our self-developed hardware, the config software uses WinPCap to capture 
and send raw packets.

Everything is working fine, but after some days of continuous capturing 
i face:
- On some machines, the latency between sending requests and receiving 
the answer
  increases to some seconds (can be up to >30 secs after capturing for a 
week!)
Closing and re-opening the driver would solve the problem, but i 
definitely need to capture
for months and longer without interrupt!

I know that the driver timestamp is drifting apart from the System 
Time(which can be
synchronized by e.g. a NTP server), therefore i timestamp the frames my 
myself(which
is also important if a use timeouts)

*My question is:
What could be the reason(s) for huge latency on long lasting captures?
*I know that the latency increases on receiving packets
Currently i don´t know if sending´s latency also increases
Maybe it has something to do with the GetSystemTimeAdjustment setting?


Thanks for reading

Best regards from Austria
Helmut


Gianluca Varenni schrieb:
> The return value of QuerySystemTime and QueryPerformanceCounter is 
> synchronized at the beginning of the capture (to compute the offset between 
> epoch time and QueryPerformanceCounter), and then the counter and frequency 
> returned by QPC are used to compute the number of seconds (and microseconds) 
> and added to the offset.
>
> The timestamping code is available in the source code of WinPcap, 
> winpcap\packetntx\driver\time_calls.h
>
> Have a nice day
> GV
>
>
>
> --------------------------------------------------
> From: "Jan Martinec" <martij12 at fel.cvut.cz>
> Sent: Tuesday, September 14, 2010 7:23 AM
> To: <winpcap-users at winpcap.org>
> Subject: [Winpcap-users] timestamp
>
>   
>> Hello!
>> I've got a question about timestamping method. I know that a timestamp
>> is got using method QueryPerformanceCounter (resp.
>> keQueryPerformanceCounter), which is a number of ticks of Performance
>> counter. But timestamp is by Winpcap returned in "Seconds since Epoch"
>> format. So how is the recomputation done?
>>
>> Thank you very much
>>
>> Best regards,
>> Jan Martinec
>>
>>
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>> Winpcap-users at winpcap.org
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>>     
>
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>   

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