[Winpcap-users] timestamping and huge latency

Gianluca Varenni gianluca.varenni at cacetech.com
Mon Sep 20 17:04:04 PDT 2010

Do you measure the latency by looking at the WinPcap timestamps or at the timestamps that you generate? How do you measure such latency?

Have a nice day

From: Helmut Vaupotitsch 
Sent: Tuesday, September 14, 2010 9:18 AM
To: winpcap-users at winpcap.org 
Subject: [Winpcap-users] timestamping and huge latency

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

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, 

Have a nice day

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

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

Winpcap-users mailing list
Winpcap-users at winpcap.org
Winpcap-users mailing list
Winpcap-users at winpcap.org


Ing. Helmut Vaupotitsch        Phone:  +43 (0)3133 3780 16
ITEC Tontechnik und            Fax:    +43 (0)3133 3780 9
Industrieelektronik GmbH       E-mail: hv at itec-audio.com
A-8200 Lassnitzthal 300        URL:    http://www.itec-audio.com


Winpcap-users mailing list
Winpcap-users at winpcap.org
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://www.winpcap.org/pipermail/winpcap-users/attachments/20100920/7c13e248/attachment.htm 

More information about the Winpcap-users mailing list