<html xmlns:v="urn:schemas-microsoft-com:vml" xmlns:o="urn:schemas-microsoft-com:office:office" xmlns:w="urn:schemas-microsoft-com:office:word" xmlns:m="http://schemas.microsoft.com/office/2004/12/omml" xmlns="http://www.w3.org/TR/REC-html40">
<head>
<meta http-equiv=Content-Type content="text/html; charset=windows-1252">
<meta name=Generator content="Microsoft Word 12 (filtered medium)">
<style>
<!--
/* Font Definitions */
@font-face
{font-family:"Cambria Math";
panose-1:2 4 5 3 5 4 6 3 2 4;}
@font-face
{font-family:Calibri;
panose-1:2 15 5 2 2 2 4 3 2 4;}
@font-face
{font-family:Tahoma;
panose-1:2 11 6 4 3 5 4 4 2 4;}
@font-face
{font-family:Consolas;
panose-1:2 11 6 9 2 2 4 3 2 4;}
@font-face
{font-family:Verdana;
panose-1:2 11 6 4 3 5 4 4 2 4;}
@font-face
{font-family:"Comic Sans MS";
panose-1:3 15 7 2 3 3 2 2 2 4;}
/* Style Definitions */
p.MsoNormal, li.MsoNormal, div.MsoNormal
{margin:0in;
margin-bottom:.0001pt;
font-size:12.0pt;
font-family:"Times New Roman","serif";
color:black;}
a:link, span.MsoHyperlink
{mso-style-priority:99;
color:blue;
text-decoration:underline;}
a:visited, span.MsoHyperlinkFollowed
{mso-style-priority:99;
color:purple;
text-decoration:underline;}
pre
{mso-style-priority:99;
mso-style-link:"HTML Preformatted Char";
margin:0in;
margin-bottom:.0001pt;
font-size:10.0pt;
font-family:"Courier New";
color:black;}
tt
{mso-style-priority:99;
font-family:"Courier New";}
span.HTMLPreformattedChar
{mso-style-name:"HTML Preformatted Char";
mso-style-priority:99;
mso-style-link:"HTML Preformatted";
font-family:Consolas;
color:black;}
span.EmailStyle20
{mso-style-type:personal-reply;
font-family:"Calibri","sans-serif";
color:#1F497D;}
.MsoChpDefault
{mso-style-type:export-only;
font-size:10.0pt;}
@page WordSection1
{size:8.5in 11.0in;
margin:1.0in 1.0in 1.0in 1.0in;}
div.WordSection1
{page:WordSection1;}
-->
</style>
<!--[if gte mso 9]><xml>
<o:shapedefaults v:ext="edit" spidmax="1026" />
</xml><![endif]--><!--[if gte mso 9]><xml>
<o:shapelayout v:ext="edit">
<o:idmap v:ext="edit" data="1" />
</o:shapelayout></xml><![endif]-->
</head>
<body bgcolor=white lang=EN-US link=blue vlink=purple>
<div class=WordSection1>
<p class=MsoNormal><span style='font-size:10.5pt;font-family:"Calibri","sans-serif";
color:#1F497D'>Another thing: if the sending and receiving/capturing systems'
clocks are not synchronized with each other, then how are you measuring the supposed
latency between sending and receiving/capturing?<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.5pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:10.5pt;font-family:"Calibri","sans-serif";
color:#1F497D'>That is to say, if the two clocks are not synchronized with one
another, then normal clock drift would completely invalidate your measured
latency in my opinion.<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.5pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:10.5pt;font-family:"Calibri","sans-serif";
color:#1F497D'>Are the two system's clocks synchronized with one another?<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.5pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:10.5pt;font-family:"Calibri","sans-serif";
color:#1F497D'>If they're not then there's your answer.<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.5pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:10.5pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:10.5pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:10.5pt;font-family:"Calibri","sans-serif";
color:#1F497D'>p.s. if/when you do synchronize them with each other, remember
to ensure that either: a) <i>neither</i> or them synchronizes with an external
clock, or: b) only ONE of them does! (but not both!) The same rule applies to
the Windows Time Service too: disable it on <i>both</i> or else ensure the one
with it enabled is configured as the "time <i>server</i>". Otherwise
your results would once again be completely invalid/inconclusive.<o:p></o:p></span></p>
<div>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span
style='font-size:7.5pt;font-family:"Arial","sans-serif"'>-- </span><span
style='color:#1F497D'><br>
</span><span style='font-size:13.5pt;font-family:"Arial","sans-serif"'>
"</span><b><span style='font-family:"Arial","sans-serif";color:green'>Fish</span></b><span
style='font-size:13.5pt;font-family:"Arial","sans-serif"'>"</span><span
style='font-size:10.0pt;font-family:"Arial","sans-serif"'> (</span><span
style='font-size:10.0pt;font-family:"Comic Sans MS";color:purple'>David B.
Trout</span><span style='font-size:10.0pt;font-family:"Arial","sans-serif";
color:#1F497D'>)</span><span style='color:#1F497D'> <br>
</span><span style='font-size:10.0pt;font-family:"Verdana","sans-serif";
color:#1F497D'> </span><span style='color:#1F497D'> </span><u><span
style='font-size:10.0pt;font-family:"Arial","sans-serif";color:blue'>fish@softdevlabs.com</span></u><span
style='color:#1F497D'><o:p></o:p></span></p>
</div>
<p class=MsoNormal><span style='font-size:10.5pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<div style='border:none;border-left:solid blue 1.5pt;padding:0in 0in 0in 4.0pt'>
<div>
<div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0in 0in 0in'>
<p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif";
color:windowtext'>From:</span></b><span style='font-size:10.0pt;font-family:
"Tahoma","sans-serif";color:windowtext'> winpcap-users-bounces@winpcap.org
[mailto:winpcap-users-bounces@winpcap.org] <b>On Behalf Of </b>Helmut
Vaupotitsch<br>
<b>Sent:</b> Tuesday, September 14, 2010 9:18 AM<br>
<b>To:</b> winpcap-users@winpcap.org<br>
<b>Subject:</b> [Winpcap-users] timestamping and huge latency<br>
<b>Importance:</b> High<o:p></o:p></span></p>
</div>
</div>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal><tt><span style='font-size:10.0pt'>Hi Gianluca and all
others,</span></tt><span style='font-size:10.0pt;font-family:"Courier New"'><br>
<br>
<tt>I am facing a major latency problem on *long lasting* capture sessions
which maybe </tt><br>
<tt>has to do with timestamping by the driver, every hint to solve it is
appreciated:</tt><br>
<br>
<tt>We developed a proprietary protocol to configure, manage and monitor </tt><br>
<tt>our self-developed hardware, the config software uses WinPCap to capture
and send raw packets.</tt><br>
<br>
<tt>Everything is working fine, but after some days of continuous capturing i
face:</tt><br>
<tt>- On some machines, the latency between sending requests and receiving the
answer </tt><br>
<tt> increases to some seconds (can be up to >30 secs after capturing
for a week!)</tt><br>
<tt>Closing and re-opening the driver would solve the problem, but i definitely
need to capture</tt><br>
<tt>for months and longer without interrupt!</tt><br>
<br>
<tt>I know that the driver timestamp is drifting apart from the System
Time(which can be</tt><br>
<tt>synchronized by e.g. a NTP server), therefore i timestamp the frames my
myself(which </tt><br>
<tt>is also important if a use timeouts)</tt><br>
<br>
<tt><b>My question is:</b></tt><b><br>
<tt>What could be the reason(s) for huge latency on long lasting captures?</tt><br>
</b><tt>I know that the latency increases on receiving packets</tt><br>
<tt>Currently i don´t know if sending´s latency also increases</tt><br>
<tt>Maybe it has something to do with the GetSystemTimeAdjustment setting?</tt><br>
</span><br>
<span style='font-size:10.0pt;font-family:"Courier New"'><br>
<tt>Thanks for reading</tt><br>
<br>
<tt>Best regards from Austria</tt><br>
<tt>Helmut</tt><br>
<br>
</span><br>
Gianluca Varenni schrieb: <o:p></o:p></p>
<pre>The return value of QuerySystemTime and QueryPerformanceCounter is <o:p></o:p></pre><pre>synchronized at the beginning of the capture (to compute the offset between <o:p></o:p></pre><pre>epoch time and QueryPerformanceCounter), and then the counter and frequency <o:p></o:p></pre><pre>returned by QPC are used to compute the number of seconds (and microseconds) <o:p></o:p></pre><pre>and added to the offset.<o:p></o:p></pre><pre><o:p> </o:p></pre><pre>The timestamping code is available in the source code of WinPcap, <o:p></o:p></pre><pre>winpcap\packetntx\driver\time_calls.h<o:p></o:p></pre><pre><o:p> </o:p></pre><pre>Have a nice day<o:p></o:p></pre><pre>GV<o:p></o:p></pre><pre><o:p> </o:p></pre><pre><o:p> </o:p></pre><pre><o:p> </o:p></pre><pre>--------------------------------------------------<o:p></o:p></pre><pre>From: "Jan Martinec" <a
href="mailto:martij12@fel.cvut.cz"><martij12@fel.cvut.cz></a><o:p></o:p></pre><pre>Sent: Tuesday, September 14, 2010 7:23 AM<o:p></o:p></pre><pre>To: <a
href="mailto:winpcap-users@winpcap.org"><winpcap-users@winpcap.org></a><o:p></o:p></pre><pre>Subject: [Winpcap-users] timestamp<o:p></o:p></pre><pre><o:p> </o:p></pre><pre> <o:p></o:p></pre>
<blockquote style='margin-top:5.0pt;margin-bottom:5.0pt'><pre>Hello!<o:p></o:p></pre><pre>I've got a question about timestamping method. I know that a timestamp<o:p></o:p></pre><pre>is got using method QueryPerformanceCounter (resp.<o:p></o:p></pre><pre>keQueryPerformanceCounter), which is a number of ticks of Performance<o:p></o:p></pre><pre>counter. But timestamp is by Winpcap returned in "Seconds since Epoch"<o:p></o:p></pre><pre>format. So how is the recomputation done?<o:p></o:p></pre><pre><o:p> </o:p></pre><pre>Thank you very much<o:p></o:p></pre><pre><o:p> </o:p></pre><pre>Best regards,<o:p></o:p></pre><pre>Jan Martinec<o:p></o:p></pre><pre><o:p> </o:p></pre><pre><o:p> </o:p></pre><pre>_______________________________________________<o:p></o:p></pre><pre>Winpcap-users mailing list<o:p></o:p></pre><pre><a
href="mailto:Winpcap-users@winpcap.org">Winpcap-users@winpcap.org</a><o:p></o:p></pre><pre><a
href="https://www.winpcap.org/mailman/listinfo/winpcap-users">https://www.winpcap.org/mailman/listinfo/winpcap-users</a> <o:p></o:p></pre><pre> <o:p></o:p></pre></blockquote>
<pre><o:p> </o:p></pre><pre>_______________________________________________<o:p></o:p></pre><pre>Winpcap-users mailing list<o:p></o:p></pre><pre><a
href="mailto:Winpcap-users@winpcap.org">Winpcap-users@winpcap.org</a><o:p></o:p></pre><pre><a
href="https://www.winpcap.org/mailman/listinfo/winpcap-users">https://www.winpcap.org/mailman/listinfo/winpcap-users</a><o:p></o:p></pre><pre><o:p> </o:p></pre><pre> <o:p></o:p></pre>
<p class=MsoNormal><br>
<br>
<o:p></o:p></p>
<pre>-- <o:p></o:p></pre><pre>----------------------------------------------------------------<o:p></o:p></pre><pre>Ing. Helmut Vaupotitsch Phone: +43 (0)3133 3780 16<o:p></o:p></pre><pre>ITEC Tontechnik und Fax: +43 (0)3133 3780 9<o:p></o:p></pre><pre>Industrieelektronik GmbH E-mail: <a
href="mailto:hv@itec-audio.com">hv@itec-audio.com</a><o:p></o:p></pre><pre>A-8200 Lassnitzthal 300 URL: <a
href="http://www.itec-audio.com">http://www.itec-audio.com</a><o:p></o:p></pre><pre>----------------------------------------------------------------<o:p></o:p></pre></div>
</div>
</body>
</html>