<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML><HEAD>
<META http-equiv=Content-Type content="text/html; charset=iso-8859-1">
<META content="MSHTML 6.00.6000.16825" name=GENERATOR>
<STYLE></STYLE>
</HEAD>
<BODY bgColor=#ffffff>
<DIV><FONT size=2></FONT> </DIV>
<BLOCKQUOTE
style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">
<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: black"><B>From:</B>
<A title=locationdev@gmail.com href="mailto:locationdev@gmail.com">John
Wang</A> </DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A title=winpcap-users@winpcap.org
href="mailto:winpcap-users@winpcap.org">winpcap-users@winpcap.org</A> </DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Wednesday, May 06, 2009 6:36
AM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> Re: [Winpcap-users] Where does
the Winpcap timestampcomefrom?andothers</DIV>
<DIV><FONT size=2></FONT><BR></DIV>Hi,<BR><BR>I'm a little bit confused about
where exactly the arrival packets timestamps come from, in our first email,
you said:<BR><BR><SPAN style="COLOR: rgb(51,51,255)">"1. Where does the NPF
get the time information to timestamp these incoming packet? The time
information comes from a on board timer in the adapter or from a CPU or
similar computer clock?</SPAN>
<DIV style="COLOR: rgb(51,51,255)"><FONT color=#000000
size=2></FONT> </DIV>
<DIV style="COLOR: rgb(51,51,255)"><FONT size=2>--GV--</FONT></DIV>
<DIV><FONT style="COLOR: rgb(51,51,255)" size=2>From the computer clock when
the packet gets delivered to WinPcap.</FONT><SPAN
style="COLOR: rgb(51,51,255)">"</SPAN><BR><BR><FONT color=#000000>I think that
means the timestamps come from computer timer, like CPU timer. But in you last
email, you said:<BR><BR><SPAN
style="COLOR: rgb(51,51,255)">"</SPAN></FONT><FONT
style="COLOR: rgb(51,51,255)"><FONT size=2>The only way to obtain that is to
have some device that timestamps packets in hardware. And even in that
case, most of the times the timestamps have microsecond precision (this is
what we have with the AirPcap adapters in hardware).</FONT></FONT><FONT
color=#000000><SPAN style="COLOR: rgb(51,51,255)">"<BR><BR><SPAN
style="COLOR: rgb(0,0,0)">That sounds like, the AirPcap adapter has a timer
build in it, and the arrival packets timestamps come from this build in
timer.<BR><BR>So I want to get the confirmation from you, whether the arrival
packets are timestamped by the computer timer or the AirPcap adapter build in
timer.<BR></SPAN></SPAN></FONT></DIV></BLOCKQUOTE>
<DIV><FONT color=#000000><SPAN style="COLOR: rgb(51,51,255)"><SPAN
style="COLOR: rgb(0,0,0)"><FONT size=2>In the case of the AirPcap adapters,
which are *custom* capture devices, we provide two timestamps: software based
ones and hardware based ones. The hardware based ones are generated by the
chipset itself and have microsecond precision.
</FONT></SPAN></SPAN></FONT></DIV>
<DIV><FONT color=#000000><SPAN style="COLOR: rgb(51,51,255)"><SPAN
style="COLOR: rgb(0,0,0)"></SPAN></SPAN></FONT> </DIV>
<DIV><FONT color=#000000><SPAN style="COLOR: rgb(51,51,255)"><SPAN
style="COLOR: rgb(0,0,0)"></SPAN></SPAN></FONT><FONT color=#000000><SPAN
style="COLOR: rgb(51,51,255)"><SPAN style="COLOR: rgb(0,0,0)"><FONT size=2>If
you use WinPcap on a standard network adapter (doesn't matter if it's wireless
or not), you just have software timestamps.</FONT></SPAN></SPAN></FONT></DIV>
<DIV><FONT color=#000000><SPAN style="COLOR: rgb(51,51,255)"><SPAN
style="COLOR: rgb(0,0,0)"></SPAN></SPAN></FONT> </DIV>
<DIV><FONT color=#000000><SPAN style="COLOR: rgb(51,51,255)"><SPAN
style="COLOR: rgb(0,0,0)"></SPAN></SPAN></FONT><FONT color=#000000 size=2><SPAN
style="COLOR: rgb(51,51,255)"><SPAN style="COLOR: rgb(0,0,0)">Let me know if
this makes any sense to you.</SPAN></SPAN></FONT></DIV>
<DIV><FONT color=#000000 size=2><SPAN style="COLOR: rgb(51,51,255)"><SPAN
style="COLOR: rgb(0,0,0)"></SPAN></SPAN></FONT> </DIV>
<DIV><FONT color=#000000 size=2><SPAN style="COLOR: rgb(51,51,255)"><SPAN
style="COLOR: rgb(0,0,0)"></SPAN></SPAN></FONT><FONT color=#000000 size=2><SPAN
style="COLOR: rgb(51,51,255)"><SPAN style="COLOR: rgb(0,0,0)">Have a nice
day</SPAN></SPAN></FONT></DIV>
<DIV><FONT color=#000000 size=2><SPAN style="COLOR: rgb(51,51,255)"><SPAN
style="COLOR: rgb(0,0,0)"></SPAN></SPAN></FONT><FONT color=#000000><SPAN
style="COLOR: rgb(51,51,255)"><SPAN style="COLOR: rgb(0,0,0)"><FONT
size=2>GV</FONT></DIV></SPAN></SPAN></FONT><FONT color=#000000><SPAN
style="COLOR: rgb(51,51,255)"><SPAN style="COLOR: rgb(0,0,0)"><FONT
size=2></FONT></SPAN></SPAN></FONT>
<BLOCKQUOTE
style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px"><FONT
color=#000000><SPAN style="COLOR: rgb(51,51,255)"><SPAN
style="COLOR: rgb(0,0,0)">
<DIV><BR>Cheers<BR><BR>John<BR></DIV></SPAN></SPAN></FONT>
<P>
<HR>
<P></P>_______________________________________________<BR>Winpcap-users
mailing
list<BR>Winpcap-users@winpcap.org<BR>https://www.winpcap.org/mailman/listinfo/winpcap-users<BR></BLOCKQUOTE></BODY></HTML>