<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<meta content="text/html; charset=ISO-8859-1"
http-equiv="Content-Type">
</head>
<body text="#000000" bgcolor="#ffffff">
<font face="Helvetica, Arial, sans-serif">You are overthinking this.
I can share with you the delays using a personal hack "tcp ping" tool
that sends a few bytes over a TCPNODELAY socket. They are consistent
with this measure.</font><br>
<br>
Measurements are never perfect, but that doesn't mean they can't tell
us a lot. I used to diagnose the Multics operating system performance
problems by studying the panel register display. Rarely needed to
write special profiling code<br>
<br>
On 09/07/2009 06:46 AM, Jeroen Massar wrote:
<blockquote cite="mid:4AA4E494.40102@spaghetti.zurich.ibm.com"
type="cite">
<pre wrap="">Ihsan Ayyub Qazi wrote:
</pre>
<blockquote type="cite">
<pre wrap=""> TCP != ICMP ;)
Sure but the large delay (and variation) is probably due to large
buffers getting filled up by TCP traffic; ping just measured the delay
rather than causing it.
</pre>
</blockquote>
<pre wrap="">
That is not what I meant. Just think of the case where there is a nice
ISP involved, or for that matter several, who are doing "QoS" and
prioritizes ICMP a lot lower than TCP... you do know that all bittorrent
is evil and that everything over port 80 is 'good' don't you? :)
Also think of that little fact that traceroute is unidirectional, you
only see the return path from your vantage point, not the path that the
packets are taking from those points, you know that the RTT is <x> but
you don't know if that is a symmetric path or not, let alone where the
delay is happening. This is why there was this feature called
source-routing which allowed one to partially make that happen, but
unfortunately that feature has a lot of abuse added to it.
David: a cooler question would involve some 6to4 hosts, then one really
does not know where the packets are truly going ;)
As long as one does not own/control/operate the complete path it will be
really quite hard to tell what happens to packets outside ones control.
Greets,
Jeroen
</pre>
</blockquote>
</body>
</html>