[Planetlab-users] TCPDUMP response side traffic lost

[Hecker W]

Thanks Sapan. I just saw your message today.

The silence period I mentioned is not only for the TCP handshakes but
also for the payload packets.

I did some tests on the machine you mention in another email
(plantlab-7 and echo). I have put the traces I produced by downloading
files in different size from my university online at
http://mot.cs.northwestern.edu/Planetlab/.

You can take a look at the traces to see the problem.  I have tried
different files with different sizes on the planetlab-7 and echo. .
For the traces captured on echo.cs.princeton.edu, the incoming traffic
always have loses. For the
traces of planetlab-7, in some cases I can get full traces even with
SYN/ACK. But in other cases it repeated the behavior I mentioned. I
notice after the stabilization period, there are no noticeable packet
loss even when the downloading speed is high, so it seems not due to
the disk bottleneck.

Here are the traces and corresponding file sizes
TRACE           FILESIZE
testfull*pcap   4572765
testsmall*pcap  25376
testtiny*pcap   2219

For planetlab-7 node
testfull2.pcap, testsmall1.pcap have obvious packet loss at the
initial silence period.

Thanks,
-Zhichun


On Mon, Jul 14, 2008 at 2:42 PM, Sapan Bhatia <sapanb at cs.princeton.edu> wrote:
>
> Hi Zhichun,
>
> I can't reproduce this problem. I tried some simple tests (wget a
> small file, wget a big file) but I could capture all incoming packets.
>
> Is the initial period of silence that you've encountered restricted to
> the TCP handshake? If that's the case, then it's expected - and you
> need to do something special to be able to see it. But you should not
> be missing any payload packets because of this.
>
> If not, then could you give me a test case to work with?
>
> Sapan
>
> On Thu, Jul 10, 2008 at 9:47 PM, Hecker W <heckerme at gmail.com> wrote:
> > I need to issue HTTP requests from Planetlab nodes and
> > to dump the whole TCP connection traces. I found it worked
> > on the FC4 version. But for the FC8 version, after the initial
> > SYN packet sent out, I cannot capture the server response
> > traffic until 0.6 second later. All the packets responded from
> > web servers are lost within this 0.6 second time window. After that
> > I can get all the traffic from both side.  I tried the big web objects to
> > make
> > sure its downloading time is longer than 1 seconds, and find this problem is
> > persistent.
> >
> > I am not sure whether it is due to the new version of Planetlab needs
> > 0.6 seconds to recognize that the new connection is issued so that it begin
> > to
> > allow TCPDUMP to see the packets?
> >
> > I guess it is not expected behavior, doesn't it? I did not use any raw
> > socket API.
> >
> > The problem is similar to the problem mentioned by Greg in the previous
> > post.
> >
> > If anyone needs the pcap trace to see the problem please reply the post. I
> > will make it available online.
> >
> > Thanks
> > -Zhichun
> >
> >
> >
> >
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>
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