Date: Wed, 13 Nov 2002 18:36:37 -0500 (EST) From: Liangping Ma <lma@mail.eecis.udel.edu> Subject: Re: tcptrace RTT caltulation Message-ID: <Pine.GSO.4.33.0211131832110.499-100000@frink.ece.udel.edu>
Hi, Ulisses,
The second scenario is not reasonable. When you use tcptrace, you should
take special care of that. In my previous experiments, I got zero RTTs
because I put the monitor in a mistaken place (in your case the receiving
end), as in the second scenario.
Liangping Ma
On Wed, 13 Nov 2002 uaca@alumni.uv.es wrote:
> On Wed, Nov 13, 2002 at 12:39:57PM -0500, Liangping Ma wrote:
> > Hi, Ulisses,
> >
> > I did TCP RTT measurement before. Based on my memory, the tcptrace
> > processes tcpdump raw data, which can be collected in a local ethernet.
> > You are right, that the measurement may not be on one of the end points
> > of a TCP conneciton. But the delay within a LAN is trivial in the case of
> > a long-haul TCP connection. Thus the measurement can be reasonably
> > accurate.
>
>
> Ok, imagine the following two scenarios
>
>
> <Monitorization Host>
> |
> |
> [Host A] >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> [Host B]
> ((((((((((((((((((((((((((<<<<<<<<<<<<<<<<<<<<<<<<<<<
>
>
>
> <Monitorization Host>
> |
> |
> [Host A] ))))))))))))))))))))))))))))))))))))))))))))))))))))> [Host B]
> ((((((((((((((((((((((((((((((((((((((((((((((((((((<
>
>
>
> If I'm right RTT meassured values differ their meaning _a lot_ depeding
> where the monitorization host is
>
>
> Am I right?
>
>
> Thanks in advance
>
>
> Ulisses
>
>
> >
> >
> > Liangping
> >
> > On Wed, 13 Nov 2002 uaca@alumni.uv.es wrote:
> >
> > >
> > > I have read rexmit.c:rtt_ackin() and I belive that RTT meassurement is the
> > > following:
> > >
> > >
> > > <Monitorization Host>
> > > |
> > > |
> > > [Host A] ))))))))))))))))))))))))))>>>>>>>>>>>>>>>>>>>>>>>>>>> [Host B]
> > > ((((((((((((((((((((((((((<<<<<<<<<<<<<<<<<<<<<<<<<<<
> > >
> > >
> > > ")" or ">" is the data segment
> > >
> > > "(" or "<" is the ACK segment for the corresponding data segment
> > >
> > >
> > > Where the time meassured for RTT is the time that is the sum of ">" and "<"
> > >
> > > I suposse here the monitorization is being done in the "middle" of the connection
> > >
> > >
> > > That is, tcptrace's RTT is not like the RTT meassured in the "ping" utility,
> > > in other words is not a "two full way transmision" meassurement
> > >
> > >
> > >
> > >
> > > Thanks in advance
> > >
> > >
> > > Ulisses
> > >
> > >
> > > Debian GNU/Linux: a dream come true
> > > -----------------------------------------------------------------------------
> > > "Computers are useless. They can only give answers." Pablo Picasso
> > >
> > > ---> Visita http://www.valux.org/ para saber acerca de la <---
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> > >
> >
>
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> -----------------------------------------------------------------------------
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>
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