Date: Wed, 13 Nov 2002 21:22:25 +0100 Subject: Re: tcptrace RTT caltulation Message-ID: <20021113202225.GA19007@pusa.informat.uv.es> From: uaca@alumni.uv.es
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
> > -----------------------------------------------------------------------------
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> >
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>
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