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Re: recent TCP changes adversive on slow links

To: amlaukka@xxxxxxxxxxxxxx (Aki M Laukkanen)
Subject: Re: recent TCP changes adversive on slow links
From: kuznet@xxxxxxxxxxxxx
Date: Thu, 1 Jun 2000 22:29:25 +0400 (MSK DST)
Cc: netdev@xxxxxxxxxxx, iwtcp@xxxxxxxxxxxxxx
In-reply-to: <Pine.OSF.4.20.0005312209550.23613-100000@xxxxxxxxxxxxxxxxxx> from "Aki M Laukkanen" at Jun 1, 0 02:17:09 pm
Sender: owner-netdev@xxxxxxxxxxx
Hello!

> you remark, as if the transmit queue length was huge. But we used ppp
> which has tx_queue_len of three.

This is impossible. In this case you would never see bursts more
than 4 packets. 4th one is dropped, which suspends transmission.


> So it seems something further down is effecting the behaviour indirectly.
> That seems to be our own fault (will do tests). The link used was
> really an emulated link (sorry, software not publicly  available and 
> it's still being beta-tested). The basic principle is to catch the PPP
> stream with a pseudo tty and from there on we can mess with packets (in
> principle like dummynet). We are aware of the gotchas this implies and the
> emulator implements flow control but apparently in those tests it wasn't
> turned on.

It is possible then. Apparently, you broke flow control on your device.

On devices without flow control (loopback is the best example) 
bursts are infinite, of course, and controlled only by TCP window
and congestion avoidance. 

Alexey

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