Subject: tcp initial window and rate pacing...

From: Luigi Rizzo <[email-masked]>
Date: Mon, 26 Oct 1998 17:03:10 +0100 (MET)

Hi,

(not sure if this is more for tcpimpl or end2end...)

I have read the recent RFCs (2414,2415,2416) about increasing the
initial window to 4K or so -- all is fine, the situation is not too
different from a regular TCP after one round, etc.

But has anyone considered, in addition to larger windows, also
pacing the generation of the initial burst of packets at a relatively
low rate so that one can an even slightly larger initial window
yet avoiding overflows at the network edges (e.g.  dialup users) ?

The implementation seems trivial (i did it with some 20 lines of code
driven by fasttimo() ) and being able to use slightly larger windows 
makes the connection less prone to ack starvation.
Lacking information the initial rate can be set to a conservative
value so that one can reuse the fasttimo code, or one can use cached
values from previous connections same as it is done with the initial
RTT and RTTVAR

comments ?

	cheers
	luigi
-----------------------------+--------------------------------------
Luigi Rizzo                  |  Dip. di Ingegneria dell'Informazione
email: [email-masked]    |  Universita' di Pisa
tel: +39-50-568533           |  via Diotisalvi 2, 56126 PISA (Italy)
fax: +39-50-568522           |  http://www.iet.unipi.it/~luigi/
_____________________________|______________________________________

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From: Mohit Aron <[email-masked]>
Date: Mon, 26 Oct 1998 13:31:47 -0600 (CST)

> yet avoiding overflows at the network edges (e.g.  dialup users) ?

I've done some work on this. Please take a look at:
	http://www.cs.rice.edu/~aron/papers/rice-TR98-318.ps

- Mohit

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From: Joe Touch <[email-masked]>
Date: Mon, 26 Oct 1998 12:51:33 -0800

>         http://www.cs.rice.edu/~aron/papers/rice-TR98-318.ps

John Heidemann here at USC/ISI has done some work on rate-pacing.I have
done some work (RFC2140) on TCP control block sharing, which
would allow rate values to be shared over multiple connections to the same
place.
There can, of course, be default initial values, as there are for the
window size.

Papers are available at:
    http://www.isi.edu/lsam/

Joe

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From: Craig Partridge <[email-masked]>
Date: Mon, 26 Oct 1998 16:07:33 -0800

Yes -- we're looking at various pacing schemes and their effects under
contract to NASA.

So far it looks promising but one never knows until one is done.

Thanks!

Craig

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From: [email-masked] (Alan Cox)
Date: Tue, 27 Oct 1998 19:39:31 +0000 (GMT)

> values from previous connections same as it is done with the initial

I played a little with pacing output frames. The overhead on fast links
when trying to do the timer stuff is nasty, on low speed ok. I had horrible
problems with half duplex media though. On AX.25 and irda throughput dropped
in both cases.

Alan