(Moving over to -net, please remove -stable from any cc's)

On Mon, 17 Dec 2001, Thomas Zenker wrote:

> I allways wondered, why the initial slowstart window is set to one
> (well some years I didn't look into the tcp code though). 9 years
> ago I had to develope the firmware for a store&foreward radio
> network, where I applied a lot of the ideas from the then net/2 tcp
> stack.  The rtt in such a network is really horrible and packetsizes
> have to be taken in account. Anyway the optimal initial window there
> was 2. With a window of two there much more probability to get a
> connection going, because you send two packets in the beginning,
> if the first is lost, the receiption of the second one gets the
> first one resent long before the timeout. Otherway round, if the
> second is lost... the third is on its way already. With a intital
> window of 1 the only recovery is by timeout. The argument against
> bigger than two was (at least in my case) not to defeat the intention
> of the slowstart.  Anyway, in tcp probably something between 2 and
> 4 could be considered.
>
> Thomas

RFC 2581 suggests that 4 is a good value (well, not exactly 4, they have a
formula which comes out to about 4 in most cases.)  I'm inclined to agree
that something between 2-4 would be a good value for our non-local
slowstart flightsize as well.  Maybe after 4.5 is released we can go look
into it.  (It's too late to be changing stuff now.)

Mike "Silby" Silbersack



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