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From: ejm@ejmmips.NOC.Vitalink.COM (Erik J. Murrey)
Newsgroups: comp.dcom.modems,comp.protocols.tcp-ip
Subject: Re: V32bis
Message-ID: <29@prang.TEST.Vitalink.COM>
Date: 17 Jan 91 18:06:13 GMT
References: <1991Jan16.210914.18482@robobar.co.uk> <3713.27832d53@hayes.uucp> <89275@lll-winken.LLNL.GOV> <81164@sgi.sgi.com>
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Reply-To: ejm@ejmmips.NOC.Vitalink.COM (Erik J. Murrey)
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In article <1991Jan16.210914.18482@robobar.co.uk>, ronald@robobar.co.uk
(Ronald S H Khoo) writes:
> vjs@rhyolite.wpd.sgi.com (Vernon Schryver) writes in defence of the TB+:
> 
> > On the contrary, X terminals would benefit from a good asymmetric splitting
> > of bandwidth.
> 
> But PEP doesn't give you split bandwidth, it gives you half duplex with
> extremely high cost to turn the line around.  Now, if you had a
> link-level protocol that reduced the number of turnrounds by letting
> whole windows through before letting the other side speak, you might
> win.  SLIP doesn't do this though, and my cursory glance at PPP doesn't
> show such an option there either (though I'd be glad to be told that I'm
> wrong).  Am I ? Does such a protocol exist ?
> 

Both SLIP and PPP only look as far as the IP header for clues on
delivery.  Even this may be considered too much of a bleed into the
network layer when a point-to-point data-link is involved. Both Van
Jacobson's Compressed SLIP and his extensions to PPP look as far as
the TCP header to determine compressability.

If SLIP or PPP were to provide TCP window optimization over the
data-link, then it would have to really dig into both the TCP header
and the TCP options to determine window size/status, etc.

While sometimes these optimizations are necessary to give a product an
edge in the market, I usually shy away from code that is *too* smart.

I tend to think that better optimization of IP over half-duplex links
can be done with smarter queuing algorithms coupled with starvation
prevention measures.  On the local machine, this may actually give the
feeling that entire windows are being sent at once, since all the
segments may be queued in one shot from the TCP code.

---
Erik J. Murrey
Vitalink Communications NOC
ejm@NOC.Vitalink.COM	...!uunet!NOC.Vitalink.COM!ejm