Path: utzoo!attcan!uunet!husc6!uwvax!tank!mimsy!chris
From: chris@mimsy.UUCP (Chris Torek)
Newsgroups: comp.dcom.modems
Subject: Re: PEP still wins over V.32 (was Re: V.32 will dominate the ma
Message-ID: <14513@mimsy.UUCP>
Date: 12 Nov 88 19:26:17 GMT
References: <11079@cup.portal.com> <1247@nusdhub.UUCP>
Distribution: na
Organization: U of Maryland, Dept. of Computer Science, Coll. Pk., MD 20742
Lines: 51

>In article <11079@cup.portal.com> David@cup.portal.com (David Michael McCord)
>suggests:
>>... I wouldn't be all that suprised if Telebit was the first on the
>>market with a uucp-spoofing v.32 device.

In article <1247@nusdhub.UUCP> rwhite@nusdhub.UUCP (Robert C. White Jr.) writes:
>Why bother?  There would be no particular gain to spoofing using V.32
>since the connection will not be impared by passing the protocol
>directly.  There is no dynamic or adaptave turnaround to slow the
>connection durring the acknowlegement phases, and the ack phases slide
>through an open window wide enough to allow streaming (e.g. ack is not
>required before next packet is sent.)

There would still be a minor gain if the computer<->modem connection is
run at >9600 bps, or if the modem's error correction protocol reduces
actual modem<->modem bit rate to <9600 bps.  UUCP's `g' packets are a
bit too small for efficient high speed communication.  If the modem is
strictly 9600 bps, you would gain nothing (since any modem-to-modem
transmission of acks suppressed by spoofing would have to occur on one
end of the modem-to-computer links anyway).

If you use ACSnet-like software, *and* your data flow is approximately
balanced, a true 9600 bps full duplex connection would outperform the
average Telebit TB+ modem in terms of time required to transmit data,
because the aggregate throughput approximates 19200 bps, not ~14000 as
in the (unidirectional flow) TB+.  If you use UUCP-like software, *or*
if your data flow is predominately unidirectional, an adaptive half
duplex protocol that provides more than 9600 bps in the primary
direction will win over a full duplex protocol that provides only 9600
bps in the primary direction.

It is worth noting that netnews flow is predominately unidirectional
for leaf USENET nodes.  Using a better transport mechanism than UUCP
would still provide no incentive to switch to full duplex modems for
such nodes, assuming that netnews makes up the bulk of your UUCP
traffic.  (At approximately 4 MB/day, it almost certainly does.  This
seems to be what Mr. McCord has missed: USENET leaf nodes are pushing
multiple megabytes of junk each day in a single direction over any
given dialup connection; we *need* most of the available bandwidth to
be allocated unidirectionally.  The data volume is high enough---and
growing fast enough---to indicate that this unidirectionality is not
likely to reverse for some time yet, despite the growing prevalence of
things like SLIP.  Netnews data flow remains unidirectional even if
sent over IP or X.25.  It will take a either a qualitative change in
usage, which seems unlikely for the near future, or an enormous
quantitative shift, which also seems unlikely, to change this.  The
exact compromise provided by the TB+ may not be appropriate a year
from now, but one like it probably will.)
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7163)
Domain:	chris@mimsy.umd.edu	Path:	uunet!mimsy!chris