Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!swrinde!zaphod.mps.ohio-state.edu!van-bc!sl
From: sl@wimsey.bc.ca (Stuart Lynne)
Newsgroups: comp.dcom.modems
Subject: PPP and V.32bis/V.42bis (was Re: Uses of V.42 (bis?) data compression)
Message-ID: <1991Apr13.070324.10288@wimsey.bc.ca>
Date: 13 Apr 91 07:03:24 GMT
References: <10334@pitt.UUCP> <3908.280363d4@hayes.uucp> <1991Apr12.132116.11546@hobbit.gandalf.ca>
Distribution: na
Organization: Computer Signal Corp, Canada
Lines: 65

In article <1991Apr12.132116.11546@hobbit.gandalf.ca> dcarr@hobbit.gandalf.ca (Dave Carr) writes:
>In <3908.280363d4@hayes.uucp> tnixon@hayes.uucp writes:
>
>>I always advise people to compress before sending if possible.  An 
>>offline compression program can make multiple passes over the data 
>>and really optimize the compression, while a modem only has one shot 
>>at it.  

I've just installed a V.32bis/V.42bis on our PPP link and first results are quite
suprising. I tried ftp'ing from a fairly close site to see what the difference 
between each of the operating modes where.

To summarize:

	DTE speed:	19.2
	Protocol:	PPP with Van Jacobsen Header compression
	Text file: 	377799 bytes, an ls-lR file
	Compressed: 	79463 bytes
	Ping:		10 bytes, 20 times to router on far side of PPP link

Link		Text		Compressed		Ping
		sec/kbps	sec/kbps		min/avg/max
V.32bis		307/1.2		64/1.2			160/211/448
V.32bis/MNP5	230/1.6		64/1.2			240/263/384
V.32bis/V.42bis	230/1.6		50/1.5			240/251/272

Results
1. If latency is a problem the best results are obtained by just running in V.32bis
with no attempt to add MNP or V.42.

2. Both MNP5 and V.42bis achieve good results for non random ASCII text files.

3. V.42bis suprisingly did quite well with the compressed file. 

4. I was pressed for time so was unable to do the tests more than twice for each
transfer, so take the above with a grain of salt.

Conclusions
Up till now running at 9600 bps with V.32 I've taken the attitude that latency was a
problem. Our main use of this link is two nntp feeds, one from a local (across town)
site and one non-local (far side of continent) site. We also handle mail for a fair
number of local sites. With the odd ftp transfer thrown in.

The subjective feeling was that the additional benefits from MNP5 compression did not 
make up for the large increases in latency (several hundreds of milli-seconds). So 
we ran V.32 in raw mode. Not reliable mode with MNP.

Given the above results, with the latency differences being about 60 milli-seconds,
V.42bis seeming to be able to handle compressed files I'm going to use V.32bis and
V.42bis for now. The average latency on the new link will still be better than on
the old V.32 link, and all data transfers should be between 50-100% faster.

BTW the subjective feeling is that the link seems a lot faster. FTP logon's seem to
be made faster. And the FTP sessions don't seem to die as often. (With two sites
constantly dunning you with nntp transfer requests, and handling about 500 SMTP
conversations a day, at 9600 bps FTP was usually quite slow, and often seemed to die
just by being too slow, the dreaded message "Netin: connection reset by peer" was
often seen.)

If anyone out there has tried ftp'ing from here in the past and has the oppourtunity
to try again I'd appreciate any comments comparing responsiveness.

-- 
Stuart Lynne	Computer Signal Corporation, Canada
		...!van-bc!sl 604-937-7785 604-937-7718(fax) sl@wimsey.bc.ca