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From: david@bacchus.esa.oz.au (David Burren [Athos])
Newsgroups: comp.dcom.modems
Subject: Re: uucp over v.32
Keywords: MNP
Message-ID: <2011@bacchus.esa.oz.au>
Date: 16 Mar 91 08:31:31 GMT
References: <1991Mar12.033518.10492@colnet.uucp> <1991Mar15.073701.10005@hq.demos.su>
Organization: Expert Solutions Australia
Lines: 67

In <1991Mar15.073701.10005@hq.demos.su> dvv@hq.demos.su (Dmitry V. Volodin) writes:

>In <1991Mar12.033518.10492@colnet.uucp> res@colnet.uucp (Rob Stampfli) writes:

>>A few basic questions about uucp over a v.32 modem:

>>1. Does the addition of MNP1-4 increase or decrease the thruput?  Theoretically
>>   it would seem that it would increase it by up to 20%, but I wonder if the
>>   windowing of "g" protocol would be adversely affected resulting in a net
>>   loss.

>IMHO MNP1-4 won't help much UUCP-g (if UUCP-g is implemented effectively,
>of course). Why run one error-correctin proto on top of another using
>approx the same technique? Aside of your question - MNP5 is worth using.

MNP classes less than 3 decrease the effective bandwidth of your line.
MNP3 gives 108%, while MNP4 gives up to 120% of the native bandwidth.
It does this by stripping start/stop bits and running the line synchronously
between modems.  I've had no trouble running UUCP-g over the top of that.

I run UUCP-g connections over 2400bps/MNP4 connections and see actual
throughput increases of close to 20%.  This is on my home machine that
services 15 other nodes.  I see similar throughput increases here at work
when using the SUN-III (ACSnet) transport protocol.

UUCP-g _does_ work with MNP4.  However, there are a few variables:

	The packet sizes used in MNP4 starts at 32 bytes, and if line quality
	is good this will increase up to 256 bytes/packet.  In most MNP modems
	you can limit the maximum packet size to 64/128/192/256 bytes.
	I've experimented with various packet sizes, and although I haven't
	noticed major differences, currently limit it to 128 bytes, as most
	UUCP-g packets are just over 64 bytes in total size.

	All the MNP4 connections I use are over local phone lines, not
	long-distance.  Mind you, the line quality between the two is
	often similar, and local calls are often across multiple exchanges.
	(This is in Melbourne, Australia)
	Thus I'm probably not affected by MNP retries very much.

Your mileage may vary.

IMHO, MNP5 is NOT worth using for UUCP.  Most traffic on my UUCP lines are
compressed news batches, which conflicts with the compression in MNP5,
reducing the bandwidth.  It's simple to compress files before sending them
(even mail, through compressed-batched-SMTP, although that requires support
on the remote host for uncompressing) and that saves on spool disk space.


>>2. If you are running MNP1-4, is "g" the best protocol to use?  If not, what
>>   is?

>IMHO it is not. You'd better use "f" or even "e", providing, of course,
>that your modems/drivers treat hardware flow control right.

'g' _does_ have the advantage of being supported on every UUCP implementation
that you may connect to.

If you use a protocol that assumes an error-free line you'd better be sure
that it _is_ error-free.  As Dmitry says, you need to have hardware flow
control working.  On both ends.

UUCP-g works well enough for me over MNP4....
_____________________________________________________________________________
David Burren [Athos]                          Email: david@bacchus.esa.oz.au
Software Development Engineer                 Phone: +61 3 819 4554
Expert Solutions Australia, Hawthorn, VIC     Fax:   +61 3 819 5580