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From: ralphw@ius2.cs.cmu.edu (Ralph Hyre)
Newsgroups: net.dcom
Subject: Re: MNP Proposed as Industry Standard
Message-ID: <283@ius2.cs.cmu.edu>
Date: Fri, 20-Dec-85 18:10:27 EST
Article-I.D.: ius2.283
Posted: Fri Dec 20 18:10:27 1985
Date-Received: Mon, 23-Dec-85 04:27:47 EST
References: <213@gould9.UUCP> <557@adelie.UUCP> <1956@hplabs.UUCP>
Organization: Carnegie-Mellon University, CS/RI
Lines: 42

In article <1956@hplabs.UUCP> faunt@hplabs.UUCP (Doug Faunt) writes:
>> 
>>  It's not clear whether
>> anything can be gained (or if it's even possible) by running MNP in
>> software in say, your PC's terminal emulator.  BUT, if you DO
>
>Is this true?  If so, why?  Is there something simple here that I don't
>see?

Well, there's and end-to-end argument in computer systems design* which
claims that it's often useful to put error correction in the application
itself rather than depend on error correction at lower levels, since the
low-level correction doesn't know all the ways in which the higher-level
applications can lose or corrupt data.  MNP might get the bits back and
forth between the modems ok, but then you have to make sure that the 
modem <-> computer (memory) <-> filesystem connection is reliable.
(Generally it is, so most people will be happy with MNP and X.PC if
they're not to paranoid)

This would argue for putting MNP closer to the application itself.
In general, it's best to just to do error correction in just one place
unless the underliying communications channels are flaky enough to
require it (some LD phone lines are certainly an example of this.)

* recommended reading, it's in an ACM Transacions on (Computer Systems?)
journal that came out recently, written by two of the following people:
{Jerry Saltzer, Dave Clark, Dave Reed}

The careful file transfer discussion is very relevant.

--
					- Ralph W. Hyre, Jr.

Internet: ralphw@c.cs.cmu.edu (cmu-cs-c.arpa)	Usenet: ralphw@mit-eddie.uucp
Fido: Ralph Hyre at Net 129, Node 0 (Pitt-Bull) Phone: (412)578-2847,578-3275

-- 
					- Ralph W. Hyre, Jr.

Internet: ralphw@c.cs.cmu.edu (cmu-cs-c.arpa)	Usenet: ralphw@mit-eddie.uucp
Fido: Ralph Hyre at Net 129, Node 0 (Pitt-Bull) Phone: (412)578-2847,578-3275