Path: utzoo!attcan!uunet!fernwood!portal!cup.portal.com!thad
From: thad@cup.portal.com (Thad P Floryan)
Newsgroups: comp.sys.amiga
Subject: Re: Modems
Message-ID: <33893@cup.portal.com>
Date: 14 Sep 90 09:02:16 GMT
References: <826.26EF2259@weyr.FIDONET.ORG>
  <90256.111652UH2@psuvm.psu.edu> <27777@pasteur.Berkeley.EDU>
Organization: The Portal System (TM)
Lines: 51

c150-ec@danube.Berkeley.EDU (Johnson Sieu) in <27777@pasteur.Berkeley.EDU>
asks:

	Just one question -- Do you need special modems on both sides of the
	line for the data to be packed and unpacked properly?

Yes, you would need, for example, MNP modems at both ends of the line to
realize the error correction and compression.

Note, too, there are "classes" of MNP; I'm presently 'playing' with a set of
Microcom QX/V.32c modems with MNP class 9 (whew!) since I test several hundred
modems each year for correct operation with my own products.

As a quick ref from the Microcom manual (the "inventors" of MNP):

MNP	Description

2	asynchronous framing for data transmission and error correction.
	Because of the protocol overhead, actual throughput is less than the
	bps rate of the modem

3	synchronous framing, giving 20% thoughput increase over class 2, with
	thoughput higher than the bps rate of the modem.  For example, a
	2400 baud modem operating at Class 3 transmits data at 2600 bps.

4	synchronous framing with adaptive packet assembly and "Optimized Data
	Phase" developed by Microcom.  A 2400 baud modem operating at Class 4
	transmits data at 2900 bps.

5	includes data compression which, with class 4, provides throughput
	of almost twice the connection speed.

6	half-duplex, fast train reliable connections at 4800 to 9600 bps,
	giving from 11000 to 19200 bps.

7	"Enhanced Data Compression" which, with Class 4 service, provides
	more than twice the connection speed

8	(not described)

9	the features of Class 7 plus V.32 operation.


Believe me, the MNP stuff DOES work, and it's mind-boggling how a dial-up
line can give performance surpassing direct hard-wired connections to a
local computer (at least at my company! :-)    I call Chile, England, Holland
and elsewhere, and the connections are literally perfect (from California).
Plus, my phone bill has dropped from $200+/month to around $40/month; these
modems pay for themselves very quickly.

Thad Floryan [ thad@cup.portal.com (OR) ..!sun!portal!cup.portal.com!thad ]