telecom@ucbvax.UUCP (01/01/86)
Microcom just sent me data sheets on their new family of "AX"
modems which incorporate their new Classes 4, 5 & 6 of the MNP(tm)
Microcom Networking Protocol "the industry standard for error-free
asynchronous communications." The new Classes are upwards compatible.
They will talk to lower Classes, (at least down to Class 2, Class 1
is not specifically mentioned, but it is implied. This may not matter
since they imply that Class 1 is rare.) but only give the functionality
of the lower of the two Classes.
They also included two technical articles. One is an in-house
note, "MNP ERROR-CORRECTING MODEMS". The other is a reprint from
the March '83 Data Communications, "Anatomy of a microcomputer
protocol." From all of those, I have extracted a summary of the
various classes. All of them use packets. TF stands for "trans-
mission efficiency" which means the realized bit rate/modem bit rate
for an error free line, and with no other delays. DE stands for
data exchange method as described by Microcom.
Class 1. DE: asynchronous byte-oriented half-duplex. TF: 70%
Comments: Class 1 is not commonly used in the US. (It places
little demand on the microprocessor used for implementing it,
but is low in functional efficiency.)
Class 2. DE: asynchronous byte-oriented full-duplex, TF: 84%
Comments: Most microprocessors used for implementation, e.g.,
Z80, 6800, can handle this Class.
Class 3. DE: synchronous bit-oriented full-duplex. TF: 108%
Comments: The 108% comes from eliminating the start and stop
bits in transmission between the modems.
Class 4. DE: ? same as Class 3?, can be same as Class 2 when talking
to Class 2. TF: 120%.
Comments: Adds two new features, Adaptive Packet Assembly (tm)
which decreases the packet size (from 256 characters down to
32 characters) when the error rate increases, and Data Phase
Optimization (tm) which cuts out some of the unvarying
administrative information in data packets.
Class 5. DE: ?same as Class 4? TF: 200%, estimated.
Comments: In addition to Class 4 features, Data Compression
using a "real-time adaptive algorithm" is added. They estimate
compression ratios of 1.3 to 1 up to 2 to 1 and higher. They
list compressability in increasing order as: "1)COM or EXE files,
2)spreadsheet files, 3)word processing files, and 4)print files."
and estimate a realistic overall rate of 1.6 to 1.
Class 6. DE: ?same as Class 4?, TF: 200%?
Comments: In addition to Class 5 features, two features are
added: Universal Link Negotiation (tm) lets it talk to another
modem and arrive at the maximum mutually acceptable speed, over a
range of speeds (e.g., 300 - 9600 bps), and Statistical Duplexing
(tm) which involves monitoring the data traffic pattern, and
allocating the line so as to achieve good full-duplex performance
suitable even for echoplex terminal operation. Microcom has only
implemented this on their high speed (9600 bps) modem.
Microcom can be reached at 1400A Providence Hwy, Norwood, MA 02062
1-800-822-8224/617/762-9210
--henry schaffer
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