Programmer 7500/MAX_PROGRAMMERS.iso/PROGRAMS/UTILS/MODEMS/MNP_10.ZIP/MNP-10.ASC

Text File | 1990-01-31 | 14.4 KB | 347 lines

                   MNP Error Correcting Modems

Overview

The Microcom Networking Protocol, MNP, is a communications
protocol that supports interactive and file-transfer
applications.  MNP is designed to conform to the International
Organization for Standardization (ISO) Open System
Interconnection (OSI) Network Reference Model, or simply the OSI
model.  The OSI model is a network protocol divided into
standardized layers (or modules).  The use of standardized
layers assists in the interconnection of different vendors
equipment.
              ┌───────────────┐
              │               │
              │ Application   │
              ├───────────────┤
              │               │
              │ Presentation  │
              ├───────────────┤
              │               │
              │ Session       │
              ├───────────────┤
              │               │
              │ Transport     │
              ├───────────────┤
              │               │
              │ Network       │
              ├───────────────┤
          ┌─  │               │   ─┐
Modem plus│   │ Data Link     │    │
File Transfer ├───────────────┤    │ MNP Modem Connection
Protocol  │   │               │    │
i.e.Xmodem└─  │ Physical      │   ─┘
              └───────────────┘
The OSI model allows users to choose how their networking
systems are partitioned and implemented.

The Link Layer of the OSI Network Model is responsible for
provide reliable date transfer.  It uses the Physical Layer to
transmit information through the data path.  In dial-up data
communications, the data transmission of the Physical Layer is
performed by "traditional" modems using standards such as Bell
103, Bell 212A and V.22 bis.

Traditional modems cannot provide guaranteed error-free data
communications.  The noise and distortion characteristics of
voice-grade telephone circuits are beyond the capabilities of
any signal processing to deliver error-free data.  It is the
task of the Link Layer to provide a means of error detection
and error control.  Error detection when accessing Bulletin
Boards is provided for file transfers by an error-correcting
protocol (Xmodem for example) but there is no error detection
present when reading ASCII text.  That's why garbled character
can sneak thru but you can transfer a file successfully.


MNP error-correcting modems provide the integrity of data
transmission over voice-grade circuits for both file and text
transmission when connected to another MNP equipment modem.
When connected to a "standard" modem there is no hardware error
checking.  The user demand for error-free data communications
has made MNP error-correcting a "standard" in the modem industry
implemented by many modem manufactures.

(There is still a possibility of errors occurring in a MNP-to-
MNP connection if they occur at either end between the serial
port and the modem (in the cable) or in the computer itself.
The probability for error is much, much less here than exists
while the data is being transferred between modems. And, if you
are transferring ZIPed or ARCed files, the CRC checking that
occurs when the file is deZIPed/deARCed is enough to show you
that the file transfer was successful.

While some people run an MNP-to-MNP file transfer with no
additional error checking protocol, there are low-overhead
protocols which transfer large blocks of data between
acknowledgments of successful data receipt that are particularly
well suited to use with the MNP-to-MNP connections.  My
experience causes me to use Omen Technology's Zmodem even though
I have a "reliable" connection.)

Performance Comparisons of MNP Classes

MNP is designed for easy implementation on many hardware
configurations.  Different applications require different cost
and performance mixes.  MNP is deliberately structured to
provide different levels of performance without sacrificing
compatibility.  Unlike other protocols, applications that
require low-cost solutions can use simpler, less demanding
implementations of MNP and MNP implementations at all
performance levels are compatible with each other.  A small
application with a simple implementation of MNP can communicate
with a more powerful system using a high performance
implementation of MNP.

The primary principle of MNP is each implementation communicates
with all other implementations.  When an MNP communications link
is being established, the MNP implementations will negotiate to
operate at the highest mutually supported class of MNP service.

MNP assembles the user data into packets before retransmission.
The use of data protocols by the overhead a protocol introduces
to the communication channel.  The protocol overhead reduces the
effective data throughout of the communications channel.

A description of each MNP performance level follows.  The
description shows how MNP offers the user greater throughput
than the basic error-prone communication channel.






Class 1

This is the first level of MNP performance.  MNP Class 1 uses an
asynchronous byte-oriented half-duplex method of exchanging
data.  MNP Class 1 implementations make minimum demands on
processor speeds and memory storage.  MNP Class 1 makes it
possible for devices with small hardware configurations to
communicate error-free.

The protocol efficiency of a Class 1 implementation is about
70%.  A device using MNP Class 1 with a 2400 bps modem will
realize 1690 bps throughput.  Modern microprocessors have become
so powerful that implementations of MNP Class 1 are uncommon in
the U.S.

Class 2

MNP Class 2 uses asynchronous byte-oriented full-duplex data
exchange.  Almost all microprocessor-based hardware is capable
of supporting MNP Class 2 performance.  Common microprocessor
selected for MNP Class 2 implementations are Z80's and 6800's.

The protocol efficiency of a Class 2 implementation is about
84%.  A device using MNP Class 2 with a 2400 bps modem will
realize 2000 bps throughput.  Most microprocessor-based hardware
can easily implement MNP Class 2.

Class 3

MNP Class 3 uses synchronous bit-oriented full-duplex exchange.
The synchronous bit-oriented data format is inherently more
efficient than the asynchronous byte-oriented data format.  It
takes 10 bits to represent 8 data bits in the asynchronous data
format because of the "start" and "stop" framing bits.  The
synchronous data format eliminates the need for start and stop
bits.  The user still sends data asynchronously to the Class 3
modem; meanwhile, the modems communicate with each other
synchronously.

The protocol efficiency of a Class 3 implementation is about
108%.  A device using Class 3 with a 2400 bps modem will realize
2600 bps throughput.  At Class 3 performance, the MNP protocol
"rewards" the user for using an error-correcting modem by
producing 8% extra throughput over an ordinary modem without
MNP.

Class 4

MNP Class 4 introduces two new concepts, Adaptive Packet
Assembly(tm) and Data Phase Optimization(tm), to further improve
the performance of an MNP modem.  During data transfer, MNP
monitors the reliability of the transmission medium.  If the
data channel is relatively error-free, MNP assembles larger data
packets to increase throughput.  If the data is introducing many
errors, then MNP assembles smaller data packets to transmit.
while smaller data packets increase protocol overhead, they
concurrently decrease the throughput penalty of data
retransmissions.  The result of smaller data packets is more
data is successfully transmitted on the first try.

MNP protocol recognizes that during the data transfer phase of a
connection, most of the administrative information in the data
packet never changes.  Data Phase Optimization provides a method
for eliminating some of the administrative information.  This
procedure further reduces protocol overhead.

The protocol efficiency of a Class 4 implementation is about
120%.  A device using MNP Class 4 with a 2400 bps modem will
realize approximately 2900 bps throughput.  With class 4
performance, the MNP protocol produces 20% more throughput than
an ordinary modem without MNP.

Microcom's AX/1200, AX/2400 and PC/2400 support class 4.

Class 5

MNP Class 5 introduces Data Compression as a new feature to MNP
Class 4 service.  MNP Data Compression uses a real-time adaptive
algorithm to compress data.  The real-time aspects of the
algorithm allow the data compression to operate on interactive
terminal data as well as file-transfer data.  Data compression
delivers faster screen updates to the user.

The adaptive nature of the algorithm means data compression is
always optimized for the user's data.  The compression algorithm
continuously analyzes the user data and adjusts the compression
parameters to maximize data throughput.  Adaptive compression
means users of file-transfers receive maximum data compression
and data transfer.

Data compression algorithms, like sort algorithms, are sensitive
to the data pattern being processed.  Most data being
transmitted will benefit from data compression.  The user will
see compression performance vary between 1.3 to 1 and 2 to 1
(some files may be compressed at even higher ratios).  The
following types of common user files are listed in order of
increasing compressibility:
       1) COM or EXE files (ARCed files too)
       2) Spreadsheet files
       3) Word Processing files
       4) Print Files
A realistic estimate of the overall compression factor a user
will experience with print files is 1.6 to 1 or 63%.  This is
equivalent to having a net protocol efficiency of 200% for an
MNP Class 5 implementation.  A device using MNP Class 5 with a
2400 bps modem will realize 4800 bps throughput.  At MNP Class 5
performance, the MNP protocol produces over 100% more throughput
than an ordinary modem without MNP.

(Typical file transfers of files that have been already
compressed using ARC ro ZIP will average 270 CPS for a 2400 baud
MNP Class-5 Zmodem transfer with the serial port to modem link
locked at 9600 baud.  This is 23% better than the same file
transfered without MNP. - mf)

Microcom's AX/1200c, AX/2400c and PC/2400c support class 5.
CASE's 4696/VS supports Class 5.
MultiTech's MT224EH and EC supports Class 5.



Class 6

MNP Class 6 introduces the new features Universal Link
Negotiation(tm) and Statistical Duplexing(tm) to MNP Class 5
service.  Universal Link Negotiation allows MNP to unify non-
compatible modem modulation technology into the same MNP Error-
Correcting Modem.  Prior to Class 6, MNP was used to enhance
current modem technology. MNP Class 6 allows Microcom to create
new universal modems.

Most 1200 bps and 2400 bps modems are designed to be compatible
with lower speed modems. Bell 212A type modems operate at 1200
bps and incorporate the Bell 103 standard for 0-300 bps
communications.  Likewise, there are V.22 bis modems that
operate as 300 bps 103 modems, 1200 bps 212A modems and 2400 bps
modems.  However, high speed V.29 and V.32 modems do not provide
compatibility with each other or with the lower speed modulation
techniques found in 212A and V.22 bis modems.  Before the advent
of MNP Class 6, it was impossible for a single modem to operate
at a full range of speeds between 300 and 9600 bps.

Universal Link Negotiation allows MNP modems to begin operations
at a common slower speed and negotiate the use of an alternate
high speed modulation technique.  The Microcom AX/9624 is an
example of a modem that uses Universal Link Negotiation.
Universal Link Negotiation uses the 2400 bps V.22 bis technology
to negotiate a link.  At the end of a successful link
negotiation for Class 6 operation, the modem shifts to operation
using 9600 bps V.29 technology.

In the case where the high-speed carrier technology uses half-
duplex modulation, MNP Class 6 provides Statistical Duplexing.
The Statistical Duplexing algorithm monitors the user data
traffic pattern to dynamically allocate utilization of the half-
duplex modulation to deliver full-duplex service.

An MNP Class 6 modem based on V.29 technology delivers high
performance in file transfer applications; up to 19.2 kbps
throughput is possible on dial-up circuits for most
applications.  In accordance with the principles of MNP, the
Class 5 Data Compression is fully incorporated in MNP Class 6.

The MNP Class 6 Modem will deliver optimum performance even on
an interactive terminal using character echoplexing. Screen
updates will occur at speeds between 9.6 kbps and 19.2 kbps.
Most screen updates will take less than a second.

Microcom's AX/9612c, AX/9624c and PC/9624c support Class 6.


Most of the above text was taken from a Microcom Features
Description by Mike Focke 7/7/87






New in 1988

Class 7

MNP Class 7 Enhanced Data Compression, combined with Class 4,
achieves improved throughput with efficiencies up to 300% via
the latest data compression technology. Microcom's enhanced
encoding technique not only dynamically adjusts to the type of
data being transmitted, but also predicts the probability of
characters in a data stream. This combined with run length
encoding, which sends repeating characters as a single number
code, results in the superior compression efficiencies supported
in MNP Class 7.

The Microcom QX/12K supports Class 7.

Class 8

No information from Microcom was available.

Class 9

MNP Class 9 utilizes Enhanced Data Compression combined with
V.32 technology to deliver maximum throughput up to 300% greater
than ordinary V.32 modems.  Class 9 also features Enhanced
Universal Link Negotiation which allows connection to both MNP
and non-MNP modems at the highest performance level.

The Microcom QX/.32c supports Class 9.

Class 10

MNP Class 10 adds what Microcom calls ACE, or Adverse Challen
Enhancements, which automatically change the transmission speed
and packet size depending on the line quality. These
enhancements are especially useful, Microcom says, when signal
clarity fades in and out, as in celular links or for
international transmission using outdated analog switching
equipment. A feature of ACE called Robust Auto Reliable also
provides backwards compatibility with non-MNP modems.

The Microcom QX2400t supports Class 10.

The above was taken from product description brochures from
Microcom by Mike Focke 8/1/88 and an ad in Byte Feb 90 issue.

Microcom
500 River Ridge Drive
Norwood, MA 02062-5028

Phone: [phone]