Contents of the WHATSMNP.TXT file
WHAT IS "MNP," ANYWAY?
edited & reprinted without permission
by Joseph Liu
What is MNP and how does it relate to your modem?
Essentially, MNP is a special protocol for the transfer of data. The
protocol is implemented as a PART of MNP modems.
I'm sure you've heard that using MNP will virtually double the effective
throughput of any given rated modem speed. Is this true?
MNP stands for Microcom Networking Protocol. It was developed by a company
of the same name to serve as an industry standard for high-speed, error-free
communications. Also, MNP is the integral part of the modem; i.e. hardware.
Modems that have MNP capabilities support common standards including Bell
103, 212A, CCITTV.22, V.22 bis, and V.29FT. In other words, all modem speeds
from 300 to 9600 baud. To better understand what MNP actually does, however,
we first need to take a look at the six different classes of MNP and how each
one is different from the other.
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.
The protocol efficiency of Class 1 MNP is about 70 percent. A device using
MNP Class 1 at 2400 baud will realize about 1700 baud. Notice that this is
actually LESS than the speed of a 2400 baud modem WITHOUT MNP. I wonder if
anyone still uses this class and, if they do, why?
MNP Class 2 uses asynchronous byte-oriented, full-duplex data exchange. The
protocol efficiency of Class 2 MNP is about 84 percent. A modem using Class 2
at 2400 baud will realize 2000 bps througput. The big difference between this
and Class 1 is the full-duplex transmission, rather than half-duplex.
This class uses synchronous bit-oriented, full-duplex data exchange. This
sounds powerful. 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 all those start and stop
bits. The user still sends data asynchronously to a Class 3 modem; meanwhile,
the modems communicate with each other synchronously. The protocol efficiency
here is about 108 percent.
Using a modem with Class 3 and 2400 baud will realize 2600 bps throughput.
At Class 3 performance, this MNP protocol "rewards" the user for using an
error-correcting modem by producing 8 percent extra throughput over an
ordinary 2400 baud modem not having any MNP capabilities.
MNP Class 4 introduces two new concepts, Adaptive Packet Assembly and Data
Phase Optimization, to further improve the performance of an MNP modem.
During data transfer, MNP monitors the reliability of the transmission medium
(the phone lines). If the dataline is relatively noise-free, MNP will
assemble larger data packets to increase throughput. If the line is
introducing too many errors because of noise or static, then MNP will put
together smaller data packets to be transmitted.
The result of sending smaller packets or chunks of data over a noisy line is
that more data is successfully transmitted on the first try, realizing greater
throughput despite the increased protocol overhead that is a result of the
MNP protocol recognizes that during the data transfer phase of the 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. The procedure further reduces protocol overhead.
The protocol efficiency of a modem using Class 4 MNP is about 120 percent.
At 2400 baud the modem will realize approximately 2900 bps throughput. This
isn't bad at all, considering this produces 20 percent more throughput than
with an ordinary 2400 baud modem without MNP.
MNP Class 5 introduces Data Compression as a new feature to this class. This
feature uses a real-time adaptive algorithm to compress all data being
The adaptive nature of the algorithm means that compression is always
optimized for the user's data. The compression algorithm continuously
analyzes the data being sent and adjusts the compression parameters to
maximize the data throughput.
Data compression algorithms, like sort algorithms, are sensitive to the type
of data being sent. The user will see compression performance vary between a
ratio of 1.3 to 1 and 2 to 1.
The files that will benefit most will be COM or EXE files, spreadsheet files,
word processing files, and print files. In most cases the overall compression
factor that an average user will experience will be 1.6 to 1 or 63 percent
A modem using Class 5 MNP at 2400 baud will realize 4800 bps throughput
and operate almost like the computer itself, analyzing data and adjusting as
This class uses new features called Universal Link Negotiation and
Statistical Duplexing. Universal Link Negotiation allows MNP modems to
begin operations at a common lower speed and negotiate the use of an alternate
high-speed modulation technique. Most modems using these two features will be
operating at speeds beyond 2400 baud, usually 9600 baud modems.
If you currently use a 9600 baud modem with Class 6 MNP, please let me know
what you discover. Daily overseas communications would obviously best benefit
from Class 6 MNP and 9600 baud.
The problem I've encountered using my modem at any of these classes is
determining the particular class of MNP at which it is operating. The red LED
light on my MultiTech modem only shows WHEN MNP is being used, not what class
of MNP is being used.
Also keep in mind that, for MNP to successfully work for you, BOTH your
modem AND the one you are connected to must have some form of MNP.
If you have an MNP modem, you can activate MNP in auto-reliable mode by
typing "AT&E1" in your terminal software when in terminal mode. If you're not
sure, consult your modem owner's manual.
It's anybody's guess how many MNP modems are now actually in use, but this is
a class of modem that will continue to grow. If you have MNP and want to
check out your modem's operation, you can call my BBS by dialing 312/622-4442
and test it out. The system supports Class 1-5 MNP up to 2400 baud.