W8SDZ@SIMTEL20.ARMY.MIL (Keith Petersen) (09/23/88)
The following is from a file, MNP-9.ARC, recently uploaded to my BBS.
It explains MNP protocols 1 through 9. I am not the author. The
information came from Microcom catalogs and was typed in by the person
whose name appears at the end of the file. This information is
supplied "as-is" and does not imply endorsement of any product.
--Keith Petersen
Maintainer of the CP/M and MSDOS archives at SIMTEL20.ARMY.MIL [26.0.0.74]
Arpa: W8SDZ@SIMTEL20.ARMY.MIL
Uucp: {ames,decwrl,harvard,rutgers,ucbvax,uunet}!simtel20.army.mil!w8sdz
GEnie: W8SDZ
RCP/M Royal Oak: 313-759-6569 - 300, 1200, 2400 (V.22bis) or 9600 (USR HST)
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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.
Microcom's 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 Microcom
MNP error-correcting modems 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 transfering ARCed files,
the CRC checking that occurs when the file is 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
receipt and these are particularly well suited to use with the
MNP-to-MNP connections.)
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.
The MultiTech 224E modem implements MNP Class 3.
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 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.
Microcom's AX/1200c, AX/2400c and PC/2400c support class 5. CASE's
4696/VS 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.22bis 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 maximum
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 andf 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
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 ndynamically adjusts to the type of data being transmitted, but
also predicts the probabality 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
Nothing 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
The above was taken from product description buochures from Microcom
by Mike Focke 8/1/88
bga@raspail.UUCP (Bruce Albrecht) (09/26/88)
Thanks for the description of the MNP classes. (I apologize for confusing Microcom with Micom in a previous posting). I'd just like to point out that Microcom's list of whose modems support which protocol class is incomplete, as I know that Multitech 224E has supported MNP class 5 for at least 6 months. As always, Caveat Emptor! Bruce