From: dogbowl@dogbox.acme.gen.nz (Kennelmeister)
Newsgroups: comp.bbs.waffle
Subject: Re: UUCICO SPEED
Date: Tue, 15 Dec 92 09:19:21 +1300
Organization: The Dawghaus BBS, Palmerston North, New Zealand (+64 6 357 9245)

fenner@postscript.cs.psu.edu (Bill Fenner) writes:

> In article <a51LVB9w165w@dogbox.acme.gen.nz> dogbowl@dogbox.acme.gen.nz (Kenn
> |Fer crissake! Read the bloody standards! If you are using v42bis, you
> |are automatically using MNP5, as it is the fallback standard.
> 
> Um... which v.42bis are you using?  You're not talking about the CCITT's
> v.42bis.
> 
> |V42bis is a COMPRESSION standard which incorporates MNP5 and V42
> 
> v.42bis is a compression standard which has nothing to do with MNP5, and
> requires an error corrected connection.  v.42 is the usual means of getting
> an error corrected connection with v.42bis, but that doesn't mean you couldn'
> have a different means.
> 
> |V42    is an error correction standard which incorporates MNP2,3 and 4
> 
> v.42 has nothing to do with MNP2,3, or 4, other than that they are all error
> correction mechanisms, and both v.42 and MNP4 strip start and stop bits.
> 

WRONG!

Read on. The following stuff is excerpted from a posting made in
comp.dcom.modems some time ago......


======
From: mmaster@parnasus.dell.com (Michael Masterson)
Newsgroups: comp.dcom.modems
Subject: Re: FAQ -- define v.32, v.42, etc.
Date: Tue, 22 Sep 1992 20:22:57 GMT
Organization: Dell Computer Co

johng@informix.com (John Galloway) writes:

>> > v.32 -- 9600 baud modem
>> > v.32bis -- v.32 modem with data compression, up to 4 times the actual data
>> > rate
>> > v.42 -- 14.4k modem
>> > v.42bis -- see v.32bis
>> > mnp-5 -- data compression algorithm providing 2 times actual data rate
>> > mnp-10 -- ???
>>I beg to differ:
>>V.32 - Signalling scheme for 9600 baud over phone lines
>>V.32bis - Signalling scheme for 14400 baud over phone lines
>>V.42 - LAP-M error correction, used over V.32 and V.32bis connections
>>V.42bis - Data compression used over V.42/V.32 and V.42/V.42bis connections
>>MNP5 - error correction and data compression - proprietary (and older)
>what about MNP2,3,4 and MNP10?? what about V.fast??
>Is there really an FAQ for comp.dcom.modems or what? Doesn't someone
>actually HAVE a CCITT book that specifiies these standards
>rather than giving us their (very well intentioned, but sometimes worng)
>recolections?

Yup.. well, close enough, for the definitive answer, we go to the
electronic dictionary, on the Computer Select CD-ROM, and we find:

(this is rather long, but comprehensive.)


 *****  Computer Select, August 1992 : Doc #179763  *****

Book:      Newton's Telecom Dictionary
           * Full Text COPYRIGHT Harry Newton 1991.
-----------------------------------------------------------------------------
Term:      V SERIES RECOMMENDATIONS
Author:    Newton, Harry.
-----------------------------------------------------------------------------

CCITT standards dealing with data communications operation over the
telephone network. The idea of standards is simple. If you have them and if
every manufacturer conforms, then every modem can talk to every other one.
That's the idea. But it's not always that simple. Sometimes you have to
conform to several standards. For example, in the higher speed modems, for
example those at 9,600 bps, you have to conform to speed (that's one
standard). You have to conform to error control. That's another standard.
And you also have to conform to data compression -- if you are using data
compression. ISDN terminal adapters are V series recommendations, too.
CCITT uses the term "bis" to designate the second in a family of related
standards and "ter" designates the third in a family.

[about 200 lines deleted]



 *****  Computer Select, August 1992 : Doc #179808  *****

Book:      Electronic Computer Glossary
           * Full Text COPYRIGHT The Computer Language Co. Inc. 1991.
-----------------------------------------------------------------------------
Term:      V.42
Author:    Freedman, Alan.
-----------------------------------------------------------------------------

CCITT standard (1989) for modem error correction that uses LAPM as the
primary protocol and provides MNP Classes 2 through 4 as an alternative
protocol for compatibility.



 *****  Computer Select, August 1992 : Doc #179809  *****

Book:      Newton's Telecom Dictionary
           * Full Text COPYRIGHT Harry Newton 1991.
-----------------------------------------------------------------------------
Term:      V.42 bis DATA COMPRESSION
Author:    Newton, Harry.
-----------------------------------------------------------------------------

Recently-approved CCITT data compression standard. It compresses files at
average ratio of 3.5:1 and can yield file transfer speeds of up to 9,600
bps on a 2,400 bps modem, or 38,400 bits per second with a 9,600 bps modem
when combined with V.42 depending upon the type of data being transferred.
If you're buying a 9,600 modem for use over dial-up phone lines, make sure
it has V.42 bis data compression, V.42 error correction and conforms to
V.32.

V.42 bis was approved by the CCITT because of its technical merits.
Existing data compression methods (MNP 5 for example) only provided up to
two-to-one compression. Also, V.42 bis provides for built-in "feedback"
mechanisms, so that the modem can monitor it's own compression performance.
If the DTE starts send pre-compressed or otherwise uncompressible data,
V.42 bis can automatically suspend it's operation to avoid expansion of the
data. It continues to monitor performance even when sending data "in the
clear", and when a performance improvement can be gained by reactivating
compression, it will do so automatically.

V.42 bis was selected because it would work with a wide variety of
different implementations -- different amounts of memory, different
processor speeds, etc. Because of this, there WILL be differences between
various manufacturer's products in terms of THROUGHPUT performance
(although they will all properly compress and decompress, some will do it
faster than others). If maximum throughput is important, users should check
benchmark tests to find the modem that provides the best performance.



 *****  Computer Select, August 1992 : Doc #179810  *****

Book:      Newton's Telecom Dictionary
           * Full Text COPYRIGHT Harry Newton 1991.
-----------------------------------------------------------------------------
Term:      V.42 ERROR CORRECTION
Author:    Newton, Harry.
-----------------------------------------------------------------------------

CCITT error-correction standard specifying both MNP4 and LAP-M. The CCITT
title says "Error-correcting procedures for DCEs using
Asynchronous-to-Synchronous Conversion". It also notes in the text that it
applies only to full-duplex devices. The CCITT modulation schemes with
which V.42 may be used are V.22, V.22 bis, V.26 ter, and V.32, and V.32
bis. LAPM, based on HDLC, is the "primary" protocol, on which all future
extensions will be based. The Alternative Protocol specified in Annex A of
the Recommendation is for backward compatibility with the "installed base"
of error-correcting modems.



 *****  Computer Select, August 1992 : Doc #179811  *****

Book:      Electronic Computer Glossary
           * Full Text COPYRIGHT The Computer Language Co. Inc. 1991.
-----------------------------------------------------------------------------
Term:      V.42bis
Author:    Freedman, Alan.
-----------------------------------------------------------------------------

CCITT standard (1989) for modem error correction and data compression.  It
uses V.42 error correction with a compression technique (British Telecom
Lempel Ziv) that increases transmission speed up to four times the bps
rating.



 *****  Computer Select, August 1992 : Doc #175007  *****

Book:      Newton's Telecom Dictionary
           * Full Text COPYRIGHT Harry Newton 1991.
-----------------------------------------------------------------------------
Term:      MICROCOM NETWORK PROTOCOL.
Author:    Newton, Harry.
-----------------------------------------------------------------------------

The Microcom Networking Protocol, MNP, is a defacto standard protocol that
provides error correction and data compression in dial-up modems. The
protocol's design allows for a broad range of services to be implemented,
while maintaining compatibility among modems with different levels of MNP
capabilities. For example, a modem capable of MNP Class 5 and Class 7 data
compression can talk to a modem that lacks MNP data compression.

According to Microcom, "MNP is an error correction protocol accepted by
international standards authorities (CCITT Rec. V.42). MNP offers a
reliable and widely accepted method of correcting errors in transmissions
over dial-up communications lines. MNP incorporates three different data
compression methods, including the CCITT recommendation, V.42bis.

Since its original definition, MNP has evolved through nine classes of
enhancements. Of those nine classes, the first four provide error control
and are in the public domain. Classes 5 through 7 may be licensed from

=====================


Microcom. Currently MNP error control (Classes 2,3 and 4) has been adopted,
along with the LAPM protocol, as mandatory elements of the Consultative
Committee on International Telegraphy and Telephony (CCITT) V.42
recommendation for modem error control.

=====================

AN OVERVIEW OF MNP SERVICE CLASSES

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 minimal demands of processor speeds and memory
storage. MNP Class 1 makes it possible for devices with few hardware
resources to communicate error-free. Class 1 implementations are no longer
included in modems.

Class 2

MNP Class 2 uses asynchronous byte-oriented full-duplex data exchange
(i.e., data goes in both directions at once). All microprocessor-based
modems are capable of supporting MNP Class 2 performance.

Class 3

This class uses synchronous bit-oriented full-duplex data exchange,
eliminating the overhead of start and stop bits used in byte-oriented
asynchronous communications. The user still sends data asynchronously to
the modem while communications between modems is synchronous.

Class 4

This class introduces two new concepts. Adaptive Packet Assembly and Data
Phase Optimization, both of which further enhance performance. Adaptive
Packet Assembly means that the size of the packets in which data is sent
between modems is altered according to the quality of the physical link.
The higher the line quality, the larger the packets. Larger packets, while
more efficient (the ratio of user data to control data is higher), are also
more susceptible to errors. Data Phase Optimization means that repetitive
control information is removed from the data stream to make packets more
efficient. Both techniques, when combined with Class 3, yield a protocol
efficiency of about 120 percent (A V.22bis 2400 bps modem will realize
approximately a 2900 bps throughput).

Class 5

This class implements MNP basic data compression to realize a net
throughput efficiency of 200 percent on average. (A 2400 bps modem will
realize 4800 bps). Class 5 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. 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.

Class 6

This class implements Universal Link Negotiation. and Statistical
Duplexing. The first feature allows a single modem to operate at a full
range of speeds between 300 and 9600 bps, depending on the maximum speed of
the modem on the other end of the link. Modems begin operation at a common
slower speed and negotiate the use of an alternative high speed modulation
technique.

The Microcom AX/9624c modem is an example of a modem that uses Universal
Link Negotiation, starting with 2400 bps. V.22bis technology and shifting
to 9600 bps V.29 fast train technology, if the other modem has that
technology too. Statistical Duplexing allows the modem to simulate
full-duplex service on the half-duplex V.29 modem connection.

Class 7

This class implements a more efficient data compression method than the one
used in Class 5. The difference between the two classes is that Class 5
realizes an average 200 percent speed improvement over a non-MNP modem,
versus an average 300 percent improvement for Class 7. Class 7 data
compression uses Huffman encoding with a predictive algorithm to represent
user data in the shortest possible Huffman codes.

In addition to Class 5 and Class 7 data compression, MNP also supports
V.42bis data compression. Based on the Lempel Ziv data compression model,
V.42bis supports an average 400 percent efficiency improvement.

Class 8

Not defined.

Class 9

This class reduces the amount of time required for the modem to perform two
frequently-occurring administrative activities: to acknowledge that a
message was received- and to retransmit information following an error.
Message acknowledgment is streamlined by "piggy-backing" the acknowledgment
in its own dedicated packet. Retransmission is streamlined by indicating in
the error or Negative Acknowledgment Packet (NAK) the order sequence number
of each of the failed messages. Rather then sending all the messages over
again (even the good ones) from the point of the error, as is usually done
with error correcting protocols, only the failed messages are resent.

Class 10

MNP Class 10 consists of Adverse Channel Enhancements that optimize
performance in environments with poor or varying line quality, such as
cellular telephones, international telephone calls, and rural telephone
service. These enchancements fall into four categories:

Multiple aggressive attempts at link setup

Adapting packet size to accommodate varying levels of interference

Negotiating transmission speed shifts to achieve the maximum acceptable line
speed

Dynamically shifting to the modem speed most suitable to transmission line
conditions.



 *****  Computer Select, August 1992 : Doc #175107  *****

Book:      Electronic Computer Glossary
           * Full Text COPYRIGHT The Computer Language Co. Inc. 1991.
-----------------------------------------------------------------------------
Term:      MNP
Author:    Freedman, Alan.
-----------------------------------------------------------------------------

(Microcom Networking Protocol)  Family of communications protocols from
Microcom, Inc., Norwood, MA, that have become de facto standards for error
correction and data compression.

Class    Features

  1  Half-duplex asynchronous transmission.

  2  Full-duplex asynchronous transmission.

  3  Full-duplex synchronous transmission using
     HDLC framing techniques using 64-byte
     blocks.  Start/stop bits stripped.

  4  Increased throughput.  Shorter headers,
     frames up to 256 bytes.  Some vendors
     adjust frame size based on line quality.

  5  Compresses data up to two times.

  6  Starts at V.22bis modulation and switches
     to V.29 if possible.  Uses pseudo-
     duplexing ping-pong method for faster
     turnaround of V.29 transmission.

  7  Compresses data up to three times.

  8  Not in use.

  9  Adds Piggy-back Acknowledgement** and
     selective retransmission for more
     efficient transport of data.  Provides
     better performance over variety of links.

 10  Adds Adverse Channel Enhancements** for
     efficient operation on noisy lines (rural,
     cellular, international, etc.).

** Proprietary Microcom techniques.



 *****  Computer Select, August 1992 : Doc #174179  *****

Book:      Electronic Computer Glossary
           * Full Text COPYRIGHT The Computer Language Co. Inc. 1991.
-----------------------------------------------------------------------------
Term:      LAP
Author:    Freedman, Alan.
-----------------------------------------------------------------------------

(Link Access Procedure)  CCITT family of error correction protocols
originally derived from the HDLC standard and used on X.25 packet
networks.

LAP-B (LAP-Balanced) Used in current X-25 networks.

LAP-D (LAP-D channel)  Used in the data channel of
                       an ISDN transmission.

LAP-M (LAP-Modem)  Defined in CCITT V.42, which
                   uses some of the LAPD methods
                   and adds additional ones.

LAP-X (LAP-Half-dupleX)  Used for ship to shore
                         transmission.



Book:      Newton's Telecom Dictionary
           * Full Text COPYRIGHT Harry Newton 1991.
-----------------------------------------------------------------------------
Term:      BIS
Author:    Newton, Harry.
-----------------------------------------------------------------------------

The French term for "second" or "encore." It is used by the CCITT to
designate the second in a family of related standards. "ter" designates
the third in a family. See V SERIES.



 *****  Computer Select, August 1992 : Doc #169056  *****

Book:      Electronic Computer Glossary
           * Full Text COPYRIGHT The Computer Language Co. Inc. 1991.
-----------------------------------------------------------------------------
Term:      baud
Author:    Freedman, Alan.
-----------------------------------------------------------------------------

(1) Signalling rate of a line.  It's the switching speed, or number of
transitions (voltage or frequency changes) that are made per second.  Only
at low speeds are bauds equal to bits per second; for example, 300 baud is
equal to 300bps.  However, one baud can be made to represent more than one
bit per second.  For example, the V.22bis modem generates 1,200bps at 600
baud.

(2) Commonly (and erroneously) used to specify bits per second for modem
speed; for example, 1,200 baud means 1,200bps.  See previous paragraph.

-- 
Operated by professionals, do not try at home, see your dealer for details.
Your mileage may vary. Call before digging. Best if eaten by date on package.
Apply only to affected area. Batteries not included. Member FDIC.
Michael Masterson                                   mmaster@parnasus.dell.com

==================end included text


--
Alan B                           See Janet's ball. See John's chainsaw
Dogbowl@dogbox.acme.gen.nz       See Spot run. Run, Spot, run!
Dawghaus BBS +64 6 357-9245      Far too slow......
Palmerston North, New Zealand    Spot's in bits. Run Janet Run!