Modem Standards

 

current modem standards (CCITT is now ITU-T). note that you have to be a subscriber to get detailed spec info.

cat News/tele
Article 17225 of comp.dcom.modems:
Newsgroups: comp.dcom.modems
Path: klic!percy!psgrain!uunet!cis.ohio-state.edu!zaphod.mps.ohio-state.edu!swrinde!news.dell.com!parnasus!mmaster
From: (Michael Masterson)
Subject: Re: FAQ -- define v.32, v.42, etc.
Message-ID:
Lines: 1160
Sender: (Net News Admin)
Nntp-Posting-Host: parnasus.dell.com
Organization: Dell Computer Co
References:
Date: Tue, 22 Sep 1992 20:22:57 GMT

(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.

 

***** Computer Select, August 1992 : Doc #179764 *****

Book: Electronic Computer Glossary
* Full Text COPYRIGHT The Computer Language Co. Inc. 1991.
-----
Term: V.110
Author: Freedman, Alan.
-----

CCITT standard (1984) that specifies how data terminal equipment (DTE)
with asynchronous or synchronous serial interfaces can be supported on an
ISDN network. It uses rate adaption, which involves a bit-by-bit
alignment between the DTE and the ISDN B channel.

 

***** Computer Select, August 1992 : Doc #179765 *****

Book: Electronic Computer Glossary
* Full Text COPYRIGHT The Computer Language Co. Inc. 1991.
-----
Term: V.120
Author: Freedman, Alan.
-----

CCITT standard (1988) that specifies how DTEs with asynchronous or
synchronous serial interfaces can be supported on an ISDN network using a
protocol (similar to LAP-D) to encapsulate the data to be transmitted. It
includes the capability of using statistical multiplexing to share a B
channel connection between multiple DTEs.

 

***** Computer Select, August 1992 : Doc #179766 *****

Book: Newton's Telecom Dictionary
* Full Text COPYRIGHT Harry Newton 1991.
-----
Term: V.13
Author: Newton, Harry.
-----

CCITT standard for simulated carrier control. Allows a full-duplex modem to
be used to emulate a half-duplex modem with interchange circuits changing
at appropriate times.

 

***** Computer Select, August 1992 : Doc #179767 *****

Book: Newton's Telecom Dictionary
* Full Text COPYRIGHT Harry Newton 1991.
-----
Term: V.14
Author: Newton, Harry.
-----

CCITT standard for asynchronous-to-synchronous conversion without error
control. Allows a modem that is actually synchronous to be used to carry
start/stop (async) characters. If a V.42 modem connects with another modem
that doesn't have error-control, it falls back to V.14 operation to work
without error-control.

 

***** Computer Select, August 1992 : Doc #179768 *****

Book: Newton's Telecom Dictionary
* Full Text COPYRIGHT Harry Newton 1991.
-----
Term: V.17
Author: Newton, Harry.
-----

New CCITT standard for simplex (one-way transmission) modulation technique
for use in extended Group 3 Facsimile applications only. Provides 7200,
9600, 12000, and 14400 bps trellis-coded modulation (the modulation scheme
is similar to V.33).

 

***** Computer Select, August 1992 : Doc #179769 *****

Book: Electronic Computer Glossary
* Full Text COPYRIGHT The Computer Language Co. Inc. 1991.
-----
Term: V.17
Author: Freedman, Alan.
-----

CCITT standard (1991) for fax transmission that uses TCM modulation at
12,000 and 14,400bps for Group 3. It adds TCM to the V.29 standard at
7,200 and 9,600bps to allow transmission over noisier lines. It also
defines special functions (echo protection, turn-off sequences, etc.) for
half-duplex operation. Modulation use is a half-duplex version of
V.32bis.

 

***** Computer Select, August 1992 : Doc #179770 *****

Book: Electronic Computer Glossary
* Full Text COPYRIGHT The Computer Language Co. Inc. 1991.
-----
Term: V.21
Author: Freedman, Alan.
-----

CCITT standard (1964) for asynchronous 0-300bps full-duplex modems for use
on dial-up lines. It uses FSK modulation.

 

***** Computer Select, August 1992 : Doc #179771 *****

Book: Newton's Telecom Dictionary
* Full Text COPYRIGHT Harry Newton 1991.
-----
Term: V.21
Author: Newton, Harry.
-----

CCITT standard for 300 bit per second duplex modems for use on the switched
telephone network. V.21 modulation is used in a half-duplex mode for Group
3 fax negotiation and control procedures (CCITT T.30).

 

***** Computer Select, August 1992 : Doc #179772 *****

Book: Newton's Telecom Dictionary
* Full Text COPYRIGHT Harry Newton 1991.
-----
Term: V.21 CH 2
Author: Newton, Harry.
-----

CCITT standard for 300 bps modem, describing the operation of modems at 300
bps, and used for critical control and handshaking functions. This low
speed is highly tolerant of noise and impairments on the phone line. Fax
machines use only Channel 2 of the V.21 recommendations (half duplex
channel).

 

***** Computer Select, August 1992 : Doc #179773 *****

Book: Newton's Telecom Dictionary
* Full Text COPYRIGHT Harry Newton 1991.
-----
Term: V.22
Author: Newton, Harry.
-----

CCITT standard for 1,200 bit per second duplex modems for use on the
switched telephone network and on leased circuits.

 

***** Computer Select, August 1992 : Doc #179774 *****

Book: Electronic Computer Glossary
* Full Text COPYRIGHT The Computer Language Co. Inc. 1991.
-----
Term: V.22
Author: Freedman, Alan.
-----

CCITT standard (1980) for asynchronous and synchronous 600 and 1,200bps
full-duplex modems for use on dial-up lines. It uses DPSK modulation.

 

***** Computer Select, August 1992 : Doc #179775 *****

Book: Newton's Telecom Dictionary
* Full Text COPYRIGHT Harry Newton 1991.
-----
Term: V.22 bis
Author: Newton, Harry.
-----

CCITT standard for 2,400 bit per second duplex modems for use on the
switched telephone network. V.22 bis also provides for 1200bps operation
for V.22 compatibility. Bis 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 #179776 *****

Book: Electronic Computer Glossary
* Full Text COPYRIGHT The Computer Language Co. Inc. 1991.
-----
Term: V.22bis
Author: Freedman, Alan.
-----

CCITT standard (1984) for asynchronous and synchronous 2,400bps full-
duplex modems for use on dial-up lines and two-wire leased lines, with
fallback to V.22 1,200bps operation. It uses QAM modulation.

 

***** Computer Select, August 1992 : Doc #179777 *****

Book: Electronic Computer Glossary
* Full Text COPYRIGHT The Computer Language Co. Inc. 1991.
-----
Term: V.23
Author: Freedman, Alan.
-----

CCITT standard (1964) for asynchronous and synchronous 0-600 and 0-
1,200bps half-duplex modems for use on dial-up lines. It has an optional
split-speed transmission method with a reverse channel of 0-75bps
(1,200/75, 75/1,200bps). It uses FSK modulation.

 

***** Computer Select, August 1992 : Doc #179778 *****

Book: Newton's Telecom Dictionary
* Full Text COPYRIGHT Harry Newton 1991.
-----
Term: V.23
Author: Newton, Harry.
-----

V.23 is the standard for a modem with a 600 bps or 1200 bps "forward
channel" and a 75 bps "reverse" channel for use on the switched telephone
network.

 

***** Computer Select, August 1992 : Doc #179779 *****

Book: Newton's Telecom Dictionary
* Full Text COPYRIGHT Harry Newton 1991.
-----
Term: V.24
Author: Newton, Harry.
-----

CCITT definitions for interchange circuits between data terminal equipment
(DTE) and data communications equipment (DCE) equipment.

 

***** Computer Select, August 1992 : Doc #179780 *****

Book: Electronic Computer Glossary
* Full Text COPYRIGHT The Computer Language Co. Inc. 1991.
-----
Term: V.24
Author: Freedman, Alan.
-----

CCITT standard (1964) that defines the functions of all circuits for the
RS-232 interface. It does not describe the connectors or pin assignments;
those are defined in ISO 2110. In the U.S., EIA-232 incorporates the
control signal definition of V.24, the electrical characteristics of V.28
and the connector and pin assignments defined in ISO 2110.

 

***** Computer Select, August 1992 : Doc #179781 *****

Book: Electronic Computer Glossary
* Full Text COPYRIGHT The Computer Language Co. Inc. 1991.
-----
Term: V.25
Author: Freedman, Alan.
-----

CCITT standard (1968) for automatic calling and/or answering equipment on
dial-up lines. It uses parallel circuits and is similar in function to
RS-366 and Bell 801 autodialers used in the U.S. The answer tone defined
in V.25 is the first thing heard when calling a modem. It serves a dual
function of identifying the answering equipment as being a modem and also
disabling the echo suppression and echo cancellation equipment in the
network so that a full-duplex modem will operate properly.

 

***** Computer Select, August 1992 : Doc #179782 *****

Book: Newton's Telecom Dictionary
* Full Text COPYRIGHT Harry Newton 1991.
-----
Term: V.25
Author: Newton, Harry.
-----

Automatic calling and/or answering equipment on the general switched
telephone network, including disabling of echo suppressors on manually
established calls.

 

***** Computer Select, August 1992 : Doc #179783 *****

Book: Newton's Telecom Dictionary
* Full Text COPYRIGHT Harry Newton 1991.
-----
Term: V.25 bis
Author: Newton, Harry.
-----

V.25 bis is an automatic calling and answering command set including
ability to work with async, bisync, and HDLC devices. Provides a small
subset of the functions of the Hayes Standard AT Command Set.

 

***** Computer Select, August 1992 : Doc #179784 *****

Book: Electronic Computer Glossary
* Full Text COPYRIGHT The Computer Language Co. Inc. 1991.
-----
Term: V.25bis
Author: Freedman, Alan.
-----

CCITT standard (1968) for automatic calling and/or answering equipment on
dial-up lines. It has three modes: asynchronous (rarely used), character-
oriented synchronous (bisync) and bit-oriented synchronous (HDLC/SDLC).
Both synchronous versions are used in IBM AS/400 and other small-to-medium
sized computers that do automatic dialing for remote job entry. Due to
the popularity of the Hayes Standard AT Command Set, V.25bis is not used
as widely in North America. It does not perform any modem configuration
functions and is limited to dialing and answering calls.

 

***** Computer Select, August 1992 : Doc #179785 *****

Book: Electronic Computer Glossary
* Full Text COPYRIGHT The Computer Language Co. Inc. 1991.
-----
Term: V.26
Author: Freedman, Alan.
-----

CCITT standard (1968) for synchronous 2,400bps full-duplex modems for use
on four-wire leased lines. It uses DPSK modulation and includes an
optional 75bps back channel.

 

***** Computer Select, August 1992 : Doc #179786 *****

Book: Newton's Telecom Dictionary
* Full Text COPYRIGHT Harry Newton 1991.
-----
Term: V.26
Author: Newton, Harry.
-----

V.26 is the CCITT standard for 2400 bps modem for use on 4-wire leased
lines.

 

***** Computer Select, August 1992 : Doc #179787 *****

Book: Newton's Telecom Dictionary
* Full Text COPYRIGHT Harry Newton 1991.
-----
Term: V.26 bis
Author: Newton, Harry.
-----

CCITT standard for 1.2/2.4 kbps modem. It is important to note that V.26
bis is a half-duplex modem (1200 or 2400 bps in only one direction at a
time); it provides an optional 75 bps reverse channel as well.

 

***** Computer Select, August 1992 : Doc #179788 *****

Book: Newton's Telecom Dictionary
* Full Text COPYRIGHT Harry Newton 1991.
-----
Term: V.26 ter
Author: Newton, Harry.
-----

V.26 ter is a FULL DUPLEX 2400 bps modem, like V.22 bis. The difference is
that V.26 ter uses echo cancellation (like V.32) instead of frequency
division (like V.22 bis), making it more expensive than V.22 bis. It was
intended to serve as a fallback mode from V.32, but most manufacturers
ignored it and provide V.22 bis as a fallback instead (V.26 ter is used
only in a few installations in France, as far as we know).

 

***** Computer Select, August 1992 : Doc #179789 *****

Book: Electronic Computer Glossary
* Full Text COPYRIGHT The Computer Language Co. Inc. 1991.
-----
Term: V.26bis
Author: Freedman, Alan.
-----

CCITT standard (1972) for synchronous 1,200 and 2,400bps full-duplex
modems for use on dial-up lines. It uses DPSK modulation and includes an
optional 75bps back channel.

 

***** Computer Select, August 1992 : Doc #179790 *****

Book: Electronic Computer Glossary
* Full Text COPYRIGHT The Computer Language Co. Inc. 1991.
-----
Term: V.26ter
Author: Freedman, Alan.
-----

CCITT standard (1984) for asynchronous and synchronous 2,400bps full-
duplex modems using DPSK modulation over dial-up and two-wire leased
lines. It includes a 1,200bps fallback speed and uses echo cancellation,
permitting a full-duplex modem to send and receive on the same frequency.

 

***** Computer Select, August 1992 : Doc #179791 *****

Book: Electronic Computer Glossary
* Full Text COPYRIGHT The Computer Language Co. Inc. 1991.
-----
Term: V.27
Author: Freedman, Alan.
-----

CCITT standard (1972) for synchronous 4,800bps full-duplex modems for use
on four-wire leased lines. It uses DPSK modulation.

 

***** Computer Select, August 1992 : Doc #179792 *****

Book: Newton's Telecom Dictionary
* Full Text COPYRIGHT Harry Newton 1991.
-----
Term: V.27
Author: Newton, Harry.
-----

CCITT standard for 4,800 bits per second modem with manual equalizer for
use on leased telephone-type circuits. May be full-duplex on four-wire
leased lines, or half-duplex on two-wire lines.

 

***** Computer Select, August 1992 : Doc #179793 *****

Book: Newton's Telecom Dictionary
* Full Text COPYRIGHT Harry Newton 1991.
-----
Term: V.27 bis
Author: Newton, Harry.
-----

CCITT standard for 2.4/4.8-kbit/s modem with automatic equalizer for use on
leased telephone-type circuits. 2.4 Kbps modem for 4-wire leased circuits.
Either speed (2400 is a fallback) can be used on either 4-wire leased lines
(full duplex) or 2-wire leased lines (half-duplex). It also provides an
optional 75 bps reverse channel.

V.27 ter
CCITT standard for 2.4/4.8-kbit/s modem for use on the switched telephone
network. Half-Duplex only. V.27 ter is the modulation scheme used in Group
3 Facsimile for image transfer at 2400 and 4800 bps. 4800 bps is a common
"fallback" speed.

 

***** Computer Select, August 1992 : Doc #179794 *****

Book: Electronic Computer Glossary
* Full Text COPYRIGHT The Computer Language Co. Inc. 1991.
-----
Term: V.27bis
Author: Freedman, Alan.
-----

CCITT standard (1976) for synchronous 2,400 and 4,800bps full-duplex
modems using DPSK modulation for use on four-wire leased lines. The
primary difference between V.27 and V.27bis is the addition of an
automatic adaptive equalizer.

 

***** Computer Select, August 1992 : Doc #179795 *****

Book: Electronic Computer Glossary
* Full Text COPYRIGHT The Computer Language Co. Inc. 1991.
-----
Term: V.27ter
Author: Freedman, Alan.
-----

CCITT standard (1976) for synchronous 2,400 and 4,800bps half-duplex
modems using DPSK modulation on dial-up lines. It includes an optional
75bps back channel. V.27ter is used in Group 3 fax transmission without
the back channel.

 

***** Computer Select, August 1992 : Doc #179796 *****

Book: Electronic Computer Glossary
* Full Text COPYRIGHT The Computer Language Co. Inc. 1991.
-----
Term: V.28
Author: Freedman, Alan.
-----

CCITT standard (1972) that defines the functions of all circuits for the
RS-232 interface. In the U.S., EIA-232 incorporates the electrical signal
definitions of V.28, the control signals of V.25 and the connector and pin
assignments defined in ISO 2110.

 

***** Computer Select, August 1992 : Doc #179797 *****

Book: Newton's Telecom Dictionary
* Full Text COPYRIGHT Harry Newton 1991.
-----
Term: V.28
Author: Newton, Harry.
-----

V.28, entitled "Electrical Characteristics for Unbalanced Double-Current
Interchange Circuits" provides the CCITT equivalent of the electrical
characteristics defined in EIA-232.

 

***** Computer Select, August 1992 : Doc #179798 *****

Book: Newton's Telecom Dictionary
* Full Text COPYRIGHT Harry Newton 1991.
-----
Term: V.29
Author: Newton, Harry.
-----

CCITT standard for 9,600 bits per second modem for use on point-to-point
leased circuits. Virtually all 9,600 bps leased line modems adhere to this
standard. V.29 uses a carrier frequency of 1700 Hz which is varied in both
phase and amplitude. V.29 also provides fallback rates of 4800 and 7200
bps. V.29 can be full-duplex on 4-wire leased circuits, or half-duplex on
two-wire and dial-up circuits. V.29 is the modulation technique used in
Group 3 fax for image transfer at 7200 and 9600bps.

 

***** Computer Select, August 1992 : Doc #179799 *****

Book: Electronic Computer Glossary
* Full Text COPYRIGHT The Computer Language Co. Inc. 1991.
-----
Term: V.29
Author: Freedman, Alan.
-----

CCITT standard (1976) for synchronous 4,800, 7,200 and 9,600bps full-
duplex modems using QAM modulation on four-wire leased lines. It has been
adapted for Group 3 fax transmission over dial-up lines at 9,600 and
7,200bps.

 

***** Computer Select, August 1992 : Doc #179800 *****

Book: Electronic Computer Glossary
* Full Text COPYRIGHT The Computer Language Co. Inc. 1991.
-----
Term: V.32
Author: Freedman, Alan.
-----

CCITT standard (1984) for asynchronous and synchronous 4,800 and 9,600bps
full-duplex modems using TCM modulation over dial-up or two-wire leased
lines. TCM encoding may be optionally added. V.32 uses echo cancellation
to achieve full-duplex transmission.

 

***** Computer Select, August 1992 : Doc #179801 *****

Book: Newton's Telecom Dictionary
* Full Text COPYRIGHT Harry Newton 1991.
-----
Term: V.32
Author: Newton, Harry.
-----

CCITT standard for 9,600 bit per second two-wire full duplex modem
operating on regular dial-up lines or 2-wire leased lines. If you're buying
a 9,600 bps modem for use on the normal dial-up switched phone lines, make
sure it conforms to V.32. If your modem also conforms to V.42 bis, you
should be able to transmit and receive at up to 38,400 bps with other
modems that conform to these two specifications. I personally use a number
of V.32/V.42 bis modem and they work wonderfully fast. V.32 also provides
fallback operation at 4,800 bps. See also V.32 bis, V.42 ERROR CORRECTION
and V.42 bis DATA COMPRESSION.

 

***** Computer Select, August 1992 : Doc #179802 *****

Book: Newton's Telecom Dictionary
* Full Text COPYRIGHT Harry Newton 1991.
-----
Term: V.32 bis
Author: Newton, Harry.
-----

New CCITT standard for full-duplex transmission on two-wire leased and
dial-up lines at 4800, 7200, 9600, 12000, AND 14,400 bps. Provides backward
compatibility with V.32. Includes "rapid rate renegotiation" feature to
allow quick and smooth rate changes when line conditions change. Some of
the newer V.32 bis/V.42 bis modems claim to transmit and receive at 57,600
bps.

 

***** Computer Select, August 1992 : Doc #179803 *****

Book: Electronic Computer Glossary
* Full Text COPYRIGHT The Computer Language Co. Inc. 1991.
-----
Term: V.32bis
Author: Freedman, Alan.
-----

CCITT standard (1991) for asynchronous and synchronous 4,800, 7,200,
9,600, 12,000 and 14,400bps full-duplex modems using TCM and echo
cancellation. Supports rate renegotiation, which allows modems to change
speeds as required.

 

***** Computer Select, August 1992 : Doc #179804 *****

Book: Electronic Computer Glossary
* Full Text COPYRIGHT The Computer Language Co. Inc. 1991.
-----
Term: V.33
Author: Freedman, Alan.
-----

CCITT standard (1988) for synchronous 12,000 and 14,400bps full-duplex
modems for use on four-wire leased lines using QAM modulation. It
includes an optional time-division multiplexor for sharing the
transmission line among multiple terminals.

 

***** Computer Select, August 1992 : Doc #179805 *****

Book: Newton's Telecom Dictionary
* Full Text COPYRIGHT Harry Newton 1991.
-----
Term: V.33
Author: Newton, Harry.
-----

CCITT standard for 14,400 and 12,000 bps modem for use on four-wire leased
lines.

 

***** Computer Select, August 1992 : Doc #179806 *****

Book: Newton's Telecom Dictionary
* Full Text COPYRIGHT Harry Newton 1991.
-----
Term: V.35
Author: Newton, Harry.
-----

CCITT standard for trunk interface between a network access device and a
packet network that defines signaling for data rates greater than 19.2
kbps. V.35 was a definition of a GROUP band modem (meaning, one that used
the bandwidth of several telephone circuits). V.36 and V.37 are other group
band modems. V.35 just happened to describe, in an appendix, electrical
characteristics for a high speed interface. IBM decided to use this for
other things, but it was never standardized for those purposes. The CCITT,
in the 1988 Blue Book, says "It is the opinion of the CCITT that the
information contained in Recommendation V.35 is out of date. Therefore it
is not recommended to use the techniques described in this Recommendation
for new designs. Alternative techniques are described in Recommendations
V.36 and V.37. It should be noted that other Recommendations make reference
to the electrical characteristics described in Appendix II to this
Recommendation [V.35]. As these characteristics are expected to allow
interworking with V.11 characteristics, use of V.11 circuits is recommended
in those cases." V.35 is no longer published by the CCITT.

 

***** Computer Select, August 1992 : Doc #179807 *****

Book: Electronic Computer Glossary
* Full Text COPYRIGHT The Computer Language Co. Inc. 1991.
-----
Term: V.35
Author: Freedman, Alan.
-----

CCITT standard (1968) for group band modems that combine the bandwidth of
several telephone circuits to achieve high data rates. V.35 has become
known as a high-speed RS-232 interface rather than a type of modem. The
large, rectangular V.35 connector was never specified in V.35, but has
become a de facto standard for a high-speed interface.

 

***** 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 #179812 *****

Book: Electronic Computer Glossary
* Full Text COPYRIGHT The Computer Language Co. Inc. 1991.
-----
Term: V.54
Author: Freedman, Alan.
-----

CCITT standard (1976) for various loopback tests that can be incorporated
into modems for testing the telephone circuit and isolating transmission
problems. Operating modes include local and remote digital loopback and
local and remote analog loopback.

 

***** Computer Select, August 1992 : Doc #179813 *****

Book: Newton's Telecom Dictionary
* Full Text COPYRIGHT Harry Newton 1991.
-----
Term: V.54
Author: Newton, Harry.
-----

CCITT standard for loop test devices in modems. Defines local and remote
loopbacks.

 

***** Computer Select, August 1992 : Doc #179814 *****

Book: Electronic Computer Glossary
* Full Text COPYRIGHT The Computer Language Co. Inc. 1991.
-----
Term: V.56
Author: Freedman, Alan.
-----

CCITT standard (1972) for a method of testing modems to compare their
performance. Newer procedures are under currently under study.

 

***** 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.