johning@ut-emx.uucp (Johning Su) (06/04/91)
a modem and which version is better? I am considering to buy a modem of 2400 baud. Someone told me the one with MNP5 is better and someone said the one with V.42 bis would be much faster. Whom should I listen to? Any suggestions about version, price and manufacturer are appreciated very much. Please send me email. Thanks in advance. ------------------------------------------------------ ---- Johning
johning@ut-emx.uucp (Johning Su) (06/04/91)
In article <49961@ut-emx.uucp> johning@ut-emx.uucp (Johning Su) writes: >a modem and which version is better? Sorry! Due to an error of using vi editor, the question was incomplete. The question was: Can someone tell me what is difference between version v.42 bis and MNP5 of a modem and which version is better? ------------------------------------------------------ ---- Johning
ericb@hplsla.HP.COM (Eric Backus) (06/05/91)
> The question was: Can someone tell me what is difference between version > v.42 bis and MNP5 of a modem and which version is better? I believe that v.42bis provides better data compression and therefore faster data rates. The v.42bis modem probably also does MNP5 (at least, mine does), and probably costs a little more. Remember that both ends of the connection must have v.42bis or MNP5 to make use of them, and you will probably find more MNP5 modems out there than v.42bis. To make much use of either v.42bis or MNP5, you will have to have communication software which can talk to the modem at perhaps 9600 baud, so that when the data coming in at 2400 baud is uncompressed, you can read it in fast enough. You'll have to decide for yourself if the extra expense of v.42bis is worth it. P.S. I have an ATI 2400etc/i (I got it with my Gateway 2000 system), which does v.42bis and MNP5, and it works great. -- Eric Backus ericb%hplsla@hplabs.hp.com (206) 335-2495
jgay@digi.lonestar.org (john gay) (06/05/91)
From article <49961@ut-emx.uucp>, by johning@ut-emx.uucp (Johning Su): > a modem and which version is better? I am considering to buy a modem of 2400 > baud. Someone told me the one with MNP5 is better and someone said the one > with V.42 bis would be much faster. Whom should I listen to? > I would try to get a modem that has both. If that is not possible then I would check with the people who's modems I was going to connect to the most. If everyone else has MNP5 then getting a modem that has only V.42bis is not going to do you much good in the compression department. I don't know which is faster, but PC Magazine had a review of modems not to long ago. -- john gay. jgay@digi.lonestar.org --
edm@hpfcmdd.hp.com (Ed Moore) (06/05/91)
Modem Terminology
-----------------
10/16/90 PC Magazine, page 102
Speed
-----
CCITT V.22bis, usually shortened to V.22bis and pronounced "V-dot-22-biss,"
means your modem runs at 2400 bits per second (bps) or 2400 baud. V.32 means
9600 bps. Bell 212A and V.22 (with no bis) are 1200-bps standards.
Data compression
----------------
Squeeze the volume out of your transmission and you double or quadruple the
effective speed. MNP 5 is today's standard (up to 2:1 compression), and CCITT
V.42bis (4:1) is where it's headed. Modems can have both; it's not an
either/or situation. "MNP" stands for Microcom Networking Protocol.
Error correction
----------------
Modems with no error correction are the most common, but MNP 4 is where it's
at, and V.42 is the future. The main V.42 error correction protocol is called
LAP-M; V.42 also includes MNP 4 error correction. MNP 5 is sometimes described
as error correction because MNP 5 (data compression) includes lower MNP classes
like MNP 4 (error correction).
Fax
---
Some modems also support Group III fax, which is what the fax machine in your
office understands. The fax terminology is called V.29, but just say Group
III.
12/11/90 PC Magazine, page 312
Modulation protocols
--------------------
Bell 103/113 Asynchronous full-duplex modem transmission at up to 300 bps.
Bell 212 Asynchronous and synchronous full-duplex modem transmission at 1200
bps.
HST U.S. Robotics' High Speed Technology; a proprietary modulation
allowing connection speeds of up to 14,400 bps. Data flows
asymmetrically at the high speed in one direction and at 450 bps in
the other. The modems dynamically negotiate, assigning the high-
speed channel to the modem with the most data to transmit.
PEP Packetized Ensemble Protocol: a Telebit proprietary modulation
protocol that analyzes the quality of the phone connection at connect
time and dynamically compensates for line impairments at 511 separate
frequency points.
V.21 Full-duplex modem transmission at up to 300 bps, also used for Group
3 fax negotiation.
V.22 Half-duplex modem transmission at 600 bps and 1200 bps, with a
reverse channel (used mostly for responses during file transfers) at
up to 75 bps.
V.22bis Full-duplex modem transmission at 1200 and 2400 bps, with fall-back
to V.22.
V.32 Full-duplex modem transmission at 4800 and 9600 bps.
V.32bis The V.32 protocol extended to speeds of 7200, 12,000 and 14,400 bps,
and with an improved renegotiation protocol.
Error control protocols
-----------------------
MNP 2,3,4 Microcom Network Protocol: a proprietary, licensed error-control
protocol. The numbers indicate specific versions or classes.
V.42 A standard error-control protocol, backward-compatible with MNP 2, 3
and 4.
Compression protocols
---------------------
MNP 5 Microcom's proprietary, licensed data-compression protocol.
V.42bis An international standard for data compression. Using Lempel-Ziv
compression techniques, V.42bis can increase throughput over V.42 by
as much as 4 to 1. (12/15/90 PC Magazine, page 450)
10/29/90 InfoWorld, page 92
MNP stands for Microcom Networking Protocol. It was developed by Microcom Inc.
of Norwood, Massachusetts, a company that makes modems, communications
software, and LAN and ISDN products.
MNP provides modems with error detection and correction -- and may also provide
data compression. MNP implementations are divided into "classes" according to
the features they support.
MNP 1 Provides error detection and correction when two systems exchange bytes
using a "half duplex" protocol -- that is, a protocol in which only one
modem transmits at a time. In practice, you'll rarely see it
implemented.
MNP 2 Also detects and corrects errors, but uses a full duplex protocol, in
which both sides can send and receive at the same time.
MNP 3 Similar to MNP 2, but uses synchronous data transmission to reduce
overhead. This is the lowest class of MNP that actually increases the
effective bps rate of the modem compared to a non-MNP modem.
MNP 4 Improves on MNP 2 and 3 by changing the size of the information packets
exchanged by the two modems according to the quality of the connection.
It also eliminates even more overhead, yielding as much as a 20%
improvement in throughput over a non-MNP modem. MNP 4 is
internationally recognized as part of the CCITT V.42 standard.
MNP 5 This is the class you should look for when buying an MNP modem. It
introduces a data compression technique that can give you up to 200% the
throughput of a non-MNP modem. MNP 5 has achieved widespread popularity
among modem manufacturers, along with V.42bis (another standard for
modem data compression).