Getting Disconnected? - =?iso-8859-1?Q?Bug=8A?=

Tim Byars (
Fri, 29 Mar 1996 15:52:12 -0800

Popular Modem Furor -- Error Correction (Not)

(NOTE: This is an excerpt from the complete BugNet, now available
exclusively on the world wide web in the Subscriber's Edition of
BugNet Online.)

HERE'S a glorious mess!

A popular chipset used in many low-cost modems often is unable to
effectively perform either error correction or data compression, as

The result is that these 14.4 bps internal and external modems suffer
from dropped connections, corrupted data, and increased cost of

The problem has created a furor in online venues like Compuserve's
PCCOM and MODEMVENDOR forums, and Internet providers including
Pacificrim Network have issued warnings to their customers.

The affected equipment reportedly includes at least one model modem by
Aspen, Best Data, Boca, Cal Com, Cambridge Telecom, Cardinal, Delrina,
Dynalink, Global Village, Logicode Quicktel, Maxtech (GVC), Supra,
U.S. Robotics, Zoltrix and Zoom. (Please see accompanying list for
complete list of RPI model modems.)

At the heart of the problem is the RPI chipset from Rockwell
International. Rockwell is a major supplier of chips for modems, and
the RPI is only one of their popular models.

One "feature" of the RPI chipset is that it moves some code from
hardware to software, shifting v.42/v.42bis processing from modem ROM
to the CPU of your computer, much as other peripherals like printers
have done.

The problem is that there is no way to get error correction and data
compression with the RPI chipset unless you are running software that
supports RPI, and unfortunately, many don't.

Rockwell acknowledges that at present only a handful of programs
support RPI, which stands for Rockwell Protocol Interface, and only in
their latest versions. These programs include Comit 1.24 (Windows),
Comit 1.123 (DOS), Quicklink II 1.43 (Windows), Quicklink II 3.03
(DOS), ProComm Plus 2 (Windows), BitCOM 3.03 (Windows), BitCOM 6.04
(DOS), and Qmodem TD 4.6.

BOB BROEN of Minneapolis, MN, is an example of a user who learned this
lesson in modem design the hard way.

The Minneapolis Compuserve node he uses regularly is fuzzy enough so
that it won't work unless he has error correction enabled. But
unfortunately, he can't enable error correction because his modem
contains an RPI chipset and his Compuserve navigation software doesn't
support RPI.

" I also have one DOS program (which apparently is not RPI-compatible)
that I use every day with Compuserve," noted Broen. "I do that now by
making a long distance call to a different Compuserve node." Grrrrr.

Karen Whitman of England adds, "I have a Zoltrix 14400 modem which
uses an RPI chipset and boy am I having problems with it! It's really
hit and miss whether I can send messages on Compuserve. I really feel
strongly that this modem is not 'fit for the purpose' (UK legal term
relating to Sale of Goods), but the shop I bought it from won't give a

The problem is so bad that Jim McKeown, sysop of the PCCOM Forum,
says, "my advice is simple: avoid buying a modem which depends on
RPI." At the same time, modem gurus say it's important not to lump all
Rockwell chipset modems together.

"You need to avoid the RPI like the plague'" advises Art Mercier on
Compuserve, "but don't automatically write off any modem that claims
to use the Rockwell chipset. If you do, you'll be ignoring some mighty
fine equipment -- most of the PPI modems, for instance."

Making matters even more confusing is the fact that it can be
difficult to diagnose whether or not your modem is a RPI modem.
Rockwell reportedly uses portion of the same chipset code in more than
one modem chipset.

As a result, some modems will respond "RPI" in the answer from ATi3,
even though they are not RPI modems (wonderful!). So how can you tell?
According to PCCOM sysop Don Hinds, "you can just type in AT+H and if
you get ERROR it's not RPI."

If you've got an RPI modem and you've just got to make the best of it,
here are a couple things you can try. When you encounter difficulty,
add +H0 to your initialization string, which "switches off" RPI error
correction. Then try reducing your baud rate to 9600 or even 4800.

Rockwell has configuration tips available on the world wide web for
Windows 95 and Windows 3.x. Click here for the latest RPI drivers for
both Windows 95 and Windows 3.x.

Rockwell can also be reached at 800-854-8099.


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