Almost Spring 1996
Rockwell's RPI chipset causes...
Popular Modem Furor --
Error Correction (Not)
A popular chipset used in many low-cost
modems often is unable to effectively perform either
error correction or data compression, as advertised.
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
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
" 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 refund."
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
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
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