20 Kermit Doesn't Work Right with My (RPI) Error-Correcting Modem!

When you buy a modern error-correcting, data-compressing, speed-buffering modem, you probably expect the modem to perform those functions, and most do. Unfortunately, some modems that claim to have these features do not have them at all, but require external software that implements them in your computer, rather than in the modem where they belong.

One example of this practice is the Rockwell Protocol Interface (RPI), a proprietary "standard" from Rockwell International Company that allows modem companies to sell modems at a lower price by incorporating Rockwell chips that do not include error-correction or compression capabilities.

This "standard" must be licensed from Rockwell, hence you will only find it implemented in commercial software, such as on the diskette (if any) that came with your modem.

In general, such software is available only for PCs running Microsoft Windows 3.x or Windows 95, or built into proprietary communications packages like Comit.

If your modem documentation says it requires "RPI-compatible" software for error correction and compression, and you want to use it with Kermit, then you are out of luck unless you also have the software driver for the modem and can use it on your computer. Otherwise you bought the wrong modem. Hopefully, you can return it.

It is usually hard to tell by reading the modem box. One user reports: "The RPI bit is hidden on the back of the box: '*Error Control* V.42 and MNP RPI software,' and '*Data Compression* V.42bis RPI software.' The box design is such that, unless you happen to already know what RPI is, you think you're getting a modem with MNP/V.42 LAPM/V.42bis compression built in."

If you can't return the modem, you can still use it without error correction, but then:

• Noise is not filtered out on the modem-to-modem connection, as it would be with a real error-correcting modem, and noise bursts will interfere with your online sessions and your file transfers.
• There is no modem-to-modem compression, because that requires error correction.
• There is no flow control, because that too requires an error-correction protocol between the modems.
• Speed buffering is ineffective because that requires flow control between the modems. Thus, if the two modems have different interface speeds, vast amounts of data will be lost.

Why RPI is a bad idea:

• Implementation of MNP, V.42, and V.42bis in software is a VERY big job. Since it is uneconomical for software companies to write software for any platform other than Microsoft Windows, it is unlikely that RPI drivers will ever be written for DOS, UNIX, OS/2, VMS, or any other platform.
• Even when a company wants to produce a driver for (say) a new release of Windows, there is generally a long lag time before it is available. Thus you might find when you install your brand-new operating system that your modem has become useless.
• The driver software slows down your computer by consuming a vast amount of CPU cycles over and above what would be used if error-correction and compression were done in the modem, and it increases memory requirements, swapping, and in general can be expected to drag down the performance of your PC.
• RPI seeks to replace an open communication method (the one that is universally used by serial communication software) by a closed, proprietary, licensed one, and potentially hold hostage all communications software developers to nondisclosure agreements.
• It precludes publication of source code.
• Since MNP 2-5 and V.42 and V.42bis are complex protocols, the software implementations will inevitably be buggy and are unlikely to be consistent, especially since the "standard" is not an open one, and the implementations themselves will not be open.
• Even if the drivers are not buggy, the underlying operating system is likely to be.
• Since not all software in the world will be "upgraded" to "support" the RPI "standard", your modem will not be usable in many of the ways you might have expected to use it.
• Many people will buy these modems under the mistaken impression that they can use their high speeds and advanced features with their favorite software. The average mass-market consumer is unlikely to understand the implications of "requires RPI-compliant software" in tiny print on the box.
• By Gresham's Law, "The bad drives out the good". RPI modems are cheaper, and might well drive reputable modems out of the marketplace, leaving the entire world's online community with no modems left to choose from but ones that will work only with Windows. This drives another nail into the coffin of "legacy" non-Windows platforms, and this, in turn, leaves the public with fewer choices for operating systems, applications, and computers themselves.

• Lower-cost modems? In order to save a few dollars, you are giving up the ability to use the modem on the platform of your choice, with the software of your choice, and you are probably going to get poorer performance than you would have had with the EC and DC protocols built-in over the life of the modem.

How do I tell if I have an RPI modem?

• According to Rockwell, all RPI modems should issue a message containing "RPI" in response to the command ATI3. Here are some examples:

  AFEP-V1.510-BP39 ROCKWELL RPI (TM) MODEM
  AFEP-V1.620z1.00 BS39 ROCKWELL RPI (TM) MODEM
  V1.620-BP39 ROCKWELL RPI (TM) MODEM
     

• The command to enable error correction (such as AT&Q5, depends on the modem) results in an ERROR response.
• They normally have AT+Hdigit commands to control the RPI interface. (This one is not dependable, since there are no standards for modem commands, and so AT+H might be used on non-RPI modems for some entirely unrelated purpose.)

Is there a list of RPI modems?

• No. Just about any modem manufacturer is likely to have RPI models. The modem market is incredibly volatile, fast-moving, and voracious. Any such list would be obsolete before you could see it. Once-scrupulous companies will now do anything to cut costs and increase margins. They have no choice -- if your competitors are doing it, you have to do it too or lose your business. Rockwell licenses RPI "technology" to anyone who will pay for it, but is under no obligation to disclose its licensees, nor are the licensees under any obligation to inform Rockwell (or anybody else) which models contain RPI chips and which do not. In many cases, the same make and model can have RPI and non-RPI variations. This makes technical support an increasingly difficult job. By saving a small amount of money for themselves, the modem manufacturers have created unneeded confusion among users and service providers, and driven up costs throughout the online world.

Is RPI the only "software driven" modem scheme?

• No. There are similar products from other companies. This further complicates the task of the help desks of the world, for even once they have ruled out that a modem problem is due to RPI, it might be some other kind of "controllerless" modem based, for example, on the HSM chipset from AT&T (now Lucent). US Robotics (now 3Com) sells a "Winmodem" (see next question). IBM has the Mwave, whose signal processing functions (the very core of a modem) must be downloaded from the computer.
• We can only expect to see more and more of this in the future. As a maker of such items commented in the comp.dcom.modems newsgroup, "There's certainly a market for platform-independent modems, but you can't expect manufacturers to ignore the market opportunity for Windows-only modems, especially when they can have a cost and performance advantage."

Of course you can't. But what about end users who don't understand any of this? Most of them do not make informed choices when buying modems. And increasingly, many of them make no choice at all -- the modem comes preinstalled in a PC they have bought, and does not even include a manual; sometimes not even a brand name. And now that RPI modems have been out for a while, we are beginning to see how they are passed from hand to hand, installed in or connected to new computers (for use, e.g., with DOS or Linux) and causing a whole new wave of problems.

If you have an RPI or other controllerless modem, and you need to use it in a setting for which a driver is not available -- that is, in most cases, any platform other than a PC running Microsoft Windows -- you are just plain out of luck. Return it and buy a real modem. This way, you will encourage modem manufacturers to continue to make real "platform-independent" modems.