VII. Buying a High-speed Modem

V.32 and V.32bis modems are clearly the standards of high-speed modems today. You should buy a V.32 or a V.32bis modem unless

Your application requires a high-speed modem with a proprietary modulation protocol. In this case, you should consider a dual-mode modem that support both the proprietary protocol and V.32 (or V.32bis).
You cannot afford a V.32 modem.

VII.1. Should you pay extra for a V.32bis modem?

A V.32bis modem costs substantially more than a V.32 modem just a few months ago. However, the price difference bewteen a V.32bis and a V.32 modem (from the same manufacturer) are diminishing. If you're thinking about buying a high-speed modem, you should probably look for a V.32bis modem.

Assuming the remote system support V.32bis, a V.32bis modem will pay for itself rather quickly if you are placing long distance calls to the remote system. However, if you are using some packet-switching networks to reach the remote system by calling a local number. A V.32bis modem will be wasted since none of the packet-switching networks currently support V.32bis. In fact, they are just starting to offer 9600 bps access service. Part III of "The Joy of Telecomputing" provides a comprehensive discussion of the issues involved.

VII.2. Should you buy a modem with a proprietary protocol?

It is generally not a good idea to purchase a modem which only supports a proprietary modulation protocol. You should consider getting a modem that supports dual modulation protocols (USR Courier Dual Standard, Telebit WorldBlazer, Hayes Ultra) if (i) you have to connect to a modem that uses a proprietary modulation protocol, or (ii) you need to have better throughput than a V.32bis modem can offer.

VII.3. Should you buy a 2400-bps modem with V.42bis?

If you are thinking of purchasing a 2400 bps modem with V.42bis data compression, think again.

We have mentioned earlier that V.42bis and MNP5 are useless for downloading compressed files. There is one more reason why a 2400 bps with V.42bis is generally not useful when you are calling commercial online services or BBS.

Online services and BBS usually have separate phone numbers for 2400-bps and high-speed modems. Most of them do not support V.42bis on their 2400-bps lines. Therefore, you won't be able to make a connection with V.42bis if you call their 2400-bps modem lines.

Couldn't you call their 9600 bps lines? Well, not really. Commercial online services, as well as many bulletin board systems, typically do not allow you to call their high-speed modem lines with a 2400-bps modem. You won't be able to make a connection even if you try.

VII.4. Beware of the Ads

Current V.32 modems typically support MNP 2-5 and V.42/V.42bis. However, there are still some earlier models of V.32 modems in the market which

may not support any error control or data compression protocol (Hayes Smartmodem 9600).
may support MNP 2-5 but not V.42/V.42bis.
may support proprietary data compression protocol (Microcom MNP9).
may support V.42 but not V.42bis (Prometheus).

When a modem is said to offer a 38400 bps speed (or throughput), it may mean that

it is a V.32 or V.32bis modem with V.42bis
it is a V.32 modem with proprietary data compression protocol (some Microcom modems)
it is a high-speed modem with proprietary modulation protocol and V.42bis (U.S. Robotics Courier HST)
it is a high-speed modem with proprietary modulation protocol and proprietary data compression protocol (CompuCom Champ)

An ad that says "USR modem, 38400 bps throughput, V.42bis" does not tell us anything except that the modem is made by U.S. Robotics. It could be any one of the three Courier modems. It could even be a Sportster 9600.

When a modem is said to offer a 9600 bps speed (or throughput), it may mean several things:

it is a V.32 modem
it is a high-speed modem using proprietary modulation protocol (Hayes V-series Smartmodem 9600, Telebit 1000, etc).
it is a 2400 bps modem with V.42bis data compression.
it is a 2400 bps modem with 9600 bps fax
it is a 2400 bps modem both V.42bis and fax.