On this page, I will discuss the modem standards, from the old 300bps to ISDN. First lets discuss a few terms common to all modems.

Standards to All Modems

There are many standards for modem protocols, but the field has evened out lately. A protocol is a method by which two devices, modems, agree to communicate. You can think of it as a language that is agreed on.

Bell Labs and the CCITT have both set standards for modem protocols. Bell Labs no longer sets standards, although they are still used in some locations. Most newer modems conform to the CCITT standards.

Some companies branched out and created modems using their own proprietary standard protocol. Such protocols are published broadly so that other manufacturers can create modems to work with it. Some of these proprietary standards have become popular.

Most modems are designed to work with several different protocols.

Almost all modems are said to be Hayes-compatible. This refers to the set of commands used to operate the modem. These commands will be listed in another section.

There is often a confusion between baud rate and bits-per-second (bps). The baud rate is the rate at which a signal between two modems changes in one second. It is actually independent of the bps. Some modems send one bit of data per modulation, so 300 baud would be 300 bps. Other modems are set to send more data per modulation, meaning that the bps will be higher than the baud rate. Therefore, the baud rate is really rather meaningless in purchasing a modem. You should be interested in the bps, as this is concerned with the actual speed.

Modulation Standards

There are many standards for modulation. I’m sure you have seen each of these terms before:

• Bell 103 & 212A. These are old standards. Bell 103 transmits at 300 bps at 1 bit per baud. Bell 212A was the next step up, capable of two bits per baud. It was capable of 1200bps at 600 baud. Each used a different type of modulation.


• V.21. Uses mainly outside the U.S., it was a sort of international standard. It is not compatible with Bell protocols, and is only capable of 300bps.


• V.22. Shares the features of V.21, but was capable of 1200bps. Later, the V.22bis protocol was used. It was used both in the U.S. and outside, and ran at 4 bits per baud for a total of 2400bps.


• V.23. Used mainly in Europe, this allowed the modem to send and receive data at the same time, although it could send data only at 75bps. This standard was developed to lower the cost of modems. A 1200 bps modem was very expensive at the time.


• V.29. A half-duplex standard, meaning one-way. It works at 9600bps. The standard is not laid out well for modems, therefore isn’t much used. The protocol is most often used for fax machines.


• V.32. This standard began to get users into the ballpark we are all in now. It was a full-duplex standard and operated at 9600bps, with a 2400 baud rate. It incorporates error-correcting and negotiation. The error-correcting allowed V.32 to work well over phone line noise.


• V.32bis. This is one step up from V.32. It transmitted 6 bits per baud, allowing throughputs of 14,400 bps. It also allowed fallback onto regular V.32 if the phone line was impaired. Many still use this modem standard primarily.


• V.32fast Better known as the 28,800 bps modem.


• V.34. The latest real modem standard. It provides a reliable 28,800 bps connection. With upgrades to the ROM BIOS on the modem, the standard is often used for 33,600 bps transmissions.

Error Correction

Error Correction is an important feature in the fastest modems. It allows fast reliable connections over standard phone lines, even past noise. All phone lines have noise which degrades the data connection. Therefore, error-correction is necessary.

All modems in a network must be using the same error-correction protocols for it to work. Fortunately, most modems use the same protocols. Most use the V.42 error correction protocol. With it, the modem can detect damaged data streams, and the data will be resent.

The V.42bis protocol is just like V.42, but incorporates data compression. Data compression allows modems to use higher bps’s. A 14.4 modem, with data compression, can boast transmission rates of 57,600 bps. A 28.8 modem will boast transmissions of 115,200 bps.

ISDN

Integrated Services Digital Network (ISDN) is the next step from the analog phone line. It takes advantage of a digital phone network, allowing transmission rates of up to 128 Kbps. ISDN requires an ISP that is capable of it, plus an initial setup fee and a monthly charge. Where you might pay $20 per month for analog service, you might pay $75 to $100 per month for ISDN service. You must also buy a special ISDN modem. You might also have to pay your phone company a per-minute rate.

I don’t wish to cover ISDN in depth, but there are several nice books out there with more details about it than you would ever want.

56K Modems

The newest, and probably last, type of modem for the analog phone line. They are the latest rage, and if you buy a new modem, it will probably be a 56K modem.

This speed is gotten by taking advantage of the digital portion of the phone system. Almost all phone systems are digital until they get to the central office. The central office then converts it to analog before sending the signal out to your home or office. 56K technology removes the conversion to analog at the ISP end, instead allowing the phone network to do it. The result is 56Kbps modems. Also, since the conversion is only removed at the host end, these higher transmission rates are only capable when receiving data. When sending data, you are on the analog end, so data rates are limited to 33,600 bps.

There are limitations to the 56K technology. First, the connection between the central office of your phone company and the central office of the company that services your ISP must be fully digital. The host must have a digital connection to the phone network. And, your host’s modem must be capable of 56K technology. For these reasons, 56K service for you is really subject to your phone company, your location, and your ISP.

Besides, an actual speed of 56Kbps is unattainable. The government, from what I hear, has limited communications to 53K per second. Plus, due to phone line noise and many other factors present on all phone systems, the average for 56K users actually is about 40K per second.

Another hitch: Until recently, there were two standards for 56K technology. Rockwell has its own set of protocols, called K56flex. U.S. Robotics has its own, called X2 technology. These standards are not compatible. Therefore, in order for you to use 56K technology, you must be using the same 56K standard as your ISP.

Recently, the International Telecommunications Union agreed on a standard for 56K modems. This puts to rest the old conflict between 3COM and Rockwell over which protocol should be standard. This new standard is termed V.90. Most manufacturers now make models using the V.90 standard, and many also have ROM updates available to make either a K56flex or X2 modem V.90 compatible.

Once you get past each of these things, 56K technology does produce a speed increase over 33.6 modems. Unless you want to get with a cable modem company such as RoadRunner, I would recommend a 56K modem.

Like what you read?

If so, please join over 28,000 people who receive our exclusive weekly newsletter and computer tips, and get FREE COPIES of 5 eBooks we created, as our gift to you for subscribing. Just enter your name and email below: