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56K Modem Information  BACK
56k modems aren't. That's the first thing.

Regular phone lines should be able to transmit data at 57600bps, but technical considerations reduce the rate to 56k. Then, FCC regulations further reduce the maximum allowable rate to 53k. Then come many limitations implicitly imposed because of the equipment used by many telephone companies, along with the quality of phone lines and the configuration of the personal computer being used.

One significant barrier to 56k performance is the presence of a SLC96 (pronounced "slick") concentrator. These are used by phone companies to split up existing phone hubs to get more numbers in high growth areas. The split nullifies the 56k capability, dropping all lines to v.34 specifications (33600bps or less).

There are no complete data showing just how many customers are connected to SLC96 concentrators, but most modem manufacturers estimate between 10-15%.

A second and similar reason is split phone lines within your home or office. This usually occurs when you add a new line and the telephone company, instead of running a new line, splits the existing one, usually with a device called a "bridged tap".

Another problem device is called an MTU. That stands for Maintenance Test Unit. MTUs were used by the phone companies to test lines between the central office and the customer premises. The devices are no longer used, but many were left in place on phone lines and they can dramatically reduce data rates. You can call your phone company repair number and ask them if your line has an MTU. If it does, ask them to remove it.

Another problem occurs when a phone line is stretched beyond 3 miles. You must be within about 3 miles of your Central Switching Station (where all of your home calls are routed by the phone company) for 56k modems to operate faster than 33600bps. Call your operator and ask where your Central Switching Station is. Two conditions apply. The phone line can be no longer than 3 miles for the 56k technology to work. If you live 3 miles from the Central Switching Station, but your phone line doesn't go in a straight line and it's over 3 miles, your modem is unlikely to work at more than 33600bps.

Office users lose capability if they are on a PBX switch, which introduces line attenuation. If you don't already connect consistently at or above 26400, you're unlikely to benefit much from a 56k modem. Also, at the Central Switching Station there must be a digital trunk routing the calls.

If you've noticed, all of the above conditions that are necessary to make 56k work effectively are controlled by the phone company, not by any Internet Service Provider. And we're still not done.

Another factor is the firmware in your modem.

Firmware is what is programmed into the modem by its manufacturer. If your modem does not have an up-to-date version of firmware, it may not work at all, or it may operate at less than optimum speed.

When modem manufacturers release their modems to the market, they come with a specific firmware version. When they make improvements to a better firmware version, not all modems will be specifically backwards compatible. It is for this reason that you must check your firmware version. Even if you bought your modem yesterday, there's no telling how long the modem sat in the store. To upgrade the firmware, contact the manufacturer of your modem. They will either send you a disk, or tell you where online you can download the new firmware. They may also help you install it. If you are unfamiliar with this it is recommended that you do not attempt it. You could very successfully delete the firmware on the modem and it will never work again. Not all modems can be upgraded.

It is also important to note that many dial up programs, especially Windows 95/98 Dial Up networking, have a "Connected At" screen. This program does not tell you the actual connection speed, nor does it tell you the Data Transfer rate. In other words, if it says "You are connected at 31200Kbps" and you are using a perfectly functioning 56k compatible modem this does not mean you are connected at and transferring data at 31200bps. This number is simply the line rate at the instant you connected. Also, if you have experience with AOL, their software is self-contained and does not rely upon your computer to report the modem connect rate. Rather, it reports the nominal rate (usually 57,600bps) regardless of the true rate.

You should also keep in mind that 56k technology only works in one direction, downloading. You will only get the increase in speed when downloading; any uploading will always be at 33600bps or less.

And there's even more bad news. Anything that adds to the line noise on telephone lines between your ISP and your modem lessens the modem performance.

If there's persistent noise on your phone line, your only solution may be to move. Complain all you want, but the telco company is currently obligated only to provide you with a clean enough line for voice connections . They are not obligated to ensure modems speeds of 28800bps or 33600bps, much less 56k, unless you order and pay for extra services, such as ISDN.

Some final comments on 56k specifications and modems.

56k specifications used today take advantage of nuances in the way the phone system is designed. In a standard call between two modems, your data must be translated into analog "tones" that can be transmitted across the telephone network. This translation is called the digital-to-analog conversion. Once your data reaches a telephone company's central office, it's translated back to digital form by a coder/decoder (codec) for transmission across the phone company's digital backbone. Unfortunately, because the telephone network contains some random noise, the analog-to-digital conversion is only an approximation of the original digital signal. To ensure that your data remains readable despite the effects of this quantization noise, transmission rates are currently limited to about 35-42 kbps.

However, because most Internet service providers connect directly to the phone company's digital backbone, data coming from an ISP need never undergo an analog-to-digital conversion. Instead, the data can be encoded (using pulse code modulation, or PCM) so that it remains entirely digital until it gets to the central office. Once it arrives, the data is put through a digital-to-analog conversion before being sent across the analog phone lines to your modem. And since digital-to-analog conversions aren't affected by quantization noise, the result, at least in theory, is throughput as high as 56 kbps from your ISP to you.

So, what's the bottom line? For most 56k modem users, expect a connect rate of about 44000bps most of the time, occasionally higher, sometimes lower.

P.S.--Internet Frontier does not endorse or recommend one brand of modem over another. Generally, all perform satisfactorily, although a modem which works well in one situation may operate poorly in another. In older computers, however, we do discourage the use of so-called "WIN Modems", "LT WIN Modems", and modems whose identification includes references to HSP or HCF. Unlike conventional modems, these aren't self-contained; they require some of the computing power of the CPU in your system. On older systems this can noticeably reduce system performance, and in many cases, even on newer systems, the modem may perform sluggishly or not connect reliably. If you do have such a modem, it is essential that you have installed on your system the latest driver supplied by the manufacturer for that modem.