How Modems Work

    Information inside your computer is in digital format: all of the data is stored in 1s and 0s. Normal phone lines are analog: they transmit data as a series of peaks and valleys. Your "modem" is a Modulator/Demodulator: it modulates outgoing data from digital to analog, and demodulates incoming data from analog to digital.

    Above a certain threshold (called Shannon's Limit) the signal-to-noise ratio of any medium becomes too low to reliably transfer data. The analog phone line is the limiting factor in the speed of data transmission because of the inherent noise it contributes. Thus the 56k needs a lesser limiting phone line.

 

How 56k Modems Work

    It has long been thought that the "theoretical limit" on modem speed over an ordinary phone line was 33.6 kbps. 56k modems achieve their speed by avoiding a conversion from digital to analog lines in the connection between user and service provider. Ordinary connections begin over an analog line, are converted to digital by the phone company and are converted back to analog in the final segment before arriving at the service provider. 56k connections begin analog, are converted to digital and are not converted back to analog at the service provider. This requires the service provider to have a direct digital connection and therefore avoids one conversion of the signal. By avoiding this second conversion, speeds of up to 56k and faster are possible. Therefore, modems users need to know that they can only achieve 56k if their service provider supports it.

    Interestingly, FCC regulations limit the speed to 53k, but modem makers are fast at work to sidestep and/or waive this rule. Just because 56k is possible, doesn't mean that every user will achieve it. Poor local phone lines and other conditions may limit speed. Users who are unable to achieve 28.8 or 33.6 with their current service are unlikely to achieve faster connections with a 56k modem.

    56k modems download at speeds up to 56kbps, but can upload at only 33.6kbps.

 

Equipment Needed For 56k

There are three things needed to operate 56k modems.

  1. A 56k modem. These are becoming the norm and are not that hard to find. The more modems produced the cheaper they are becoming to purchase.
  2. Once you have the 56k modem, you need a place to call. Nearly all of the Internet service providers have pledged support for 56k technology.
  3. The third requirement is the one that may prevent some people from using 56k speed. For 56k to work, you can only have one analog-to-digital conversion between your home or office and the Internet service provider. If there is more than one, you can't use 56k, and your connection will be limited to V.34 speeds (a maximum of 28.8k or 33.6k).

 

Advantages vs. Disadvantages

 

Advantages

  1. The 56k obviously are faster than the modems before them. Although it is more realistic to receive speeds more like 40-50k, it is still natural progression over today's speeds and will definitely be the technology used in new computers today.
  2. The cost compared to ISDN lines or ADSL or any other new technology is extremely cheaper. There are no additional charges for enhanced phone lines, you simply use the ones already in place
  3. The other high-speed technologies on the market are not as widely available as 56k. It is practically available everywhere in the US. There are not limitations on how far the telephone wire has to be from the switch like ISDN and ASDL has to have. Cable companies have yet to offer Internet service to everyone yet as well.

Disadvantages

  1. You can't use the technology if there is more than one analog-to-digital conversion in the local phone loop.
  2. You have to buy the same type of 56k modem that your Internet service provider has support for.
  3. The 56k modem is used only for downloading purposes. To upload you really only realize a modest 28.8k to 33.6k speed.