Most modems are analog products. They are designed to send sound along the same sort of twisted-pair wires that your voice telephone uses. This twisted-pair wiring literally extends from the phone to your phone company's "central office," where it is led to a "switch," which both provides dial tone and honors your dialing requests.
Along the way, the strength of the signal diminishes. So the phone company uses analog amplifiers to improve the quality of the signal. Each time the signal is amplified, there is a potential loss of signal strength, which makes this approach less than desirable for many types of data communications.
When a phone company "goes digital," it is generally referring to a multi-step process. Many phone services have long since gone digital: the switch, for example, is a computer, so communication between central offices is generally already digital.
The "going digital" part refers to the relationship in the "local loop," which is to say, between your location and the central office. Generally, this means that they will be doing the following:
- Installing an analog-to-digital/digital-to-analog converter near your house's "demarcation point" (which is where the phone company plugs into your house).
- Replacing the analog amplifiers with digital repeaters.
The main advantages of this process are:
- Improved data reliability.
- Support for higher bandwidths.
- Potentially better voice quality.
- Better support for digital technologies like ISDN (in general).
In general, unless you have specifically ordered digital telephone service such as ISDN or (in the future, possibly ADSL), or you have installed additional hardware such as a Public Branch Exchange (PBX), then your phone service will continue to be analog and your modem will continue to work as it did before. If your telephone company has not notified you that the telephone at your location needs to be upgraded then your modem will not have to be upgraded either.
This article was published in the 16 June 1997 "Information Alley".