Early dial-up Internet service required an Internet service Provider (ISP), a modem, and a dedicated telephone line. To use dial-up service, early or current, in order to connect to the ISP, and the Internet, communications software provided by the ISP would dial a local telephone number and establish a connection, via the modem, between the computer and the ISP.
A modem, required for any dial-up service, is an abbreviation of the phrase "MOdulator/DEModulator", which explains what a modem does. Simply put, a modem places the digital data required by computers onto/with the analog signal required by a telephone system (called modulation), and converts the analog signal back into digital data for the computer to use (called demodulation).
Early modulation techniques were often disrupted by thunderstorms and distortions which occurred due to mixing digital data and analog signals. With the advent of new encoding techniques, the quality of modem service greatly improved. Data transfer rates increased.
As different sizes and styles of modems became available, for both desktops and laptops, automatic features were added to make modems less dependent on external control. Features built into a modem included autoanswer, autodial, autoredial, and autodisconnect. Security features were offered, including autocorrection of transmission errors.
A hybrid modem system was designed which utilized both digital signals and analog signals. The new design increased transmission rates beyond the limits of the rate of transfer of analog signals. In order for the modem to work efficiently with the telephone system, to which it was attached, the modem design allowed for faster downstream link transmission rates, via digital signals, and slower (although maximum) upstream link transmission rates via analog signals, which gave users faster downloads than uploads. The hybrid system was called a 56k modem, named for its faster downstream transmission, approximately 56 Kbps. The upstream transmission rate remained at the previous maximum analog transfer rate of 33.6 Kbps.
Improvements in the type of medium, used by a telephone service to transmit signals, were also a contributing factor in the creation of the 56k modem. Old-style telephone relay lines had been upgraded to include broadband multi-channel thick coaxial cable, used in shorter distance computer system links. Broadband cable provided the required medium over which digital signals could be transmitted.
T-1 leased line service then became available, due to the improved media, through telephone companies for businesses which required a high-speed connection for data transfer, such as Internet Service Providers. By allowing customers access to a portion of the T-1 line, ISPs provided the link needed for the 56k modem downstream link to the Internet.
As greater access to digital signaling becomes available, and modems improve, data transfer rates will increase. In the real world, this means that it will become even easier to transfer larger-size files, such as those required by multimedia applications. Eventually, an all-digital signal modem will be created, and data will flow even faster through a modem than today's 56k modem.