A dial-up modem allows a computer to transmit data to an Internet service provider’s server over a standard telephone line. Also called an analog modem, this device converts the computer’s digital signal into an audio tone. Early modems provided very slow transfer speeds — only about 300 bps. The most recent dial-up modem standard, V.92, provides theoretical speeds of up to 56 Kbps, but seldom reach their top-rated speed due to line noise and other issues. Where it’s available, broadband Internet access, including DSL, has largely replaced dial-up access, but in many places dial-up may be all that’s available or all a user needs. It can also serve as a backup when DSL or another broadband service has problems.
High-speed Dial-up Access
Special high-speed dial-up Internet access is available from some providers. This technology uses compression techniques to speed delivery of data. It does not speed up the modem’s rate of transfer. This technique can allow subscribers to receive images and webpages considerably more quickly than they would over a conventional modem connection, but in some cases it can affect the quality of the data received.
Digital Subscriber Line (DSL) access makes use of normal copper telephone wires, but in a way that allows much higher rates of data transfer and also allows the lines to be used for both phone and Internet simultaneously. DSL connections require a filter to prevent interference betwen phone and Internet signals, and a DSL modem to deliver digital data to the computer. Most DSL connections are ADSL (Asymmetric Digital Subscriber Line), and can provide speeds up to 1 Mbps for uploading and 8 Mbps for downloading. ADSL lines all offer different upload and download rates. Subscribers may pay different rates for different speed ranges. DSL speeds may degrade by distance from the transmission source, and beyond a certain distance DSL is not available. Even though your ISP or phone company may offer DSL, you must contact them to determine whether it’s available to your specific location.
Some providers offer higher-speed DSL Internet connections via VDSL (Very-high-bitrate Digital Subscriber Line) or ADSL2+ (Asymmetric Digital Subscriber Line version 2+). These technologies can both share lines with the telephone, but use different transfer methods to provide more data at once. VDSL can offer between 1.6 and 6.4 Mbps upstream and between 13 and 52 Mbps downstream. ADSL2+ provides between 1.3 and 3.3 Mbps upstream and as much as 24 Mbps downstream.