Digital Subscriber Line
DSL is an always-on service, which means that there is no need to dial up each time you want to connect to the Internet. DSL uses the existing copper telephone lines to provide high-speed digital data communication between end users and telephone companies. Unlike ISDN, where the digital data communications replaces the analog voice communications, DSL shares the telephone wire with analog signals.
With DSL, the voice and data signals are carried on different frequencies on the copper telephone wires. A filter prevents DSL signals from interfering with phone signals. A DSL filter is connected between each telephone and phone jack.
The DSL modem does not require a filter. The DSL modem is not affected by the frequencies of the telephone. A DSL modem can connect directly to your computer, or it can be connected to a networking device to share the Internet connection with multiple computers.
Asymmetric Digital Subscriber Line
ADSL has different bandwidth capabilities in each direction. Downloading is the receiving of data from the server to the end user. Uploading is the sending of data from the end user to the server. ADSL has a fast download rate which is beneficial to users who are downloading large amounts of data. The upload rate of ADSL is slower than the download rate. ADSL does not perform well when hosting a web server or FTP server, both of which involve upload-intensive Internet activities.