The document discusses different types of modems and digital subscriber line (DSL) technologies. It defines what a modem is, including that it modulates and demodulates digital and analog signals to allow computers to communicate over phone lines. It then describes DSL technology, how it uses existing phone lines to provide high-speed internet access. Finally, it focuses on asymmetric DSL (ADSL), explaining how ADSL works using an ADSL modem, splitter, and other components to transmit data faster downstream than upstream over phone lines while still allowing phone use.