Digital Subscriber Line (DSL) refers to a class of technology used to obtain more bandwidth over existing copper telephone cabling that is running between a customer's premises and an Internet service provider (ISP).
DSL allows simultaneous voice and high-speed data services over a single pair of copper telephone wires. Modem speeds have gradually increased through the use of various compression and other techniques, but at today's fastest (56 kbps), they are approaching the theoretical limit for this technology. DSL technology enables much higher speeds across the twisted pair lines from the central office to the home, school, or business. Speeds up to 2 Mbps are achievable in some areas. PPP is typically used over serial communications like dial-up modem connections. Many DSL Internet service providers now use PPP over Ethernet (PPPoE) because of its added login and security features.
A DSL modem is a device that is placed at either end of the copper telephone line to allow a computer (or LAN) to be connected to the Internet through a DSL connection. Unlike a dial-up connection, it typically does not require a dedicated telephone line (a POTS splitter box enables the line to be shared simultaneously). Although DSL modems resemble conventional analog modems, they provide much higher throughput.