# Modem ## What is a Modem A modem is a device that converts digital signals from a computer into a format that can be transmitted over an analog communication medium, and converts incoming analog signals back into digital form. The word modem is a combination of modulator and demodulator, describing its two core functions. Modulation is the process of encoding digital data onto an analog signal for transmission. Demodulation is the reverse process of extracting digital data from a received analog signal. Modems are used to connect computers and local networks to internet service providers over various types of communication infrastructure. ## DSL Modem A DSL modem connects to the internet service provider through a standard telephone line. DSL stands for Digital Subscriber Line and uses sophisticated modulation techniques to transmit high-speed data over the copper telephone wires that were originally designed only for voice calls. Different variants of DSL technology achieve different speeds. ADSL provides faster download speeds than upload speeds, which suits typical home usage where more data is downloaded than uploaded. VDSL provides much higher speeds than ADSL but over shorter distances from the exchange. ## Cable Modem A cable modem connects to the internet service provider through the cable television coaxial cable infrastructure. Cable internet uses a portion of the available bandwidth on the cable television network to carry internet data. Cable modems typically achieve higher speeds than DSL modems and can provide speeds of hundreds of megabits per second or more. ## Fiber Optic Modem With fiber optic internet connections, the device that connects the home or business to the provider's fiber network is often called an Optical Network Terminal rather than a modem. It converts the optical signals from the fiber optic cable into the electrical signals that a router can use. ## Modem vs Router A modem and a router are different devices that serve different functions. The modem connects to the internet service provider's network. The router connects to the modem and distributes the internet connection to multiple devices in the home or business. Many internet service providers supply a single device that combines both modem and router functions. This combined device is often called a gateway or a home hub.