Multiplexing

In networking, it's often inefficient and costly to have a separate physical link for every pair of communicating devices. Multiplexing is a technique that allows multiple communication signals to be combined and transmitted simultaneously over a single shared medium. The device that performs the combining is called a multiplexer (MUX), and the device that separates them at the receiving end is a demultiplexer (DEMUX). There are three main types of multiplexing. Frequency Division Multiplexing (FDM) is an analog technique where the bandwidth of the link is divided into several smaller, non-overlapping frequency bands. Each user is allocated a unique frequency band to send their signal. This is how broadcast radio and analog cable TV work. Time Division Multiplexing (TDM) is a digital technique where users take turns using the entire bandwidth of the link for a short period of time. The transmission time is divided into fixed-length time slots, and each user is assigned one or more time slots in a repeating cycle. A more efficient version is Statistical TDM, which allocates time slots dynamically based on user demand. Wavelength Division Multiplexing (WDM) is used in fiber-optic communication. It is conceptually similar to FDM but for light signals. It combines multiple light streams of different wavelengths (colors) onto a single fiber. Dense WDM (DWDM) can transmit over 100 different wavelengths on one fiber, enabling massive data rates.