How does Wi-Fi carry the internet through the air?

Wi-Fi swaps the last stretch of cable for radio. Your phone and a wireless router, which is plugged into the wired internet, exchange data by radio waves instead of along a wire. Wi-Fi is a family of wireless protocols based on the IEEE 802.11 standards, designed to work well with its wired sibling, Ethernet, so the router can pass your traffic onto the wired network and the rest of the internet.

The radio waves sit in the 2.4 and 5 gigahertz bands, each divided into channels. Channels can be shared between networks, but within range only one transmitter can talk on a channel at a time, so devices take turns. That is why Wi-Fi slows down in a crowded apartment block. Many access points even default to the same channel when first switched on, which adds to the congestion.

There is a trade-off hidden in the bands. In general, lower frequencies have longer range but less capacity, and the 5 GHz band is absorbed more by building materials, so it usually gives a shorter range than 2.4 GHz. The 2.4 GHz band is also the one microwave ovens use, so it is subject to interference.

The name has a funny origin. A branding firm, Interbrand, coined Wi-Fi after it was hired to find something catchier than "IEEE 802.11b Direct Sequence". It was partly chosen because it sounds like Hi-Fi, and people still dispute whether it is short for Wireless Fidelity.