Wireless Tutorial

This tutorial covers the wireless networking concepts that show up on the CCNA exam: how a WLAN works at a basic level, the IEEE 802.11 standards, the two modes a WLAN can run in, how radio signals get encoded, the security standards built around Wi-Fi, and the everyday sources of interference that can disrupt a wireless network.

Wireless LAN basics

A Wireless LAN (WLAN) lets devices communicate without a physical cable — something most people already rely on daily through a laptop or phone. Here’s roughly what a simple WLAN looks like:

Every WLAN needs a wireless Access Point (AP) to send and receive data for connected clients. A wired network can send and receive at the same time (full-duplex), but a wireless network can’t — it’s half-duplex — which is part of why an AP is sometimes called a “wireless hub.”

The core difference between a wired LAN and a WLAN is the medium itself: a WLAN carries data as radiated radio waves rather than electrical signals over copper.

Because a wireless device can’t transmit and listen at the same time, WLANs can’t use CSMA/CD (the collision-detection method wired Ethernet relies on). Instead they use CSMA/CA — Carrier Sense Multiple Access with Collision Avoidance — which works like this:

• Listen first to confirm the medium is free; if it is, wait a random backoff time before sending.
• Once that random time elapses, listen again — if the medium is still free, send; if not, pick another random wait and try again.
• Wait for an acknowledgment confirming the data arrived.
• If no acknowledgment comes back, resend the data.