Understanding Wi-Fi (Wireless Fidelity)

In the wired world, we're talking about IEEE 802.3. But the moment we cut the cable, we move into IEEE 802.11 — the world of wireless communication: Wi-Fi, Bluetooth, and friends.

Wi-Fi uses radio frequencies (RF) to send signals through the air. But for two devices to talk, they need to agree on a few things:

• Same frequency
• Same communication channel
• Same protocol

That’s the deal. And also: they can’t talk at the same time. At least not with the basic setup. That’s what we call half-duplex communication — each host takes turns. To solve that, we use full-duplex, which relies on separate frequencies (or channels) for the upstream and downstream traffic.

WLAN Topologies

Basic Service Set (BSS)

In a BSS, all communication happens through the Access Point (AP). Devices can't talk to each other directly.

Terminology:

• AP: Access Point
• SSID: The public name of the network
• BSSID: The MAC address of the AP
• BSS: The actual Wi-Fi coverage area of one AP

Distribution System (DS)

Want to segment multiple wireless networks with one AP? Use Virtual LANs (VLANs) with multiple BSSIDs. Each BSSID maps to a specific VLAN. This setup is compliant with IEEE 802.1Q.

Extended Service Set (ESS)

When multiple APs are deployed to cover a large area (like a building), each AP creates its own BSS, but all of them together form an ESS. Channels must be carefully chosen to avoid interference.

Ad-Hoc Networks (IBSS)

No AP here. Just two devices directly talking to each other. This is called an Independent Basic Service Set (IBSS) — like Bluetooth. Both devices must use the same frequency, channel, and parameters.

Wi-Fi Repeater Topology

A repeater extends the coverage of a BSS by retransmitting the signal. It should be placed right at the edge of the AP’s BSS.

Workgroup Bridge (WGB)

A WGB allows a device that only supports wired Ethernet to connect to a wireless network through a bridge (e.g., connect a wired PC to Wi-Fi via a smartphone or dedicated bridge device).

How Wi-Fi Uses Radio Waves

Wi-Fi transmits data using electromagnetic waves. Each wave consists of:

• One electric component
• One magnetic component, perpendicular to the electric one

These waves propagate spherically in all directions.

A cycle = one unit of data.
If we see 3 cycles in 1 second, the frequency is 3 Hz. In Wi-Fi, frequencies are way higher: up to 2.4 GHz or 5 GHz.

Example:

• 2.4 GHz = 2,400,000,000 cycles per second
• Each cycle carries 1 byte (in a simplified view)

Frequency Bands

2.4 GHz Band

• Frequency range: 2.400 GHz to 2.486 GHz
• Channels are 22 MHz wide and overlap, so only channels 1, 6, and 11 are usable without interference. Others can be used for other protocols.

5 GHz Band

• Frequency range: 5.15 GHz to 5.825 GHz
• Channels do not overlap → All can be used without interference

Wi-Fi Standards (Amendments)

Wi-Fi Security

Wi-Fi broadcasts data over the air — so anyone nearby can listen if it's not protected. That’s why security is critical.

The IEEE 802.11 standard defines three pillars of security:

• Confidentiality: prevent others from reading your data
• Authentication: confirm who is allowed to connect
• Integrity: ensure data wasn’t modified in transit

Authentication

Access Points validate whether the device trying to connect is legit or not.

• Client: Who are you ?
• Server: I am < BSSID >
• Client: Here are my credentials.

Message Confidentiality

Modern Wi-Fi uses encryption protocols (like WPA2/WPA3) to ensure all messages are encrypted.

Message Integrity Check (MIC)

• A hash (MIC (Message Integrity Check)) is calculated on the original message
• The message is encrypted and sent
• The receiver decrypts it, recalculates the MIC
• If the MICs match → the message is valid

If they don’t? It’s rejected. That’s how tampering is detected.

Here you go!