Wi-Fi is the everyday name for wireless local area networking based on the IEEE 802.11 standards. (The IEEE is the engineering organisation that writes the standards; 802.11 is the family of standards for wireless LANs, just as 802.3 is the family for Ethernet.) Instead of sending electrical signals down a cable, a Wi-Fi device sends radio waves through the air to an access point, which connects it to the rest of the network.
💡 In simple terms: Wi-Fi is like a meeting room where everyone talks through the chairperson (the access point). Only one person can speak at a time, everyone hears everything, and people further from the chair have to speak more slowly to be understood.
What Wi-Fi is
A Wi-Fi network is a WLAN (wireless LAN): a local network where the last hop to each device is a radio link. Wi-Fi works at the bottom two layers of the OSI model:
- Layer 1 (Physical): the radio itself: which frequency to use, how wide the channel is and how bits are turned into radio waves.
- Layer 2 (Data Link): Wi-Fi frames with MAC addresses, rules for taking turns on the air, and acknowledgements for every frame.
Everything above these two layers is unchanged. Your device still has an IP address, a default gateway and a DNS server, and it still uses TCP and UDP. A web page loads over Wi-Fi in exactly the same way as over a cable; only the first hop is different.
Why Wi-Fi exists
Cables are fast and reliable, but they tie a device to one spot. Wi-Fi solves three problems:
Mobility
You can carry a laptop or phone from room to room and stay connected.
Devices without ports
Phones, tablets, watches, cameras and smart speakers have no Ethernet socket at all.
Low-cost coverage
One access point on one cable can serve dozens of devices across a whole floor.
The price you pay is that radio is a shared, noisy and open medium. Every device shares the same airwaves, walls weaken the signal, and anyone nearby can receive it. Most of this lesson, and the next two, explain how Wi-Fi deals with these three facts.
Where Wi-Fi sits in a network
Wi-Fi only covers the short hop between a device and the access point. After the access point, traffic travels over ordinary Ethernet cables like any other traffic.
- 1. Radio hop. The laptop sends a Wi-Fi (802.11) frame through the air to the access point.
- 2. Wired hops. The access point turns it into an Ethernet frame and sends it down its cable. From here on, it is ordinary wired traffic.
- 3. Out to the internet. The router forwards the IP packet towards the internet, exactly as it would for a wired PC.
The important parts
Client (station)
Any device that joins a Wi-Fi network: laptop, phone, printer, TV. The 802.11 standards call it a station, or STA.
Access point (AP)
The device that runs the Wi-Fi network and bridges it to the wired LAN. At home, it is built into the home router.
SSID
Service Set Identifier: the network name you pick from the list, such as “Home-WiFi”. Up to 32 characters.
BSSID
Basic Service Set Identifier: the MAC address of one AP radio serving one SSID. It tells apart APs that use the same name.
Band and channel
The band is the range of radio frequencies used (2.4, 5 or 6 GHz). The channel is the small slice of that band that one AP uses.
Security
The rules for who may join and how traffic is encrypted, such as WPA2 or WPA3 with a password.
SSID vs. BSSID
One AP plus the clients joined to it is called a BSS (basic service set). When several APs broadcast the same SSID with the same security, together they form an ESS (extended service set). To the user it looks like one network. Behind the scenes, each AP radio has its own BSSID, and your device picks the one with the best signal.
| SSID | BSSID | |
|---|---|---|
| What it is | A human-readable network name | A 48-bit MAC address |
| Example | Office-Staff | 02:00:00:00:a0:01 |
| Unique? | No: many APs (and your neighbour) can use the same name | Yes: one per AP radio and SSID |
| Who uses it | People, to choose a network | Devices, to address frames to one specific AP |
- 1. Near AP 1. Both APs broadcast the SSID “Office-Staff”. The phone joins AP 1, whose signal is stronger.
- 2. It roams. As the user walks, AP 1 fades and AP 2 grows stronger. The phone re-associates with AP 2's BSSID: same SSID, same IP address, new AP.
How a device joins a Wi-Fi network, step by step
Joining happens in a fixed order. The first steps are specific to Wi-Fi; after that, the device gets an IP address just as a wired device would.
- Discover. The AP sends a beacon frame about ten times a second, announcing its SSID, security type and supported speeds. The client can also ask actively with a probe request, and the AP replies with a probe response.
- Authenticate (802.11). A short “may I talk to you?” exchange. With WPA2, it is a formality called open system authentication; the real password check comes later. With WPA3, this is where the password exchange (SAE, Simultaneous Authentication of Equals) happens.
- Associate. The client asks to join, and the AP gives it an association ID and adds it to its table of connected clients.
- Agree on encryption keys. A 4-way handshake proves that both sides know the password (or have passed an enterprise login) and creates fresh keys for this session. Until it finishes, the AP drops any normal data from the client.
- Get an IP address. Now the client is on the LAN. It runs DHCP through the AP to get its IP address, subnet mask, default gateway and DNS server.
1. Beacon · AP → everyone in range
“Home-WiFi is here, WPA2/WPA3, these speeds supported.”
- IP address:
- 192.168.1.20/24
- Gateway:
- 192.168.1.1
- Associated to:
- 02:00:00:00:a0:01
The access points lesson follows the same join from the AP's side, through a real office network. The wireless security lesson explains the password and key steps.
Learn more: Wireless Access PointsWireless Security
What is inside a Wi-Fi frame
Wi-Fi uses its own frame format, different from the Ethernet frame. There are three types of Wi-Fi frame:
| Frame type | What it is for | Examples |
|---|---|---|
| Management | Finding, joining and leaving networks | Beacon, probe, authentication, association, deauthentication |
| Control | Taking turns on the air and confirming delivery | ACK, RTS, CTS |
| Data | Carrying your actual traffic (IP packets) | A web request, a DNS query, a video stream |
A data frame normally carries three MAC addresses, not two as in Ethernet. It must name the radio that should receive it (the AP's BSSID) as well as the real source and destination. For a laptop sending a frame to the router through the AP:
| Address field | Value | Meaning |
|---|---|---|
| Receiver (BSSID) | 02:00:00:00:a0:01 | The AP radio that should pick this frame out of the air |
| Source | 02:00:00:00:00:51 | The laptop |
| Destination | 02:00:00:00:00:01 | The router, the real next hop (found with ARP) |
Inside the frame is an ordinary IP packet: 192.168.1.20 → 203.0.113.80, for example. The AP removes the Wi-Fi header, builds an Ethernet frame with the same source and destination MAC addresses, and sends it on. Unlike a wired frame, every Wi-Fi unicast frame must be acknowledged, by a short ACK frame or, on newer standards, a block ACK that covers several frames at once. If no ACK arrives, the sender assumes the frame was lost and sends it again.
How Wi-Fi shares the air
Half duplex: one talker at a time
A radio cannot send and listen on the same channel at the same time, because its own signal drowns out everything else. So Wi-Fi is half duplex: on one channel, only one device (the AP or one client) transmits at any moment. All the devices on that channel share its capacity. This is very different from modern switched Ethernet network, where every cable is full duplex and each device has its own link.
📻 A Wi-Fi channel behaves like the old shared Ethernet hub: one big collision domain. Ten laptops on one AP channel don't each get the full speed; they take turns.
CSMA/CA: listen, wait, then talk
If two devices transmit at the same time, their signals mix and both frames are lost. This is a collision. Ethernet on old shared hubs used CSMA/CD, detecting collisions while sending. A radio can't hear a collision while it is transmitting, so Wi-Fi tries to avoid them instead. This is CSMA/CA: Carrier Sense Multiple Access with Collision Avoidance.
This has two consequences. First, a busy channel wastes time on waiting and retries, so speed drops as more devices become active. Second, a slow device costs everyone: an old phone far from the AP sends at a low rate, so its frames occupy the air for much longer, and everyone else waits.
The hidden node problem: two laptops at opposite ends of a room can both hear the AP but not each other. Carrier sense fails because each thinks the air is free, so their frames collide at the AP. Wi-Fi can use a short RTS/CTS exchange (Request to Send / Clear to Send) in which the AP announces “the air is reserved” to everyone. Wi-Fi 6 adds OFDMA, which lets the AP split one channel into small pieces and talk to several clients in the same transmission, reducing the waiting.
Channels in one minute
Each AP radio works on one channel: a slice of frequency, usually 20 to 160 MHz wide. APs that can hear each other on the same channel must take turns, as if they were one network. APs on different, non-overlapping channels can transmit at the same time. That is why neighbouring APs should use different channels: in the 2.4 GHz band, channels 1, 6 and 11. The next lesson explains each band in detail, with diagrams.
Learn more: Wi-Fi Frequency Bands
Wi-Fi standards: from Wi-Fi 4 to Wi-Fi 7
Each new 802.11 amendment adds speed and efficiency. In 2018, the Wi-Fi Alliance (the industry group that certifies products) gave them simple generation numbers. Both kinds of name are still used, so it helps to know both.
| Name | IEEE standard | Approx. year | Bands | Max channel width | Max theoretical rate | What it added |
|---|---|---|---|---|---|---|
| (Legacy) | 802.11b / a / g | 1999–2003 | 2.4 / 5 / 2.4 GHz | 20 MHz | 11 / 54 / 54 Mbps | The first popular Wi-Fi |
| Wi-Fi 4 | 802.11n | 2009 | 2.4 and 5 GHz | 40 MHz | 600 Mbps | MIMO: several antennas sending several streams at once |
| Wi-Fi 5 | 802.11ac | 2013 | 5 GHz | 160 MHz | About 3.5–6.9 Gbps | Wider channels, faster coding, MU-MIMO (later versions) |
| Wi-Fi 6 | 802.11ax | 2019 | 2.4 and 5 GHz | 160 MHz | 9.6 Gbps | OFDMA, better performance in crowded places, Target Wake Time for battery life |
| Wi-Fi 6E | 802.11ax | 2020 | 2.4, 5 and 6 GHz | 160 MHz | 9.6 Gbps | Same as Wi-Fi 6, plus the new, empty 6 GHz band |
| Wi-Fi 7 | 802.11be | 2024 | 2.4, 5 and 6 GHz | 320 MHz | About 46 Gbps | 320 MHz channels, Multi-Link Operation (using two bands at once) |
⚠️ Theoretical rates are not real speeds. The maximum assumes the widest channel, the most antennas and a perfect signal. A typical phone has two antennas and may be a room away, so it might connect at 500–1,200 Mbps on Wi-Fi 6 and see roughly half that as real throughput. A link also only uses a standard that both ends support: a Wi-Fi 4 laptop on a Wi-Fi 7 AP is still a Wi-Fi 4 laptop.
Signal strength: RSSI and dBm
What the numbers mean
Your device constantly measures how strong the AP's signal is when it arrives. This reading is called the RSSI (Received Signal Strength Indicator). Tools usually show it in dBm: decibels relative to one milliwatt of power. Received Wi-Fi signals are tiny fractions of a milliwatt, so the numbers are negative, and closer to zero means stronger.
- −45 dBm is stronger than −70 dBm.
- The scale is logarithmic: every 3 dB less is about half the power, and every 10 dB less is one tenth. So −70 dBm is about 300 times weaker than −45 dBm, not just “a bit” weaker.
- Windows shows a percentage (“Signal: 88%”) instead. This is a convenience scale calculated from the RSSI, not a real unit of measurement, so use dBm when you can.
Signal strength is only half the story. What really matters is how far the signal stands above the background radio noise, called the SNR (signal-to-noise ratio). A −65 dBm signal is fine in a quiet house but may struggle next to a microwave oven that is running. As the SNR falls, devices automatically switch to slower, more reliable data rates, which is why Wi-Fi slows down long before it disconnects.
What weakens a Wi-Fi signal
| Cause | Effect | Notes |
|---|---|---|
| Distance | Signal fades quickly | Doubling the distance costs about 6 dB even in open space |
| Plasterboard or wooden walls | Small loss | A few dB per wall |
| Brick and concrete walls, floors | Large loss | Often 10–20 dB or more, worse at 5 and 6 GHz |
| Metal (fridges, filing cabinets, foil-backed insulation, lift shafts) | Blocks or reflects | Putting the router behind a TV or in a metal cupboard is a classic mistake |
| Water and people | Absorbs signal | Fish tanks and crowded rooms noticeably weaken Wi-Fi |
| Interference | Raises the noise, lowers SNR | Neighbours' Wi-Fi, microwave ovens and Bluetooth (2.4 GHz), baby monitors |
| Low client power | One-way link | A phone transmits with less power than the AP, so it may hear the AP while the AP can't hear it |
A real-world example: the slow back bedroom
A family's ISP router sits in a cupboard by the front door. In the back bedroom, two brick walls away, a laptop shows two bars and video calls freeze. Here is what is happening:
- The laptop measures the AP at about −79 dBm, in the poor zone.
- To stay connected, it lowers its data rate from hundreds of Mbps to about 20–30 Mbps.
- Frames get lost and must be resent, and every slow frame takes airtime from the rest of the family too.
- Moving the router out of the cupboard to a central shelf brings the bedroom to about −63 dBm. Adding a second AP (or mesh unit) cabled to the router would do even better.
The internet connection was never the problem; the Wi-Fi hop was.
What happens when Wi-Fi fails
| Symptom | Likely cause | What to check |
|---|---|---|
| Network not in the list | Out of range, AP off or wrong band (for example, an old device can't see a 6 GHz-only SSID) | Move closer; check the AP; check which bands the device supports |
| “Can't connect” right after typing the password | Wrong password, or a security mismatch | Retype it carefully (it is case-sensitive); check the security settings on both sides |
Connected, “No internet”, address 169.254.x.x | Wi-Fi joined but DHCP failed | ipconfig; is the DHCP server reachable from the AP? |
| Connected with a good address, but nothing loads | Gateway, ISP or DNS problem, not Wi-Fi | Ping the gateway, then a public IP, then a name |
| Slow or keeps dropping | Weak signal, interference, crowded channel | RSSI in dBm; channel and neighbouring networks |
Troubleshooting and useful commands
Work through the problem in layers: first the radio (is the device associated, and how strong is the signal?), then IP (did it get an address?), then everything above.
Windows: is the radio link healthy?
C:\>netsh wlan show interfaces There is 1 interface on the system: Name : Wi-Fi Description : Intel(R) Wi-Fi 6 AX201 160MHz Physical address : 02:00:00:00:00:51 State : connected SSID : Home-WiFi BSSID : 02:00:00:00:a0:01 Network type : Infrastructure Radio type : 802.11ax Authentication : WPA2-Personal Cipher : CCMP Connection mode : Auto Connect Band : 5 GHz Channel : 36 Receive rate (Mbps) : 288.2 Transmit rate (Mbps) : 288.2 Signal : 58% Profile : Home-WiFi
What to look for: State shows whether you are associated at all. SSID and BSSID show which network and which AP radio you are on. Radio type shows the standard in use (802.11ax is Wi-Fi 6). Receive/Transmit rate is the current link rate, which drops as the signal weakens. Signal at 58% is mediocre, so expect slower speeds.
C:\>netsh wlan show networks mode=bssid Interface name : Wi-Fi There are 2 networks currently visible. SSID 1 : Home-WiFi Network type : Infrastructure Authentication : WPA2-Personal Encryption : CCMP BSSID 1 : 02:00:00:00:a0:01 Signal : 58% Radio type : 802.11ax Band : 5 GHz Channel : 36 BSSID 2 : 02:00:00:00:a0:02 Signal : 81% Radio type : 802.11ax Band : 2.4 GHz Channel : 6 SSID 2 : Flat4-Broadband Network type : Infrastructure Authentication : WPA2-Personal Encryption : CCMP BSSID 1 : 02:00:00:00:b0:11 Signal : 66% Radio type : 802.11n Band : 2.4 GHz Channel : 6
What to look for: every BSSID in range, with its signal, band and channel. Here, the home router's 2.4 GHz radio (BSSID 2, 81%) is stronger than its 5 GHz radio (BSSID 1, 58%) at this spot, because 2.4 GHz travels further. A neighbour's network, Flat4-Broadband, also uses channel 6.
Linux: the same checks
$ iw dev wlan0 link Connected to 02:00:00:00:a0:01 (on wlan0) SSID: Home-WiFi freq: 5180 RX: 48211904 bytes (41260 packets) TX: 3302116 bytes (12873 packets) signal: -71 dBm rx bitrate: 288.2 MBit/s 80MHz HE-MCS 3 HE-NSS 2 HE-GI 0 HE-DCM 0 tx bitrate: 216.2 MBit/s 80MHz HE-MCS 2 HE-NSS 2 HE-GI 0 HE-DCM 0
What to look for: signal gives the real signal in dBm; −71 dBm is in the fair zone. “HE” means High Efficiency, the technical name for Wi-Fi 6. The low MCS number (modulation and coding scheme) shows that the device has stepped down to a slower, more reliable rate because of the weak signal.
$ nmcli dev wifi list IN-USE BSSID SSID MODE CHAN RATE SIGNAL BARS SECURITY * 02:00:00:00:A0:01 Home-WiFi Infra 36 540 Mbit/s 52 ▂▄__ WPA2 02:00:00:00:A0:02 Home-WiFi Infra 6 195 Mbit/s 81 ▂▄▆█ WPA2 02:00:00:00:B0:11 Flat4-Broadband Infra 6 130 Mbit/s 66 ▂▄▆_ WPA2 02:00:00:00:C0:2F Cafe-Guest Infra 11 65 Mbit/s 24 ▂___ --
What to look for: the * under IN-USE marks the BSSID you are connected to. SIGNAL is a 0–100 quality score, and CHAN shows the channel. -- under SECURITY means an open network with no encryption.
If the radio side looks fine, continue with the normal IP checks: ipconfig or ip addr for the address, then ping the default gateway.
Learn more: Essential Windows Network CommandsEssential Linux Network Commands
Quick fixes that often work
- Weak signal: move the AP to a central, open, high spot; add a cabled AP or mesh unit for far rooms.
- Crowded channel: pick a less busy channel, or use 5 GHz instead of 2.4 GHz.
- One old device slowing everyone: move it closer, connect it by cable, or put it on the 2.4 GHz band only.
- Can't join at all: “forget” the network on the device and join again with the correct password.
Common mistakes
- Treating Wi-Fi as “the internet”. A Wi-Fi icon only proves that the radio link to the AP works.
- Reading dBm the wrong way round. −80 dBm is weaker than −60 dBm.
- Expecting the speed printed on the box. Wi-Fi is shared and half duplex, so real throughput is far below the theoretical maximum.
- Hiding the router. Cupboards, metal and floors often cost more signal than distance does.
- Turning AP power up to the maximum. More AP power doesn't help a weak phone reply, and it increases interference with neighbours.
- Confusing SSID and BSSID. Several APs can share a name; only the BSSID tells you which one you are on.
- Wi-Fi (IEEE 802.11) replaces the cable on the first hop only; IP, TCP and everything above are unchanged.
- The SSID is the network name; the BSSID is the MAC address of one AP radio.
- Joining: discover (beacon/probe), authenticate, associate, 4-way handshake, then DHCP.
- Wi-Fi is half duplex and shared: devices take turns using CSMA/CA, and unicast frames are acknowledged.
- Wi-Fi 4/5/6/6E/7 are 802.11n/ac/ax/ax/be; both ends must support a standard to use it.
- Signal is measured in dBm: closer to 0 is stronger; about −67 dBm or better is good for calls.
Knowledge check
Your laptop shows two Wi-Fi networks named “Office-Staff” in netsh output, with different BSSIDs. What does that mean?
Twelve laptops are joined to the same AP on the same channel. All twelve start a large download. What happens?
You check Wi-Fi signal strength in four rooms. Which reading shows the strongest signal?
A laptop joins Wi-Fi and shows full bars, but it has the address 169.254.12.7 and no internet. Which step failed?
A laptop advertises Wi-Fi 5 (802.11ac) and the AP is Wi-Fi 7 (802.11be). Which standard does their link use?
Where to go next
Continue with Wi-Fi frequency bands to see why 2.4, 5 and 6 GHz behave so differently, then Wireless security for passwords, WPA2 and WPA3. To revisit the hardware, go back to Wireless access points. Wi-Fi is one type of network among many; see Types of networks for how a WLAN compares with a LAN and a WAN.