A wireless access point (AP) is a device that creates a Wi-Fi network and connects it to a wired network. Phones, laptops and tablets talk to the AP by radio. The AP is plugged into a switch with an Ethernet cable, so the wireless devices can reach everything on the wired network, and the internet beyond it.
💡 In simple terms: an AP is a bridge over a river. On one bank are the wireless devices, on the other is the wired network. The AP carries traffic across, in both directions, without changing where it is going.
Why access points exist
Cables are fast and reliable, but people want to move around with laptops and phones, and many devices don't even have an Ethernet port. An AP solves this by giving those devices a way into the wired network:
- Mobility: people can work anywhere within range, and move between rooms.
- Fewer cables: one cable to the AP serves dozens of devices.
- Coverage: several APs together cover a whole building, and devices move between them as people walk around.
Where an AP sits
In an office
Office APs are usually mounted on ceilings, spread out so their coverage areas overlap a little. Each one is cabled back to an access switch, which often powers it using Power over Ethernet (PoE).
- 1. The laptop reaches a wired PC. Radio to AP 1, then Ethernet through the switch. Same subnet, so no router is involved.
- 2. The phone goes online. AP 1 bridges its traffic onto the wired LAN; the switch delivers it to the router, the default gateway.
- 3. The switch powers the APs. One cable carries both electricity (PoE) and data, so no power socket is needed on the ceiling.
At home
At home the AP is usually hidden inside the wireless router (or the ISP's all-in-one box). That one box is a router, a small switch and an access point together. Its built-in AP behaves exactly like a separate one: it bridges Wi-Fi devices onto the same LAN as the devices plugged into its Ethernet ports.
- 1. Phone to desktop. The built-in AP bridges the phone's Wi-Fi frames to the built-in switch, which delivers them to the desktop's cable.
- 2. Laptop to the internet. The AP part receives it, then the router part routes it out to the internet.
Important terms and parts
Radios
Most APs have two or three radios, for the 2.4 GHz, 5 GHz and sometimes 6 GHz bands, each with its own antennas.
Ethernet uplink
The cable to the switch. Often PoE-powered. This is the AP's link to everything else.
SSID
The network name you see in the Wi-Fi list, such as “Office-Staff”. One AP can broadcast several SSIDs, e.g. staff and guest.
BSSID
The MAC address of one AP radio for one SSID. Several APs can share an SSID; each has its own BSSID, which is how your device tells them apart.
Channel
The slice of radio frequency the AP uses. Neighbouring APs use different channels so they don't interfere.
Security settings
WPA2 or WPA3, with a shared password (Personal) or individual logins (Enterprise).
Bands and channels are covered in Wi-Fi frequency bands, and WPA2/WPA3 in Wireless security.
How a device joins an AP, step by step
- 1. Discover. The AP sends beacons several times a second announcing its SSID. The phone can also ask “who's there?” with a probe request.
- 2. Authenticate and associate. The phone asks to join. The AP accepts and adds it to its list of associated clients.
- 3. Prove the password and agree keys. A four-message key exchange proves both know the password and creates the encryption keys for this phone.
- 4. Get an IP address. Now the phone is on the LAN. Its DHCP request crosses the AP like any other traffic and reaches the router.
- 5. Online. The router's DHCP reply comes back through the AP. The phone has an address, gateway and DNS server.
The address step is ordinary DHCP. The AP doesn't usually hand out addresses itself: it simply passes the DHCP messages along.
What the AP does to frames
Wi-Fi uses its own frame format (802.11), different from Ethernet (802.3). The AP converts between the two. Wi-Fi frames carry up to four MAC addresses; for normal traffic three are used, because the frame must name the AP it is passing through as well as the real source and destination.
| Leg | Frame type | Addresses in the frame |
|---|---|---|
| Phone → AP (radio) | 802.11 Wi-Fi | Receiver: AP's BSSID 02:00:00:00:a0:01 · Source: phone 02:00:00:00:00:51 · Destination: router 02:00:00:00:00:01 |
| AP → switch (cable) | 802.3 Ethernet | Destination: router 02:00:00:00:00:01 · Source: phone 02:00:00:00:00:51 |
Notice that the source MAC stays the phone's and the IP addresses inside are not touched. To the switch and the router, the phone looks like any device plugged into the AP's switch port. That is what a bridge does, and why an AP is a Layer 2 device. The AP also encrypts and decrypts the radio side, so traffic is protected in the air.
| OSI layer | Access pointradio + Wi-Fi/Ethernet frames | SwitchEthernet frames | Wireless routerAP + switch + router |
|---|---|---|---|
| L7 ApplicationHTTP, DNS | – | – | – |
| L6 PresentationEncoding, encryption | – | – | – |
| L5 SessionSessions | – | – | – |
| L4 TransportTCP/UDP ports | – | – | some |
| L3 NetworkIP addresses | – | – | ✓ |
| L2 Data LinkFrames, MAC addresses | ✓ | ✓ | ✓ |
| L1 PhysicalBits on cable or radio | ✓ | ✓ | ✓ |
Ways to deploy access points
Standalone (autonomous) APs
Each AP is configured on its own, through its web page. Fine for one or two APs, but painful for twenty: every SSID or password change must be made twenty times, and the APs don't coordinate channels or power.
Controller-managed APs
A wireless LAN controller (WLC) manages many “lightweight” APs from one place. You set the SSIDs, security and rules once on the controller and it pushes them to every AP. It also picks channels and power levels for each AP, and helps devices roam smoothly from AP to AP. The controller can be a box in the server room, software, or a cloud service (cloud-managed APs).
Mesh
In a mesh system, only one unit needs a cable to the router. The others connect to each other by radio and pass traffic along. That makes it easy to cover a large house or a hall where cables are hard to run. The cost: each radio hop uses airtime, so units far from the wired one are slower. Units connected by cable (“wired backhaul”) avoid this.
- 1. Traffic hops between units. The laptop joins the nearest unit, which relays the traffic by radio to the main unit. One SSID throughout the house.
Comparing the options
| Standalone APs | Controller / cloud-managed | Mesh | |
|---|---|---|---|
| Configured | One by one | Centrally | Through an app, centrally |
| Link to network | Cable | Cable | One by cable, others by radio (or cable) |
| Roaming between APs | Basic | Smooth, coordinated | Coordinated |
| Typical use | Small office, one extra AP at home | Offices, campuses, hotels | Homes, small offices without cabling |
A real-world example: a busy meeting room
An office has one AP in the corridor. Everyone complains Wi-Fi is slow in the big meeting room. The signal bars are full, so the AP is within range. The real problem is capacity: thirty laptops share one radio channel, and Wi-Fi devices must take turns to talk. The fix is not a “stronger” AP, but a second AP inside the meeting room on a different channel, so the devices are split between two channels.
When an AP fails
| Symptom | Likely cause | What to check |
|---|---|---|
| SSID not visible at all | AP off or its radio disabled; PoE power missing | AP lights; switch port PoE status; is the SSID hidden? |
Connects, but “No internet” with a 169.254.x.x address | The AP's uplink, VLAN or DHCP is broken | Uplink cable; DHCP server; wired devices on the same network |
| Wrong password errors | Password typo or security mismatch (e.g. an old device that can't do WPA3) | Re-enter the password; try WPA2/WPA3 mixed mode |
| Slow or drops in some rooms | Weak signal, interference, or too many devices on one channel | Signal strength; channel overlap with neighbours |
| Calls drop when walking between rooms | Poor roaming between standalone APs | Overlap between APs; controller-managed roaming |
Useful commands
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 : Office-Staff BSSID : 02:00:00:00:a0:01 Network type : Infrastructure Radio type : 802.11ax Authentication : WPA3-Personal Cipher : CCMP Band : 5 GHz Channel : 36 Receive rate (Mbps) : 864.6 Transmit rate (Mbps) : 720.6 Signal : 88%
BSSID tells you exactly which AP radio you are joined to. Signal, Band and Channel explain most speed problems.
$ iw dev wlan0 link Connected to 02:00:00:00:a0:01 (on wlan0) SSID: Office-Staff freq: 5180 signal: -52 dBm rx bitrate: 864.8 MBit/s tx bitrate: 720.6 MBit/s
The AP's BSSID, the frequency (5180 MHz is channel 36) and the signal strength in dBm. Closer to 0 is stronger: −50 dBm is excellent, −80 dBm is poor.
Common mistakes
- Thinking an AP is a router. A plain AP doesn't route or hand out addresses; the router does.
- Adding a second wireless router as an “AP” without changing its mode. It runs its own DHCP and NAT, creating a separate network. Use its AP mode, or turn off DHCP and connect it by a LAN port.
- Putting all APs on the same channel. They interfere with each other.
- Turning the AP power up to the maximum. Phones still can't shout back that far, and neighbouring APs interfere more.
- Hiding the SSID for security. It is still visible to anyone with simple tools; strong WPA2/WPA3 security is what protects you.
- An AP bridges Wi-Fi devices onto a wired Ethernet network; it works at Layers 1 and 2.
- The SSID is the network name; the BSSID is the MAC address of one AP radio.
- Joining means: discover, authenticate and associate, agree encryption keys, then get an IP address by DHCP.
- Offices use many APs, usually PoE-powered and centrally managed by a controller or cloud service.
- Mesh systems link APs by radio; a home wireless router is a router, switch and AP in one box.
Knowledge check
A laptop on the office Wi-Fi and a wired PC are both connected through the same AP and switch. Which device gave the laptop its IP address?
Three APs all broadcast the SSID “Office-Staff”. How does a laptop know which one it is connected to?
A phone sends a frame through an AP to the router. On the Ethernet cable after the AP, what is the frame's source MAC?
Wi-Fi is slow in a meeting room full of people, although every laptop shows full signal bars.
Where to go next
Wi-Fi itself, its bands and its security are covered in the Wireless Fundamentals unit, starting with Wi-Fi basics. To see every device in this unit side by side, continue to Comparing network devices.