Wired Ethernet (IEEE 802.3) provides reliable local area networking, but cables limit device placement and mobility. IEEE 802.11 (Wi-Fi) provides wireless Ethernet networking, enabling untethered devices within buildings, campuses, and hotspots while maintaining compatibility with Ethernet network protocols.
IEEE 802.11 is the wireless LAN (WLAN) standard that provides Ethernet-like connectivity over radio waves. It uses CSMA/CA (Collision Avoidance) with ACK and RTS/CTS mechanisms, operates in the 2.4 GHz and 5 GHz bands, and defines the MAC and physical layer for wireless local networking.
The MAC Protocol (CSMA/CA):
- Before transmitting, a station senses the channel
- If busy, it waits; if idle, it waits for a random backoff period (collision avoidance)
- The station transmits, receives an ACK from the destination (if not received, collision assumed and transmission retries)
- For larger frames, RTS/CTS exchange (per MACA) avoids hidden terminal collisions
Physical Layer Variants:
- 802.11b (1999): DSSS; 11 Mbps; 2.4 GHz band; longest range
- 802.11a (1999): OFDM; 54 Mbps; 5 GHz band; shorter range due to frequency
- 802.11g (2003): OFDM backward-compatible with 802.11b; 54 Mbps; 2.4 GHz band
- 802.11n (2009): MIMO + OFDM; up to 600 Mbps; dual-band (2.4/5 GHz)
- 802.11ac (2013): MU-MIMO; up to 3.46 Gbps; 5 GHz only
- 802.11ax (2021): OFDMA; up to 9.6 Gbps; Wi-Fi 6 (6E extends to 6 GHz)
- MAC: CSMA/CA with ACK (not CSMA/CD like Ethernet)
- CSMA/CA: random backoff before transmission to avoid collisions
- RTS/CTS for hidden terminal avoidance in large frames
- Infrastructure mode: communication through AP; Ad Hoc mode: direct device-to-device
- Security: WEP → WPA → WPA2 → WPA3 (evolving encryption)
- OFDM (from 802.11a): uses multiple orthogonal subcarriers for efficiency
- Built from: Hidden Terminal Problem — 802.11 uses RTS/CTS to handle this
- Built from: Spread Spectrum — DSSS (802.11b) and FHSS (Bluetooth) are the two spread spectrum techniques
- Built from: MACA — 802.11’s CSMA/CA is based on MACA’s RTS/CTS mechanism
- Related: IEEE 802.15 — the PAN standard (Bluetooth) sibling to 802.11
- Related: Bluetooth — coexists with 802.11 in 2.4 GHz but uses FHSS, not DSSS
- 2.4 GHz is crowded with microwaves, Bluetooth, and other devices; interference is common
- 5 GHz band (802.11a/n/ac/ax) is cleaner but has shorter range (more wall absorption)
- Wi-Fi operates in unlicensed spectrum — no exclusivity; interference from neighbors is a constant issue
- Security: WEP was cracked; WPA is mandatory in modern devices