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Wireless networking has more jargon per square metre than almost any other part of IT. This glossary defines the terms used across the wireless fundamentals posts on this site and in most vendor documentation, grouped by topic so that related ideas sit together. Each definition is short; where a topic is covered in depth elsewhere, the entry links to it. An A–Z acronym table at the end gives quick expansions.

Architecture and Topology

Access Point (AP)

A device with one or more 802.11 radios that lets wireless clients join a network and bridges their traffic to the wired network (the distribution system). Enterprise APs usually have two or three radios (2.4, 5 and 6 GHz) and are powered over Ethernet.

Wireless Controller (WLC)

A device or virtual appliance that centrally manages many APs: it pushes configuration, coordinates channel and power settings, handles client authentication and roaming, and in many designs terminates tunnels carrying user traffic from the APs. Some vendors call it a mobility controller or gateway. Cloud-managed and controllerless designs move these functions to the cloud or into the APs themselves.

Station (STA)

Any device with an 802.11 interface. Strictly, an AP is also a station; in everyday use “station” or “client” means the end-user device.

Basic Service Set (BSS)

One AP radio and the clients associated to it — the fundamental building block of a WLAN. An AP broadcasting three SSIDs on two radios forms six BSSs.

Basic Service Area (BSA)

The physical area in which clients can communicate with a BSS’s AP — its coverage cell. Its size and shape depend on transmit power, antennas, frequency, obstacles and the client’s own capabilities, and it changes as conditions change.

Service Set Identifier (SSID)

The human-readable network name, up to 32 bytes, advertised in beacons and probe responses. Several APs, and several BSSs, can share one SSID.

Basic Service Set Identifier (BSSID)

The 48-bit identifier of a single BSS, normally the MAC address of the AP radio (with a different derived MAC for each SSID on the radio). Clients use the BSSID to tell individual APs apart within an SSID.

Extended Service Set (ESS)

Two or more BSSs sharing the same SSID and security settings and connected by a distribution system, so that clients see a single network and can roam between APs. The ESSID is simply the SSID of an ESS.

Distribution System (DS)

The system that connects APs to one another and to the rest of the network — almost always switched Ethernet, sometimes a wireless mesh. Frames travelling “to DS” or “from DS” are crossing between the wireless and wired sides.

Independent BSS (IBSS) / ad hoc

A network of stations communicating directly without an AP. Rare today; replaced by Wi-Fi Direct for device-to-device use.

Mesh BSS / Mesh AP

APs that relay traffic for one another over the air (802.11s, or vendor mesh). A mesh portal or root AP has a wired uplink; mesh points reach it wirelessly.

Roaming

A client moving its association from one AP to another within the same ESS, typically because the signal from the current AP has weakened. The client — not the network — decides when to roam; networks can only assist (802.11k, 802.11v) and speed it up (802.11r, key caching). Seamless roaming keeps the client’s IP address and sessions.

Autonomous AP / Lightweight AP

An autonomous AP is configured and operates on its own. A lightweight (controller-based, or “thin”) AP depends on a controller for configuration and some functions. Cloud-managed APs take their configuration from a SaaS platform.

Forwarding mode (tunnel / bridge / split-tunnel)

In controller-based WLANs, whether user traffic is tunnelled from the AP to the controller (tunnel), bridged onto the AP’s local switchport (bridge, or “local switching”), or split between the two. The Aruba APs post compares them.

CAPWAP

Control And Provisioning of Wireless Access Points — the IETF protocol (RFC 5415) used by Cisco and others between lightweight APs and controllers, with a control channel (UDP 5246) and a data channel (UDP 5247). Aruba uses its own PAPI and GRE instead.

WLAN Channel Layout and Coverage

WLAN channel layout (channel plan)

The assignment of channels to APs so that neighbouring cells use different channels and cells on the same channel are as far apart as possible. In 2.4 GHz the classic plan reuses channels 1, 6 and 11 in a honeycomb pattern; 5 and 6 GHz offer many more channels and therefore more freedom. Most enterprise systems assign channels automatically (RRM). See Frequency Bands and Channels.

Cell overlap

The area where two neighbouring BSAs both provide usable signal. Enough overlap lets clients roam before the old signal drops away; too much wastes airtime and encourages sticky clients. Design guides often cite around 15–20% overlap at the target signal level.

Cell edge

The boundary at which a BSA no longer meets the design target (for example −67 dBm and 25 dB SNR for voice). Coverage designs are specified at the cell edge, not at the AP.

Channel reuse

Using the same channel again in cells far enough apart that they do not hear each other. Reuse is what lets a WLAN scale beyond a handful of channels.

Site survey

Measuring or modelling RF coverage to place APs: predictive surveys use building plans and software, pre-deployment (AP-on-a-stick) surveys measure a temporary AP, and validation surveys verify the finished network.

Coverage vs capacity design

A coverage design asks “can every location get a signal?”; a capacity design asks “can every location carry the expected number of clients and applications?” Modern WLANs are almost always capacity-limited, needing more APs at lower power than coverage alone would suggest.

Sticky client

A client that stays associated to a distant AP even though a much better one is available. Mitigated by good cell design, minimum basic rates and client steering.

RF and Physical Layer

Radio frequency (RF)

Electromagnetic waves used for wireless communication. Wi-Fi uses the 2.4, 5 and 6 GHz bands.

Frequency, wavelength, amplitude, phase

The four properties of a wave. Frequency (Hz) is cycles per second; wavelength is the distance of one cycle (about 12.5 cm at 2.4 GHz, 6 cm at 5 GHz); amplitude is signal strength; phase is the position within the cycle. Modulation changes amplitude and/or phase to carry data.

dB, dBm, dBi, dBd

Logarithmic units. dB is a ratio (+3 dB doubles power, +10 dB multiplies it by ten); dBm is absolute power relative to 1 mW (0 dBm = 1 mW, 20 dBm = 100 mW); dBi is antenna gain relative to an isotropic radiator; dBd is gain relative to a dipole (dBi = dBd + 2.15). See RF Power and OFDM.

Transmit power (Tx power)

The power the radio delivers to its antenna, usually in dBm.

EIRP

Equivalent Isotropically Radiated Power: transmit power minus cable losses plus antenna gain — the power an isotropic antenna would need to produce the same signal in the strongest direction. Regulators limit EIRP.

Antenna gain

How much an antenna concentrates energy in some directions compared with an isotropic radiator. Gain does not create energy; it redistributes it, making coverage stronger in one direction and weaker in others.

Omnidirectional / directional antenna

Omnidirectional antennas radiate roughly equally around the horizontal plane (most ceiling APs); directional antennas (patch, panel, sector, Yagi, dish) focus energy in a beam for long corridors, warehouses, stadiums and point-to-point links.

Beamwidth

The angle within which an antenna’s gain stays within 3 dB of its peak.

Polarization

The orientation of the electric field (vertical, horizontal, circular). Mismatched polarization between transmitter and receiver costs signal; indoors, reflections reduce the effect.

Isotropic radiator

A theoretical antenna that radiates equally in all directions — the 0 dBi reference.

Free space path loss (FSPL)

The weakening of a signal as it spreads out with distance, even with no obstacles. Doubling the distance adds about 6 dB of loss.

Attenuation / absorption

Loss of signal strength as RF passes through materials: drywall a few dB, brick and concrete much more, metal and elevator shafts nearly total. Higher frequencies are generally attenuated more.

Reflection, refraction, diffraction, scattering

Ways RF changes direction: bouncing off surfaces, bending as it passes between materials, bending around edges, and spreading off rough or small objects.

Multipath

A signal arriving at the receiver over several paths (direct and reflected) at slightly different times. It once caused errors; MIMO and OFDM turn it into an advantage.

Fresnel zone

The football-shaped region around the line of sight of a point-to-point link that should be kept clear (at least 60%) for full signal.

RSSI

Received Signal Strength Indicator. Strictly a vendor-specific relative index; in practice most tools display received signal strength directly in dBm (for example −62 dBm).

Noise floor

The background RF energy on a channel when nobody is transmitting, typically around −90 to −95 dBm in a quiet 20 MHz channel.

SNR

Signal-to-Noise Ratio: received signal minus noise floor, in dB. A −65 dBm signal over a −92 dBm noise floor gives 27 dB SNR. Higher SNR allows faster data rates.

SINR

Signal to Interference plus Noise Ratio — like SNR but also counting interference from other transmitters.

Receive sensitivity

The weakest signal a radio can decode at a given data rate. Faster rates need stronger signals.

Link budget

An accounting of every gain and loss between transmitter and receiver, used to predict whether a link will work.

Interference

Any unwanted RF energy that degrades reception. Co-channel interference (CCI), better called co-channel contention, comes from other Wi-Fi devices on the same channel, which share airtime. Adjacent-channel interference (ACI) comes from overlapping neighbouring channels and corrupts frames. Non-Wi-Fi interference comes from microwave ovens, Bluetooth, cordless phones, video senders, radar and jammers, and is found with spectrum analysis.

Modulation

Encoding data onto a carrier by varying amplitude, phase or frequency. Wi-Fi uses BPSK, QPSK and QAM (16 up to 4096 points) on OFDM subcarriers.

QAM

Quadrature Amplitude Modulation: varies both amplitude and phase. 256-QAM carries 8 bits per symbol, 1024-QAM 10, 4096-QAM 12.

OFDM / OFDMA

Orthogonal Frequency Division Multiplexing splits a channel into many narrow, overlapping-but-orthogonal subcarriers; OFDMA (Wi-Fi 6 onward) assigns groups of those subcarriers — resource units — to different clients in the same transmission.

Subcarrier / tone

One of the narrow carriers inside an OFDM channel: 312.5 kHz apart in Wi-Fi 4/5, 78.125 kHz in Wi-Fi 6 and 7.

Resource Unit (RU)

A group of OFDMA subcarriers allocated to one client; the smallest is 26 tones.

Guard interval (GI)

A gap (cyclic prefix) between OFDM symbols that absorbs multipath echoes: 0.4 or 0.8 µs in Wi-Fi 4/5; 0.8, 1.6 or 3.2 µs in Wi-Fi 6/7.

MCS

Modulation and Coding Scheme: an index combining modulation and coding rate. Together with channel width, spatial streams and guard interval it determines the data rate.

Coding rate

The fraction of transmitted bits that are user data rather than error correction (1/2, 2/3, 3/4, 5/6).

Data rate / PHY rate

The raw bit rate on the air for a given frame. Real throughput is much lower because of protocol overhead and shared airtime.

Throughput / goodput

Throughput is the actual data delivered per second; goodput is the application-useful part after retransmissions and headers.

Rate adaptation (rate shifting)

Changing the MCS frame by frame as signal quality changes.

MIMO / spatial stream

Multiple-Input Multiple-Output uses several antennas to send independent spatial streams at once. An “NxN:S” notation (for example 4×4:4) gives transmit chains, receive chains and spatial streams.

MU-MIMO

Multi-User MIMO: an AP sends (downlink, Wi-Fi 5 Wave 2) or receives (uplink, Wi-Fi 6) different spatial streams to or from several clients simultaneously.

Beamforming (TxBF)

Adjusting the phase of signals on multiple antennas so they combine constructively at a particular client, improving SNR. Requires channel sounding feedback from the client.

Spatial diversity / MRC

Using multiple receive antennas and combining their signals (Maximal Ratio Combining) to improve reception.

Spectrum analysis

Viewing raw RF energy across frequencies to find and classify interference that Wi-Fi radios cannot decode.

Channels and Spectrum

ISM band

Industrial, Scientific and Medical band — unlicensed spectrum shared with many other uses, including 2.4 GHz.

UNII bands

Unlicensed National Information Infrastructure bands (US/FCC terminology) — the sub-bands of 5 GHz (UNII-1 to UNII-4) and 6 GHz (UNII-5 to UNII-8).

Channel / centre frequency

A numbered slice of a band identified by its centre frequency. In 2.4 GHz, channel n is centred at 2407 + 5n MHz; in 5 GHz at 5000 + 5n MHz; in 6 GHz at 5950 + 5n MHz.

Non-overlapping channels

Channels far enough apart that their transmissions do not interfere. In 2.4 GHz only three exist in most regions (1, 6, 11).

Channel width

The bandwidth a transmission occupies: 20, 40, 80, 160 or 320 MHz. Wider channels are faster but leave fewer channels for reuse.

Channel bonding

Combining adjacent 20 MHz channels into a wider channel, with one primary 20 MHz channel and one or more secondary channels. See Channel Bonding and Frame Types.

Preamble puncturing

Transmitting on a wide channel while skipping a busy 20 MHz (or larger) slice inside it — optional in Wi-Fi 6, a key feature of Wi-Fi 7.

DFS

Dynamic Frequency Selection: on certain 5 GHz channels, APs must check for radar before transmitting and leave the channel quickly if radar appears. See Spectrum Management, QoS and Security.

CAC (DFS)

Channel Availability Check — the listening period (normally 60 seconds; longer for weather-radar channels in some regions) before using a DFS channel. Not to be confused with Call Admission Control.

TPC

Transmit Power Control: adjusting transmit power to meet regulatory limits and reduce interference (802.11h).

PSC

Preferred Scanning Channel: every fourth 20 MHz channel in 6 GHz (5, 21, 37 …), where clients are allowed to probe and APs are expected to place their primary channel.

LPI / SP / VLP / AFC

6 GHz power classes: Low Power Indoor, Standard Power (requires Automated Frequency Coordination — a database check to protect incumbent users) and Very Low Power for portable devices.

Regulatory domain / country code

The set of rules (channels, power, DFS) for a country or region, configured on every AP.

MAC Layer, Frames and Medium Access

MAC (Medium Access Control)

The 802.11 sublayer responsible for addressing, framing, medium access, acknowledgements, retransmission, power saving and encryption.

Frame

The 802.11 unit of transmission. There are three main types: management (beacons, probes, authentication, association, action frames), control (RTS, CTS, ACK, Block Ack, trigger frames) and data.

Beacon

A management frame each AP sends for each SSID roughly every 102.4 ms (100 TU), advertising the network’s name, capabilities and parameters.

Probe request / response

A client’s active query for networks, and an AP’s reply.

Authentication / association

The two 802.11 management exchanges by which a client joins a BSS. 802.11 “authentication” is usually just Open System (or SAE for WPA3-Personal); real authentication follows with 802.1X or a passphrase.

Reassociation

The association exchange a client uses when roaming to a new AP in the same ESS.

Deauthentication / disassociation

Management frames that end a client’s authentication or association. Unprotected deauthentication frames can be spoofed for denial-of-service attacks; PMF prevents this.

Action frame

A management frame carrying a specific function: channel switch announcements, Block Ack setup, neighbour reports (802.11k), BSS transition requests (802.11v), Fast BSS Transition (802.11r) and more.

CSMA/CA

Carrier Sense Multiple Access with Collision Avoidance — Wi-Fi’s listen-before-talk access method, using carrier sense, interframe spaces, random backoff and acknowledgements. See WLAN Fundamentals.

DCF / EDCA

Distributed Coordination Function is the basic CSMA/CA method; Enhanced Distributed Channel Access (802.11e/WMM) adds four access categories with different priorities.

CCA

Clear Channel Assessment — physical carrier sense: a radio checks for Wi-Fi preambles (signal detect) and raw energy (energy detect) before transmitting.

NAV

Network Allocation Vector — virtual carrier sense: a timer each station sets from the Duration field of frames it hears, deferring until it expires.

SIFS, DIFS, AIFS, slot time

Interframe spaces and the backoff time unit. SIFS (shortest) precedes ACKs and CTS; DIFS precedes normal data under DCF; AIFS varies by access category under EDCA.

Contention window (CW) / backoff

The range from which a station picks its random backoff count; it doubles after each failed transmission up to a maximum.

ACK / Block Ack

Acknowledgement of a single unicast frame, or of a whole batch of frames at once.

RTS/CTS, CTS-to-self

Request To Send / Clear To Send reserves the medium before a transmission (solving hidden nodes); CTS-to-self is a lighter version used for protection.

Hidden node

Two stations that can both hear the AP but not each other, and therefore collide at the AP.

Protection mode

Extra RTS/CTS or CTS-to-self exchanges, sent at legacy rates, that let newer stations coexist with older ones — at a cost in airtime.

Frame aggregation (A-MPDU, A-MSDU)

Packing multiple frames into one transmission to reduce per-frame overhead (Wi-Fi 4 onward).

Fragmentation

Splitting a frame into smaller pieces so each has a better chance of surviving a noisy channel. Rarely used today.

Basic rates / supported rates

Basic rates are the rates every client must support to join and that management and broadcast frames use; supported rates are additional optional rates. Raising the lowest basic rate shrinks cells and saves airtime.

Airtime

Time on the shared medium — the real currency of Wi-Fi capacity. A slow client uses more airtime to send the same data.

Duty cycle / channel utilization

The percentage of time a channel is busy.

Power save / DTIM / TIM

Clients can sleep while the AP buffers frames for them. The Traffic Indication Map in each beacon lists clients with buffered unicast data; every DTIM (Delivery TIM) beacon the AP releases buffered broadcast/multicast. U-APSD and Target Wake Time (TWT) are more efficient power-save methods.

BSS colouring

A Wi-Fi 6 feature that tags frames with a 6-bit BSS colour so a station can ignore weak frames from neighbouring BSSs on the same channel instead of deferring to them.

TWT

Target Wake Time: Wi-Fi 6 scheduling of when clients wake to exchange data, saving battery and reducing contention.

MLO

Multi-Link Operation: a Wi-Fi 7 feature letting a client use links in two or three bands at once, or switch between them without re-associating.

Security and Authentication

WEP / WPA / WPA2 / WPA3

Successive Wi-Fi security generations: WEP (1997, broken), WPA (2003, TKIP, deprecated), WPA2 (2004, AES-CCMP) and WPA3 (2018, SAE, mandatory PMF, 192-bit option). Each WPA generation has Personal (passphrase) and Enterprise (802.1X) modes.

RSN / RSNE

Robust Security Network — the 802.11i security framework; the RSN Information Element in beacons advertises supported ciphers and key management methods.

CCMP / GCMP / TKIP

Encryption protocols: CCMP (AES in counter mode with CBC-MAC) is WPA2’s standard; GCMP (AES-GCM) is used with WPA3-Enterprise 192-bit and the newest PHYs; TKIP is obsolete.

PSK

Pre-Shared Key — a passphrase shared by all users of a WLAN (WPA2/WPA3-Personal).

MPSK / iPSK / DPSK

Vendor names for multiple pre-shared keys on one SSID, each device or group having its own passphrase.

SAE

Simultaneous Authentication of Equals — WPA3-Personal’s password-based key exchange, resistant to offline dictionary attacks and providing forward secrecy.

OWE (Enhanced Open)

Opportunistic Wireless Encryption — encryption without a password for public and guest networks.

802.1X

Port-based network access control: the client (supplicant) authenticates through the AP or controller (authenticator) to an authentication server, normally RADIUS.

EAP

Extensible Authentication Protocol — the framework carried by 802.1X. Common methods: EAP-TLS (certificates on both sides), PEAP-MSCHAPv2 and EAP-TTLS (password inside a TLS tunnel), EAP-FAST, EAP-SIM/AKA (mobile operator credentials).

RADIUS

Remote Authentication Dial-In User Service — the AAA protocol between authenticator and authentication server (UDP 1812/1813), also used to return policy such as VLAN and role. RadSec carries RADIUS over TLS.

AAA

Authentication (who are you?), Authorization (what may you do?) and Accounting (what did you do?).

Supplicant / authenticator / authentication server

The three 802.1X roles: the client software, the network device enforcing access, and the server making the decision.

PMK, PTK, GTK

Key hierarchy: the Pairwise Master Key comes from 802.1X, the passphrase or SAE; the 4-way handshake derives the Pairwise Transient Key (unicast encryption) and delivers the Group Temporal Key (broadcast/multicast).

4-way handshake

The EAPOL-Key exchange that proves both sides hold the PMK and installs fresh encryption keys.

PMF (802.11w)

Protected Management Frames — integrity protection for deauthentication, disassociation and robust action frames, preventing spoofed disconnects. Mandatory with WPA3 and on 6 GHz.

Captive portal

A web page that intercepts a new client’s browser until it accepts terms, registers or logs in — common on guest networks.

MAC authentication / MAB

Authenticating a device by its MAC address against a list or RADIUS — a weak identifier, used for devices that cannot do 802.1X.

NAC

Network Access Control — policy servers (such as ClearPass or Cisco ISE) that combine authentication, device profiling and posture to decide each device’s access.

CoA

Change of Authorization (RFC 5176) — a RADIUS message letting the policy server change or end an active session.

Rogue AP

An unauthorized AP connected to the corporate network — a backdoor. Distinct from a neighbour or interfering AP, which is simply someone else’s network.

Evil twin

An attacker’s AP impersonating a legitimate SSID to lure clients.

WIDS / WIPS

Wireless Intrusion Detection / Prevention Systems that monitor the air for rogues, attacks and policy violations, and can contain threats.

QoS, Roaming and Client Steering

WMM

Wi-Fi Multimedia — the Wi-Fi Alliance certification of 802.11e QoS with four access categories: Voice, Video, Best Effort and Background.

Access category (AC) / user priority (UP)

WMM queues (AC_VO, AC_VI, AC_BE, AC_BK) and the 802.1D priority values 0–7 that map to them.

DSCP

Differentiated Services Code Point — the IP-header QoS marking that is mapped to Wi-Fi user priorities and back (for example EF/46 for voice).

TSPEC / admission control

A client’s request for guaranteed airtime for a traffic stream, accepted or refused by the AP (Call Admission Control).

Airtime fairness

A vendor feature that shares airtime, rather than frame opportunities, fairly among clients so slow clients cannot monopolize the channel.

802.11k

Radio Resource Measurement — neighbour reports and measurements that help clients find roaming candidates quickly.

802.11v

Wireless Network Management — including BSS Transition Management, which lets the network suggest a better AP to a client.

802.11r (FT)

Fast BSS Transition — folds key exchange into authentication/reassociation so roams take tens of milliseconds.

OKC / PMK caching

Opportunistic Key Caching and PMK caching reuse an earlier 802.1X result to skip full re-authentication when roaming.

Band steering / client steering / load balancing

Network techniques for encouraging clients onto a better band, AP or less loaded radio.

RRM

Radio Resource Management — automatic channel and power assignment (Aruba ARM/AirMatch, Cisco RRM, and others).

Standards, Organizations and Generations

IEEE 802.11

The IEEE standard defining Wi-Fi’s PHY and MAC layers, extended by lettered amendments (802.11a, b, g, n, ac, ax, be …) and periodically consolidated (802.11-2020).

Wi-Fi Alliance (WFA)

The industry body that certifies interoperability, owns the Wi-Fi trademark, and defines programs such as WPA3, WMM, Wi-Fi 6 and Wi-Fi 7 certification.

Wi-Fi 4 / 5 / 6 / 6E / 7

Generation names for 802.11n, 802.11ac, 802.11ax, 802.11ax in 6 GHz, and 802.11be. See WLAN Fundamentals.

HT / VHT / HE / EHT

The 802.11 names for the Wi-Fi 4, 5, 6 and 7 PHYs: High Throughput, Very High Throughput, High Efficiency, Extremely High Throughput. Often seen in packet captures and AP settings.

FCC, ETSI, ISED, Ofcom, MIC

Regulators and standards bodies setting radio rules in the US, Europe, Canada, the UK and Japan.

IETF

The Internet Engineering Task Force, author of RADIUS, EAP methods, CAPWAP and other protocols used around Wi-Fi.

Passpoint (Hotspot 2.0)

A Wi-Fi Alliance program for automatic, secure roaming onto public and partner networks using credentials, as with mobile networks. Based on 802.11u.

Acronyms A–Z