HCIP-WLAN key terms

The three frame classes defined by the 802.11 MAC: management frames (beacons, probes, authentication, association), control frames (RTS, CTS, ACK, Block ACK), and data frames that carry user payload. Each type has its own subtype field and header layout.

The fixed period, commonly 100 TU (about 102.4 ms), at which an AP broadcasts a beacon frame announcing its SSID, supported rates, security settings, and capability information. Clients use beacons for discovery and to keep timing synchronized with the BSS.

A client discovery method in which the station listens on each channel for beacon frames instead of transmitting probes. It avoids airtime overhead but takes longer to find an AP, so it is often used on channels where active probing is restricted.

A discovery method where the client transmits probe request frames on each channel and waits for probe responses from nearby APs. It finds networks faster than passive scanning but consumes more airtime and battery power.

Received Signal Strength Indicator, a relative measure of the power at which a station hears a signal, usually reported in dBm after calibration. It drives roaming decisions, rate adaptation, and band steering thresholds, but is not an absolute link-quality metric.

Signal-to-Noise Ratio, the difference in dB between the received signal level and the noise floor. Higher SNR supports denser modulation and higher MCS rates; a low SNR forces fallback to lower rates and increases retransmissions.

A number in the 802.11n/ac/ax rate tables that jointly specifies modulation order, coding rate, and number of spatial streams. The applicable MCS depends on channel width, guard interval, and measured SNR, and maps directly to a PHY data rate.

Combining adjacent 20 MHz channels into 40, 80, or 160 MHz channels to raise peak throughput. Wider channels reduce the number of non-overlapping channels available and raise noise and interference exposure, so they suit low-density areas rather than crowded deployments.

Interference caused when multiple APs or clients transmit on the same channel within range, forcing stations to contend for the medium and defer transmissions. It is managed through channel planning, power reduction, and denser cell design rather than by changing modulation.

Clear Channel Assessment, the mechanism by which an 802.11 station senses the medium before transmitting. Physical CCA detects energy or valid preambles; virtual CCA uses the NAV timer set by duration fields in overheard frames. Both must indicate idle before sending.

Carrier Sense Multiple Access with Collision Avoidance, the distributed access method of 802.11. Stations sense the medium, wait a random backoff, and use positive acknowledgements, because a wireless station cannot reliably detect collisions while transmitting.

An optional handshake in which a sender transmits a Request to Send and waits for Clear to Send before sending data. It reduces collisions from hidden nodes at the cost of extra overhead, so it is usually enabled only above a configurable frame-size threshold.

A condition where two stations associated with the same AP cannot hear each other, so both may transmit simultaneously and collide at the AP. Symptoms include high retry counts with strong client RSSI; mitigations include RTS/CTS and better AP placement.

An 802.11e aggregation feature that lets a receiver acknowledge a whole burst of QoS data frames with one Block ACK frame instead of per-frame ACKs. It greatly improves efficiency at high data rates by cutting acknowledgement overhead.

Control and Provisioning of Wireless Access Points, the IETF protocol used between an AP and an AC. It runs control traffic over UDP 5246 and data traffic over UDP 5247, carrying management messages, configuration, and optionally tunneled user frames.

The process by which an AP locates candidate ACs, using static configuration, DHCP options, DNS resolution, or broadcast and multicast discovery. The AP then selects an AC and proceeds to establish a CAPWAP session.

An architecture that divides 802.11 functions between AP and AC: real-time operations such as beacons, ACKs, and encryption stay on the AP, while association control, roaming decisions, and policy are handled by the AC.

A CAPWAP data mode in which user traffic is bridged from the AP directly onto the local wired network, while control traffic still goes to the AC. It avoids backhauling all user data through the AC and reduces latency at branch sites.

A CAPWAP data mode in which user frames are encapsulated and sent to the AC, which then forwards them into the wired network. It centralizes security policy and roaming anchoring but concentrates traffic and adds latency at the AC.

Datagram Transport Layer Security, used to protect CAPWAP control and optionally data traffic between AP and AC. It provides encryption and integrity for the UDP-based tunnel, and certificate-based DTLS is part of how APs authenticate the AC.

The end-to-end sequence that brings a new AP into service: power-up and image load, IP address acquisition, AC discovery and DTLS setup, CAPWAP join, configuration delivery, and radio bring-up. Failures at any stage leave the AP unable to serve clients.

Fast BSS Transition, which lets a client re-establish security keys before roaming by pre-authenticating with a target AP, either over the distribution system or by exchanging a mobility domain element. It removes the full 802.1X exchange from the roam, cutting handover time.

An amendment that lets an AP provide a client with a list of neighboring APs, their channels, and BSSIDs, so the client scans only relevant channels. It shortens scan time before roaming and improves the quality of the roam target choice.

An amendment providing BSS Transition Management frames, with which an AP can suggest or steer a client toward a better AP, including load-balancing hints. Clients are not obliged to comply, so effectiveness depends on client support.

A technique that encourages dual-band clients to associate on 5 GHz or 6 GHz instead of 2.4 GHz, typically by suppressing probe responses on 2.4 GHz or delaying association there. It relieves congestion on the narrow, interference-prone 2.4 GHz band.

The signal level at which a client decides to look for another AP, often configured as a minimum RSSI on the infrastructure side. Setting it too high causes sticky clients; too low causes late roams and dropped voice quality.

A key-caching method in which the pairwise master key derived during 802.1X authentication is stored on the AC and reused when the client roams to another AP. It skips a full RADIUS exchange, shortening reconnection time.

The WPA3 personal mode, which replaces the WPA2 pre-shared key handshake with Simultaneous Authentication of Equals, a password-authenticated key exchange. It resists offline dictionary attacks on captured handshakes and provides forward secrecy.

Wi-Fi security using a pre-shared key with CCMP/AES encryption under 802.11i. The four-way handshake derives per-session keys, but an eavesdropper who captures the handshake can attempt offline guessing of a weak passphrase.

The 802.11i exchange that confirms both parties hold the pairwise master key and derives fresh pairwise transient keys and the group key. It also installs keys and protects against replay, and it runs after 802.1X or PSK authentication.

Port-based network access control in which a supplicant authenticates through an authenticator to an authentication server before being granted network access. In WLAN it is the enterprise authentication framework used with EAP methods and RADIUS.

Extensible Authentication Protocol, a framework carried over 802.1X or RADIUS that supports methods such as EAP-TLS, PEAP, and EAP-TTLS. The chosen method determines whether certificates, passwords, or both are used and how the client verifies the server.

Remote Authentication Dial-In User Service, the AAA protocol an AC or controller uses to relay 802.1X and MAC authentication requests to a central server. It carries attributes such as VLAN and authorization profile in Access-Accept messages.

Access control in which the client's MAC address is checked against a local list or a RADIUS server before the client is permitted. It requires no client software but is weak because MAC addresses can be spoofed, so it is often combined with portal or 802.1X.

A web-based access method where a client associates and obtains an address, then is redirected to a login page before being granted internet access. It suits guest networks and is often paired with a pre-authentication or MAC-triggered flow.

Public Key Infrastructure, the system of certificate authorities, certificates, and revocation that binds public keys to identities. In WLAN it supports EAP-TLS client and server authentication, CAPWAP DTLS, and secure management access.

Wi-Fi Multimedia, the Wi-Fi Alliance certification of 802.11e QoS. It defines four access categories (voice, video, best effort, background) with different contention parameters, giving latency-sensitive traffic priority on the air interface.

A scheduling policy that gives each client a share of transmission time rather than equal frame counts, preventing slow low-rate clients from consuming disproportionate airtime. It improves aggregate throughput and perceived performance in mixed-rate cells.

An AC high-availability mode in which two ACs form a master and backup pair sharing a virtual address, so APs and clients keep service if the master fails. State synchronization lets the backup take over established AP sessions.

An AC redundancy scheme in which APs maintain CAPWAP sessions to a primary and a secondary AC over separate links. If the primary path fails, the AP switches to the backup AC, reducing outage time compared with re-discovery.

Combining multiple physical ACs into one logical AC so that APs and configurations are managed as a single entity. It simplifies configuration consistency and roaming across a campus while allowing capacity to be added by joining more members.

The process of loading a new AP image, usually staged by the AC, which compares the AP's running version with the target and pushes the file. Upgrades can be automatic on onboarding or scheduled, and failed upgrades often leave APs in a fallback state.

A planning tool that uses floor plans and RF propagation models to predict AP placement, coverage, and channel assignment before deployment. It helps size AP counts and avoid coverage holes, and its output can seed the live configuration.

Assigning channels and widths to APs so that neighboring cells use non-overlapping channels where possible, minimizing co-channel and adjacent-channel interference. It is done statically at design time and dynamically by radio resource management.

A cloud-managed campus network architecture in which APs and switches are onboarded to a cloud controller for configuration, monitoring, and policy. It reduces on-site AC dependency and centralizes management across many sites.

WLAN-based positioning that estimates a client's position from RSSI fingerprints or ranging measurements reported by multiple APs, often via a dedicated server. Accuracy ranges from a few meters indoors to room-level, depending on AP density.