CWSS flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Wavelength formula

Wavelength in meters equals 300 divided by frequency in MHz. At 2.4 GHz the wavelength is about 12.5 cm; at 5 GHz it is about 6 cm.

Free-space path loss

FSPL in dB equals 32.44 plus 20 log of frequency in MHz plus 20 log of distance in km. Loss increases 6 dB per doubling of distance or frequency.

dBm to milliwatts

Convert with mW = 10^(dBm/10). So 0 dBm is 1 mW, 10 dBm is 10 mW, 20 dBm is 100 mW, and 30 dBm is 1 watt.

Three dB rule

A 3 dB change doubles or halves power. A 6 dB gain quadruples power, and a 10 dB change multiplies or divides power by ten.

EIRP calculation

Effective isotropic radiated power equals radio transmit power in dBm plus antenna gain in dBi minus cable and connector loss in dB. Regulators limit EIRP.

First Fresnel zone

The ellipsoid around the line of sight where signal energy concentrates. Keep at least 60 percent of its radius clear to avoid diffraction loss on outdoor links.

Multipath fading

Signals arrive by several paths with different delays and phases, causing fading, nulls, and intersymbol interference. Diversity, MIMO, and OFDM guard intervals reduce the impact.

Frequency versus penetration

At equal power, higher frequencies suffer more path loss and penetrate walls and foliage less, while allowing smaller antennas and more available spectrum.

Link budget

Sum transmit power and antenna gains, subtract cable losses and path loss, to predict received power in dBm at the far end of a link.

Management frames

802.11 frames that build and tear down relationships: beacon, probe request and response, authentication, association, reassociation, disassociation, and deauthentication.

CSMA/CA operation

A station senses the medium, waits a DIFS interval, and backs off a random number of slots before transmitting. A positive acknowledgment confirms delivery.

RTS/CTS purpose

A control-frame exchange that reserves the channel and reduces collisions from hidden nodes. It adds overhead, so it is usually enabled only for large frames.

Client roaming

Roaming is decided by the client station, which scans for a better access point and re-associates. 802.11k neighbor reports and 802.11r speed the process.

WPA2 four-way handshake

After open authentication and association, the four-way handshake derives fresh pairwise keys from the pre-shared key or 802.1X credentials and installs them for CCMP encryption.

WPA3 improvements

WPA3 replaces the PSK handshake with SAE to resist offline dictionary attacks, adds forward secrecy, and requires protected management frames under 802.11w.

OFDMA in 802.11ax

Orthogonal frequency-division multiple access splits a channel into resource units so several clients transmit in the same time slot, improving efficiency in dense deployments.

Channel width tradeoff

Wider channels raise peak throughput but consume spectrum and raise the noise floor. Narrow 20 MHz channels give more non-overlapping channels and better range.

Non-overlapping channels

In 2.4 GHz only channels 1, 6, and 11 avoid overlap in North America. The 5 GHz and 6 GHz bands provide many more clean 20 MHz channels.

SSID versus BSSID

An SSID is the network name clients select. A BSSID is the MAC address of one access point radio serving that SSID.

BSS coloring

An 802.11ax feature that tags frames with a color so stations can ignore overlapping basic service set traffic and transmit sooner, raising spatial reuse.

Access point modes

Common modes include local (tunneled to controller), FlexConnect (local switching), monitor, sniffer, and mesh. Each changes how traffic and scanning are handled.

Antenna selection rule

Use omnidirectional antennas for broad 360-degree coverage and directional antennas such as Yagi, panel, or dish for point-to-point links and long-range coverage.

Antenna gain is reciprocal

Gain shapes the radiation pattern rather than adding power. It improves both transmit and receive performance and narrows coverage as gain increases.

PoE power standards

802.3af supplies about 15.4 W per port and 802.3at about 30 W. Total device draw must stay within the switch power budget.

Controller-based versus autonomous

A wireless LAN controller centralizes configuration, roaming, and RF management across access points. Autonomous access points are configured and managed individually.

CAPWAP function

A protocol that lets access points discover a wireless LAN controller and exchange configuration, firmware images, and optionally tunneled client traffic.

Site survey types

Passive surveys measure existing RF conditions, active surveys test association and throughput, and predictive surveys model coverage from floor plans before installation.

Spectrum analyzer use

A tool that displays RF energy across frequencies, revealing interference sources, channel utilization, and non-Wi-Fi devices that protocol analyzers cannot decode.

Design signal targets

Common planning thresholds are about -67 dBm RSSI for voice, -70 dBm for data, and 25 dB SNR or better for high-density and real-time applications.

Capacity planning

Estimate usable throughput per access point, divide by expected per-client demand, and add access points at lower power when density exceeds that client count.

Guest network isolation

A separate guest SSID mapped to its own VLAN, with a captive portal and firewall rules blocking access to internal subnets while allowing internet traffic.

Wireless change management

Stage firmware and configuration changes, test in a pilot area, keep a documented rollback plan, and schedule work in maintenance windows to protect availability.