1.7 Wireless Principles

RF bands and tradeoffs

Wi-Fi is half-duplex shared radio: only one device transmits at a time per channel, and stations use CSMA/CA (carrier sense multiple access with collision avoidance) to take turns. Two main bands, plus a newer one:

• 2.4 GHz: longer range, better wall penetration, but crowded (microwaves, Bluetooth, cordless phones) and only three non-overlapping channels (1, 6, 11) in the US.
• 5 GHz: shorter range, less penetration, but many (24+) non-overlapping channels, so far less co-channel interference and higher throughput.
• 6 GHz (Wi-Fi 6E/Wi-Fi 7): even more spectrum and clean channels, newest.

802.11 standards

Key facts: 802.11n introduced MIMO (multiple antennas) and dual-band; 802.11ac is 5 GHz only; 802.11ax (Wi-Fi 6) adds OFDMA, MU-MIMO in both directions, and BSS coloring to thrive in dense, high-client environments.

Channel planning

Because each 2.4 GHz channel is 20 MHz wide and the band is narrow, only 1, 6, and 11 avoid overlap. Adjacent APs must use different non-overlapping channels to prevent co-channel and adjacent-channel interference. In 5 GHz the abundance of channels makes planning far easier and supports channel bonding (40/80/160 MHz) for speed.

Service sets and SSIDs

• SSID (Service Set Identifier): the human-readable network name, up to 32 characters.
• BSS (Basic Service Set): a single AP and its clients; the AP's MAC is the BSSID.
• ESS (Extended Service Set): two or more APs sharing the same SSID, letting clients roam seamlessly across a building.
• IBSS (Independent BSS): ad hoc, peer-to-peer with no AP.

AP architecture

Autonomous APs carry their own config. Lightweight APs join a wireless LAN controller (WLC) over a CAPWAP tunnel; the controller centralizes channel selection, transmit power, RF optimization, and security policy. FlexConnect lets a lightweight AP keep switching traffic locally if the controller is unreachable.

Worked example

Three APs cover one open office. To avoid interference at 2.4 GHz, assign them channels 1, 6, and 11. If a fourth AP is added, reuse channel 1 in the corner farthest from the existing channel-1 AP so the two cells do not overlap.

RF behavior and interference

Radio signals weaken with distance and obstacles, an effect called attenuation (free-space path loss). Walls, metal, and water absorb RF, which is why 2.4 GHz penetrates better (longer wavelength) while 5 GHz is faster but shorter-range. Two interference types matter on the exam: co-channel interference, where APs on the same channel must take turns and slow each other, and adjacent-channel interference, where APs on overlapping channels (say 1 and 3 at 2.4 GHz) corrupt each other's signals. The fix for both is disciplined channel planning, hence the 1/6/11 rule at 2.4 GHz.

Wi-Fi 6 (802.11ax) features

The v1.1 blueprint expects familiarity with the newest features:

• OFDMA (Orthogonal Frequency-Division Multiple Access): subdivides a channel into resource units so the AP serves multiple clients in one transmission, ideal for many small frames.
• MU-MIMO: multiple simultaneous spatial streams to different clients, now in both downlink and uplink.
• BSS coloring: tags frames with a color so an AP can ignore overlapping transmissions from a different BSS and reuse the channel, boosting density.
• Target Wake Time (TWT): schedules client wake-ups to save battery on IoT devices.

The roaming and association process

A client joining a wireless network performs three steps: probe (discover SSIDs), authenticate, then associate with one AP. In an ESS, as the client moves it roams, re-associating to a stronger AP that shares the same SSID, ideally transparently to the application. A wireless LAN controller coordinates this so the handoff is fast and the client keeps its IP.

Security note

WPA2 (AES-CCMP) and the newer WPA3 secure modern Wi-Fi; the obsolete WEP and WPA (TKIP) are deprecated. The exam pairs WPA3-Personal (SAE) with home use and WPA3-Enterprise (802.1X/RADIUS) with corporate use.

Common traps

• 2.4 GHz has exactly three non-overlapping channels (1/6/11), not 11 usable channels.
• 802.11ac does not operate at 2.4 GHz, only 5 GHz.
• ESS requires multiple APs sharing one SSID, a single AP is just a BSS.
• Wi-Fi is half-duplex; clients contend with CSMA/CA, not full-duplex switching.
• OFDMA (a Wi-Fi 6 multi-user feature) is different from plain OFDM used in earlier standards.

Wireless deployment models

The CCNA expects you to compare three AP deployment models:

In the centralized model, CAPWAP forms two tunnels between the lightweight AP and the WLC: a control tunnel (UDP 5246) for management and a data tunnel (UDP 5247) for client traffic. Knowing those ports and the split-tunnel concept is fair game on the exam.

Throughput vs data rate

A standard's advertised rate is the PHY rate, the raw signaling speed; real throughput is always lower because of half-duplex contention, management overhead, and retransmissions, often roughly half the PHY rate in practice. Adding more clients to one channel divides that throughput further because they share airtime. This is why dense environments lean on 5/6 GHz, more non-overlapping channels, and Wi-Fi 6 features like OFDMA that pack more clients into each transmission rather than simply chasing a higher headline rate.