AP Subject A 34 — Wireless LAN: from CSMA/CA, hidden terminals and channel design to WPA3 and 802.1X

AP Subject A · Installment 34 · An independent study resource for the 2026 exam and Syllabus Ver.7.2. It is not affiliated with IPA and does not guarantee a pass. Open the series hub

Based on the 2026 IPA Applied Information Technology Engineer Examination (AP), Subject A, Syllabus Ver.7.2; checked 2026-10-22. This is independent study material from Motitory: it is not affiliated with, reviewed or endorsed by IPA, IEEE or the Wi-Fi Alliance. It does not cover every item of Ver.7.2 or the whole IEEE 802.11 standard, and does not guarantee a pass. All examples and questions here are Motitory originals, not IPA past questions.

This is AP34 (a supplement) of the fixed AP33–38 completion plan, not the last article of the series; every installment is listed in the series hub. OSI layers, TCP/UDP and ports were covered in AP16, IPv4, CIDR and routing in AP17, and DNS, HTTP, TLS and mail in AP18. They are not retaught here; this article covers only what is specific to the wireless link (the physical and data link layers).

1. Terminology and generations at a glance

English	日本語 (exam term)	한국어	One-line definition
wireless LAN access point (AP)	無線LANアクセスポイント	무선 LAN 액세스 포인트	Base station that groups wireless stations and relays to the wired LAN
infrastructure mode	インフラストラクチャモード	인프라스트럭처 모드	Stations communicate through an AP
ad hoc mode (IBSS)	アドホックモード	애드혹 모드	Stations communicate directly, no AP
SSID (service set identifier)	SSID	SSID	Human-chosen network name (up to 32 octets)
BSSID (basic service set identifier)	BSSID	BSSID	48-bit identifier of one BSS
hidden terminal problem	隠れ端末問題	숨은 단말 문제	Two stations that cannot hear each other send to the same receiver and collide
exposed terminal problem	さらし端末問題	노출 단말 문제	A station that could safely send waits because it hears someone else
CSMA/CA	CSMA/CA	CSMA/CA	Access control that avoids collisions with carrier sense, random backoff and ACK
roaming	ローミング	로밍	A station switching APs within the same wireless LAN
handover	ハンドオーバー	핸드오버	Changing base station (AP) while keeping the session

IEEE standard	Wi-Fi Alliance generation	Bands	Key techniques	Maximum PHY rate in the standard (theoretical)
802.11b	no official generation name	2.4 GHz	DSSS/CCK	11 Mbps
802.11a	no official generation name	5 GHz	OFDM	54 Mbps
802.11g	no official generation name	2.4 GHz	OFDM	54 Mbps
802.11n	Wi-Fi 4	2.4 / 5 GHz	MIMO (up to 4 streams), 40 MHz width	600 Mbps
802.11ac	Wi-Fi 5	5 GHz only	up to 160 MHz width, downlink MU-MIMO	about 6.9 Gbps
802.11ax	Wi-Fi 6	2.4 / 5 GHz	OFDMA, uplink and downlink MU-MIMO	about 9.6 Gbps
802.11ax	Wi-Fi 6E	Wi-Fi 6 plus 6 GHz	Wi-Fi 6 techniques also in 6 GHz	about 9.6 Gbps
802.11ah	Wi-Fi HaLow	below 1 GHz (country-specific)	narrow channels, long range, low power	low (for IoT)

The maximum PHY rate is the physical-layer theoretical value under the best conditions (widest channel, most streams, highest modulation). Real throughput is much lower (worked example 3).
Not every generation supports every band. 802.11ac is a 5 GHz standard, so even a dual-band Wi-Fi 5 device runs 802.11n or older on 2.4 GHz. 6 GHz needs both an AP and a station that support Wi-Fi 6E or later, and the country must permit 6 GHz use.
Later generations such as 802.11be (Wi-Fi 7) are outside the scope of this article.

2. Components and the two modes

STA (station): a device with a wireless LAN interface (laptop, smartphone and so on). Broadly, an AP is also a kind of STA.
Wireless LAN access point (無線LANアクセスポイント): groups wireless stations and usually connects to the wired LAN (Ethernet) to relay frames.
BSS: the basic unit formed by one AP (or one group of stations). ESS: several BSSs using the same SSID, joined by a distribution system such as a wired LAN.

Aspect	Infrastructure mode (インフラストラクチャモード)	Ad hoc mode (アドホックモード)
AP	required	not required (IBSS)
Path	station → AP → station or wired network	station ↔ station directly
Scale	wide area as an ESS, roaming between APs	small, temporary
Management	security and access policy applied centrally at the AP	configured per station

Note that Wi-Fi Direct has one device act as group owner in an AP role, so it is not the same as classic ad hoc (IBSS).

3. SSID and BSSID

Item	SSID	BSSID
Meaning	network name	identifier of one BSS
Format	string of 0–32 octets	48 bits (MAC address format)
Set by	the administrator	usually the MAC address of the AP’s radio interface
Across APs	shared within an ESS	different per AP (radio interface and SSID)

An SSID is not authentication. It only names which network to join; it does not verify who connects.
SSID stealth (leaving the SSID out of beacons) is not a security control either. The SSID travels in station probe requests and association frames, so it can be observed. MAC address filtering cannot replace authentication because MAC addresses can be spoofed. Real access control and encryption come from WPA2/WPA3 in section 11.

4. A shared, half-duplex medium

Wireless stations on the same channel share one radio space. A station’s radio works half-duplex: it does not transmit and receive on a channel at the same time. If two signals overlap at a receiver, both can be lost. That is why media access control is needed to decide who sends when.

Wired Ethernet’s CSMA/CD means “while sending, detect a collision, stop and retransmit”. Why this is not the answer for wireless LAN:

A sender can hardly detect a collision while transmitting. Its own signal is far stronger at its receiver input than any other signal on the channel.
Collisions happen at the receiver, not the sender. As with the hidden terminal in section 6, the medium can look idle at the sender while signals overlap at the receiver.

So wireless LAN avoids (CA) collisions instead of detecting (CD) them, and confirms success with an ACK. (Note: modern Ethernet connected full-duplex to a switch effectively no longer uses CSMA/CD.)

5. Collision-avoidance access control

Basic CSMA/CA operation (a simplified DCF model, including the immediate-access exception):

Carrier sense: when a frame is ready, listen to see whether the medium is idle (physical sensing plus virtual sensing via the NAV).
Choose the access path: if a newly pending frame finds the medium already idle for at least DIFS, DCF may transmit it immediately without drawing a new random backoff. If the medium is busy, or the frame was deferred or must be retried, use the contention path below.
DIFS and random backoff after deferral: after the medium becomes idle, wait DIFS, choose a random number of slots from 0 to CW and count down. The counter decreases only while the medium is idle; when it becomes busy the counter freezes and resumes after the medium is idle for DIFS again.
Transmit: send immediately under the exception in step 2, or when the backoff counter reaches 0.
ACK: the receiver returns an ACK after a SIFS. Because SIFS < DIFS, the ACK takes priority over any other station’s new transmission.
Retransmit: with no ACK, treat it as a collision or error, roughly double CW (up to a cap) and retransmit. Give up after the retry limit.

CSMA/CA reduces collisions; it does not eliminate them. If two stations pick the same backoff value they still collide. Wireless LAN with QoS (EDCA) uses different waits and CWs per traffic class, but the principle is the same.

6. Hidden and exposed terminals

Hidden terminal problem (隠れ端末問題): stations A and C can both talk to the AP, but walls or distance stop them hearing each other. While A is sending, C’s carrier sense still sees an idle medium, so C sends too and the two signals collide at the AP. Neither A nor C notices the collision; they learn of the failure only when no ACK comes back.

RTS/CTS: before the data, the sender transmits a short RTS and the receiver (AP) replies with a CTS. Both frames carry the time the rest of the exchange needs (Duration), and any station that hears them sets its NAV (virtual carrier sense) for that time and defers. The key point is that C cannot hear A’s RTS but does hear the AP’s CTS.

Shared assumptions (worked examples 1 and 3)

A simplified exam model. Real values depend on the amendment, rate and band.

SIFS 16 µs, DIFS 34 µs, slot 9 µs
data frame time = preamble and header 40 µs + payload bits ÷ PHY rate
RTS 30 µs, CTS 27 µs, ACK 27 µs (preamble included)
propagation delay and errors are ignored.

Worked example 1 — hidden terminal and RTS/CTS

A sends a 1,500-byte payload to the AP at a PHY rate of 100 Mbps. C hears the AP but not A.

Data frame time: 1,500 × 8 = 12,000 bits, 12,000 ÷ 100 Mbps = 120 µs. Add 40 µs: DATA = 160 µs.
CTS Duration (the exchange left after the CTS) = SIFS + DATA + SIFS + ACK = 16 + 160 + 16 + 27 = 219 µs. From the moment it hears the CTS, C sets its NAV for 219 µs and does not transmit.
RTS Duration (the exchange left after the RTS) = SIFS + CTS + 219 = 16 + 27 + 219 = 262 µs. Stations near A set their NAV from this value.
Protection cost: RTS 30 + SIFS 16 + CTS 27 + SIFS 16 = 89 µs added to every exchange.
Decision: without RTS/CTS, a collision throws away the whole 160 µs DATA and the frame is resent after backoff. If two RTSs collide, only 30 µs is lost. Conversely, with a 100-byte payload DATA = 40 + 8 = 48 µs, so the 89 µs protection cost exceeds the data itself. That is why RTS/CTS is usually used only for frames above a set size (the RTS threshold).

Exposed terminal problem (さらし端末問題): B is sending to A, and C, near B, wants to send to D, far from A. C’s transmission might not disturb A’s reception, yet C senses B’s carrier and waits. The result is not a collision but a lost opportunity (lower throughput). Caveats:

RTS/CTS does not solve the exposed terminal. If C hears B’s RTS, it waits on its NAV all the same.
“Just let it send” is not the answer either. 802.11 needs an ACK after each transmission, and while B is sending, C’s surroundings are filled with B’s signal, so C may fail to receive D’s ACK.

7. Frequency bands and channel design

Band	Typical advantages	Typical drawbacks and cautions
2.4 GHz	under the same conditions, better range and penetration; many supporting devices	few, overlapping channels; shared with Bluetooth, microwave ovens and more
5 GHz	many non-overlapping channels, wide channels possible	under the same conditions, shorter range; some channels require radar avoidance (DFS), causing channel changes and waits
6 GHz	where permitted, new wide spectrum without legacy devices	needs Wi-Fi 6E or later devices; under the same conditions, shorter range; permitted range and power rules are country-specific

These are tendencies “for the same power, antennas and environment”, not absolute rules. Real performance depends on wall materials, interference and device capability.

Country and regulatory caveat: usable channels, indoor/outdoor conditions, maximum power and DFS requirements differ by country. Before a design, check the current local radio regulations and the devices’ certification; this article does not prescribe a country-specific channel list.

Channel-width trade-off: widening a channel from 20 → 40 → 80 → 160 MHz raises the maximum PHY rate, but reduces the number of non-overlapping channels in the band and takes in noise over a wider range. In an office with dense APs, several narrow channels can give better total throughput.

Worked example 2 — 2.4 GHz channel overlap

Assumptions: the centre frequency of 2.4 GHz channel n (1–13) is 2407 + 5n MHz, and the occupied width is 20 MHz (OFDM; DSSS 802.11b is about 22 MHz).

Channel	Centre	Occupied range
1	2412 MHz	2402–2422 MHz
4	2427 MHz	2417–2437 MHz
6	2437 MHz	2427–2447 MHz
11	2462 MHz	2452–2472 MHz

Channels 1 and 4: 2417–2422 MHz overlaps → 5 MHz overlap. Each receives the other as interference and both lose.
Channels 1 and 6: 5 MHz gap between 2422 and 2427 → no overlap. Channels 6 and 11 are the same.
In this simplified rectangular-width model, 20 MHz centres must be at least 20 MHz apart, i.e. channel numbers at least 4 apart, for the occupied ranges not to overlap (at exactly 4 the edges touch). For the modelled 22 MHz width it is 5 or more. Real spectral masks are not sharp rectangles, so the practical example here uses the widely supported 1/6/11 plan; always verify the local channel rules.
Conclusion: three neighbouring APs go on 1, 6 and 11. With 40 MHz width in 2.4 GHz, almost no room is left for non-overlapping channels.

Worked example 3 — airtime and effective throughput

On top of the shared assumptions: no RTS/CTS, no collisions or errors, backoff fixed at 7 slots (= 63 µs) every time, no frame aggregation.

Fixed time per frame = DIFS 34 + backoff 63 + preamble and header 40 + SIFS 16 + ACK 27 = 180 µs. The payload is 1,500 bytes (12,000 bits).

Case	Payload time	Total time per frame	Effective throughput
(a) PHY 100 Mbps, one station	120 µs	300 µs	12,000 ÷ 300 µs = 40 Mbps
(b) PHY 200 Mbps, one station	60 µs	240 µs	12,000 ÷ 240 µs = 50 Mbps
(c) 100 Mbps station X and 20 Mbps station Y alternate one frame each	X 120 µs, Y 600 µs	300 + 780 = 1,080 µs (both together)	24,000 ÷ 1,080 µs ≈ 22.2 Mbps (about 11.1 Mbps each)

(a)→(b): doubling the PHY rate gives only 1.25× the throughput, because the fixed overhead does not shrink. PHY rate ≠ throughput.
(c): X, which reached 40 Mbps alone, drops to about 11.1 Mbps when sharing with slow Y, because the slow station holds the airtime longer. Designs that retire old standards and distant stations or split them onto another band are effective for this reason.
From 802.11n onward, real devices aggregate several frames (A-MPDU) to share the overhead and raise efficiency. The numbers above are a model for checking the principle.

8. Multi-antenna and multi-user techniques

Technique	What it divides	Effect	Generation where it first became common
MIMO (SU-MIMO)	space: several antennas send several streams to one station	higher maximum rate (spatial multiplexing), stability through diversity	802.11n
MU-MIMO	space: different streams to several stations at the same time	simultaneous transmission to many stations	802.11ac (downlink), 802.11ax (uplink and downlink)
OFDMA	frequency: the channel is split into resource units (RUs) assigned to several stations at once	less waiting and overhead when there are many small frames	802.11ax
Beamforming	direction: per-antenna phase and amplitude steer the signal toward a station	better SNR → higher modulation and stability	specified in 802.11n; interoperable explicit beamforming became broadly deployed with 802.11ac

The usable number of streams is set by the smaller side. With a 4×4 AP and a 2×2 smartphone, that smartphone gets at most 2 streams.
Beamforming does not add streams, and OFDMA does not add antennas. In the exam, tell them apart by “does it handle space, frequency or direction?”.

9. Roaming and handover

Roaming in wireless LAN (ローミング): a station reassociating with another AP within the same ESS (same SSID and security settings). When and to which AP to move is basically the station’s decision. That is why “sticky clients” stay on the old AP even as the signal weakens.
APs and controllers only assist. 802.11k provides a list of neighbouring APs, and 802.11v can request a move to another AP, but the station may decline. 802.11r (fast BSS transition) shortens the key exchange during the move, keeping the interruption short where 802.1X authentication is used.
Handover in mobile communication (ハンドオーバー): changing base station while keeping the session. In cellular networks it is usually network-controlled, based on the terminal’s measurement reports.
Terminology caution: in mobile communication, roaming usually means “using another operator’s network (for example abroad)”. This differs from AP-to-AP roaming in wireless LAN, so judge by context.

10. Mesh Wi-Fi and Wi-Fi HaLow

Mesh Wi-Fi: several nodes (APs) relay for each other to cover a wide area with one SSID. The links between nodes (backhaul) are wireless or wired.

Wireless backhaul sends the same data over the air once more, so it uses extra airtime. If a single radio receives and resends on the same channel, the relayed segment’s throughput roughly halves even in the ideal case. A dedicated backhaul radio or wired backhaul reduces this loss.
IEEE defines a mesh capability (802.11s), but commercial mesh products may use vendor-specific methods or a Wi-Fi Alliance interoperability programme.

Wi-Fi HaLow (IEEE 802.11ah): wireless LAN in country-specific licence-exempt bands below 1 GHz, aiming at long range and low power with narrow channels. It targets IoT such as sensors and meters, and its rates are lower than 2.4/5 GHz wireless LAN. It is not a replacement for fast home Wi-Fi, and ordinary 2.4/5 GHz-only stations cannot join HaLow.

11. Security boundaries

Mode	Access authentication	Encryption on the wireless link	What it stops	What it does not stop, cautions
Open (no encryption)	none	none	—	anyone can join; anyone nearby can sniff plaintext
Enhanced Open (OWE)	none	yes (per-station key exchange)	passive eavesdropping	anyone can join; the AP itself is not authenticated, so no defence against a fake AP (evil twin)
WPA2-Personal (PSK)	shared passphrase	yes (AES-CCMP)	joining and sniffing by people who do not know the passphrase	a captured handshake allows offline guessing of a weak passphrase; weak protection between people who know the passphrase; cannot cut off one person
WPA3-Personal (SAE)	shared password	yes; Protected Management Frames (PMF) mandatory	resistant to offline dictionary attacks; forward secrecy	weak passwords can be guessed online; implementation flaws possible; downgrade risk in WPA2-compatible (transition) mode; cannot cut off one person
WPA2/WPA3-Enterprise	IEEE 802.1X/EAP (e.g. EAP-TLS), RADIUS as authentication server	yes (per-user, per-session keys)	per-user authentication, revocation and logging	if stations do not validate the server certificate, credentials can leak to a fake AP; needs operation (certificate and account management)

The three 802.1X roles: supplicant (station) – authenticator (AP, wireless LAN controller) – authentication server (RADIUS). The AP blocks data traffic until authentication finishes and relays EAP messages. Review authentication in general (MFA and so on) in AP20 and cryptography in AP19.
WEP and WPA (TKIP) are obsolete methods that are no longer secure.
Wireless LAN encryption protects only the station–AP link. The wired network behind the AP and the internet path need separate upper-layer protection such as TLS (AP18).
WPA3 does not guarantee safety either. Password strength, firmware updates, transition-mode management and certificate validation all have to be right too.

12. Quick sheet and traps

Infrastructure = via an AP, ad hoc = station to station (IBSS). ESS = several APs with the same SSID.
SSID = name (up to 32 octets), BSSID = BSS identifier (usually the AP radio’s MAC). Neither is authentication.
Wireless = half-duplex shared medium → collisions hard to detect → CSMA/CA. A newly pending frame may transmit when the medium was already idle for at least DIFS; after deferral/retry: DIFS → random backoff (freeze while busy) → send → ACK after SIFS → if none, widen CW and retry.
Hidden terminal → RTS/CTS + NAV (stations that hear the CTS wait). Exposed terminal → lost opportunity, not solved by RTS/CTS.
Avoiding 20 MHz overlap in 2.4 GHz: channel numbers 4 or more apart; in practice usually 1/6/11. Channel availability is country-specific.
n = Wi-Fi 4 (2.4/5), ac = Wi-Fi 5 (5 only), ax = Wi-Fi 6 (2.4/5), 6E = ax + 6 GHz, ah = HaLow (below 1 GHz).
MIMO = spatial streams, MU-MIMO = several stations at once, OFDMA = frequency division, beamforming = directional focus.
Wireless LAN roaming is the station’s decision; APs advise with 11k/11v and shorten the transition with 11r.
Traps: “SSID stealth or MAC filtering = authentication”, “WPA3 means safe”, “600 Mbps PHY = 600 Mbps measured”, “802.11ac also supports 2.4 GHz”, “CSMA/CA has no collisions”, “RTS/CTS solves the exposed terminal”, “Enhanced Open authenticates users”.

13. Five original diagnostic questions

The questions below are Motitory originals (non-official); they do not use or adapt IPA past questions.

Q1 — Hidden terminal

Stations A and C are on opposite sides of an AP. Both receive the AP’s signal but not each other’s. Which statement is correct?

A. A and C detect collisions directly while transmitting, so they stop sending immediately.

B. C cannot hear A’s RTS, so RTS/CTS has no effect at all.

C. When the AP answers A’s RTS with a CTS, C sets its NAV from the CTS Duration value and defers for that time.

D. This is the exposed terminal problem, and hiding the SSID solves it.

A: Incorrect. Wireless stations can hardly detect collisions while transmitting, and the collision happens at the receiver, the AP. Failure shows up as a missing ACK.
B: Incorrect. C cannot hear the RTS but does hear the CTS the AP sends. That is why RTS/CTS works against hidden terminals.
C: Correct. As in worked example 1, C waits for the CTS Duration (e.g. 219 µs).
D: Incorrect. Colliding because they cannot hear each other is the hidden terminal problem. Hiding the SSID also has nothing to do with access control.

Q2 — Standards and techniques

Which statement is correct?

A. IEEE 802.11ac (Wi-Fi 5) is a standard that operates in both 2.4 GHz and 5 GHz.

B. Beamforming splits the channel into resource units (RUs) and assigns them to several stations at once.

C. The 600 Mbps maximum of 802.11n is the value you can expect as real application throughput.

D. Wi-Fi 6E refers to IEEE 802.11ax devices that also use the 6 GHz band, and the usable 6 GHz range differs by country.

A: Incorrect. 802.11ac is a 5 GHz standard. Dual-band devices run 802.11n or older on 2.4 GHz.
B: Incorrect. That is OFDMA. Beamforming focuses the signal in a direction through per-antenna phase and amplitude.
C: Incorrect. 600 Mbps is the PHY theoretical value under maximum conditions. Overhead and sharing make throughput much lower (worked example 3).
D: Correct. 6E is the 6 GHz extension, and the permitted 6 GHz range and conditions differ by country.

Q3 — CSMA/CA

Which statement correctly gives why wireless LAN uses CSMA/CA instead of CSMA/CD and how it works?

A. A transmitting wireless station can hardly detect a collision because of its own signal, and collisions can happen at the receiver. A deferred frame waits for DIFS and random backoff, while a newly pending frame may access immediately if the medium was already idle for at least DIFS; success is confirmed with an ACK.

B. The backoff counter keeps decreasing even while the medium is busy, to shorten the wait.

C. When no ACK comes back, the contention window (CW) is halved to retransmit sooner.

D. With CSMA/CA, collisions in principle never occur.

A: Correct. It states both DCF paths accurately: immediate access for the stated idle-medium case, and random backoff after deferral, with success confirmed by ACK.
B: Incorrect. While the medium is busy the counter freezes, then resumes once idle.
C: Incorrect. After a failure CW is roughly doubled (up to the cap) to lower the chance of colliding again.
D: Incorrect. Collisions occur if two stations pick the same backoff or if there is a hidden terminal. CSMA/CA only reduces them.

Q4 — Airtime calculation

Under the same assumptions as worked example 3 (fixed time 180 µs per frame, 1,500-byte payload, no collisions or errors, one station), which is closest to the effective throughput at a PHY rate of 150 Mbps?

A. 150 Mbps

B. about 46.2 Mbps

C. about 66.7 Mbps

D. 75 Mbps

A: Incorrect. This takes the PHY rate as the throughput.
B: Correct. 12,000 ÷ 150 Mbps = 80 µs, 180 + 80 = 260 µs, 12,000 ÷ 260 µs ≈ 46.2 Mbps.
C: Incorrect. This is 12,000 ÷ 180 µs, leaving out the 80 µs payload time.
D: Incorrect. This is a “half the PHY rate” rule of thumb, not a value calculated from the given assumptions.

Q5 — Choosing a security mode

A company with 200 employees is designing its office wireless LAN. It must be able to cut off just one departing employee immediately and log who connected, per user. Which is most appropriate?

A. SSID stealth and MAC address filtering

B. WPA3-Personal with one strong password shared by all employees

C. WPA3-Enterprise (or WPA2-Enterprise): IEEE 802.1X/EAP (e.g. EAP-TLS) with a RADIUS server, and stations validating the server certificate

D. Enhanced Open (OWE)

A: Incorrect. The SSID can be observed in frames and MAC addresses can be spoofed. Neither is authentication.
B: Incorrect. SAE resists offline dictionary attacks, but it is a shared secret: cutting off one person means changing everyone’s password, and there is no per-user log.
C: Correct. It authenticates per user or certificate and allows revocation and logging. Operation such as server-certificate validation and account management must still be right, and this alone does not guarantee safety.
D: Incorrect. It encrypts the wireless link but does not authenticate who connects, so anyone can join.

Answers: C, D, A, B, C

14. Self-check and review schedule

I can state the differences between infrastructure and ad hoc mode, and between SSID and BSSID, without the tables.
I can give two reasons why wireless LAN does not use CSMA/CD.
I can distinguish DCF’s immediate-access exception from the deferred/retry path (DIFS, backoff, send, ACK, retransmit).
I can recompute 219 µs and 262 µs from worked example 1.
I can show by calculation why channels 1 and 4 overlap by 5 MHz and 1 and 6 do not.
I can recompute 40 / 50 / 22.2 Mbps from worked example 3 and explain the difference between PHY rate and throughput.
I can tell MIMO, MU-MIMO, OFDMA and beamforming apart by “what it divides”.
I can explain the five modes in the security table by “authentication, encryption, what it does not stop”.

Recommended review cycle (separate from the publishing schedule): same day, redo worked examples 1–3 without looking → after 1 day, Q1–Q5 → after 3 days, fill in blanks in the terminology and generation tables from the quick sheet only → after 7 days, change the PHY rate and payload size and compute airtime afresh → after 14 days, recheck only the questions you missed and the security table.

15. Official sources

IPA Applied Information Technology Engineer Examination Syllabus Ver.7.2 — mapped to Major Category 3 / Middle Category 10 Network: 1. ネットワーク方式 / (4) 無線LAN (access point, infrastructure and ad hoc, SSID, hidden and exposed terminals); 2. データ通信と制御 / (5) media access control (CSMA/CA); 3. 通信プロトコル / (1) ⑥ LAN and WAN interfaces (IEEE 802.11a/b/g/n/ac/ax, Wi-Fi 4/5/6/6E, mesh Wi-Fi); 5. ネットワーク応用 / (6) ③ mobile communication technology (handover and roaming, MIMO, beamforming, IEEE 802.11ah); and, as a linked item, Middle Category 11 セキュリティ / 5. セキュリティ実装技術 (WPA2/WPA3, Enhanced Open, IEEE 802.1X/EAP). Checked 2026-10-22.
IPA syllabus and revision hub — check here whether the syllabus has been revised. Checked 2026-10-22.
IEEE 802.11-2024 — the current consolidated IEEE 802.11 standard. Checked 2026-10-22.
IEEE 802.11-2020 (superseded) — the previous edition, superseded by 802.11-2024, showing the revision chain. Checked 2026-10-22.
Wi-Fi Alliance: Security — Wi-Fi security certification programmes such as WPA3 and Enhanced Open. Checked 2026-10-22.

This article is the second installment of the AP33–38 completion plan. The next planned topic is AP35 distributed databases and data warehouses, and the series ends at AP38.