802.11 Wireless Standards Compared: b/g/n/ac/ax (Wi-Fi 4/5/6)

The IEEE 802.11 family defines how Wi-Fi works, and each amendment — b, a, g, n, ac, and ax — changed the frequency band, the maximum data rate, or both. The short version: 802.11b and 802.11g are 2.4 GHz-only (11 Mbps and 54 Mbps respectively), 802.11a and 802.11ac are 5 GHz-only (54 Mbps and multi-gigabit), while 802.11n (Wi-Fi 4) and 802.11ax (Wi-Fi 6) run in both bands. Later standards layered on antenna and scheduling technologies — MIMO, MU-MIMO, and OFDMA — that matter as much as the raw speed numbers.

The generations at a glance

The Wi-Fi Alliance retroactively assigned friendly generation names: 802.11n became Wi-Fi 4, 802.11ac became Wi-Fi 5, and 802.11ax became Wi-Fi 6 (or Wi-Fi 6E when it uses the 6 GHz band). The earlier standards — b, a, and g — never received generation numbers, but the exam still tests them because their band and speed combinations are easy discriminators.

Standard	Wi-Fi name	Band(s)	Max theoretical rate	Signature feature
802.11b	—	2.4 GHz only	11 Mbps	DSSS modulation
802.11a	—	5 GHz only	54 Mbps	First OFDM standard
802.11g	—	2.4 GHz only	54 Mbps	OFDM, backward compatible with b
802.11n	Wi-Fi 4	2.4 and 5 GHz	600 Mbps	MIMO, 40 MHz channels
802.11ac	Wi-Fi 5	5 GHz only	~6.9 Gbps	MU-MIMO (downlink), 80/160 MHz channels
802.11ax	Wi-Fi 6/6E	2.4, 5, and 6 GHz	~9.6 Gbps	OFDMA, TWT, uplink MU-MIMO

Three memory anchors sort out the older trio. First, 802.11b is the slow 2.4 GHz standard at 11 Mbps — it used DSSS (direct-sequence spread spectrum) rather than the OFDM (orthogonal frequency-division multiplexing) modulation everything since uses. Second, 802.11a launched at the same time but chose the 5 GHz band exclusively and reached 54 Mbps with OFDM; it never saw wide consumer adoption because 5 GHz radios were expensive at the time. Third, 802.11g brought OFDM’s 54 Mbps into the 2.4 GHz band while staying backward compatible with 802.11b clients — that compatibility came at a cost, since a single b client forces protection mechanisms that slow the whole cell.

What each modern standard actually added

802.11n (Wi-Fi 4) was the first standard to operate in both 2.4 GHz and 5 GHz, and the first to use MIMO — multiple-input, multiple-output antenna technology. MIMO transmits several independent spatial streams over the same channel at once by exploiting multipath: each transmit/receive antenna pair carries its own data stream. With four spatial streams and 40 MHz channel bonding, 802.11n tops out at a theoretical 600 Mbps.

802.11ac (Wi-Fi 5) retreated to the 5 GHz band exclusively, where wider channels are available. It added 80 MHz (and optional 160 MHz) channel widths, denser 256-QAM (quadrature amplitude modulation) encoding, up to eight spatial streams, and — in its “Wave 2” hardware — downlink MU-MIMO (multi-user MIMO), which lets an access point transmit to several clients simultaneously instead of one at a time. Dual-band “AC” routers pair an 802.11ac 5 GHz radio with an 802.11n 2.4 GHz radio.

802.11ax (Wi-Fi 6) returned to both bands and was designed around dense environments rather than peak single-client speed. Its headline feature is OFDMA (orthogonal frequency-division multiple access), which subdivides a channel into smaller resource units so the access point can serve many clients within a single transmission opportunity — earlier OFDM standards gave the entire channel to one client at a time. Wi-Fi 6 also introduced uplink MU-MIMO, 1024-QAM, BSS coloring to reduce co-channel contention, and Target Wake Time (TWT), which schedules client wake intervals to extend battery life on IoT devices. Wi-Fi 6E is the same 802.11ax standard extended into the 6 GHz band. For a deeper look at how OFDMA and MU-MIMO divide up airtime, see MU-MIMO, OFDMA, and beamforming.

Why marketing numbers and real throughput diverge

Router boxes advertise labels like “AC1900” or “AX3000.” These figures are the sum of the maximum theoretical PHY rates of every radio in the box — for AC1900, roughly 600 Mbps on the 2.4 GHz radio plus 1,300 Mbps on the 5 GHz radio. No single client can ever see that number, for two structural reasons:

1. The aggregate spans both radios. A laptop connects to one band at a time, so at best it sees one radio’s share of the label.
2. The PHY rate assumes maximums a client rarely has. The 1,300 Mbps figure assumes three spatial streams; most laptops and nearly all phones have two or fewer antennas, halving the starting point immediately.

On top of that, real throughput is always well below the connected PHY rate because Wi-Fi is half-duplex and spends airtime on acknowledgments, contention, management frames, and retries — Wi-Fi data rates and airtime walks through that accounting. A rule of thumb: expect 50–60 percent of the negotiated link rate as actual TCP throughput under good conditions. A two-stream laptop on an AC1900 router therefore lands around 300–400 Mbps real-world — exactly the “underperformance” users report that is, in fact, normal.

How the N10-009 exam tests this

• Band-plus-speed identification. A stem gives you a band and a max rate and asks which standard matches — “5 GHz only, 54 Mbps” is 802.11a; “2.4 GHz only, 11 Mbps” is 802.11b; “2.4 GHz only, 54 Mbps, backward compatible with b” is 802.11g. Memorize the table above cold.
• Feature-to-standard matching. “Which standard introduced MIMO, runs in both bands, and reaches 600 Mbps?” points to 802.11n. Anything mentioning OFDMA, TWT, or BSS coloring points to 802.11ax.
• Dense-environment scenarios. A lecture hall or stadium upgrading to Wi-Fi 6 with a question about what OFDMA does — the answer is that it splits a channel into resource units so multiple clients transmit in the same time slot, not that it makes any one client faster.
• Marketing-vs-reality troubleshooting. A user’s single device measures a fraction of the router’s advertised rating; the correct explanations involve aggregate multi-radio ratings and client spatial-stream limits, not a faulty router.

The table only sticks with repetition — drill it with exam-style practice questions until every band-and-speed pair is instant.

This table is foundational for the whole wireless domain — see where it fits in the full N10-009 study guide.

Quick reference

• 802.11b: 2.4 GHz only, 11 Mbps, DSSS.
• 802.11a: 5 GHz only, 54 Mbps, OFDM.
• 802.11g: 2.4 GHz only, 54 Mbps, OFDM, backward compatible with 802.11b.
• 802.11n = Wi-Fi 4: both bands, MIMO, up to 600 Mbps.
• 802.11ac = Wi-Fi 5: 5 GHz only, downlink MU-MIMO, 80/160 MHz channels.
• 802.11ax = Wi-Fi 6: both bands (6E adds 6 GHz), OFDMA, uplink MU-MIMO, TWT, BSS coloring.
• Advertised ratings (AC1900, AX3000) sum every radio’s theoretical maximum; one client sees far less.
• Real throughput runs roughly half the negotiated PHY rate due to half-duplex airtime overhead.