Wireless standards, frequencies and the channel plan nobody made

Why this matters

Wireless is where most modern support calls start, and it is the part of networking where the physics is closest to the surface. A cable either carries the signal or it does not. A radio link shares a medium with every other device in range, including devices that are not networks at all.

The exam tests this in two ways: naming the standards and their capabilities, and reasoning about why a network performs badly in a stated environment. The first is memorisation and the second is the physics. Both are needed, and the second is what makes the first stick.

Lesson 41 applies all of this to fault finding. This lesson builds the model: what the generations changed, what the bands trade against each other, and why the channel numbering looks like a mistake.

The lesson

The 802.11 generations by name and number, and what each one changed

CompTIA use both the letter designations and the marketing generation names, so both are worth holding.

• 802.11a — 5 GHz, up to 54 Mbps. Early, and the first use of 5 GHz.
• 802.11b — 2.4 GHz, up to 11 Mbps. Long range, low speed.
• 802.11g — 2.4 GHz, up to 54 Mbps, backward compatible with b.
• 802.11n (Wi-Fi 4) — both bands, multiple antennas (MIMO), channel bonding to 40 MHz. The first standard that felt fast.
• 802.11ac (Wi-Fi 5) — 5 GHz only, wider channels up to 160 MHz, more spatial streams, multi-user downstream. Gigabit-class in practice.
• 802.11ax (Wi-Fi 6 and 6E) — both bands, and 6E adds the 6 GHz band. The headline change is efficiency in crowded environments rather than raw peak speed: it subdivides channels so several clients can be served in one transmission, and adds a scheduling mechanism that lets devices sleep.
• 802.11be (Wi-Fi 7) — wider channels again and the ability to use multiple bands at once.

The pattern worth understanding: the early generations raised the peak rate; the recent ones raise the achievable rate when many devices share an access point. That is why a Wi-Fi 6 upgrade helps an office far more than it helps a home with three devices.

2.4 GHz against 5 GHz against 6 GHz: range, throughput and obstruction

One trade-off governs all three bands: lower frequency travels further and penetrates better; higher frequency carries more data.

• 2.4 GHz. Best range, best wall penetration, lowest throughput, and by far the most congested — it is shared with Bluetooth, microwave ovens, cordless phones, baby monitors and wireless peripherals. Three non-overlapping channels in practice.
• 5 GHz. Much more spectrum, many non-overlapping channels, higher throughput, shorter range and worse through walls. Some channels require radar detection and will move the network automatically.
• 6 GHz. More spectrum again, restricted to Wi-Fi 6E and newer clients, so it is currently uncongested. Shortest range of the three and the least tolerant of obstructions.

This is what makes the standard advice correct: put devices that need throughput and are close to the access point on 5 or 6 GHz, and leave 2.4 GHz for devices that are far away or only need a trickle. It also explains the common complaint "the connection is strong but slow", which is usually a device that has chosen 2.4 GHz for its better signal.

Channels, width and overlap, and why three channels exist in practice at 2.4 GHz

The 2.4 GHz band is divided into channels numbered 1 to 11 in most regions, spaced 5 MHz apart. A channel is 20 MHz wide. Five does not go into twenty, so adjacent channels overlap heavily — channel 1 and channel 2 are mostly the same spectrum.

Only 1, 6 and 11 are far enough apart not to overlap. That is the whole reason for the standard advice, and the reason an access point set to channel 3 degrades both of its neighbours rather than avoiding them.

Channel width is the other half:

• Wider channels carry more data and pick up more interference, and they consume more of the band.
• At 2.4 GHz, bonding to 40 MHz uses most of the available spectrum and is almost always a mistake in any populated area.
• At 5 and 6 GHz there is enough room for 40, 80 and 160 MHz channels, though the widest still reduce the number of networks that can coexist.

Interference comes in two forms and they need different fixes. Co-channel interference is other networks on the same channel: they take turns politely, so the effect is reduced throughput. Adjacent-channel interference is partial overlap, where the transmissions are not coordinated at all, and the effect is far worse. Moving to a properly separated channel fixes the second and only shares the load on the first.

Wireless security modes in order of age, and which ones a current device should refuse

The exam asks you to place these in order and to identify the right one.

• WEP. Broken. Recoverable in minutes with freely available tools. Its presence in a scenario is always the fault.
• WPA. An interim fix over the same flawed hardware, using TKIP. Obsolete.
• WPA2. Uses AES-CCMP. Still widely deployed and acceptable, with the caveat that the pre-shared key form is only as strong as the passphrase.
• WPA3. Current. Replaces the pre-shared key handshake with one that resists offline guessing, and adds encryption for open networks.

There are two flavours of each of the modern ones:

• Personal, using a pre-shared key that everyone shares. Anyone who has it can join, and it can only be revoked by changing it for everybody.
• Enterprise, where each user authenticates individually against an authentication server. Credentials are revoked per user, which is the reason it exists.

Two more things worth knowing as not security controls: hiding the network name, and filtering by hardware address. Both are trivially defeated and both appear as distractors.

Long-range and short-range alternatives: why not every wireless link is Wi-Fi

The exam's scope includes wireless technologies that are not 802.11, and the distinguishing question is always range against data rate against power.

• Bluetooth. Around ten metres, low power, device-to-device. Covered in lesson 4.
• NFC. A few centimetres, where proximity is the security control.
• RFID. Centimetres to metres depending on whether the tag is passive or powered. Inventory, access badges, asset tracking.
• Infrared. Line of sight, short range, still used in remote controls and some sensing.
• Long-range fixed wireless. Point-to-point links between buildings, replacing a cable run across a site.
• Satellite. Global coverage, high latency on geostationary systems and considerably lower on the low-orbit ones. The examinable property is latency rather than bandwidth.
• Cellular, covered in lesson 5, which is a wide-area wireless link with a subscription attached.

When a scenario describes a requirement — two buildings 400 metres apart, an asset tag that needs no battery, a rural site with no wired service — the answer is usually decided by range and power rather than by speed.