802.11h (5 GHz with DFS/TPC): number of non-overlapping 20 MHz channels: Considering 802.11h operation in the 5 GHz band (DFS/TPC enabling access to additional UNII bands), approximately how many non-overlapping 20 MHz channels are available?

Introduction / Context:
802.11h adds Dynamic Frequency Selection (DFS) and Transmit Power Control (TPC) to 802.11a so that Wi-Fi equipment can legally use more of the 5 GHz spectrum (particularly UNII-2 and UNII-2e) while protecting incumbent radar systems. A common study point is how many non-overlapping 20 MHz channels are available in the 5 GHz band when these extensions are allowed.

Given Data / Assumptions:

• We are discussing 20 MHz channels, not 40/80/160 MHz bonded channels.
• Regulatory availability varies by country; the question targets the widely cited count enabled by DFS/TPC in many regions.
• 802.11h is an amendment that broadens usable channels compared to basic 802.11a.

Concept / Approach:

Classic 802.11a in the U.S. without DFS typically exposes about 12 non-overlapping channels. With 802.11h and DFS/TPC, devices can operate across additional UNII-2 and UNII-2e ranges, raising the practical count to roughly 23 non-overlapping 20 MHz channels (exact sets depend on local regulations and device support).

Step-by-Step Solution:

Verification / Alternative check:

Consult current regulatory domain tables for your country to confirm exact channels. Enterprise controller GUIs also list enabled 5 GHz channels when DFS is permitted.

Why Other Options Are Wrong:

3 is the 2.4 GHz non-overlapping count (802.11b/g in most regions).

12 is typical for basic 802.11a without DFS.

40 greatly exceeds commonly allowed 20 MHz channels in a single regulatory domain.

Common Pitfalls:

Confusing 2.4 GHz and 5 GHz channel counts; ignoring that DFS availability is regulatory-dependent; mixing 20 MHz counts with bonded-channel (40/80/160 MHz) planning.

Final Answer:

23