Wireless networking (IEEE 802.11a): How many non-overlapping 20-MHz channels are available in the 5 GHz 802.11a band (typical U.S. regulatory domain)?

Introduction / Context:
Channel planning is a core skill in Wi-Fi design. Unlike 2.4 GHz (802.11b/g/n), the 5 GHz band used by 802.11a offers many more non-overlapping channels, enabling denser deployments with less co-channel interference.

Given Data / Assumptions:

• Standard: IEEE 802.11a (5 GHz band).
• Channel width considered: 20 MHz (legacy 11a operation).
• Regulatory domain: U.S. (common exam assumption).

Concept / Approach:
Non-overlapping channels are center frequencies spaced so 20-MHz channels do not overlap. In 5 GHz, the U-NII bands provide far more such channels than the three non-overlapping channels commonly available at 2.4 GHz, which is why 5 GHz scales better.

Step-by-Step Solution:

Verification / Alternative check:
Vendor design guides and CWNA-level materials list 23 usable 20-MHz channels (subject to DFS/TPC requirements) for U.S. indoor planning, confirming the common answer.

Why Other Options Are Wrong:

• 3: This is the 2.4 GHz non-overlapping count, not 5 GHz.
• 12/40/8: Do not match the standard planning count used for 11a 20-MHz channels in the U.S.

Common Pitfalls:
Confusing regulatory domains; mixing 20-MHz channel counts with bonded widths (40/80/160 MHz) which reduce the number of available channels.

Final Answer:
23