2.3 Given a scenario, select and configure wireless devices and technologies
Channels
📘CompTIA Network+ (N10-009)
1. What is 802.11h?
- 802.11h is an amendment to the 802.11 standard (the standard for Wi-Fi networks).
- It was created to help Wi-Fi devices follow international regulations, especially in the 5 GHz frequency band.
- Its main goal is to avoid interference with other devices that also use 5 GHz, like radar systems used by airports and weather monitoring.
Think of it as a set of “rules” that Wi-Fi devices must follow so they don’t disrupt other important services.
2. Why 802.11h Exists (The Problem It Solves)
- Problem: Many devices use the 5 GHz band (Wi-Fi, radar, satellite, etc.). Without rules, Wi-Fi could interfere with important systems.
- Solution (802.11h): Wi-Fi devices must check and adjust themselves to avoid causing interference.
Key idea: It’s about regulatory compliance and dynamic adjustments to protect other devices.
3. Key Features of 802.11h
There are two main mechanisms in 802.11h:
A. Dynamic Frequency Selection (DFS)
- Wi-Fi devices scan the frequency band before transmitting.
- If a radar or other high-priority device is detected on a channel:
- The Wi-Fi device switches to a different channel automatically.
- This prevents interference with critical systems.
Example in IT environment:
- A Wi-Fi access point in an office building is using channel 52 in the 5 GHz band.
- A radar signal is detected on channel 52.
- The access point moves to channel 56 automatically without disrupting users significantly.
B. Transmit Power Control (TPC)
- Wi-Fi devices adjust their transmit power based on the environment.
- Purpose: use the minimum power necessary to communicate effectively, reducing interference with other devices.
Example in IT environment:
- An access point in a small office room doesn’t need full power.
- Using TPC, it lowers power to cover just the office, avoiding interference with neighboring offices.
4. Where 802.11h is Used
- Primarily in the 5 GHz Wi-Fi band (used by 802.11a, 802.11n, 802.11ac).
- Required in countries with strict regulations like Europe (ETSI regulations).
- Often seen in enterprise networks where multiple Wi-Fi access points coexist near sensitive equipment (like in hospitals, offices, or data centers).
5. Why It Matters for CompTIA Exam
For the Network+ exam, you need to know:
- Purpose: 802.11h ensures Wi-Fi devices follow regulatory rules in the 5 GHz band.
- Key Features:
- DFS (Dynamic Frequency Selection) – automatically changes channels to avoid interference.
- TPC (Transmit Power Control) – adjusts power to avoid interference.
- Regulatory Impact: Helps Wi-Fi coexist with radar, weather monitoring, and other high-priority devices.
- Practical Outcome: Wi-Fi networks are more stable and compliant in restricted environments.
6. Quick Exam Tip
If a question mentions:
- 5 GHz Wi-Fi avoiding radar interference → Think 802.11h.
- Automatic channel change or power adjustment → Think DFS and TPC.
- Regulatory compliance in Wi-Fi → Also 802.11h.
✅ Summary Table for Students
| Feature | What it Does | Why it Matters |
|---|---|---|
| DFS | Detects radar signals & changes channels | Prevents interference with critical systems |
| TPC | Adjusts transmit power | Minimizes interference with other devices |
| Regulatory compliance | Ensures devices meet country rules | Wi-Fi is legal and safe to use |
This is exactly what you need to know for CompTIA Network+ exam about regulatory impacts and 802.11h.
