📘 CCNA 200-301 v1.1
1.11 Describe wireless principles
1.11.a Nonoverlapping Wi-Fi Channels
Wireless networks use radio waves to transmit data.
These radio waves are divided into frequency bands and channels.
- A frequency band is a range of frequencies Wi-Fi uses to communicate.
- A channel is a smaller range inside that band, like a specific “lane” for wireless data.
Different Wi-Fi devices use different bands and channels to send and receive data.
If two nearby Wi-Fi networks use the same or overlapping channels, their signals can interfere, causing slow performance or disconnections.
So, to have efficient and stable Wi-Fi, we use nonoverlapping channels — channels that do not share frequencies with each other.
2. Wi-Fi Frequency Bands
There are two main frequency bands used for Wi-Fi:
| Frequency Band | Common Wi-Fi Standards | Channels Available | Common Use |
|---|---|---|---|
| 2.4 GHz | 802.11b, 802.11g, 802.11n | 14 total channels (but 11 used in most countries) | Longer range, slower speed |
| 5 GHz | 802.11a, 802.11n, 802.11ac | More than 20 channels | Higher speed, shorter range |
The 6 GHz band (802.11ax / Wi-Fi 6E) is newer and used for very high performance, but it’s optional in CCNA-level detail.
3. 2.4 GHz Band – Nonoverlapping Channels
2.4 GHz Overview
- Each channel in 2.4 GHz is 22 MHz wide.
- Channels are spaced 5 MHz apart.
- Because of this spacing, most channels overlap with each other.
Overlapping channels interfere with each other’s signals.
To avoid interference, we use only channels that do not overlap.
Nonoverlapping Channels in 2.4 GHz
In most countries (like the U.S.), we use channels 1, 6, and 11 as the three nonoverlapping channels.
| Channel | Center Frequency | Overlaps With | Nonoverlapping With |
|---|---|---|---|
| 1 | 2.412 GHz | Channels 2–5 | Channels 6, 11 |
| 6 | 2.437 GHz | Channels 4–8 | Channels 1, 11 |
| 11 | 2.462 GHz | Channels 9–13 | Channels 1, 6 |
So, when setting up multiple access points (APs) in the same area, you should assign:
- AP1 → Channel 1
- AP2 → Channel 6
- AP3 → Channel 11
This ensures they don’t interfere with each other.
✅ Exam Tip:
For 2.4 GHz, remember only 3 nonoverlapping channels: 1, 6, and 11.
4. 5 GHz Band – Nonoverlapping Channels
The 5 GHz band has many more channels and much less overlap, which is why it’s preferred in enterprise Wi-Fi.
Channel Details
- Each channel is 20 MHz wide (can be bonded for 40, 80, or 160 MHz in newer standards).
- Channels are separated by 20 MHz, so they don’t overlap like in 2.4 GHz.
- Available channels depend on country regulations.
Common Nonoverlapping Channels in 5 GHz
| Channel Range | Frequency Range (approx) | Notes |
|---|---|---|
| 36–48 | 5.180–5.240 GHz | UNII-1 (indoor use) |
| 52–64 | 5.260–5.320 GHz | UNII-2 (requires DFS) |
| 100–144 | 5.500–5.720 GHz | UNII-2 Extended (DFS) |
| 149–165 | 5.745–5.825 GHz | UNII-3 (outdoor allowed) |
DFS = Dynamic Frequency Selection — required to avoid radar interference in some frequencies.
Because of the wide spacing, the 5 GHz band has many nonoverlapping channels, especially for 20 MHz channel width.
If you use 40 MHz, 80 MHz, or 160 MHz, the number of available nonoverlapping channels decreases (since they combine multiple smaller ones).
5. Channel Bonding (in 802.11n and newer)
Channel bonding means combining multiple 20 MHz channels into one larger channel to increase data rates.
- 20 MHz = one channel
- 40 MHz = two combined channels
- 80 MHz = four combined channels
- 160 MHz = eight combined channels
While bonding increases speed, it reduces the number of available nonoverlapping channels, and may cause interference if not carefully planned.
Example in an IT setup:
- A small office with few users might use 80 MHz channels for high speed.
- A large office with many APs might use 20 MHz channels to avoid interference.
6. Why Nonoverlapping Channels Are Important
When multiple Wi-Fi networks operate in the same physical area (for example, multiple access points in a company), overlapping channels cause co-channel interference (CCI) and adjacent channel interference (ACI).
Co-Channel Interference (CCI):
- Happens when two access points use the same channel.
- Devices must take turns communicating, reducing performance.
Adjacent Channel Interference (ACI):
- Happens when access points use overlapping channels.
- Signals interfere with each other’s frequency, causing packet loss and retransmissions.
Solution:
Use nonoverlapping channels to prevent both types of interference.
This allows smooth communication, stable connections, and better Wi-Fi speed.
7. Summary Table
| Band | Total Channels | Channel Width | Nonoverlapping Channels | Common Channel Numbers |
|---|---|---|---|---|
| 2.4 GHz | 11 (in most countries) | 22 MHz | 3 | 1, 6, 11 |
| 5 GHz | 24+ (varies by country) | 20 MHz | Many | 36, 40, 44, 48, 149, 153, 157, 161, 165 |
8. Exam Focus Points
For the CCNA 200-301 exam, make sure you can:
- Identify which channels are nonoverlapping in 2.4 GHz (1, 6, 11).
- Recognize that 5 GHz has many nonoverlapping channels.
- Understand that overlapping channels cause interference.
- Understand channel bonding increases bandwidth but reduces the number of available nonoverlapping channels.
- Know DFS and UNII bands terms at a basic level.
✅ Key Takeaways for Students:
- Wi-Fi uses channels within 2.4 GHz and 5 GHz frequency bands.
- Overlapping channels = interference = slow Wi-Fi.
- Use nonoverlapping channels (1, 6, 11) for 2.4 GHz.
- 5 GHz has more channels and fewer interference issues.
- Plan channel use carefully when deploying multiple access points.
