Frequency Bands and Non-Overlapping Channels

Introduction

Wi-Fi networks don’t just “work by magic.”
They rely on specific frequency bands and channels that make communication possible.

Based on the 802.11 WLAN standards, there are two main frequency bands:

  • 2.4 GHz Band: 2.4 – 2.4835 GHz
  • 5 GHz Band: 5.150 – 5.825 GHz, divided into four sub-bands:
    • 5.150 – 5.250 GHz
    • 5.250 – 5.350 GHz
    • 5.470 – 5.725 GHz
    • 5.725 – 5.825 GHz

These bands are where Wi-Fi devices “talk” to each other and exchange data.

  • The 2.4 GHz band covers larger areas and penetrates walls better, but it suffers more from interference.
  • The 5 GHz band provides faster speeds and more channels, but with a shorter range.

Let’s start with the 2.4 GHz band, the one most common in everyday Wi-Fi.

2.4 GHz Band

The 2.4 GHz band ranges from 2.4 GHz to 2.4835 GHz and is commonly used for Wi-Fi networks.

Diagram of 2.4 GHz Wi-Fi band showing channel distribution and overlap between channels 1, 6, and 11 for wireless networks.
Figure 1 – 2.4 GHz Wi-Fi Channels

How It Works:

  • The Access Point (AP) decides which channel to use.
  • Devices connect to the AP and follow its channel selection.

Understanding Channel Interference

Even though Wi-Fi channels are 5 MHz apart, each channel is actually 22 MHz wide.

Issue:

  • If an AP is on channel 1, its signal overlaps with channels 2, 3, 4, and 5.
  • This overlap creates interference, slowing down network performance.

Non-Overlapping Channels

Solution: Use channels 1, 6, and 11 to avoid interference.

Diagram showing non-overlapping Wi-Fi channels 1, 6, and 11 with access points to avoid interference in 2.4 GHz networks.
Figure 2 – Non-Overlapping Channels

Example Setup:

  • AP 1 on channel 1
  • AP 2 on channel 6
  • AP 3 on channel 11

This setup ensures each AP operates without interference.

Watch Out for External Interference

Other devices using 2.4 GHz can disrupt Wi-Fi performance:

  • Microwaves
  • Bluetooth devices
  • Smart home IoT gadgets
Microwave, Bluetooth device, and radio causing external interference to 2.4 GHz Wi-Fi signals.
Figure 3 – External Interference Sources

In larger networks, channel planning is critical to avoid interference.

5 GHz Band

The 5 GHz band is widely used in high-performance networks because each channel is non-overlapping by default. This structure allows multiple access points (APs) to operate simultaneously on different channels without causing interference.

Each channel in the 5 GHz band is 20 MHz wide by default.

5 GHz Wi-Fi band channel allocation chart showing UNII-1, UNII-2, and UNII-3 frequency ranges.
Figure 4 – 5 GHz Band Channel Structure

How Channels Are Structured in the 5 GHz Band

In the 5 GHz band, channels are numbered in increments of 4, starting with channel 36. This means the sequence of channels looks like this: 36, 40, 44, 48, 52, 56, and so on.

Because each channel occupies 20 MHz without overlapping adjacent channels, access points using different channels can function independently in the same space without interference.

Channel Bonding in the 5 GHz Band

In the 5 GHz band, channels can be bonded together to form wider channels, multiplying the data rate:

  • A 40 MHz channel bonds two adjacent 20 MHz channels, doubling the data rate.
  • An 80 MHz channel bonds four 20 MHz channels, quadrupling the data rate.
  • A 160 MHz channel bonds eight 20 MHz channels, providing the highest throughput but using a large portion of the spectrum.

Channel bonding increases throughput but reduces the number of available channels. In dense environments with multiple APs, this can lead to limited channel availability.

Example of AP Deployment with 20 MHz Channels

Let’s put this into practice with a simple setup:

Diagram showing Wi-Fi access points on non-overlapping 5 GHz channels 36, 40, and 44 for optimal network performance.
Figure 5 – AP Deployment with 20 MHz Channels
  1. AP 1: Channel 36 (20 MHz width).
  2. AP 2: Channel 40 (20 MHz width).
  3. AP 3: Channel 44 (20 MHz width).

Since each AP uses a separate, non-overlapping channel, they can operate simultaneously without interfering with one another. This setup is ideal in an office or home environment where multiple APs are needed for coverage.

However, if you increase the width to 80 MHz, one AP could use channels 36, 40, 44, and 48 for a single connection. This reduces the number of available channels for other APs, potentially causing congestion.

Conclusion

To optimize Wi-Fi performance, remember:

  • The 2.4 GHz band has only three non-overlapping channels (1, 6, 11) and is prone to interference from overlapping channels and external devices.
  • The 5 GHz band offers non-overlapping channels by default, with each channel 20 MHz wide.
  • Channel bonding in the 5 GHz band increases throughput but reduces the number of available channels.

For the CCNA, focus on the differences between the two frequency bands and how channel selection affects performance.