Frequency Bands and Non-Overlapping Channels

1. Introduction

📡 Wi-Fi-enabled devices communicate by using specific channels within their frequency bands.

You might be thinking, “What are channels and frequency bands? I don’t understand this!” You’re not alone—when I first learned this, I was confused too. But don’t worry, I’m here to make sure everything is clear and simple!

Wi-Fi networks operate within two main frequency bands based on 802.11 WLAN standards:

  • 2.4 GHz Band: Ranges from 2.4 GHz to 2.4835 GHz.
  • 5 GHz Band: Ranges from 5.150 GHz to 5.825 GHz, further divided into four smaller sub-bands:
    • 5.150 GHz to 5.250 GHz
    • 5.250 GHz to 5.350 GHz
    • 5.470 GHz to 5.725 GHz
    • 5.725 GHz to 5.825 GHz

📢 These frequency bands are where your Wi-Fi devices “talk” to each other and send data.

Key Differences:

  • The 2.4 GHz band covers larger areas and passes through walls easily but suffers from interference.
  • The 5 GHz band offers faster speeds and more channels but has a shorter range.

💡 For the CCNA, focus on understanding the two main frequency bands: 2.4 GHz and 5 GHz.

2. 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.

802.11 Standards 2.4 GHz

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.

Non Overlapping Channels in the 2.4 GHz Bands

💡 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
Wireless External Interference

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

3. 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 Bands

🔍 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.

Key trade-off: Bonding channels provides higher throughput but reduces the total number of available non-overlapping 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:

Non Overlapping Channels in the 5 GHz Band
  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.

4. 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.

802.11 Frames