Friday, November 8, 2013

Referencing Wi-Fi Channel Numbers Correctly

It occurred to me today that many people still use the old Wi-Fi terminology for referencing wide channel numbers in the 5 GHz band. Since channel numbering changed with 802.11ac, I thought it might be helpful to get everyone on the same page when we're talking about channel number.

So here is a quick reference guide to referencing the 5 GHz Wi-Fi channels.

Wide channel numbering changed with 802.11ac:

  • 802.11n Channels (the "old" way)
    • One 20 MHz primary channel, with a channel extension above or below
    • 40 MHz Example: Channel 36, +1
    • 40 MHz Example: Channel 40, -1
    • 40 MHz Example: Channel 36+40
    • This terminology should no longer be used

  • 802.11ac Channels (the "new" way)
    • Reference the center channel frequency for the entire 40/80/160 MHz wide channel
    • Designate one 20 MHz portion of the wide channel as the Primary 20 MHz
    • 40 MHz Example: Channel 38 with Primary 20 MHz channel 36
    • 80 MHz Example: Channel 155 with Primary 20 MHz channel 149
    • 160 MHz Example: Channel 50 with Primary 20 MHz channel 44

Andrew von Nagy


  1. Is there a standard, short notation for the "new" way? In the "old" way you'd have "36, +1" (or 36+40), but I haven't seen any form of short notation to denote the wide channel along with the primary channel for 802.11ac channels. I think it would be very convenient to establish one.

    1. Hi Adrian,
      I agree, a short form notation would be really handy. I've been thinking about using the form "42p36" to indicate the wide channel and primary channel.


  2. Andrew, great reference, espec the 'visual' on DFS. But, can you explain why the 160 MHz primary 20 MHz channel is 44 and not 36? In the same light, how would you designate the 160 MHz primary 20 MHz channel?

    1. Any of the smaller 20 MHz channels within a larger 40/80/160 MHz channel can be designated as the primary 20 MHz channel. It is up to the administrator to decide. It comes into play when channels overlap and they need to back down to smaller non-overlapping channels. See my previous articles on 802.11ac for reference. The primary channel is also used to send broadcast management frames such as beacons and broadcast / multicast data traffic.

  3. How about C42P36/40 to describe centre/primary/width?

    1. Well, the channel number implicitly tells you the width.