WiFi 802.11ac really compatible with 802.11n?

[killingtime]

Hi,

I've been looking at the new WiFi standard 802.11ac. It works on the 5GHz band (no 2.4GHz support), and data rates are huge. There are lots of ifs around just how much faster AC is over N; MIMO streams, interference from other users, channel bandwidth selected etc, but one aspect that's got me confused is backward compatibility.

The AC standard is meant to be fully compatible with the A and N standard, lots of documents report this (Cisco etc) but if AC is a 5GHz only standard, I don't see how it can be fully backward compatible with N, as N used the 2.4GHz band (mandatory spec), and 5GHz was optional spec.

Many N network adapters only came out using the 2.4GHz band, with 5GHz capable N adapters marketed as 'dual band' or 802.11agn instead of the more usual 802.11bgn (2.4GHz support only).

If AC really is only 5GHz capable, then there are going to be a lot of unhappy N users who find their Access Point isn't found in the network search.

Anyone see it differently?

 

[killingtime]

I found an article on Agilents website, that states:

The 802.11ac physical layer is an extension of the existing 802.11n standard, and maintains backward compatibility with it.

There's some interesting info on mandatory and optional parts of the (currently draft) AC standard.

So the 2.4GHz band must be supported on AC devices.

What confused me is that lots of people (including WiKi) talk about AC as a 5GHz standard only. That's only true if you operate in pure AC mode. The moment you put your AP into compatibility mode, it would have to go dual band.

I also see all current AC APs are being marketed as 'Dual Band', which makes sense.