Recommended Beacon Interval for 2.4GHz vs 5GHz dual band networks with single SSID

[Jouni Malinen]

On Mon, Jan 05, 2015 at 03:31:40PM -0500, Jeremy Ward wrote:
> Looking for a reccomendation as to what should be specified for a beacon
> interval on each wireless interface when using two cards under hostAPd, one
> operating at 2.4GHz the other at 5GHz, with the same SSID on each.
> 
> The goal is to increase the likelihood that an STA will see the 5GHz beacon
> before the 2.4GHz beacon, and thus associate with the 5GHz AP and not the
> 2.4GHz AP.

Please note that most station use active scanning on 2.4 GHz and
changing the beacon interval won't have almost any effect on them
finding the AP from the 2.4 GHz band. On 5 GHz, passive scanning is much
more commonly used, but even then, I'd assume there to be only a very
small difference when changing for AP discovery when changing the beacon
interval between reasonable values. It needs to be understood that
beacon interval changes will have significant drawbacks for other areas
by either increasing latency on power save data delivery or increasing
power consumption on stations.

> A number of enterprise-class dual-band APs use exactly this tactic to
> "entice" a dual-band STA to associate with the 5GHz radio, mostly because
> out in the wild, 5GHz is less encumbered than 2.4GHz and has close to 10x
> the amount of available spectrum (regulatory domain dependent, of course)

I would not recommend doing this for the purpose of trying to steer STAs
to 5 GHz. This is yet another doomed attempt at doing something with
vendor specific hacks on AP side. Proper way of providing guidance for
STAs is a mechanism that is actually designed and standardized for that
exact purpose and is used in co-operation by both the APs and STAs. BSS
transition management and neighbor reports are such examples.

-- 
Jouni Malinen                                            PGP id EFC895FA