[PATCH] wpa_supplicant: Prefer 5 GHz networks over 2.4 GHz networks.

Dan Williams dcbw at redhat.com
Tue Aug 16 18:50:22 EDT 2011


On Tue, 2011-08-16 at 10:43 -0700, Sam Leffler wrote:
> On Mon, Aug 15, 2011 at 3:41 PM, Dan Williams <dcbw at redhat.com> wrote:
> > On Fri, 2011-08-05 at 16:23 -0700, Gary Morain wrote:
> >> In scan.c, merge a channel's noise value into the scan results.  When comparing
> >> scan results, compute the signal-to-noise ratio and use it when available.
> >> Prefer a 5 GHz network if its SNR is really big (> 30) or if its SNR is
> >> relatively close to the other network's.
> >
> > Honestly I'd rather have something like a "bands" option on a
> > per-netblock basis, so you could do this:
> >
> > bands=5
> > bands=5,2
> > bands=2,5
> > bands=2
> >
> > ie, the connection manager can set whichever band it prefers, or leave
> > it out entirely to let the supplicant do whatever it's already doing.
> > The problem with micro-optimizations like this are that they often
> > break, and they aren't necessarily clear.  I'd advocate for simpler,
> > clearer rules here, with behavior set by the connection manager, rather
> > than continually more complicated matching rules in the supplicant
> > itself...
> 
> I'm trying to understand how this would be used.  The point of Gary's
> change is to prefer the 5GHz band only when two AP's have equivalent
> signal quality. (5GHz is considered better because it has
> non-overlapping channels, less likely to have interference, etc.)
> This is meant to improve the algorithm by which a BSS is selected.

Yeah, I guess that's different than I'm proposing.  But making this
decision is still a policy decision that I'm not sure should be done in
the supplicant.

> Also, specifying a preference on a per-netblock basis seems odd; when
> would you want to control band preferences only for a specific SSID?

I've had this request come up periodically.  If your institution uses
the same SSID between the 5GHz and 2.4GHz wifi networks, but you'd like
to always be on the 5GHz segment because it's less loaded.  But other
places you may not want to be on the 5GHz network.  It really is a
per-SSID (ie per network) preference.

> You can lock down a netblock using bssid= and assign priority though
> it might be painful to list all the AP's in an ESS.  If we really want
> to add this complexity it seems like it belongs per-interface or
> global (or at compile-time).

I disagree.  It's not global to the entire decision, it's specific to
the netblock.  You may not always want to prefer 5GHz networks
everywhere you are.  The problem with the freq= parameter is that to
achieve this behavior you'd have to list *all* the frequencies in the
5GHz and 2.4GHz range, while using bssid= is a no-go because the
situation where you want this behavior is one where there are a ton of
APs around.

Dan



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