Re: [RFCv1] mac80211: Adds Software / Virtual AMP 80211

[Mat Martineau <mathewm@codeaurora.org>]

Andrei and Johannes -

On Wed, 18 Apr 2012, Johannes Berg wrote:

> Hi Andrei,
>
>>> No, this is incorrect. If one device wants to connect on one
>>> channel, the other typically has to use the same channel. If one
>>> device wants to scan, the other will be affected. Some hardware may
>>> support switching around between two channels, but might also
>>> support more than 2 virtual interfaces, so again they won't be
>>> independent.
>> 
>> BTW: which devices can switch channels?
>
> None today, I'm working on it.
>
>>> Therefore, you need something managing all this concurrency. This is
>>> in a small part the driver which will enforce restrictions (it will
>>> reject new impossible things), but mostly the supplicant which can
>>> make policy decisions about which usage should win.
>> 
>> This doesn't sound like a rocket science to me. IMO this might be done in
>> drivers. Those drivers which can switch channels why do they need
>> wpa_supplicant involved making this decision?
>
> I don't think you understand.
>
> Say our device can do 3 virtual interfaces, on 2 channels. Then if the user 
> is connected to some managed network (say office network), one interface & 
> channel is used up. Now the user has AMP running, another channel might be 
> used up. Now the user wants to do P2P negotiation. Now the supplicant, which 
> is doing the negotiation, needs to know that it can negotiate only one of 
> those two channels, not any other. Or maybe P2P should win, then it might 
> disconnect the AMP or the managed connection. But all those are policy 
> decisions, so the driver can't really handle them.

I concur with Johannes...

All of the AMP PALs I've seen are restricted to using the current 
wireless channel if a wireless interface is active.  The consequence 
is that if you have two BT3.0+HS devices, and their wireless 
interfaces are associated with different APs on different channels, 
then they are unable to use AMP.

Trying to manage two active channels with a single-radio wireless 
devices is non-trivial -- there may be simultaneous beacons on 
different channels, for example.  I suppose it could be a different 
situation when a wireless device has independent radios for 2.4GHz and 
5GHz bands, but there's still a need to make decisions about which 
channel(s) to use and how they are to be shared.

--
Mat Martineau
Employee of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum