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

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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

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

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