Re: DFS implementation status update

[Simon Wunderlich <simon.wunderlich@s2003.tu-chemnitz.de>]

[-- Attachment #1: Type: text/plain, Size: 2499 bytes --]

Hello Victor,

thank you for the update, it is nice to hear that you're working on this!

I have a few questions regarding your implementation and whether you have
some features on your list for possible future extensions, please see below.
If you don't have them on your list, I could work on some of them too, please
don't take this as if I'd expect that you need to do that. ;)

On Tue, Jan 10, 2012 at 10:22:44AM +0200, Goldenshtein, Victor wrote:
> Main DFS procedures
> ===================
> 
> 1. Hostapd gets driver's DFS capabilities.

Do you plan to support IBSS/Ad-Hoc as well?

> 
> 2. If 80211h is enabled in the hostapd.conf and the driver supports
> one of the above radar detection techniques, hostapd may use DFS
> channels.

I guess you're implementing the channel switch part for now, any plans
on the rest of 802.11h? (station measurement, TPC, etc). 

> 
> 3. Hostapd selects an operational channel (default from hostapd.conf),
> if selected channel is a DFS channel, hostapd sends
> start_radar_detection command to the device/driver which starts
> monitoring for radar interference while hostapd sets a timer for a CAC
> (Channel Availability Check) time, which is 60 seconds (DFS spec).
> 
> 4. As CAC timer expires and no radar has been detected, hostapd may
> continue with the init flow, otherwise if interference is detected
> hostapd randomly selects another channel (later on this can be changed
> to ACS). If the new channel is also a DFS channel hostapd performs CAC
> once again, while the original channel is added to a "black list" for
> a period of ''No-Occupancy'' time (time that the channel can't be
> used/selected).

Do you plan to allow band selection or channel selection? For example,
it would be desirable to only select indoor channels or outdoor channels,
exclude weather channels (5600-5650 MHz) or only select a specific subband where
high tx power is allowed.

I'm also not sure if pre-selecting a start channel is conforming to 
ETSI EN 301 893 V1.5.1 - as I'd interpret it (but I might be wrong), a
channel should always be randomly selected from the available channel list
(4.7.2.6 Uniform Spreading) - there is not test specified for this though (Annex A).

I'm also missing the channel switch announcement for associated clients in your
flow chart, but maybe you skipped this to keep it simple. It looks like a good approach, 
I'm really looking forward to your patchset.

Cheers,
	Simon

[-- Attachment #2: Digital signature --]
[-- Type: application/pgp-signature, Size: 198 bytes --]