Sunday, September 11, 2011

Wireless update - DFS wrapup

Now that the DFS work has been completed, tested and paid for, I guess I can now write about it.

The DFS work was sponsored by KBC Networks, a wireless product company based in the USA. The eventual aim is to integrate this DFS work into their mesh product. I can't talk any further about what's going on there, except to say that they very graciously allowed the FreeBSD work to be released back to the community.

So FreeBSD now has:

  • Updated DFS master (hostap) and DFS slave (station) support in net80211;
  • Updated regulatory domain entries for the USS ("FCC3");
  • Changes to the ath(4) driver to fix corner cases in DFS master and DFS slave modes.
All of this work is now in FreeBSD-HEAD and will be available in FreeBSD-9.0.

Future work will hopefully include DFS IBSS and DFS mesh functionality. This work didn't include 802.11n DFS - but that's not too difficult to do (hint: if someone would like the mini-project, please contact me!)

Along with that was a port of the Atheros radar detection code (from Fusion, their earlier carrier codebase) which is currently proprietary. The Linux wireless developers have been working towards DFS compliance for a while, but haven't yet integrated working radar detection into any drivers. So this was a good exercise in uncharted territory to see how difficult it would be.

It turns out that it wasn't terribly difficult at all. After spending a bit of time chasing down missing bits in the FreeBSD atheros HAL driver, the third party doing said radar code porting managed to get FreeBSD doing radar detection at the same level as the commercial firmware.

During this particular exercise we discovered a few things about the software radar detection, which I think the community at large should know about.

The process of getting a device FCC/ETSI certified is just that - the whole device. This includes the NIC, the internal cabling, the enclosure, the antenna(s) and any external cabling. Maybe even whether it's indoors or outdoors, I wasn't involved in that. This likely has repercussions for any open source DFS implementation - although the DFS machinery in a specific FreeBSD release could be certified, the software based radar matching code may need tuning for the specific hardware used. So it's likely that Linux/FreeBSD can't just publish a single "ath_dfs" source module that will work for all Atheros NICs - or even a single NIC. It's likely that things will need tuning based on how a given NIC is used, the environment it's intending to be used in, and a variety of other things I haven't even thought about yet.

So if/when this does occur, the open source wireless community (FreeBSD, Linux, NetBSD, OpenBSD, DragonflyBSD, whatever..) will have to be responsible and not just simply run an "ath_dfs" radar module, assuming that it works. For complete, correct, certified behaviour, it's going to likely need the community to work with vendors and users in order to create "working, certified" combinations of hardware and software. So, if a vendor (call them U) wishes to release a new "SR-M" NIC, they could work with the open source wireless community to create a certified NIC+board+enclosure+antenna combination and publish a set of radar patterns and settings. They could leverage the proposed existing open source radar pattern matching code and simply add whatever configuration is needed. Users should then be responsible - they should only use the given radar dfs code with the correct setup. If they wish to run a modified setup, they should work with the vendor and upstream community to get things re-certified.

This way the DFS and radar pattern matching code is open source - what then changes is the radar patterns and configuration, which depends upon the NIC, cabling, antenna and environment.

For home users/developers, having a set of certified hardware combinations will make things easier for them.

For commercial vendors, if they adopt open-source FreeBSD or Linux on their platforms then (in an ideal world) they could get their equipment certified once (which as I note, they have to do anyway) and then publish the relevant radar patterns and configuration. The rest of the driver (including the radar pattern matching source and the general DFS support) would already be open source. Users can then use this when running their own kernel/distribution/OS on that platform.

I know this is all very fluffy and assumes that vendors/users act in a responsible, open manner. But I think this is what needs to occur if the open source community wishes to see stable, supported DFS regulatory compliance in their open source project.

To wrap this up, if you're a company wishing to leverage open source on their (Atheros) wireless platform and are interested in regulatory compliance, please drop me a line. I'll put you in contact with the relevant people inside Qualcomm Atheros to discuss how to best achieve this.

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