Virtual WiFi on Linux?

Jean Tourrilhes jt at hpl.hp.com
Wed Oct 19 15:00:58 EDT 2005


On Wed, Oct 19, 2005 at 08:24:04AM -1000, Jim Thompson wrote:
> 
> On Oct 19, 2005, at 7:35 AM, coderman wrote:
> 
> >On 10/19/05, Jean Tourrilhes <jt at hpl.hp.com> wrote:
> >
> >>... Basically, you connect to multiple network at once. Of
> >>course, because you have only a single transmitter/receiver in your
> >>hardware, what you really do is time slotted hopping, you  
> >>periodically
> >>hop between each AP.
> >>
> >
> >with multiple radios this becomes more efficient/effective.  MIMO plus
> >multiple devices for example. (I've used as many as 8 mini-PCI radios
> >on a single host and you could probably double this if you tried hard
> >enough.)
> 
> Great.
> 
> Please show us how you run more than one radio in 2.4GHz without  
> impacting the noise floor of both.
> 
> Without co-ordination, this doesn't work.
> 
> (I've been through this discuss so many times that I wince every time  
> it comes up now.)

	Performance is not everything. Sometime, you want more
flexibility. I can see scenario where I would be willing to trade
performance for the flexibility given by this scheme. I can see
scenario where I would even be willing to use the AP scheduling
described above, which in term of performance is really a drag.

> >one of my favorite ideas for AP virtualization is client mobility:
> >instead of worrying about association/authentication hand off between
> >distinct AP's as a client moves, make each client a supplicant of
> >their own virtual AP that moves from radio to radio as they move; to
> >them it would appear to be a single AP with an incredibly pervasive
> >signal :)
> 
> This wasn't a big deal until WPA/WPA2 showed up. If the STA knows  
> its still part of the same BSS, then
> there isn't much reason to re-run things like DHCP.   With WPA, being  
> able to 'virtualize' the AP across a set of APs means that
> you don't have to get all that encryption state going again, and  
> thats a major bonus.

	Correct.
	And personally, I believe there may be other way to deal with
this particular problem that may be simpler. Usually, fixing things in
the infrastructure ends up being more efficient. The APs can easily
share security info without having to create a distributed AP. It's a
shame that IAPP got shot down.

> But ... given that there is code released soon that *can* serve as a  
> basis for this kind of technology, the "WiFi switch" vendors
> had better watch out.  :-)   (they typically simplify the problem by  
> having most of the 802.11 stack run in a central controller,
> and use Ethernet to extend all but 802.11's "control frames" back to  
> this central (virtual) AP.

	Maybe, maybe not. There are many legacy 802.11 clients that
you want to support, especially with 802.11 going into embedded
systems, which are usually difficult to upgrade. Entreprise have to
update their 802.11 infra every few years just to keep up with the
array of new features the vendors throw in, removing the need for a
single feature won't make that much difference.

> jim

	Jean



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