Virtual WiFi on Linux?

coderman coderman at gmail.com
Wed Oct 19 13:35:19 EDT 2005


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.)


>         To implement this on Linux, the Wireless Tools would be the
> least of your problems. What you would need to do is to extend IP
> aliasing. You create multiple virtual interfaces on top of your real
> interface (wlan0:0, wlan0:1, wlan0:2). You assign each of this virtual
> interface an ESSID (using regular Wireless Tools). Somehow, you need
> to put an AP scheduler between the virtual interfaces and the real
> interface, the scheduler can control the real interface using regular
> Wireless Tools, it check how much traffic there is on each virtual
> interface to decide how long to spend with each AP. Obviously, if you
> want the performance to not suck, you need fast AP switching
> (currently available only with HostAP, doable with any card using the
> kernel ieee stack).

it gets even uglier if you have to aggregate traffic across multiple
networks these AP's are connected to.  in that case you are looking at
something akin to mobile-IP with a home agent to act as your public
endpoint for sessions and manage complex datagram routing/aggregation
between virtual STA's, APs, out to home agent.

the linux TUN/TAP devices are helpful if you are dealing with a single
subnet/network for the multiple APs.


>         That would be a nice project, however you have to ask yourself
> if it is worth the effort (the example they present are far from
> compelling). I believe they might be some interesting applications of
> that along the line of Connection Diversity, but they are a few years
> down the line.

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 has its own share of technical difficulties, mainly the inter AP
protocol and backhaul for managing the scheduling of various virtual
AP's among a fixed set of radio devices. not to mention extremely
flexible hardware/driver requirements]

best regards,



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