virtual wireless interfaces / WDS

The other night I sketched out some benefits of adding two kinds of
virtual wireless interface to *BSD.

The first virtual interface type is probably familiar, since Linux has
it. Call it wds(4). It represents a link from AP to AP. A property of
a wds(4) is the RA field of the 4-address 802.11 header. You can bind a
bunch of wds(4) to a bridge(4) and run STP on it. Maybe you're familiar
with this notion in Linux.

The second virtual interface type I call a sta(4). Each host associated
with a host access point may get its own sta(4). Also, each host in
an Independent BSS may get its own sta(4). Reasons for sta(4): it is
useful to keep per-destination statistics, WEP keys, Tx power, and 802.11
parameters such as fragmentation threshold, RTS/CTS threshold, etc. I
think that this is all justified (necessitated, really) by the fact that
conditions on a wireless subnet are not ordinarily uniform, as they are
on a wired network, but some STAs may be more distant or they may have
weaker transmitters/receivers, they may or may not be mobile, etc.

Sta(4) lets one use an existing abstraction in BSD, the interface, to
get link-layer information into a routing daemon. Just for instance,
as soon as a STA disassociates, you may delete its sta(4), which will
provoke an RTM_IFANNOUNCE on a routing socket and also take some ARP
entries out of the routing table (I think). An RTM_IFINFO can indicate
severe packet loss. These sorts of indications are important for routing
in mobile wireless networks.

A sta(4) lets you track and control a station's data rate and media
(DSSS/OFDM).  I think that it will also let you set per-STA queueing
disciplines using, e.g., ALTQ (hmmm---may or may not be useful).

Like a wds(4), you will ordinarily put all the sta(4) into a bridge(4),
which will take the IP number.

Is the usefulness of sta(4) clear?

I imagine that the device attachment will look something like this,

  sta0 at wi0 ...
  sta1 at wi0 ...
  wds0 at wi0 ...

Your thoughts?

Dave

-- 
David Young             OJC Technologies
[email protected]      Urbana, IL * (217) 278-3933
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