Re: virtual wireless interfaces / WDS

On Mon, Apr 14, 2003 at 05:00:10PM -0600, M. Warner Losh wrote:
> In message: <[email protected]>
>             David Young <[email protected]> writes:
> : 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?
> 
> Not entirely.

  The argument for sta(4) is that link conditions in a BSS are not
  always alike for every STA, so it is not always desirable for STAs to
  have configuration and statistics in common. Contrast this with a wire
  ethernet where, no matter where you attach a station, link conditions
  are virtually the same.  A single broadcast interface suits the latter
  in the way that it does not suit the former.

  Put another way, a wireless interface is in many ways an aggregation
  of point-to-point links, not a broadcast link.

  (Perhaps meaningful comparisons can be drawn between wireless and VCs
  in an ATM network or VLANs in an Ethernet; I am not too familiar with
  those technologies.)

  But besides the link conditions consideration, sta(4) is a handy way
  to expose STAs' status and configuration (WEP keys, media, data rate,
  powersave state, etc.) to the operator and to daemons.

  I choose to model wireless links with virtual network interfaces because
  a network interface is a familiar abstraction to BSD operators, because
  there are opportunities for code re-use, and because it lets me more
  effectively use already-existing, unmodified utilities and daemons
  (ifconfig, routed, ospfd, etc.) without modification in 802.11 networks.

> How does one put all the sta(4) things into a bridge(4)?  These things
> come and go on a regular basis.

  Off the top of my head: a daemon listens to the wi(4) parent for the AP
  to send the STA an association response or, in an IBSS, for the STA to
  send a beacon or any other packet. Then it creates a sta(4), adds it
  to the bridge, and attaches it to the wi(4), in that order. Sometimes
  the daemon will not create the sta(4) and add it to the bridge before
  the STA sends a packet. I think that is ok if the wi(4) belongs to
  the bridge, also.

  It occurs to me that a sta(4) can and should be exempted from spanning
  tree computations.

Dave

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