On Jul 17, 2008, at 5:36 AM, RB wrote:
That's what I was thinking: isn't it a problem to have to APs with
same SSID
(and maybe the same channel) in reach of each other?
Don't the clients get confused? Or are the drivers usually smart
enough not
to flap between the two?
Many righteous WLAN cards have the election process hard-wired,
well, in firmware, but even these can be over-ridden for the most part.
and some can even be tweaked by driver.
Others are under complete control of the driver (anything that uses
athX in FreeBSD, for example)
Others that are the radio equivalent of a WinModem do it completely
in software,
Uh, no. Sorry. You're not going to run the receiver section of an
802.11 PHY in software on your laptop.
Now, some of them (anything that uses athX in FreeBSD, for example),
implement a very large part of the 802.11 MAC
in software. Take a look at the net80211 layer in FreeBSD.
but the net result is that [nearly] all of them are wise enough to
roam only when
necessary.
Software gets to decide 'when' in nearly all ases.
Adjacent BSSIDs (APs for this discussion) on the same
channel can make it hard for some devices to elect and they will
waffle, but that can usually be solved by moving two feet and
channelization, which itself is a lecture for another day/place.
Er...
adjacent BSSIDs in the same ESSID make roaming easy. Putting them co-
channel makes roaming even easier (see previous message.)
Note that there is some frequency-specific fading even in a static
environment. Start moving things around (even if the radios don't move)
and the fading gets worse. This is why you (and the radios) see SNR
values bounce up and down.
One issue is that some (stupid) clients will re-run DHCP on every
association event, but otherwise, the 802.11 standards are mostly
in place for all but seamless walking-speed roaming. See 802.11f/
IAPP, or here: http://www.cs.umd.edu/~mhshin/iapp/
See also: http://www.freebsd.org/projects/ideas/#p-wpa2preauth, and
http://www.freebsd.org/cgi/cvsweb.cgi/src/contrib/hostapd/iapp.c?rev=1.1.1.3
(getting this work (or similar) into freebsd would be a win,
especially if it got adopted into pfSense)
Jim
