Archived from groups: alt.internet.wireless (
More info?)
On Tue, 12 Oct 2004 17:27:04 -0500, "MousePad"
<adyoungentirely.too.much.junk.mail.in.my.mailbox@sbcglobal.net>
wrote:
>I'm trying to plan out a wireless network for a building, including multiple
>WAPs. I want users to be able to roam between access points seamlessly.
So does everyone else. Dream on.
>Maybe I'm just being dense, but I can't seem to find any information on
>exactly how to set this up. Google hasn't helped much.
There's plenty available with Google. Search for "wireless roaming".
The problem is that you'll find very little commodity hardware that
claims to do it seamlessly. There are no current specifications for
how to do roaming and how to handle the handoff.
IEEE 802.1f defines the best practices for wireless roaming.
http://standards.ieee.org/getieee802/download/802.11F-2003.pdf
802.1r is the proposed fast wireless roaming standard. I don't this
it's available for general consumption quite yet.
See article:
http://www.winnetmag.com/Windows/Article/ArticleID/23294/23294.html
There's a short list of vendors in the above article that provide
proprietary wireless roaming solutions.
>What I think I'm seeing is that you can connect multiple WAPs to a single
>wired router. The WAPs should be configured with the same SSID and
>encryption, but the broadcast channels would have to be different (if
>they're in range of each other).
Correct. Use the same SSID so that Windoze XP and other client will
automatically switch to the "best" access point signal if you select a
particular SSID as the "prefered" SSID. Actually, I don't think you
have to select preferred as once associated with an SSID, Windoze XP
SP2 will try to stay associated. The non-overlapping channels (1, 6,
and 11) are to prevent RF interference between WAP's.
>This would allow some sort of
>technological magic to happen between the WAPs and wireless devices, and
>roaming would occur without the user noticing.
Magic? Here's the problem. Your Windoze laptop client radio connects
to an access point, an associates an SSID with the access points BSSID
(same as MAC address of the wireless access point). Now, you move to
a different location, the signal evaporates, and you pickup another
access point with the same SSID. Just one problem, different MAC
address. Are you gonna give up on the old MAC address and switch to
the new address? Sure, but after how long a delay? Meanwhile, the
original access point still has your client radios MAC address in its
bridging table, and is furiously trying to get your attention. Your
laptop is still trying to talk to the old access point.
Eventually they will both give up, but if it takes too long, you may
find yourself with two (or more) access points trying to get your
attention. Meanwhile, the switch in the router is going nuts as your
client radios MAC address is seen moving from port to port. At least
this can be done fairly quickly. Anyways, lots of other things can go
wrong during roaming.
The usual solution is to use very short DHCP lease times, force a
disconnect when the client radio switches to a different access point,
and deliver a new IP address to the client via DHCP. This will drop a
connection in progress, trash a VPN connection, and ruin a VoIP phone
call, but will not really affect normal email and web browsing (other
than a small delay).
>Am I on the right track here?
Yeah, sorta. If you can tolerate disconnects and re-assigned IP
addresses when switching WAP's, then you're done. Just about anything
with control over the DHCP lease time will work. If you absolutely
want seamless roaming, you'll need to find a proprietary solution.
Plan on emptying your bank account.
Due to lack of detail on your proposed system, I don't wanna offer a
specific hardware recommendation. However, you might wanna look into
a "wireless switch" such as:
http://www.symbol.com/products/wireless/ws_5000_brochure.html
which are intelligent switches, with brain dead radios attached. With
all the brains in the central box, port switching and roaming is much
easier. See the section in the above URL for some detail on roaming.
--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831.336.2558 voice
http://www.LearnByDestroying.com
# jeffl@comix.santa-cruz.ca.us
# 831.421.6491 digital_pager jeffl@cruzio.com AE6KS
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