ipw2200-1.1.3 and CVS HEAD 1.993

[Bill Moss <bmoss CLEMSON EDU>]

1. When the scan list contains 6 or more assess points, the scan list is 
not fully developed on the first scan after a cold boot. It usually 
takes 2 scans, sometimes 3, to fully develop a long scan list. The scans 
are fast, taking only about 0.4 seconds. An early version of NM, fired 
off two quick scans before trying to make a wireless connection. This no 
longer appears to be the case which causes some interesting problems 
when the scan list is long.

2. Wireless drivers typically scan based on one or more of consecutive 
missed beacons, successive retries, signal to noise ratio. ipw2200 uses 
only the count of consecutive missed beacons.  ipw2200 roaming is in two 
stages. In stage 1, ipw2200 remains associated, examines the scan list, 
and tries to find a better assess point. If it finds one, it passes to 
stage 2 in which it disassociates, and runs the test for a better access 
point again. If it finds a better access point, it tries to associate 
with it, other wise it remains in the disassociated state. If the module 
option associate=0 is set, ipw2200 will not make any further attempts to 
connect. If the default option associate=1 is set, ipw2200 will begin to 
scan (about once every 0.4 seconds), and will try to connect to a 
suitable access point in its scan list. Since this behavior duplicates 
code in NM, I recommend setting associate=0 so that NM alone generates 
scan requests.

3. When I walk between my office and the next building, ipw2200 roams 
and switches access points in less than a second and NM is not even 
aware of the change.

4. If I walk out of access point range, ipw2200 first roams and then 
disassociates. Within a few seconds, NM manager will pick up this 
change, deactivate wireless (which includes releasing the dhcp lease), 
and will start to search for an access point. If no access point is 
found within the timeout period, NM will show the no-connection icon. If 
you walk back into range of an access point, NM will not attempt to 
re-connect. A forced connection using the NM menu is required (select 
the wireless network you want to connect to).

5. Without standardized driver reporting of signal to noise ratio, 
missed beacons, or successive retries, NM is limited in what it can do 
with respect to roaming or filtering out weak access points from its 
scan list.

6. The proposed capwap standard will allow an access point with a single 
bssid, to broadcast a public essid and respond to up to 16 hidden 
essids. At our campus convention center, we have access points that are 
broadcasting an unencrypted guest essid and also the campus encrypted, 
hidden essid, both with a single bssid. To deal better with this 
scenario, a boolean 'broadcast' key could be added to Gconf. The value 
should be set within the scan processing function, not later. When NM 
tries to resolve hidden essids by matching bssids, NM should only look 
at the networks in Gconf which are hidden (broadcast value false).

--
Bill Moss
Alumni Distinguished Professor
Mathematical Sciences
Clemson University