Handoff with wpa_supplicant and madwifi driver

[Leonardo Maccari]

On Sat, Nov 19, 2005 at 01:14:45PM -0800, Stephan Schlumbohm wrote:
> Hi all,
> 
> I'm having serious trouble with the handoff from one access point to another using wpa_supplicant (stable 0.3.8 and development 0.4.6) with the madwifi driver (madwifi-ng latest svn snapshot from madwifi.org).
> 
> Both access points have the same ESSID and operate on the same channel and have the same security settings. In fact, those access points are mesh access points - both are connected to a FreeRADIUS server.
> 
> Authentication (Open, WPA-PSK, WPA-802.1X-TLS/PEAP/TTLS) works fine in this setup to each access point.
> 
> But, when I try to roam from one access point to another, wpa_supplicant does not initiate a reassociation request to the new access point. Instead, it disassociates the old access point, then it performs the scanning and then finally goes through a full new authentication with the new access point.

My experience says that scan time is not the real bottlenck, delay is
introduced by loss of conectivity _before_ triggering a new scan, then from
RADIUS authentication (multi-hop packets, worse in a mesh environment),
and finally some delays that I couldn't really explain after
authentication and before first EAPOL packet. Jouni said a few time ago
that a bug was cleaned that caused hostapd waste some time after
authentication.
Anyway if you use WPA/WPA2 you must renegotiate the PMK key (whatever
authentication method you use) and renegotiate the PTK/GTK.

> 
> This causes the handoff to take about 1.5 to 3 seconds. This is not acceptable and is not intended by the developers. A single channel handoff should take about 10 to 300 ms (depending on authentication).
> 

there is an old thread about handoff times that you might read in the
archives. 

a couple questions: how do you trigger handoff procedure from one AP to
another? and what does mesh access points means? how do they authenticate
each other ?

ciao,
leonardo.

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