1. doc.: IEEE 802.11-04/1072r0 Dan Harkins Trapeze Networks
September 2004
doc.: IEEE /1072r0
September 2004
Pretty Good Handoffs
Dan Harkins
Trapeze Networks
Dan Harkins, Trapeze Networks
Dan Harkins, Trapeze Networks

2. Pretty Good Handoffs This group has not defined the word “fast”
September 2004
Pretty Good Handoffs
This group has not defined the word “fast”
How do we know whether a proposal is actually a solution to the problem then?
But the ITU has: it’s 50ms
The number was not PDOOMA’d
Is a 50ms handoff “fast” for us? Is it possible to even do?
Dan Harkins, Trapeze Networks

3. Pretty BAD Handoffs Current handoffs are S-L-O-W Reasons
September 2004
Pretty BAD Handoffs
Current handoffs are S-L-O-W
Charles Wright showed (in 0989) handoffs from 2-8 seconds even without security!
Reasons
Active scanning is chewing up a significant portion of the handoff latency budget (shown by Areg Alimian and Bernard Aboba showed in 0377), especially bad for a/b/g devices
Doing an full 802.1X reauthentication is expensive
802.1X implementations and OSs are not optimized to do an efficient 4way handshake
Dan Harkins, Trapeze Networks

4. September 2004
Pretty Good Handoffs
What can be done to fix the problem with handoff latencies
Optimize the scanning function! Not in our charter, but is in TGk’s. And TGk is already addressing this problem.
Don’t do a full 802.1X reauthentication when handing off! Cache PMKs and just do a 4 way handshake.
Fix our 802.1X implementations to “fast switch” packets for the 4way handshake through our kernels.
Dan Harkins, Trapeze Networks

5. September 2004
Pretty Good Handoffs
Independent analysis (Bill Arbaugh from Univ of Maryland) shows it is feasible to do a 4 way handshake in under 25ms.
“neighbor list” from TGk can give a STA a list of valid APs to which a handoff should be made. This can drastically reduce scan times.
Possible to fit an optimized scan and 4way handshake in a 50ms budget without any protocol changes (and with room to spare)!
That’s a “Pretty Good” handoff
Dan Harkins, Trapeze Networks

6. Pretty Good Handoffs What about QoS?
September 2004
Pretty Good Handoffs
What about QoS?
(note to presenter: wave hands here)
Need some way to set up service (TSPECS) prior to handoff
TGk should help with identification of valid APs prior to handoff
What other kinds of state needs to be transferred, how long does it take to set-up and how critical is it?
Not sure at this point but security state is NOT one
Dan Harkins, Trapeze Networks

7. Pretty Good Handoffs TGk can optimize scan times
September 2004
Pretty Good Handoffs
TGk can optimize scan times
TGi already handles a quick and secure reconnect with PMK caching
We can get “pretty good handoffs” already
Dan Harkins, Trapeze Networks