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

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

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

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

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

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 This is something TGr should solve 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

Pretty Good Handoffs Benefits of PGH Drawback of PGH September 2004 Pretty Good Handoffs Benefits of PGH No new key hierarchies No new or overloaded management frames No change to ASs necessary Does not break, change, or modify the way existing protocols work Cuts down on code bloat 100% KISS-compliant! It satisfies this TG’s definition of “fast” No new protocol necessary Drawback of PGH Dan Harkins, Trapeze Networks