1. IAPP handover scenarios
May 2000
doc.: IEEE /127
May 2000
IAPP handover scenarios
Gary Spiess
Gary Spiess, Intermec Technologies
Gary Spiess, Intermec Technologies

2. Necessary and sufficient and handoff sequence (baseline)
May 2000
doc.: IEEE /127
May 2000
Necessary and sufficient and handoff sequence (baseline)
1) Station issues association request to new AP.
2) New AP sends the association response to the station.
3) New AP sends multicast handover request to old AP.
4) If Old APs association with the station is younger than a handover hold-down period (e.g. 5 seconds), the Old AP sends disassociation to station. If old association is older, disassociation has no benefit. 3
New AP
Old AP 2 4
Potential errors
Handover request is lost
Benefits
No handover response
Can be adapted to non stations
Handover request heard by all in broadcast domain
Drawbacks
Handover blocked by routers 1
Station
Gary Spiess, Intermec Technologies
Gary Spiess, Intermec Technologies

3. Using an alert to recover from a lost handover
May 2000
doc.: IEEE /127
May 2000
Using an alert to recover from a lost handover
1) Old AP discards a frame for a station, which should have responded. Since it queued the frame for the station, it saw no frame from the station (no control, data, or management).
2) Old AP includes station in list of potentially lost handovers in a multicast announce frame (an alert). This is rate limited to prevent announce storms.
3) Any AP that has an association with the station regenerates a handover that needs no response. 2 3
New AP
Old AP 1
Station
Advantages
Heals the system shortly after an old AP receives traffic destined to a station for which it missed the handover.
Disadvantages
False alerts will happen (could be considered diagnostic information)
Gary Spiess, Intermec Technologies
Gary Spiess, Intermec Technologies

4. Handover with optional response from old AP
May 2000
doc.: IEEE /127
May 2000
Handover with optional response from old AP
3) Old AP makes a unicast response to a handover request from the new AP.
4) New AP waits for old AP response before sending association response to station. 2 3
New AP
Old AP 4
Additional potential errors from baseline
Handover response is lost or obsolete
Additional benefits from baseline
Transfers useful station information from old AP, e.g., QoS parms (migratory database)
Additional drawbacks from baseline
Delay (or failure) of response to station due to handover response 1
Station
Gary Spiess, Intermec Technologies
Gary Spiess, Intermec Technologies

5. Handover with optional response from regional database
May 2000
doc.: IEEE /127
May 2000
Handover with optional response from regional database
2) Regional DB sees multicast handover request from new AP requesting information from the regional database.
3) Regional DB makes a unicast response to the handover request from the new AP.
4) New AP waits for Regional DB response before sending association response to station.
Regional DB 3 2
New AP
Old AP
Additional potential errors from baseline
Regional DB response is lost or obsolete
Additional benefits from baseline
Transfers useful station information from Regional DB, e.g., QoS parms
Additional drawbacks from baseline
Delay (or failure) of response to station 4 1
Station
Gary Spiess, Intermec Technologies
Gary Spiess, Intermec Technologies

6. May 2000
doc.: IEEE /127
May 2000
Summary of changes
Allow handover request to be multicast as well as unicast
Not trusting station to provide old AP address for unicast
Allow handover to include optional requests for specific information from a regional database and/or old AP
Supports regional and/or migratory database
Possible to implement things like QoS handover
Handover responses from the regional DB or old AP are not necessary unless responding to requested information
APs identify possible handover races when handover is received
must actively disassociate if own association is younger than hold-down
may passively disassociate if own association is older than hold-down
Cures obsolete handovers
Allow any AP to solicit a handover request with an “alert”
Cures lost handovers
Gary Spiess, Intermec Technologies
Gary Spiess, Intermec Technologies