1. Multiple Concurrent Associations as a Means of Doing Fast Roaming
May 2004
IEEE /0000r0
May 2004
Multiple Concurrent Associations as a Means of Doing Fast Roaming
Bob Beach
Symbol Technologies
Bob Beach
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2. What makes roaming slow?
May 2004
What makes roaming slow?
The association handshake is simple and fast
Two packet exchange and we are associated
It’s the stuff after association that is painful and takes time
Authentication and key negotiation/security context
QoS negotiation
If we could just do the association handshake, then roaming, at least the active transitioning part, would go quickly
Bob Beach

3. What Does “Being Associated” Mean?
May 2004
What Does “Being Associated” Mean?
Defines the BSS the STA addresses packets to and receives packets from
Enables the AP to forwards packets from/to a station
DS to RF, RF to DS, RF to RF
AP assigns AID
Used for polling, etc.
May trigger authentication process
Strictly speaking, association is independent of authentication and QoS negotiation
Bob Beach

4. Why cannot a STA be associated with multiple APs concurrently?
May 2004
Why cannot a STA be associated with multiple APs concurrently?
The most obvious problem
Multiple APs will forward packets for a given STA
Wastes bandwidth
Actually the APs will not forward the packets since most wired infrastructures will prevent it
Ethernet switches will forward packets only via one port to one AP
If one tells the infrastructure, the AP will not receive any traffic for the MU and hence the AP will have nothing to send
A few other problems
AID usage/TIM fields
2K STAs per AP are sufficient
Memory space within AP
Its cheap
QoS reserved bandwidth
Could be released/timed out
Bob Beach

5. How might multiple associations work?
May 2004
How might multiple associations work?
Several possible approaches, this is just one
Associate and authenticate just like one does now for all APs of interest
Maintain key, sequence number, etc.. Information for all of them
“Cost” is mostly memory space on STA
When one wants to roam send a packet to infrastructure via new AP
An empty data packet with my Source Address
Wired switches will reconfigure themselves accordingly to indicate my new location
This packet is secure since it is encrypted using keys of new AP
AP responds with a packet to indicate mode change
protocol changes
APs do not tell one another of roaming nor do they delete STA from internal data base
Cost is mostly memory on AP
Bob Beach

6. From the AP’s perspective
May 2004
From the AP’s perspective
The STA is just “quiet” with no packets moving either direction
There is precedence for such modes in the PSP mode
STA goes away for potentially long period of time (minutes/hours)
STA can pick up again at any point in time
One might define a new mode “suspend”
Similar to PSP mode
Frees any QoS reservations
Bob Beach

7. May 2004
Conclusions
“Fast roaming”, at least the active transition part, may be accomplished with relatively simple mechanisms
We need to challenge to some of the basic assumptions of regarding what an association involves
Bob Beach