doc.: IEEE r Submission November 2004 Bob Beach, Symbol TechnologiesSlide 1 Fast Roaming Using Multiple Concurrent Associations Bob Beach Symbol Technologies

doc.: IEEE r Submission November 2004 Bob Beach, Symbol TechnologiesSlide 2 Abstract This proposal enables fast roaming between Access Points by allowing Mobile Stations to establish “local”associations with multiple Access Points concurrently and providing a means for the mobile stations to quickly select which AP they want to use to access the DS.

doc.: IEEE r Submission November 2004 Bob Beach, Symbol TechnologiesSlide 3 Agenda Background Basic Model Proposed Protocol Enhancements Mobile Station Issues Summary

doc.: IEEE r Submission November 2004 Bob Beach, Symbol TechnologiesSlide 4 Associations in 1999 IEEE When a STA associates with a “1999” AP, four major actions result: –(A1) The AP allocates data structures for the STA –(A2) The AP accepts additional types of packets for the STA –(A3) The AP begins forwarding data to/from the DS for the STA –(A4) The AP notifies other APs and the wired infrastructure of the new “location” of the STA Two of these actions (A1 and A2) are “local” to the AP and two are visible to the “DS” (A3 and A4) For a 1999 AP, all of these actions take place at virtually the same time A STA may be associated with only one AP at time

doc.: IEEE r Submission November 2004 Bob Beach, Symbol TechnologiesSlide 5 The Effect of TGi and TGe on Roaming Tgi introduces new tasks that occur between the association step and the enabling of data transfer –Authentication and Key Derivation –These can significantly delay start of data transfer Tge introduces TSPEC negotiation –Cannot negotiate TSPEC until after association and Tgi tasks are complete –AP may not be able to grant TSPEC –STA may need to find yet another AP and try again –This process can further delay the start of data transfer

doc.: IEEE r Submission November 2004 Bob Beach, Symbol TechnologiesSlide 6 Associations with Tge and TGi There are now 6 actions involved in an association –(A1) The AP allocates data structures for the STA –(A2) The AP accepts additional types of packets for the STA –(A3) Authentication/key derivation –(A4) Negotiation of TSPEC –(A5) The AP begins forwarding data to/from the DS for the STA –(A6) The AP notifies other APs and the wired infrastructure of the new “location” of the STA Actions A1 to A4 are Local to the AP and do not involve the DS, Actions A5 and A6 involve the DS One could conceivably perform steps A1 to A3 with multiple APs without any impact to DS or current AP

doc.: IEEE r Submission November 2004 Bob Beach, Symbol TechnologiesSlide 7 Proposed Model The roaming problems caused by Tge and Tgi can be solved by allowing STAs to establish multiple “local” associations with different APs A “Local” association consists of actions A1 to A3 –The association is just between the AP and STA –The DS is not aware of the association –These are established as a background activity by the STA Actions A5 and A6 are triggered by the STA sending either an Action Frame or a Data Frame –Action Frame with Tspec allows conditional roaming –Data Frame allows secure roaming Action A4 may occur anytime after A3

doc.: IEEE r Submission November 2004 Bob Beach, Symbol TechnologiesSlide 8 From the STA’s Perspective The STA identifies “interesting” APs and performs actions A1 to A3 with them –This may take place once or on an ongoing basis The STA thus has a collection of ‘N’ ports to the DS with N-1 of them in “hot standby” A roam simply consists of a two data packet exchange with the AP of choice The STA maintains as many APs in this state as it desires. It may add or drop APs over time.

doc.: IEEE r Submission November 2004 Bob Beach, Symbol TechnologiesSlide 9 Proposed Protocol Enhancements Definition of “Data Transfer Gate (DTG)” Multiple Types of Associations Mechanisms for Enabling and Disabling the DTG Security Issues

doc.: IEEE r Submission November 2004 Bob Beach, Symbol TechnologiesSlide 10 Data Transfer Gate (DTG) Conceptually it controls transfer of data frames between DS and a STA Similar to, but distinct from, the data gate in 802.1x –802.1x data gate is controlled by the authentication process –The DTG is controlled by the STA –The two gates operate in “series”, both must be enabled to transfer data between DS and STA Enabled by frames sent from STA Disabled either by frame from STA or by an indication from another AP that the STA has roamed to it.

doc.: IEEE r Submission November 2004 Bob Beach, Symbol TechnologiesSlide 11 Multiple Types of Associations Two Types of Associations: Type 1 and Type 2 Type 1 Associations are identical to current Associations –DTG is automatically enabled –STA may establish it with only one AP at a time Type 2 associations are similar to current Associations except: –DTG is not automatically enabled –STA may establish it with many APs at a time –May have a defined lifetime

doc.: IEEE r Submission November 2004 Bob Beach, Symbol TechnologiesSlide 12 Obtaining Type 2 Associations AP advertises support for Type 2 associations via bit in Capability field in Beacons and Probe Responses STA uses Association and Reassociation Frames –Add a new Element that indicates a Type 2 association is being requested –Absence of this element results in a Type 1 association AP may accept or reject Type 2 association If the AP accepts the Type 2 Association request, it may impose a lifetime on it via an new Element included in the Association Response

doc.: IEEE r Submission November 2004 Bob Beach, Symbol TechnologiesSlide 13 Enabling the DTG (1) Always enabled with Type 1 associations For Type 2 associations, the STA requests the DTG to be enabled by either of two mechanisms –Data Packet or Action Frame with TSPEC Data Frame –A3 must contain an address other than the AP –Must be encrypted using algorithm and key that the STA previously negotiated with the AP

doc.: IEEE r Submission November 2004 Bob Beach, Symbol TechnologiesSlide 14 Enabling the DTG (2) Action Frame with TSPEC –If the AP can meet the TSPEC, it will indicate this to the STA and open the DTG –If the AP cannot meet the TSPEC, it will indicate this to STA and the DTG will remain disabled –Permits “Conditional Roaming” If the DTG is opened, the AP will –Send the current broadcast key to the STA –Notify other APs of the roam –Begin forwarding data frames between the DS and STA

doc.: IEEE r Submission November 2004 Bob Beach, Symbol TechnologiesSlide 15 Disabling the DTG May be done by STA or by another AP STA sends Disassociate Frame with “Type 2 Element” Another AP as a result of a roam indication When the DTG is disabled, the AP will –Discard all buffered frames for the STA –Release all QoS reservations

doc.: IEEE r Submission November 2004 Bob Beach, Symbol TechnologiesSlide 16 Security Issues AP may reissue broadcast key at any time AP attempts to individually update each STA with the new key A STA with a Type 2 association and a disabled DTG will not listen to updates Change to AP Behavior –An AP will not attempt to update the broadcast key to a STA with a Type 2 association and a disabled DTG –The AP will pass the current broadcast key/key index to the STA when the STA enables its DTG

doc.: IEEE r Submission November 2004 Bob Beach, Symbol TechnologiesSlide 17 Mobile Station Issues (1) STA discovers and performs Type 2 associations and Tgi tasks with multiple APs as a background activity. –Can be done easily when no application or a non real-time application is running (FTP, , web browsing) When an application starts that needs fast roaming, the STA has a pool of APs to which it can roam quickly While such an application is running the STA will perform scans APs interleaved with real-time data exchanges –Need to discover which APs can be heard and hence are candidates for roaming –This is done currently by Stations that run real-time applications –This kind of interleaving is not something new

doc.: IEEE r Submission November 2004 Bob Beach, Symbol TechnologiesSlide 18 Mobile Station Issues (2) Should the STA discover a brand new AP, it can perform association and other related tasks with the new AP using PSP techniques so as not to miss real-time traffic on its current AP –The new AP will buffer all authentication and key derivation packets until the STA asks for them –The STA need not wait for beacons in order to poll the new AP

doc.: IEEE r Submission November 2004 Bob Beach, Symbol TechnologiesSlide 19 Summary This approach allows mobile stations to maintain multiple associations with different APs Roaming with this approach is very fast since all the time consuming work is done before the roam occurs. A roam can occur in as little as two packets Roams can be performed conditionally based upon the ability of an AP to grant a TSPEC The approach uses existing mechanisms in rather than replacing them. The proposed changes to the specification are very simple and very limited.