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What is the difference between FT over the Air and FT over the DS under WiNG5?

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TitleWhat is the difference between FT over the Air and FT over the DS under WiNG5?
Question
What is the difference between FT (Fast Transition) over the Air and FT (Fast Transition) over the DS (Distributed System) under WiNG5?
Environment
  • WirelessWiNG
  • WiNG v5
  • WiNG5
  • 802.11r
  • IEEE
  • RFS6010
  • RFS7010
  • RFS4010
  • NX9XXX
  • NX75XX
  • NX65XX
  • NX45XX
  • NX55XX
  • AP8432
  • AP8533
  • AP82XX
  • AP8132
  • AP75xx
  • AP76xx
  • AP71xx
  • AP6521
  • AP6522
  • AP650
  • AP621
  • AP622
  • AP75xxE
  • AP65xxE
  • NX55XX-E
  • NX75XX-E
Answer
Fast BSS Transition (a.k.a 802.11r, a.k.a FT)
  • IEEE 802.11r or Fast BSS transition (FT) helps the wireless clients to roam faster as they move between Access Points, without compromising on the security and QoS (Works with EAP or PSK, CCMP encryption is required)
  • For 802.1X wireless networks, the initial authentication exchange requires an 802.1X exchange and a 4-way handshake
  • With mechanisms like PMK Caching and OPMK Caching, the clients don’t need to cover the complete 802.1X authentication, but they still need to go through the 4-way handshake
  • 802.11r makes roaming faster by eliminating the need for 4-way handshake and is faster than PMK and OPMK caching
  • Critical to applications that require high quality and low latency mobility, particularly voice
  • The 802.11r-over-the-Air has been supported on WiNG Wireless since WiNG 5.4.2

802.11r Options
 

Typical Authentication sequence during roaming is:

802.11 Authentication
802.11 Re-Association
EAPOL Exchange (Higher level authentication)
 

802.11r IEEE spec offers two options to speed up the authentication exchange

FT over the Air (mandatory)
The wireless client exchanges the 802.11 authentication and re-association requests wirelessly during the roam
The key exchange handshakes are piggybacked with authentication and re-association frames

FT over the DS (optional)
The initial handshake with the roam candidate (New AP) is done via the AP that the wireless client is currently associated to
The wireless client uses FT Action Frames and Re-association frames for the key exchange authentication

FT over DS Aggregate
 

FT over DS

The wireless client is connected to AP1
The Wireless client performs the initial handshake with the target roam candidate (AP2) through the AP that it is currently associated to (AP1)
If there are multiple roam candidates, the client repeats the same with multiple APs
The wireless client completes the handshake exchange through the re-association packets

FT Over DS Aggregate

The enhancement in WiNG 5.8 will reduce the Client effort of sending individual FT-over-DS requests to multiple possible roam candidates
Client can complete initial handshake with multiple neighboring APs at one time by aggregating FT requests and obtain aggregated FT responses as a single frame
The wireless client completes the handshake exchange through the Re-Association packets
 

Additional notes

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