Being the majority of WiFi Client devices as mobile, they need to equipped enough to be able to roam (move) seamlessly between WiFi Access Points (APs). The major difference between a cellular device and WiFi device is that, in cellular network client roaming is managed and handled completely by Base stations of Cellular Infrastructure (which is identical to WiFi AP in WiFi network), whereas in WiFi network roaming decisions and trigger to roam are to be handled by WiFi client device itself. Though this seems to provide a flexibility for WiFi client to decide, this also leaves a bigger responsibility to WiFi Client device to maintain the constant connection while its in motion.

The WiFi client's responsibility of staying connected to network is little bit challenging job, knowing about the uncertainties in wireless environment (dependency on surroundings, construction structure, orientation of client towards AP etc....will be a long list). To make this challenge easier for client, new 802.11 amendments started evolving for infrastructure (APs) to provide additional support. Some of such relevant amendments are listed below

802.11k (Radio Resource Management)

802.11r (Fast BSS Transition)

802.11v (Wireless Network Management)

802.11k (Radio Resource Management - RRM)

802.11k RRM is a MAC layer amendment, which added support for set of measurement request/response support for client and AP to exchange information, which can be useful for making roaming simplified. To list few of roaming related request/responses

• Neighbor Report

• Beacon Report

802.11r (Fast BSS Transition)

802.11r Fast BT refers to fast roaming standard, which is mainly focused on reducing the time required for re-authentication with Enterprise Wireless security (EAP) methods. Once the client is associated to an infrastructure network using full EAP authentication, it proves the identity of client is valid and it doesn't need to prove its identity on every re-association. Think of a authorized person entered into an office building showing the RFID based ID card at the entrance of the building, he doesn't need to be authorized for accessing each of the room inside office. 802.11r works on the same concept.

Once client completes initial authentication with full EAP transactions, the standard defines methods to handle the required key derivations during re-assoc process instead of forcing the client device to go through full authentication. This specific topic deserves a separate post, which will be covered in future posts.

802.11v (Wireless Network Management - WNM)

802.11v WNM is MAC layer enhancement, which defines set of additional frames and IEs (Information Elements) to allow the configuration of client from WiFi infrastructure (AP) side. Below is list of roaming related feature

• BSS Transition Management (BTM), which allows AP to instruct client to start roaming

#80211r #80211k #80211v #RRM #FastRoaming #WNM #WiFiroaming #WiFiSTA #WLAN #WiFi