Understanding roaming and 802.11 k/v/r

Zyxel_Judy

Roaming is a mechanism on “clients” to connect to the other access point while remaining connected to the network. Without roaming, devices need to take more time to reconnect to the other AP and suffer for longer disconnection.

Roaming process

Station will undergo three stages to complete a roaming process:

Step 1: Monitor current signal. If signal is lower than a threshold, moves to Step 2

Step 2: Probe Target AP

• Client probes signal from surrounding APs for evaluation
• When current signal lower than another threshold, move to Step 3

Step 3: Establish the connection. Client picks up an AP and do Authentication for connection.

After station roams to 2nd AP, it then disconnects from 1st AP. Client always keeps network connection during roaming period.

802.11v

In normal roaming scenario, client purely refers to signal strength to trigger roaming to trigger roaming action. However, there are still other factors related to connection performance. With 802.11v, AP will consider “band” for connection quality, and inform station to roam if needed. Client connecting to 2.4GHz radio will be informed to connect to 5GHz.

802.11v is called “BSS Transition”.

Process of 11v

When clients connect to AP, they will verify the capability through management frames. If AP detects client support 11v, it will then trigger behavior afterwards.

If AP find this client has 5GHz capability, but connects to 2.4GHz radio, it will inform the station to roam to 5GHz.

• Station can accept or refuse the recommendation.
• After got refused for over 3 times, AP will stop informing station.

Supported by all managed and cloud mode APs. Make sure that both the “Band select” and “Assisted Roaming” are checked.

Configuration path:

Configuration > Object > AP profile > SSID > SSID list > Add/ Edit

802.11k

During probing period, stations might take long time to thoroughly scan every signal to find the best target AP. The moving period can’t afford station to find out the best AP. With 802.11k, station directly ask a candidate list from AP instead of scanning each signal. Probing period can be largely shortened.

802.11k is also called “neighbor report”.

Process of 11k

For APs activated 802.11k, they will exchange SSID information each other through broadcast packet.

When clients connect to AP, they will verify the capability through management frames. If AP detects client support 11k, it will then trigger behavior afterwards. During the connection period, AP will ask station for the neighbor list including SSID detected. When the station is about to roam, it will request a candidate list from AP. AP will compare the information and inform the most appropriate signal.

Supported by AP in any modes.

802.11r

When SSID security is set with WPA-Personal or Enterprise, it requires long period to establish the connection. Long roaming time caused by authentication and key generation. With 802.11r, authentication and key generation can be completed as soon as connecting, shortening the connection period.

802.11r is also called “fast roaming”.

Process of 11r:

Integrate client authentication and key information inside management frames, shorten the roaming period.

Supported only on Cloud/ Managed mode APs.

Configuration path:

Configuration > Object > AP profile > SSID > Security List > Add/ Edit