Case Study: A PDA Goes Offline During Roaming Due to Low Roaming Sensitivity

Symptom

As shown in Figure 6-6, a PDA goes offline unexpectedly when roaming between APs.

Figure 6-6 PDA attempting to roam between APs

Relevant Alarms and Logs

None

Cause Analysis

The PDA roaming sensitivity is low. When the AC disconnects the PDA to enable it to roam, the PDA does not quickly reassociate with the WLAN.

Procedure

1. Check the steering record of the STA on the AC.

   [wlan-ac] display station steer-history | include sta-mac
   S/T/A:Source/Target/Actual
   Flag:V[Voice/Video/Active STA]
   BTM success times/BTM total times:665/1697
   Deauth success times/Deauth total times:122/351
   ------------------------------------------------------------------------------------------------------------------------------------
   Time                Sta    Device(S/T/A)   Radio(S/T/A)  Rssi(S/T/A)   Reason       Move-mode  BTM_CODE  Flag  Result
   ------------------------------------------------------------------------------------------------------------------------------------
   2021-03-30/17:31:43 x-x-x  13/-/-          1/-/-         -78/-/-       Sticky       Deauth     -         -     Time Out
   2021-03-30/17:31:20 x-x-x  36/-/13         1/-/1         -89/-/-74     Sticky       BTM        -         -     Success
   2021-03-30/17:31:10 x-x-x  36/-/13         1/-/1         -88/-/-74     Sticky       BTM        -         -     Success
   2021-03-30/17:30:44 x-x-x  36/-/36         1/-/1         -74/-/-72     Sticky       BTM        -         -     Not Move
   2021-03-30/17:29:48 x-x-x  26/-/36         1/-/1         -85/-/-69     Sticky       BTM        -         -     Success
   2021-03-30/17:29:38 x-x-x  26/-/36         1/-/1         -79/-/-69     Sticky       BTM        -         -     Success
   2021-03-30/17:29:28 x-x-x  26/-/26         1/-/1         -79/-/-76     Sticky       BTM        -         -     Not Move

   Based on the steering record:

   • Check the Device(S/T/A) field. It is found that the STA is steered from AP26 to AP36 and then to AP13.
   • Check the Reason field. It is found that the STA is always marked as Sticky in the entire steering record. That is, the STA is identified as a sticky STA, therefore triggering smart roaming.
   • Check the Result field. It is found that before successful steering, the steering result Not Move (steering is complete, but the STA is still associated with the original AP) or Time Out (steering times out) is obtained, indicating a steering failure.
   • Check the Rssi(S/T/A) field. It is found that the STA is successfully steered in BTM mode only when the RSSI of the STA received by the AP is lower than –80 dBm.

2. Check the packet exchange process during STA roaming using the station-trace function.
   1. Check the AC's operations of steering and disconnecting STAs.

      AC steering operation:

      <7>Mar 30 2021 17:23:19.600.7 APxx WSRV/7/BTRACE:(BTRACE)(WLAN_AP)(xxxx-xxxx-xxxx):AC send move msg
       Target Bssid ffff-ffff-ffff
       Chanel: 0
       Mode: 2
       Reason: 2
       RestricTime: 10
      <7>Mar 30 2021 17:23:19.600.8 APxx WSRV/7/BTRACE:(BTRACE)(WLAN_AP)( xxxx-xxxx-xxxx):wstak_sta_lb_move_proc[2260]: Dst Bssid:ffff-ffff-ffff,LDBC move, mode[2], reason[2], RestricTime[10]

      Operation of disconnecting STAs:

      <7>Mar 30 2021 17:25:13.0.2 APxx WSRV/7/BTRACE:(BTRACE)(WLAN_AP)(x-x-x): WUAMK_AssocreqCallChainHandle[863]: Enter:
          radio id    :1
          wlan id     :1
          packet type :disassociation
          result      :0
          reason      :The STA is forced to go offline because its signal strength is too low. (0x1000009)
          sta ability

   2. Check the association request sent by the STA after it is disconnected. It is found that the STA associates with a new AP more than 10 seconds after being steered by the AC.

      <7>Mar 30 2021 17:23:20.100.6 APxx WSRV/7/BTRACE:(BTRACE)(WLAN_AP)(x-x-x):WUAMK_AssocreqCallChainHandle[863]: Enter: 
      radio id    :1 
       wlan id     :1 
       packet type :disassociation
       result      :0 
       reason      :The STA is forced to roam to another ap. (0x100001f) 
       sta ability :0 
       SFN roam    :0 
       SNR 
       ......
      ......
       <7>Mar 30 2021 17:23:38.590.28 APyy WSRV/7/BTRACE:(BTRACE)(WLAN_AP)(x-x-x):WUAMK_AssocreqCallChainHandle[886]: Enter: 
       radio id    :1 
       wlan id     :0 
       packet type :association req
       result      :Successful (0) 
       reason      :0x0 
       sta ability :65 
       SFN roam    :0 
       SNR         :20 

3. Adjust the device configuration as follows:
   1. In the RRM profile of the AC, disable the function of disconnecting STAs and the steering function in Deauthentication mode.

      <AC> system-view
      [AC] wlan
      [AC-wlan-view] rrm-profile name default
      [AC-wlan-rrm-prof-default] smart-roam quick-kickoff-threshold disable  //Disable the function of quickly disconnecting STAs so that PDAs roam in steering mode.
      [AC-wlan-rrm-prof-default] sta-load-balance dynamic disable  //Disable the dynamic load balancing function to prevent repeated roaming of PDAs between APs.
      [AC-wlan-rrm-prof-default] sta-load-balance dynamic deauth-fail-times 0   //Set the maximum number of attempts to steer STAs in Deauthentication mode to 0. That is, STAs are not steered in Deauthentication mode. If the success rate of STA steering triggered in Deauthentication mode is low or STA services are affected, set this parameter to 0.

   2. Increase the STA roaming sensitivity to facilitate STA roaming.