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[Subscriber Management] MX bbesmgd daemon reports 'RTT exceeded threshold for FPC X, throttle_phase_count xxx'



Article ID: KB35431 KB Last Updated: 17 Jan 2020Version: 1.0

This article explains the reason for 'RTT exceeded threshold' message on MX broadband network gateway (BNG), and introduces the feature of RTT Load Throttle of resource-monitor.


Example 'RTT exceeded threshold' message:

Jan  6 02:09:27 2020  MX-BNG bbesmgd[18216]: %DAEMON-4-SMD_RSMON_RTT_EXCEEDED: RTT exceeded threshold for FPC 3, throttle_phase_count 1
Jan  6 02:09:30 2020  MX-BNG bbesmgd[18216]: %DAEMON-4-SMD_RSMON_RTT_NOMINAL: RTT returned below threshold for FPC 3
Jan  6 12:27:36 2020  MX-BNG bbesmgd[18216]: %DAEMON-4-SMD_RSMON_RTT_EXCEEDED: RTT exceeded threshold for FPC 3, throttle_phase_count 2
Jan  6 12:28:18 2020  MX-BNG bbesmgd[18216]: %DAEMON-4-SMD_RSMON_RTT_NOMINAL: RTT returned below threshold for FPC 3

When this message is seen, the subscriber login may be failed.


With RTT Load Throttle feature enabled, when PFE becomes too busy, RSMON RTT Load Throttle feature kicks in and deny the new subscriber login; on subscriber login retry and PFE CPU in normal level, login will succeed. Without this feature, the subscriber would have gone to active state but no traffic will be flowing for a period of time.

Use the command below  to check if RTT Load Throttle feature has been enabled:

user@MX-BNG> show system resource-monitor summary 
Resource Usage Summary

Throttle                       : Enabled      
Load Throttle                  : Enabled  <-- indicates RTT Load Throttle has been enabled   
Heap Mem Threshold             : 70  %
IFL Counter Threshold          : 95  %
Round Trip Delay Threshold(ms) : 1000     <-- RTT Throttle value
Filter Counter Threshold       : 100 %
Expansion Threshold            : 95  %
CoS Queue Threshold            : 100 %
MFS threshold                  : 70  %        Used : 0   

Slot # 0   
     Client allowed                   : Yes  
     Service allowed                  : Yes  
     Heap memory used                 : 339204848       In % : 18  
     Average Round-trip Delay(ms)     : 103  (30  )     Round-trip Delay(ms) : 103  <-- RTT Delay, the 30 in bracket means that the average is taken for last 30 secs
     MAX session rate allowed(%)      : 100 
     Client denied                    : 1524  <-- the counter of new subscribers have been denied    
     Service Denied                   : 0     
     Performance Denial Client        : 1524  <-- 
     Performance Denial Service       : 0   
     IFL Denied                       : 0   

                Filter counter memory      IFL counter memory   Expansion memory
      PFE #         used  |   %             used  |   %          used  |   %
          0       17848880     44           304096      0             0      0
          1       17754480     44           274832      0             0      0

     CoS Queue Utilization
     PFE #   Scheduler Block #        Used      %
         0                   0          88      0
         0                   1          88      0
         1                   0          24      0
         1                   1          24      0

If 'Average Round-trip Delay' is 'exceeded Round Trip Delay Threshold', the 'RSMON RTT Load Throttle' is triggered and system reports the log message.


There is a hidden command to adjust RTT Threshold value. Setting it to a large value can decrease the frequency of logging.

user@MX-BNG# set system services resource-monitor rtt-parameters rt-delay-threshold <value-in-millisecs>
If you prefer to disable this feature, use command below:
user@MX-BNG# set system services resource-monitor no-load-throttle

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