Contents

1   Overload Control Function

The SAPC provides different mechanisms to control overload situations.

1.1   Load Regulation Mechanism

The SAPC detects that it is working in overload situation when any of the traffic processors is working at CPU load or memory load higher than a configured value. In overload situation, the SAPC prioritizes the messages handled with higher priority and rejects messages handled with lower priority.

The SAPC applies load regulation priorities to Gx, Rx, and Smp session establishment. Rest of incoming messages are not under load regulation control. So modification and termination messages for already active sessions are never rejected due to load regulation.

The SAPC applies the same priority to Gx and Smp session establishment, and a higher priority to Rx session establishment. This means that, if the SAPC is overloaded, Rx session establishment messages are rejected only if Gx and Smp session establishments are being rejected due to load regulation control. The SAPC rejects these messages answering them with DIAMETER_TOO_BUSY.

When the SAPC is overloaded and detects a PCEF or an AF restart, the SAPC executes massive clean up with low priority. The SAPC provides a mechanism to avoid load peaks due to the massive clean up, so incoming messages are not affected.

1.2   Massive Reauthorizations Mechanisms

The SAPC implements following Massive Reauthorization Congestion Control mechanisms to prevent an overload situation in the system that could degrade the SAPC performance.

• Disable Massive Reauthorizations Based on Subscriber Update

  The sending of reauthorization messages to the enforcement function when massive changes on subscriber data are performed, can be disabled with a configured value to prevent network traffic overload.

• Disable Massive Reauthorizations Associated to Time Conditions

  The SAPC policies can evaluate conditions based on date and time, so, the result is only applicable during a period. When the applicable period is reached or expired, the SAPC then triggers a particular action (refer to Subscription and Policy Management). The following mechanisms avoid congestion in the node because of a massive processing of reauthorizations owing to validity time expiration.

  • Limit the maximum number of reauthorization due to Time of Day conditions that can be triggered per second.

    This limit value is configured by Ericsson personnel (default value is 700) and depends on network traffic model and the SAPC capacity. For example, if a time condition that applies to 210.000 sessions is set to 12:00 and reauthorization throughput is set by default, the SAPC processes the reauthorizations from 12:00 to 12:05.

    If the number of reauthorization messages to send is higher than this maximum number, the SAPC sends the additional messages at the next second that it is possible.

  • Disable the sending of reauthorization messages associated to time conditions if network traffic overload is too high.

    In this case, the new data is sent to the enforcement function when any message request is received from it.

• Disperse Reauthorizations due to Fair Usage Reset on Specific Dates

  If fair usage feature is active and it is configured reset on specific dates for postpaid subscriber groups, it is recommended not to specify the exact time in the configured period to avoid congestion situations. If not specified the SAPC calculates the expiration date for every subscriber of the subscriber group adding a random number of seconds (dispersion). In this way, it is avoided a massive reauthorization messages and the corresponding massive reception of IP session update messages at the same second for all the subscribers belonging to the same subscriber group.

  The dispersion applied for every subscriber is a random number from 0 to the number of seconds of the period not specified:

  • If hour is not specified: 23 hours, 59 minutes, and 59 seconds.
  • If minute is not specified: 59 minutes and 59 seconds.
  • If second is not specified: 59 seconds.

Reference List

Ericsson Documents
[1] Subscription and Policy Management.