Oracle Communications Diameter Signaling Router (DSR)
 

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After upgrading DSR from Release 5.0 to Release 7.0.1 with abatement timer in egress throttling set to a high value and there is a spike in ingress traffic, one or more egress connection/s may send very low traffic.

In this Document

Symptoms

Changes

Cause

Solution

References

Created from <SR 3-11475289281>

Applies to:

Symptoms

Depending on customer configuration of egress message throttling and Per connection Egress Message Throttling prior to R7.0.1 upgrade, customer may see lower than expected egress message rates while egress message throttling is occurring.

Changes

Upgrade to a Diameter Signaling Router (DSR) release containing the enhanced Egress Throttling Group (ETG) feature. Feature details: ETG is designed to throttle messages to protect upstream nodes in the case of excess traffic so that they will not go into congestion or recover faster if they do.

Customer must examine the network to determine the traffic patterns and determine whether if the current configuration is consistent with the traffic patterns.

Cause

Egress connection(s) sending low traffic because the abatement timer is set too high (e.g., 10 secs).   ...smoothing factor removal...

Verification:

1. Ingress diameter connection is congested: In Main Menu > Alarms and Events > View Active
          TIMESTAMP: 2015-10-04 10:44:18.108 CDT
          NETWORK_ELEMENT: dsrMP_xxxxxxx
                  SERVER: xxxxxx
                 SEQ_NUM: 972605
            EVENT_NUMBER: 22328
                SEVERITY: [Minor, Major]
                 PRODUCT: DPI
                 PROCESS: dsr
                    TYPE: DIAM
                INSTANCE: RxConnMsgRate[xxxxxxxx], DIAM
                    NAME: Ingress MPS Rate
                   DESCR: The diameter connection specified in the alarm instance is processing higher than normal ingress messaging rate.
                ERR_INFO:
            GN_BLWTHRESH/CLR Metric RxConnMsgRate below minor threshold
           ^^ Current: 91  Onset: 5000  Abatement: 4500
           ^^ [9508:SysMetricIf.cxx:1881]
2. A long abatement time as seen on the Diameter > Configuration > Egress Throttle Groups page. 

Justification:

• Configured onset threshold level 1 is 100%.
• Configured onset abatement threshold level 1 is 80% with long abatement time (10 s)
• Ingress request messages were mostly of priority 0 (zero).
• Once egress traffic goes above the onset threshold level 1 (100% of the Maximum Egress Request Rate)  then egress throttling / Per Connection Egress Message Throttling will occur.
• This will allow only messages with Priority 1, 2 or 3 to pass. It will block messages with Priority 0.
• When egress throttling / Per Connection Egress Message Throttling has brought the traffic to any value below the abatement threshold (i.e., any value below 80%) then the abatement timer will begin and the rate will need to stay at this low value for the abatement time, which is 10 s.
• After this abatement time, the congestion level will be lowered down, then traffic will be allowed to flow through again until the onset threshold level 1 is reached again and the cycle will continue.

Solution

• Customer should consider examining their ETG and PCEMT configuration with an aim to reduce the high abatement time (e.g. 10 s).
• Add additional congestion levels (onset/Abatement thresholds (TT/AT)).
• Prioritize the incoming request messages using the Message Priority feature.

Justifications

• In the DSR 5.0.1 Maintenance Release (MR) the Egress Throttle Group (ETG) feature was fixed to calculate the smoothed rate for ETG / PCEMT.
• Aggregated Message Rate using the configured Smoothing factor (Alpha). On DSR 5.0 the convergence of smoothed rate will be slow allowing more egress traffic to go through as a result of using default alpha (98%).
• In the DSR 7.0.1 Maintenance Release (MR), additional enhancements were done to the Egress Throttle Group (ETG) feature to allow it to be more responsive to traffic bursts (faster sampling rate and smoothing factor removal).
• Once aggregated egress traffic for any defined ETG group goes above the onset threshold level X+1, then egress throttling will occur, blocking lower priority request messages (0, 1, .., X) than current congestion level observed on the ETG group.
• In the scenario with a high abatement time (e.g. 10 s), the throttling will continue at least for that time (e.g. 10 s) even if the egress message rate drops below abatement threshold level X+1 immediately after crossing the onset threshold. The abatement time allows the user to specify the amount of time that a throttled ETG’s egress message rate must remain below an abatement level before allowing it to abate to a lower Congestion Level.

References

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