SIP Call Loop elimination

Last Updated : May 03, 2017 |

Loop Administration

Session Manager can sometimes receive identical INVITE requests within a short interval.

Session Manager sets up separate sessions for each INVITE. Multiple identical INVITE requests can initiate SIP call loops and deplete network resources. Session Manager provides administration features to track and terminate call looping instances in the network.

You administer loop parameters when you create a SIP entity that is not of Type Session Manager on the SIP Entity Details page under Elements  > Routing  > SIP Entities.

Session Manager rejects requests if the number of incoming requests that have the same combination of the R-URI, To, From, and PAI header values reaches the administered Loop Count Threshold value within the Loop Detection Interval time. The frequency of the call loops is a function of the latency and the number of network elements in the loop path. An administrator must set the Loop Detection parameters based on the customer network configuration. Setting improper values of Loop Count Threshold and Loop Detection Interval can result in:

  • System performance overhead.

  • Non-detection of call looping scenarios in the network.

For example, if the successive loop call arrives at Session Manager after 40 milliseconds (because of the propagation delay of the intermediate hops) and the administrator needs to break the loop on the fifth loop call instance, the recommended Firewall configuration must have Loop Count Threshold set to 5 and Loop Detection Interval set to 200 milliseconds.

Note:

Set the Loop Count Threshold value higher than the default value of 5, if the network has:

  • Communication Manager administered as IPv6 with ANAT configured

  • The Loop Detection Mode set to ON

Alarm Generation

The Session Manager SIP Firewall generates a minor-level alarm for a call loop detection event based on the Loop Detection parameters settings. You can administer Loop Detection alarms on the Session Manager Administration page.

When an alarm is generated for the Loop Detection event, Session Manager does not generate any more alarms for the administered Loop Detection Alarm Threshold interval after the event. For example, if the Loop Detection Alarm Threshold is set to 24 hours and a Loop Detection alarm is generated, the SIP Firewall does not generate any new Loop Detection alarms for the next 24 hours. During this interval, the SIP Firewall continues to detect and break loops without generating any new alarms, but continues to log loop detection summary events.