In this section:
The SBC Core supports signaling and media overload protection when the call load exceeds the specified performance and capacity limits. Overload protection works best when the IP ACL policers and the congestion/overload controls are configured according to overload control best practices:
Expected calls/sec x 5 x 2
Use default values for all congestion controls and overload profiles.
Set TrunkGroup CAC controls appropriate to the associated customer.
The SBC checks CPU utilization against a predefined threshold to decide whether to allow resource allocation. This check is performed in two phases:
Phase 1: Allocation – Once the resource allocation message is received, the SBC checks if the CPU idle time for that second is within the predefined threshold or not. If the CPU is within the threshold, the call is allowed. Otherwise, the SBC fails the call.
Phase 2: Activation – All allocated calls may not be activated at the same time, which may lead to transient calls in answering state. To manage this situation, overload state is checked at the activation time. The transient calls are not allowed if the system is in CPU overload condition during activation.
Overload handling is supported separately for Pass-through, SRTP, and DSP calls.
Key highlights:
The Overload Profile controls SBC signaling overload by specifying a set of congestion thresholds, congestion durations, and overload controls. When a particular threshold is exceeded for a particular duration for any of the call processing related processes, the congestion level is raised to a higher level and the overload control is applied to help alleviate the congestion. The profile also specifies clear congestion thresholds and durations. These values require that the overload conditions fall below their configured clear threshold values for a specific duration in order to return to the previous congestion level. These minimum clear durations prevent repeatedly switching in and out of congestion levels.
When assigning an Overload Profile to the system (throughout the SBC), you may specify and manage CPU utilization congestion criteria through this facility:
The following default Overload Profiles are automatically created for system congestion levels 1-3:
You must disable an Overload Profile to change its configuration. When you disable a profile, the SBC application continues to utilize the previous profile values for congestion control processing.
Once you enable the profile, all parameter values get validated and applied to the (system) congestion level that references the profile. In this situation, the system congestion level is cleared if the Overload Profile was being referenced. Standby modules also perform congestion processing but the module settings are
not configurable.
For more information on configuring overload profiles, refer to:
For details of assigning an Overload Profile to a system congestion configuration, refer to: