The IMSI Manager is the Demux process that selects the Session Manager instance based on the Demux algorithm logic to host a new session for 2G/3G/4G subscribers for SGSN/MME. The IMSI Manager maintains the IMSI-SMGR mapping for SGSN (2G/3G) and MME (4G) subscribers. The mapping maintained at IMSIMGR task is usually in sync with the mapping maintained at all session managers. But in some rare cases, there is a mismatch due to problems during the synchronization process. In such scenarios, the IMSIMGR task sends out a broadcast message to all session managers hoping that at least one of them will be hosting that session and could respond positively to this broadcast.
If none of the Session Managers respond with the mapping, the IMSI Manager considers it as request for an UNKNOWN (unregistered) subscriber and forwards it to a random Session Manager, which in turn sends an error response for the HLR request. The broadcasts from the IMSI Manager happen through a non-blocking vector call to all active Session Managers which can lead the IMSI Manager into a CPU overload condition considering the high number of session managers.
IMSI Manager broadcast control is implemented by the following:
In IMSI Manager, broadcast disabling CPU threshold value defined; once the CPU utilization crosses this threshold, the IMSI Manager will not broadcast any unknown subscriber requests from HLR. Default value of this threshold is set as 50%. A CLI command is provided to optionally define the CPU threshold.
In IMSI Manager, congestion threshold value of 70% is defined; once the CPU utilization crosses this threshold, the IMSI Manager will trigger congestion control action and will drop all unknown subscriber requests from HLR.
This feature is enabled by default.