ICSR and Session Recovery
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At Session Management Function, during transition, the most recent is considered as the stable state and a full checkpoint is triggered once handover is complete from LTE to Wi-Fi (S2BGTP) or vice-versa. This is applicable to Session Recovery and ICSR. User Plane has individual session recovery and ICSR check pointing on every message received.
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During handover failure, that is, when SMF and UPF are out of sync, the SMF session is recovered on the most recently accessed state and UPF is recovered in the new transition state. This behavior is applicable during UPF failure.