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Sandbox Lab advanced 30 min3 graded questions
Break the Core: What Happens When the UPF Dies
A UE is live with an active PDU session. Kill the UPF, watch the cascade of failures propagate from N4 heartbeat loss all the way back to the UE, then recover.
Scenario
A senior engineer asks: "What actually happens if the UPF crashes mid-call?"
You have a live sandbox with UE imsi-999700000000001 sitting on a PDU session through upf-internet-01. You will:
1. Confirm the baseline — the session is active.
2. Stop the UPF.
3. Watch the SMF detect the outage via missed N4 heartbeats (PFCP node failure).
4. Watch the SMF release the SM context and the AMF send NAS PDU Session Release to the UE.
5. Bring the UPF back up and re-establish the session.
By the end you will understand why UPF redundancy / session restoration is non-negotiable in production and what signalling actually crosses the wire when user plane dies.
What you'll do
- Verify baseline: UE has an active session
- Stop the UPF
- Observe the cascade
- Recover: restart UPF and re-establish the session
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