forked from acouzens/open5gs
060acee5df
Bug:
In case that AMF does not have subscription data for the UE,
PDU session remains unreleased after implicit de-registeration.
The exact test case:
- UE registered (integrity protection applied)
- UE deregistered (Nudm_SDM_Unsubscribe, Nudm_UECM_Registration (purgeFlag))
- UE registered, PDU session activated
UE data are still stored in AMF. So if integrity protected applies,
the steps 4 - 14 [ETSI TS 123 502 V16.7.0](https://www.etsi.org/deliver/etsi_ts/123500_123599/123502/16.07.00_60/ts_123502v160700p.pdf) are skipped.
Only AM Policy Association Establishment is performed.
- UE is moved out of radio coverage, 2 x (4 min + Timer t3512) expires
Result: UE is implicitly de-registered, PDU session is not released
The steps of implicit de-registeration:
1. Implicit Timer Expiration
2. UDM_SDM_Unsubscribe
3. UDM_UECM_Deregistration
4. PDU session release request
5. PDUSessionResourceReleaseCommand + PDU session release command
6. PDUSessionResourceReleaseResponse
7. AM_Policy_Association_Termination
So PDU session release is performed after the confirmation of
UDM_UECM_Deregistration.
Since there is no UDM_SDM subscription, the UDM steps are skipped
and PDU session is not released.
Fix:
If the AMF does not have subscription data for the UE which registers,
the AMF registers with the UDM using Nudm_UECM_Registration and
retrieves subscription data with Nudm_SDM_Get.
[ETSI TS 123 502 V16.7.0](https://www.etsi.org/deliver/etsi_ts/123500_123599/123502/16.07.00_60/ts_123502v160700p.pdf), 4.2.2.2.2 General Registration, 14a-c:
> If the AMF does not have subscription data for the UE, the AMF retrieves the Access and Mobility Subscription data, SMF
> Selection Subscription data, UE context in SMF data and LCS mobile origination using Nudm_SDM_Get.
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