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Reset E1 UE contexts after E1 Setup Response

Robert Schmidtrequested to merge
fix-cuup-assert-reconnect into develop

38.463 sec. 8.2.3 says

This procedure also re-initialises the E1AP UE-related contexts (if any) and erases all related signalling connections in the two nodes like a Reset procedure would do.

Hence, delete all contexts after reception of E1 Setup Response. This minimizes a risk of receiving an E1 bearer setup req for an existing UE, which currently leads to an assert [we trust the CU-CP does not send the same UE ID twice, as we only "mirror" the existing UE ID].

After this MR, this is what happens if these entities fail:

  • CU-CP: all context lost implicitly, upon reconnection, both DU and CU-UP reset all contexts (like "start from zero")
  • DU fails: CU-CP triggers NGAP UE context release request immediately (radio connection with UE lost), all UE contexts attached to this DU cleared (like "start from zero" for affected DU)
  • CU-UP fails: initially, nothing (UE has no user plane); upon reconnection of CU-UP, CU-CP triggers NGAP UE context release request (cause radio connection with UE lost) and sends F1 Reset to DU, all UE contexts associated to this DU cleared (like "start from zero")

for the last case, a possible improvement could be to use the F1 Reset message to only clear affected UE conetxts. I chose not to do this, because this MR is very big now already, and possible "victim" UEs that were not at that CU-UP will reconnect as well

Edited by Robert Schmidt

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