Question: What triggers the attempted UE-associated logical S1-connection establishment from eNB to MME, as measured by the S1SIG.ConnEstabAtt parameter?
Option 1: Transmission of an INITIAL UE MESSAGE by the eNodeB to the MME
Option 2: Receipt of a UE capability information message from the UE
Option 3: Establishment of a new EPS bearer context
Option 4: Release of a UE-associated logical S1-connection
Explanation: The attempted UE-associated logical S1-connection establishment from eNB to MME is triggered by the transmission of an INITIAL UE MESSAGE by the eNodeB to the MME, as specified in 36.413 [9]. This measurement provides insight into the accessibility of the E-RAB (E-UTRAN Radio Access Bearer) and supports the Accessibility KPI "E-RAB Accessibility" defined in [13].