Question: What is a prerequisite for the Trace Start procedure in E-UTRAN, involving a request from the MME to the eNB for tracing a specific UE, if not already present?
Option 1: An existing Non-Access Stratum (NAS) connection between the UE and the MME.
Option 2: Activation of the trace function on the UE itself.
Option 3: Establishment of a direct X2 connection between the eNB and a neighboring eNB.
Option 4: Establishment of a UE-associated logical S1-connection, if one does not already exist.
Explanation: The Trace Start procedure requires communication between the MME and eNB specifically related to a UE. For this purpose, a UE-associated logical S1 connection is necessary to manage the signaling pertinent to that UE. If such a connection doesn't exist at the time of the request, it must be established as part of initiating the trace function, ensuring targeted and efficient tracing operations for the specified UE.