Question: In an E-UTRA network, when a UE initiates an RRCConnectionReestablishment procedure due to handover failure, how does it set the `physCellId` in the RRCConnectionReestablishmentRequest message?
Option 1: To the physical cell identity of the target cell indicated by the last handover command.
Option 2: To the physical cell identity of the source PCell from which the handover failure occurred.
Option 3: To the physical cell identity of the current serving cell where the re-establishment is being attempted.
Option 4: To a default value as specified by the UE's manufacturer.
Explanation: According to the 3GPP specifications for RRCConnectionReestablishment, when the procedure is initiated due to handover failure (among other scenarios like radio link failure), the UE sets the `physCellId` in the RRCConnectionReestablishmentRequest message to the physical cell identity of the source PCell (in case of handover and mobility from E-UTRA failure) or of the PCell where the trigger for re-establishment occurred. This ensures that the network can correctly identify the context of the re-establishment request, facilitating efficient recovery from the failure.