What is the use of Handover report message in x2ap?

Question

Please explain in detail?

Answer 1

The purpose of the Handover Report procedure is to transfer mobility related information between eNBs controlling neighbouring cells (This was introduced in R9)

An eNB initiates the procedure by sending an HANDOVER REPORT message to another eNB controlling neighbouring cells. By sending the message eNB1 indicates to eNB2 that, following a successful handover from a cell of eNB2 to a cell of eNB1, a radio link failure occurred and the UE attempted RRC Re-establishment either at the original cell of eNB2 (Handover Too Early), or at another cell (Handover to Wrong Cell).
The report contains the source and target cells, and cause of the handover. If the Handover Report Type IE is set to "HO to wrong cell", then the Re-establishment cell ECGI IE shall be included in the HANDOVER REPORT message.

Credit: 3GPP 36.423

HandoverReport ::= SEQUENCE {
   protocolIEs ProtocolIE-Container {{HandoverReport-IEs}},
   ...
}

HandoverReport-IEs X2AP-PROTOCOL-IES ::= {
   { ID id-HandoverReportType CRITICALITY ignore TYPE HandoverReportType PRESENCE mandatory}|
   { ID id-Cause CRITICALITY ignore TYPE Cause PRESENCE mandatory}|
   { ID id-SourceCellECGI CRITICALITY ignore TYPE ECGI PRESENCE mandatory}|
   { ID id-FailureCellECGI CRITICALITY ignore TYPE ECGI PRESENCE mandatory}|
   { ID id-Re-establishmentCellECGI CRITICALITY ignore TYPE ECGI PRESENCE conditional}
   -- The IE shall be present if the Handover Report Type IE is set to "HO to Wrong Cell" -- |
   { ID id-TargetCellInUTRAN CRITICALITY ignore TYPE TargetCellInUTRAN PRESENCE conditional}
   -- The IE shall be present if the Handover Report Type IE is set to "InterRAT ping-pong" --|
   { ID id-SourceCellCRNTI CRITICALITY ignore TYPE CRNTI PRESENCE optional}|
   { ID id-MobilityInformation CRITICALITY ignore TYPE MobilityInformation PRESENCE optional}|
   { ID id-UE-RLF-Report-Container CRITICALITY ignore TYPE UE-RLF-Report-Container PRESENCE optional},
   ...
}