Merge remote-tracking branch 'origin/fix-up-ho-fail' into integration_2025_w45 (!3739)

Bugfix: save old tunnel info to remain the user plane connection while rolling
back to source DU due to handover failure

This MR closes issue #984 that UE lost the data plane connection while rolling
back to the source DU due to handover failure.

openair2/RRC/NR/rrc_gNB.c

@@ -1283,6 +1283,20 @@ static rrc_gNB_ue_context_t *rrc_gNB_get_ue_context_source_cell(gNB_RRC_INST *rr
   return NULL;
 }
 
+/**
+ * @brief Rollback F1-U DL TL and TEID in RRC
+ */
+static void f1u_dl_gtp_rollback(gNB_RRC_UE_t *UE)
+{
+  DevAssert(UE != NULL);
+  DevAssert(UE->ho_context->source != NULL);
+
+  FOR_EACH_SEQ_ARR(drb_t *, drb, &UE->drbs) {
+    drb->du_tunnel_config = UE->ho_context->source->old_du_tunnel_config;
+    LOG_W(NR_RRC, "DRB id %d rollback to tunnel TEID %x\n", drb->drb_id, drb->du_tunnel_config.teid);
+  }
+}
+
 static void rrc_handle_RRCReestablishmentRequest(gNB_RRC_INST *rrc,
                                                  sctp_assoc_t assoc_id,
                                                  const NR_RRCReestablishmentRequest_IEs_t *req,
@@ -1361,6 +1375,7 @@ static void rrc_handle_RRCReestablishmentRequest(gNB_RRC_INST *rrc,
     }
 
     source_ctx->ho_cancel(rrc, UE);
+    f1u_dl_gtp_rollback(UE);
 
     /* we need the original CellGroupConfig */
     ASN_STRUCT_FREE(asn_DEF_NR_CellGroupConfig, UE->masterCellGroup);

openair2/RRC/NR/rrc_gNB_mobility.c

@@ -160,6 +160,12 @@ static void nr_initiate_handover(const gNB_RRC_INST *rrc,
     ho_ctx->source->du_ue_id = ue_data.secondary_ue;
     ho_ctx->source->old_rnti = ue->rnti;
 
+    // Save the GTP-U tunnel info for source DU before process UE context setup request/response
+    // since tunnel info will be updated by calling store_du_f1u_tunnel() in rrc_CU_process_ue_context_setup_response()
+    FOR_EACH_SEQ_ARR(drb_t *, drb, &ue->drbs) {
+      ho_ctx->source->old_du_tunnel_config = drb->du_tunnel_config;
+    }
+
     int result = asn_copy(&asn_DEF_NR_CellGroupConfig, (void **)&ho_ctx->source->old_cellGroupConfig, ue->masterCellGroup);
     AssertFatal(result == 0, "error during asn_copy() of CellGroupConfig\n");
   }

openair2/RRC/NR/rrc_gNB_mobility.h

@@ -56,6 +56,8 @@ typedef struct nr_ho_source_cu {
   ho_cancel_t ho_cancel;
   /// status transfer
   ho_status_transfer_t ho_status_transfer;
+  /// old (source) downlink tunnel
+  gtpu_tunnel_t old_du_tunnel_config;
 } nr_ho_source_cu_t;
 
 /* acknowledgement of handover request. buf+len is the RRC Reconfiguration */