Add NGAP Handover Notify encoder and trigger on the target NG-RAN

This commit introduces the NG Mobility Management Procedure known as
Handover Notification. The outbound message is sent by the target NG-RAN
and is known as Handover Notify. The procedure is used to indicate to
the AMF that the UE has arrived to the target cell and the NG-based
handover has been successfully completed

* after RRCReconfiguration complete, in the N2 callback for HO success
* add NGAP encoder for the message
* RRC callback to trigger Handover Notify message

Co-authored-by: batuhan duyuler <batuhan.duyuler@firecell.io>

openair2/COMMON/ngap_messages_def.h

@@ -74,6 +74,7 @@ MESSAGE_DEF(NGAP_PDUSESSION_RELEASE_RESPONSE    , MESSAGE_PRIORITY_MED, ngap_pdu
 MESSAGE_DEF(NGAP_HANDOVER_REQUIRED, MESSAGE_PRIORITY_MED, ngap_handover_required_t, ngap_handover_required)
 MESSAGE_DEF(NGAP_HANDOVER_FAILURE, MESSAGE_PRIORITY_MED, ngap_handover_failure_t, ngap_handover_failure)
 MESSAGE_DEF(NGAP_HANDOVER_REQUEST_ACKNOWLEDGE, MESSAGE_PRIORITY_MED, ngap_handover_request_ack_t, ngap_handover_request_ack)
+MESSAGE_DEF(NGAP_HANDOVER_NOTIFY, MESSAGE_PRIORITY_MED, ngap_handover_notify_t, ngap_handover_notify)
 
 /* NGAP -> RRC messages */
 MESSAGE_DEF(NGAP_DOWNLINK_NAS              , MESSAGE_PRIORITY_MED, ngap_downlink_nas_t              , ngap_downlink_nas )

openair2/COMMON/ngap_messages_types.h

@@ -70,6 +70,7 @@
 #define NGAP_HANDOVER_REQUEST(mSGpTR) (mSGpTR)->ittiMsg.ngap_handover_request
 #define NGAP_HANDOVER_REQUEST_ACKNOWLEDGE(mSGpTR) (mSGpTR)->ittiMsg.ngap_handover_request_ack
 #define NGAP_HANDOVER_COMMAND(mSGpTR) (mSGpTR)->ittiMsg.ngap_handover_command
+#define NGAP_HANDOVER_NOTIFY(mSGpTR) (mSGpTR)->ittiMsg.ngap_handover_notify
 
 #define NGAP_UE_CONTEXT_RELEASE_REQ(mSGpTR)     (mSGpTR)->ittiMsg.ngap_ue_release_req
 #define NGAP_PDUSESSION_RELEASE_COMMAND(mSGpTR)      (mSGpTR)->ittiMsg.ngap_pdusession_release_command
@@ -680,6 +681,23 @@ typedef struct {
   byte_array_t handoverCommand;
 } ngap_handover_command_t;
 
+/* 9.3.1.16 3GPP TS 38.413 */
+typedef struct {
+  // NR user location information
+  target_ran_node_id_t target_ng_ran;
+  uint32_t nrCellIdentity;
+} user_location_information_t;
+
+/* 9.2.3.7 3GPP TS 38.413 */
+typedef struct {
+  // RAN UE NGAP ID
+  uint32_t gNB_ue_ngap_id;
+  // AMF UE NGAP ID
+  uint64_t amf_ue_ngap_id;
+  // User Location Information
+  user_location_information_t user_info;
+} ngap_handover_notify_t;
+
 typedef struct ngap_ue_cap_info_ind_s {
   uint32_t  gNB_ue_ngap_id;
   byte_array_t ue_radio_cap;

openair2/RRC/NR/rrc_gNB_NGAP.c

@@ -1334,6 +1334,28 @@ void rrc_gNB_send_NGAP_HANDOVER_REQUEST_ACKNOWLEDGE(gNB_RRC_INST *rrc, gNB_RRC_U
   itti_send_msg_to_task(TASK_NGAP, rrc->module_id, msg_p);
 }
 
+/** @brief Prepare NG Handover Notify message and inform NGAP */
+void rrc_gNB_send_NGAP_HANDOVER_NOTIFY(gNB_RRC_INST *rrc, gNB_RRC_UE_t *UE)
+{
+  LOG_I(NR_RRC, "Triggering NGAP Handover Notify\n");
+
+  MessageDef *msg_p = itti_alloc_new_message(TASK_RRC_GNB, 0, NGAP_HANDOVER_NOTIFY);
+  ngap_handover_notify_t *ho_notify = &NGAP_HANDOVER_NOTIFY(msg_p);
+  memset(ho_notify, 0, sizeof(*ho_notify));
+  nr_rrc_du_container_t *du = get_du_by_cell_id(rrc, rrc->nr_cellid);
+
+  ho_notify->gNB_ue_ngap_id = UE->rrc_ue_id;
+  ho_notify->amf_ue_ngap_id = UE->amf_ue_ngap_id;
+  ho_notify->user_info.nrCellIdentity = rrc->nr_cellid;
+  ho_notify->user_info.target_ng_ran.tac = *du->setup_req->cell->info.tac;
+  ho_notify->user_info.target_ng_ran.targetgNBId = rrc->node_id;
+  ho_notify->user_info.target_ng_ran.plmn_identity.mcc = du->setup_req->cell->info.plmn.mcc;
+  ho_notify->user_info.target_ng_ran.plmn_identity.mnc = du->setup_req->cell->info.plmn.mnc;
+  ho_notify->user_info.target_ng_ran.plmn_identity.mnc_digit_length = du->setup_req->cell->info.plmn.mnc_digit_length;
+
+  itti_send_msg_to_task(TASK_NGAP, rrc->module_id, msg_p);
+}
+
 void rrc_gNB_send_NGAP_PDUSESSION_RELEASE_RESPONSE(gNB_RRC_INST *rrc, gNB_RRC_UE_t *UE, uint8_t xid)
 {
   int pdu_sessions_released = 0;

openair2/RRC/NR/rrc_gNB_NGAP.h

@@ -104,4 +104,6 @@ void rrc_gNB_send_NGAP_HANDOVER_REQUEST_ACKNOWLEDGE(gNB_RRC_INST *rrc, gNB_RRC_U
 void rrc_gNB_process_HandoverCommand(gNB_RRC_INST *rrc, const ngap_handover_command_t *msg);
 void rrc_gNB_free_Handover_Command(ngap_handover_command_t *msg);
 
+void rrc_gNB_send_NGAP_HANDOVER_NOTIFY(gNB_RRC_INST *rrc, gNB_RRC_UE_t *UE);
+
 #endif

openair2/RRC/NR/rrc_gNB_mobility.c

@@ -476,6 +476,13 @@ static void nr_rrc_n2_ho_acknowledge(gNB_RRC_INST *rrc, gNB_RRC_UE_t *UE)
   free_byte_array(hoCommand);
 }
 
+/** @brief This callback is used by the target gNB
+ *         to trigger the Handover Notify towards the AMF */
+static void nr_rrc_n2_ho_complete(gNB_RRC_INST *rrc, gNB_RRC_UE_t *UE)
+{
+  rrc_gNB_send_NGAP_HANDOVER_NOTIFY(rrc, UE);
+}
+
 /** @brief Callback function to trigger NG Handover Failure on the target gNB, to inform the AMF
  * that the preparation of resources has failed (e.g. unsatisfied criteria, gNB is already loaded).
  * This message represents an Unsuccessful Outcome of the Handover Resource Allocation */