Add NGAP Handover Failure message

This message is sent from the Target NG-RAN to the AMF.

The commit introduces:
* NGAP encoding function
* N2 callback for the target gNB
* handle the failure in RRC, inform NGAP
* send NGAP message to AMF via SCTP

Note: UE context in NGAP is fetched from the amf_ue_ngap_id

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

openair3/NGAP/ngap_gNB.c

@@ -334,6 +334,46 @@ void ngap_gNB_init(void) {
   itti_mark_task_ready(TASK_NGAP);
 }
 
+static int ngap_gNB_handover_failure(instance_t instance, const ngap_handover_failure_t *msg)
+{
+  ngap_gNB_ue_context_t *ue_context_p = NULL;
+  uint8_t *buffer = NULL;
+  uint32_t length;
+
+  ngap_gNB_instance_t *ngap_gNB_instance_p = ngap_gNB_get_instance(instance);
+  DevAssert(msg != NULL);
+  DevAssert(ngap_gNB_instance_p != NULL);
+
+  NGAP_NGAP_PDU_t *pdu = encode_ng_handover_failure(msg);
+  if (!pdu) {
+    NGAP_ERROR("Failed to encode NG Handover Failure\n");
+    ASN_STRUCT_FREE(asn_DEF_NGAP_NGAP_PDU, pdu);
+    return -1;
+  }
+
+  if (ngap_gNB_encode_pdu(pdu, &buffer, &length) < 0) {
+    NGAP_ERROR("Failed to encode HANDOVER FAILURE MESSAGE\n");
+    ASN_STRUCT_FREE(asn_DEF_NGAP_NGAP_PDU, pdu);
+    return -1;
+  }
+
+  ngap_gNB_amf_data_t *amf = ngap_gNB_get_AMF_from_instance(ngap_gNB_instance_p);
+  if ((ue_context_p = ngap_get_ue_context_from_amf_ue_ngap_id(msg->amf_ue_ngap_id)) == NULL) {
+    //The context for this gNB ue ngap id doesn't exist in the map of gNB UEs
+    NGAP_WARN("Failed to find UE context associated with amf_ue_ngap_id=%ld\n", msg->amf_ue_ngap_id);
+    /*In this case there is no ue context since HO REQ might be failed at preprocessing stage itself.
+    * so sctp message send to AMF based on its assoc_id  */
+    ngap_gNB_itti_send_sctp_data_req(ngap_gNB_instance_p->instance, amf->assoc_id, buffer, length, 0);
+    ASN_STRUCT_FREE(asn_DEF_NGAP_NGAP_PDU, pdu);
+    return -1;
+  }
+
+  ngap_gNB_itti_send_sctp_data_req(ngap_gNB_instance_p->instance, amf->assoc_id, buffer, length, amf->nextstream);
+  ASN_STRUCT_FREE(asn_DEF_NGAP_NGAP_PDU, &pdu);
+
+  return 0;
+}
+
 void *ngap_gNB_process_itti_msg(void *notUsed) {
   MessageDef *received_msg = NULL;
   int         result;
@@ -415,6 +455,10 @@ void *ngap_gNB_process_itti_msg(void *notUsed) {
         }
         break;
 
+      case NGAP_HANDOVER_FAILURE:
+        ngap_gNB_handover_failure(instance, &NGAP_HANDOVER_FAILURE(received_msg));
+        break;
+
       default:
         NGAP_ERROR("Received unhandled message: %d:%s\n", ITTI_MSG_ID(received_msg), ITTI_MSG_NAME(received_msg));
         break;

openair3/NGAP/ngap_gNB_mobility_management.c

@@ -191,3 +191,36 @@ NGAP_NGAP_PDU_t *encode_ng_handover_required(const ngap_handover_required_t *msg
 
   return pdu;
 }
+
+NGAP_NGAP_PDU_t *encode_ng_handover_failure(const ngap_handover_failure_t *msg)
+{
+  NGAP_NGAP_PDU_t *pdu = malloc_or_fail(sizeof(*pdu));
+
+  /* Prepare the NGAP message to encode */
+  pdu->present = NGAP_NGAP_PDU_PR_unsuccessfulOutcome;
+  asn1cCalloc(pdu->choice.unsuccessfulOutcome, head);
+  head->procedureCode = NGAP_ProcedureCode_id_HandoverResourceAllocation;
+  head->criticality = NGAP_Criticality_reject;
+  head->value.present = NGAP_UnsuccessfulOutcome__value_PR_HandoverFailure;
+  NGAP_HandoverFailure_t *out = &head->value.choice.HandoverFailure;
+
+  // AMF_UE_NGAP_ID (M)
+  {
+    asn1cSequenceAdd(out->protocolIEs.list, NGAP_HandoverFailureIEs_t, ie);
+    ie->id = NGAP_ProtocolIE_ID_id_AMF_UE_NGAP_ID;
+    ie->criticality = NGAP_Criticality_reject;
+    ie->value.present = NGAP_HandoverFailureIEs__value_PR_AMF_UE_NGAP_ID;
+    asn_uint642INTEGER(&ie->value.choice.AMF_UE_NGAP_ID, msg->amf_ue_ngap_id);
+  }
+
+  // Cause (M)
+  {
+    asn1cSequenceAdd(out->protocolIEs.list, NGAP_HandoverFailureIEs_t, ie);
+    ie->id = NGAP_ProtocolIE_ID_id_Cause;
+    ie->criticality = NGAP_Criticality_ignore;
+    ie->value.present = NGAP_HandoverFailureIEs__value_PR_Cause;
+    encode_ngap_cause(&ie->value.choice.Cause, &msg->cause);
+  }
+
+  return pdu;
+}

openair3/NGAP/ngap_gNB_mobility_management.h

@@ -27,5 +27,6 @@
 #include "ngap_messages_types.h"
 
 NGAP_NGAP_PDU_t *encode_ng_handover_required(const ngap_handover_required_t *msg);
+NGAP_NGAP_PDU_t *encode_ng_handover_failure(const ngap_handover_failure_t *msg);
 
 #endif /* NGAP_GNB_MOBILITY_MANAGEMENT_H_ */

openair3/NGAP/ngap_gNB_ue_context.c

@@ -76,6 +76,12 @@ struct ngap_gNB_ue_context_s *ngap_get_ue_context(uint32_t gNB_ue_ngap_id)
   return RB_FIND(ngap_ue_map, &ngap_ue_head, &temp);
 }
 
+ngap_gNB_ue_context_t *ngap_get_ue_context_from_amf_ue_ngap_id(uint32_t amf_ue_ngap_id)
+{
+  ngap_gNB_ue_context_t temp = {.amf_ue_ngap_id = amf_ue_ngap_id};
+  return RB_FIND(ngap_ue_map, &ngap_ue_head, &temp);
+}
+
 struct ngap_gNB_ue_context_s *ngap_detach_ue_context(uint32_t gNB_ue_ngap_id)
 {
   struct ngap_gNB_ue_context_s *tmp = ngap_get_ue_context(gNB_ue_ngap_id);

openair3/NGAP/ngap_gNB_ue_context.h

@@ -81,6 +81,7 @@ typedef struct ngap_gNB_ue_context_s {
 void ngap_store_ue_context(const ngap_gNB_ue_context_t *ue_desc_p);
 
 ngap_gNB_ue_context_t *ngap_get_ue_context(uint32_t gNB_ue_ngap_id);
+ngap_gNB_ue_context_t *ngap_get_ue_context_from_amf_ue_ngap_id(uint32_t amf_ue_ngap_id);
 ngap_gNB_ue_context_t *ngap_detach_ue_context(uint32_t gNB_ue_ngap_id);
 
 #endif /* NGAP_GNB_UE_CONTEXT_H_ */