Request release for UEs if DU disconnects

38.473 section 8.2.3.1 says that upon F1 Setup Request, UE associated
signalling should be erased. In this commit, we trigger a release of all
UEs that were still connected to a DU when we received the SCTP
shutdown, i.e., when the DU disconnects.

openair2/RRC/NR/nr_rrc_proto.h

@@ -63,6 +63,7 @@ void rrc_parse_ue_capabilities(gNB_RRC_INST *rrc,NR_UE_CapabilityRAT_ContainerLi
 void rrc_add_nsa_user(gNB_RRC_INST *rrc, rrc_gNB_ue_context_t *ue_context_p, x2ap_ENDC_sgnb_addition_req_t *m);
 
 void rrc_remove_nsa_user(gNB_RRC_INST *rrc, int rnti);
+void rrc_remove_ue(gNB_RRC_INST *rrc, rrc_gNB_ue_context_t *ue_context_p);
 
 void fill_default_reconfig(NR_ServingCellConfigCommon_t *servingcellconfigcommon,
                            NR_ServingCellConfig_t *servingcellconfigdedicated,

openair2/RRC/NR/rrc_gNB.c

@@ -1940,6 +1940,19 @@ static void rrc_delete_ue_data(gNB_RRC_UE_t *UE)
   ASN_STRUCT_FREE(asn_DEF_NR_MeasResults, UE->measResults);
 }
 
+void rrc_remove_ue(gNB_RRC_INST *rrc, rrc_gNB_ue_context_t *ue_context_p)
+{
+  gNB_RRC_UE_t *UE = &ue_context_p->ue_context;
+  /* we call nr_pdcp_remove_UE() in the handler of E1 bearer release, but if we
+   * are in E1, we also need to free the UE in the CU-CP, so call it twice to
+   * cover all cases */
+  nr_pdcp_remove_UE(UE->rrc_ue_id);
+  rrc_gNB_send_NGAP_UE_CONTEXT_RELEASE_COMPLETE(0, UE->rrc_ue_id);
+  LOG_I(NR_RRC, "removed UE CU UE ID %u/RNTI %04x \n", UE->rrc_ue_id, UE->rnti);
+  rrc_delete_ue_data(UE);
+  rrc_gNB_remove_ue_context(rrc, ue_context_p);
+}
+
 static void rrc_CU_process_ue_context_release_complete(MessageDef *msg_p)
 {
   const int instance = 0;
@@ -1950,16 +1963,8 @@ static void rrc_CU_process_ue_context_release_complete(MessageDef *msg_p)
     LOG_E(RRC, "could not find UE context for CU UE ID %u, aborting transaction\n", complete->gNB_CU_ue_id);
     return;
   }
-  gNB_RRC_UE_t *UE = &ue_context_p->ue_context;
 
-  /* we call nr_pdcp_remove_UE() in the handler of E1 bearer release, but if we
-   * are in E1, we also need to free the UE in the CU-CP, so call it twice to
-   * cover all cases */
-  nr_pdcp_remove_UE(UE->rrc_ue_id);
-  rrc_gNB_send_NGAP_UE_CONTEXT_RELEASE_COMPLETE(instance, UE->rrc_ue_id);
-  LOG_I(NR_RRC, "removed UE CU UE ID %u/RNTI %04x \n", UE->rrc_ue_id, UE->rnti);
-  rrc_delete_ue_data(UE);
-  rrc_gNB_remove_ue_context(rrc, ue_context_p);
+  rrc_remove_ue(RC.nrrrc[0], ue_context_p);
 }
 
 static void rrc_CU_process_ue_context_modification_response(MessageDef *msg_p, instance_t instance)
@@ -2672,23 +2677,6 @@ rrc_gNB_generate_RRCRelease(
   };
   deliver_ue_ctxt_release_data_t data = {.rrc = rrc, .release_cmd = &ue_context_release_cmd, .assoc_id = ue_data.du_assoc_id};
   nr_pdcp_data_req_srb(ctxt_pP->rntiMaybeUEid, DCCH, rrc_gNB_mui++, size, buffer, rrc_deliver_ue_ctxt_release_cmd, &data);
-
-  /* a UE might not be associated to a CU-UP if it never requested a PDU
-   * session (intentionally, or because of erros) */
-  if (ue_associated_to_cuup(rrc, UE)) {
-    sctp_assoc_t assoc_id = get_existing_cuup_for_ue(rrc, UE);
-    e1ap_bearer_release_cmd_t cmd = {
-      .gNB_cu_cp_ue_id = UE->rrc_ue_id,
-      .gNB_cu_up_ue_id = UE->rrc_ue_id,
-    };
-    rrc->cucp_cuup.bearer_context_release(assoc_id, &cmd);
-  }
-
-#ifdef E2_AGENT
-  signal_rrc_state_changed_to(UE, RC_SM_RRC_IDLE);
-#endif
-
-  /* UE will be freed after UE context release complete */
 }
 
 int rrc_gNB_generate_pcch_msg(sctp_assoc_t assoc_id, const NR_SIB1_t *sib1, uint32_t tmsi, uint8_t paging_drx)

openair2/RRC/NR/rrc_gNB_NGAP.c

@@ -73,6 +73,10 @@
 #include "conversions.h"
 #include "RRC/NR/rrc_gNB_radio_bearers.h"
 
+#ifdef E2_AGENT
+#include "openair2/E2AP/RAN_FUNCTION/O-RAN/ran_func_rc_extern.h"
+#endif
+
 #include "uper_encoder.h"
 
 extern RAN_CONTEXT_t RC;
@@ -1178,7 +1182,7 @@ int rrc_gNB_process_NGAP_UE_CONTEXT_RELEASE_REQ(MessageDef *msg_p, instance_t in
     itti_send_msg_to_task(TASK_NGAP, instance, msg_fail_p);
     return (-1);
   } else {
-    /* TODO release context. */
+
     /* Send the response */
     MessageDef *msg_resp_p;
     msg_resp_p = itti_alloc_new_message(TASK_RRC_GNB, 0, NGAP_UE_CONTEXT_RELEASE_RESP);
@@ -1195,7 +1199,7 @@ int rrc_gNB_process_NGAP_UE_CONTEXT_RELEASE_REQ(MessageDef *msg_p, instance_t in
 */
 int rrc_gNB_process_NGAP_UE_CONTEXT_RELEASE_COMMAND(MessageDef *msg_p, instance_t instance)
 {
-  //-----------------------------------------------------------------------------
+  gNB_RRC_INST *rrc = RC.nrrrc[0];
   uint32_t gNB_ue_ngap_id = 0;
   protocol_ctxt_t ctxt;
   gNB_ue_ngap_id = NGAP_UE_CONTEXT_RELEASE_COMMAND(msg_p).gNB_ue_ngap_id;
@@ -1214,9 +1218,34 @@ int rrc_gNB_process_NGAP_UE_CONTEXT_RELEASE_COMMAND(MessageDef *msg_p, instance_
   }
 
   gNB_RRC_UE_t *UE = &ue_context_p->ue_context;
-  PROTOCOL_CTXT_SET_BY_INSTANCE(&ctxt, instance, GNB_FLAG_YES, UE->rrc_ue_id, 0, 0);
-  ctxt.eNB_index = 0;
-  rrc_gNB_generate_RRCRelease(&ctxt, ue_context_p);
+#ifdef E2_AGENT
+  signal_rrc_state_changed_to(UE, RC_SM_RRC_IDLE);
+#endif
+
+  /* a UE might not be associated to a CU-UP if it never requested a PDU
+   * session (intentionally, or because of erros) */
+  if (ue_associated_to_cuup(rrc, UE)) {
+    sctp_assoc_t assoc_id = get_existing_cuup_for_ue(rrc, UE);
+    e1ap_bearer_release_cmd_t cmd = {
+      .gNB_cu_cp_ue_id = UE->rrc_ue_id,
+      .gNB_cu_up_ue_id = UE->rrc_ue_id,
+    };
+    rrc->cucp_cuup.bearer_context_release(assoc_id, &cmd);
+  }
+
+  /* special case: the DU might be offline, in which case the f1_ue_data exists
+   * but is set to 0 */
+  if (cu_exists_f1_ue_data(UE->rrc_ue_id) && cu_get_f1_ue_data(UE->rrc_ue_id).du_assoc_id != 0) {
+    PROTOCOL_CTXT_SET_BY_INSTANCE(&ctxt, instance, GNB_FLAG_YES, UE->rrc_ue_id, 0, 0);
+    ctxt.eNB_index = 0;
+    rrc_gNB_generate_RRCRelease(&ctxt, ue_context_p);
+
+    /* UE will be freed after UE context release complete */
+  } else {
+    // the DU is offline already
+    rrc_remove_ue(rrc, ue_context_p);
+  }
+
   return 0;
 }
 

openair2/RRC/NR/rrc_gNB_du.c

@@ -20,6 +20,7 @@
  */
 
 #include "rrc_gNB_du.h"
+#include "rrc_gNB_NGAP.h"
 #include "common/ran_context.h"
 #include "nr_rrc_defs.h"
 #include "rrc_gNB_UE_context.h"
@@ -211,10 +212,14 @@ static int invalidate_du_connections(gNB_RRC_INST *rrc, sctp_assoc_t assoc_id)
     f1_ue_data_t ue_data = cu_get_f1_ue_data(ue_id);
     if (ue_data.du_assoc_id == assoc_id) {
       /* this UE belongs to the DU that disconnected, set du_assoc_id to 0,
-       * meaning DU is offline */
+       * meaning DU is offline, then trigger release request */
       cu_remove_f1_ue_data(ue_id);
-      f1_ue_data_t new = {.secondary_ue = ue_data.secondary_ue, .du_assoc_id = 0 };
-      cu_add_f1_ue_data(ue_id, &new);
+      ue_data.du_assoc_id = 0;
+      cu_add_f1_ue_data(ue_id, &ue_data);
+      rrc_gNB_send_NGAP_UE_CONTEXT_RELEASE_REQ(0,
+                                               ue_context_p,
+                                               NGAP_CAUSE_RADIO_NETWORK,
+                                               NGAP_CAUSE_RADIO_NETWORK_RADIO_CONNECTION_WITH_UE_LOST);
       count++;
     }
   }