CU: handle UE context release properly, not telling the DU to notify the UE over a broken link (DU-side already supports this

openair2/RRC/NR/nr_rrc_defs.h

@@ -238,6 +238,7 @@ typedef struct gNB_RRC_UE_s {
   uint32_t                           ue_reconfiguration_counter;
   bool ongoing_reconfiguration;
   bool an_release; // flag if core requested UE release
+  bool rl_failure; // flag if DU reported radio link failure (skip RRC Release)
 
   /* NGUEContextSetup might come with PDU sessions, but setup needs to be
    * delayed after security (and capability); PDU sessions are stored here */

openair2/RRC/NR/rrc_gNB.c

@@ -2645,6 +2645,12 @@ static void rrc_CU_process_ue_context_release_request(MessageDef *msg_p, sctp_as
 
   /* TODO: marshall types correctly */
   LOG_I(NR_RRC, "received UE Context Release Request for UE %u, forwarding to AMF\n", req->gNB_CU_ue_id);
+  /* remember radio link failure so CU skips RRC Release in the release command
+   * (per TS 38.473 8.3.3: omit RRC-Container when radio link is dead) */
+  if (req->cause == F1AP_CAUSE_RADIO_NETWORK
+      && (req->cause_value == F1AP_CauseRadioNetwork_rl_failure_rlc
+          || req->cause_value == F1AP_CauseRadioNetwork_rl_failure_others))
+    UE->rl_failure = true;
   ngap_cause_t cause = {.type = NGAP_CAUSE_RADIO_NETWORK, .value = NGAP_CAUSE_RADIO_NETWORK_RADIO_CONNECTION_WITH_UE_LOST};
   rrc_gNB_send_NGAP_UE_CONTEXT_RELEASE_REQ(instance, ue_context_p, cause);
 }

openair2/RRC/NR/rrc_gNB_NGAP.c

@@ -43,6 +43,7 @@
 #include "NR_HandoverCommand.h"
 #include "NR_HandoverCommand-IEs.h"
 #include "E1AP_RLC-Mode.h"
+#include "F1AP_CauseRadioNetwork.h"
 #include "NR_PDCP-Config.h"
 #include "NGAP_CauseRadioNetwork.h"
 #include "NGAP_Dynamic5QIDescriptor.h"
@@ -1338,7 +1339,22 @@ int rrc_gNB_process_NGAP_UE_CONTEXT_RELEASE_COMMAND(MessageDef *msg_p, instance_
   /* 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) {
-    rrc_gNB_generate_RRCRelease(rrc, UE);
+    if (UE->rl_failure) {
+      /* Radio link is dead (DU reported rl-failure): send F1AP UE Context
+       * Release Command without RRC-Container per TS 38.473 section 8.3.3.
+       * The DU will release resources locally without signaling the UE. */
+      LOG_I(NR_RRC, "UE %u: radio link failure, sending release command without RRC Release\n", UE->rrc_ue_id);
+      f1_ue_data_t ue_data = cu_get_f1_ue_data(UE->rrc_ue_id);
+      f1ap_ue_context_rel_cmd_t cmd = {
+        .gNB_CU_ue_id = UE->rrc_ue_id,
+        .gNB_DU_ue_id = ue_data.secondary_ue,
+        .cause = F1AP_CAUSE_RADIO_NETWORK,
+        .cause_value = F1AP_CauseRadioNetwork_rl_failure_rlc,
+      };
+      rrc->mac_rrc.ue_context_release_command(ue_data.du_assoc_id, &cmd);
+    } else {
+      rrc_gNB_generate_RRCRelease(rrc, UE);
+    }
 
     /* UE will be freed after UE context release complete */
   } else {