Provide means to look-up if UE has a CU-UP

It might happen that a UE has no CU-UP (e.g., never requested a PDU
session). When triggering a release, we previously and implicitly
associated a CU-UP in that case. That is not good, and confusing.

This commit adds a function to look up if the UE has an associated
CU-UP. We only send a release if it is the case.

The function get_existing_cuup_for_ue() now instead verifies that a
CU-UP exist, and does not implicitly create an association (which might
be unwanted, see above).

openair2/RRC/NR/nr_rrc_proto.h

@@ -125,6 +125,7 @@ rrc_gNB_generate_dedicatedRRCReconfiguration_release(
 
 void rrc_gNB_generate_dedicatedRRCReconfiguration(const protocol_ctxt_t *const ctxt_pP, rrc_gNB_ue_context_t *ue_context_pP);
 
+bool ue_associated_to_cuup(const gNB_RRC_INST *rrc, const gNB_RRC_UE_t *ue);
 sctp_assoc_t get_existing_cuup_for_ue(const gNB_RRC_INST *rrc, const gNB_RRC_UE_t *ue);
 sctp_assoc_t get_new_cuup_for_ue(const gNB_RRC_INST *rrc, const gNB_RRC_UE_t *ue, int sst, int sd);
 int rrc_gNB_process_e1_setup_req(sctp_assoc_t assoc_id, e1ap_setup_req_t *req);

openair2/RRC/NR/rrc_gNB.c

@@ -2542,12 +2542,16 @@ 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);
+  }
 
   /* UE will be freed after UE context release complete */
 }

openair2/RRC/NR/rrc_gNB_cuup.c

@@ -75,14 +75,16 @@ static const nr_rrc_cuup_container_t *select_cuup_round_robin(size_t n_t, const
   return NULL;
 }
 
+bool ue_associated_to_cuup(const gNB_RRC_INST *rrc, const gNB_RRC_UE_t *ue)
+{
+  f1_ue_data_t ue_data = cu_get_f1_ue_data(ue->rrc_ue_id);
+  return ue_data.e1_assoc_id != 0;
+}
+
 sctp_assoc_t get_existing_cuup_for_ue(const gNB_RRC_INST *rrc, const gNB_RRC_UE_t *ue)
 {
   f1_ue_data_t ue_data = cu_get_f1_ue_data(ue->rrc_ue_id);
-  if (ue_data.e1_assoc_id == 0) {
-    LOG_W(RRC, "UE %d should be associated to CU-UP, but is not\n", ue->rrc_ue_id);
-    /* we could possibly check the SST/SD from the PDU session */
-    return get_new_cuup_for_ue(rrc, ue, 0, 0);
-  }
+  AssertFatal(ue_data.e1_assoc_id != 0, "UE %d should be associated to CU-UP, but is not\n", ue->rrc_ue_id);
   LOG_D(RRC, "UE %d using CU-UP assoc_id %d\n", ue->rrc_ue_id, ue_data.e1_assoc_id);
   return ue_data.e1_assoc_id;
 }