Store spCellConfig during reestablishment for reconfiguration

The spCellConfig is to be dropped during reestablishment and to be
applied after reconfiguration. Implement this using the
RRCReconfigurationComplete acknowledgment from the CU to the DU,
applying the spCellConfig if present (which signals a prior
reestablishment). Remove a prior flag that is not needed anymore, and
do not "guess" when is the reconfiguration, because it is now handled in
the case of the ack.

The spCellConfig is not relevant as long as we use a common search space
for DCIs (and the activation of dedicated search space happens after
applying spCellConfig). For PUCCH, there is the PDSCH transmission of
RRCReconfiguration which gets ack'ed in the default PUCCH.
RRCReconfigurationComplete is sent in PUSCH (again through common
search space). In theory, there cannot be another PUCCH before the
application of spCellConfig, as all bearers are still suspended, and
there should not be another SRB1 transmission in the meantime, as only
one RRC transaction can be active at a time.

Co-authored-by: francescomani <email@francescomani.it>

openair2/LAYER2/NR_MAC_gNB/gNB_scheduler_primitives.c

@@ -2104,6 +2104,7 @@ NR_UE_info_t *find_ra_UE(NR_UEs_t *UEs, rnti_t rntiP)
 void delete_nr_ue_data(NR_UE_info_t *UE, NR_COMMON_channels_t *ccPtr, uid_allocator_t *uia)
 {
   ASN_STRUCT_FREE(asn_DEF_NR_CellGroupConfig, UE->CellGroup);
+  ASN_STRUCT_FREE(asn_DEF_NR_SpCellConfig, UE->reconfigSpCellConfig);
   ASN_STRUCT_FREE(asn_DEF_NR_UE_NR_Capability, UE->capability);
   NR_UE_sched_ctrl_t *sched_ctrl = &UE->UE_sched_ctrl;
   seq_arr_free(&sched_ctrl->lc_config, NULL);

openair2/LAYER2/NR_MAC_gNB/mac_rrc_dl_handler.c

@@ -774,12 +774,19 @@ void ue_context_modification_request(const f1ap_ue_context_modif_req_t *req)
           "RRC reconfiguration outcome unsuccessful, but no rollback mechanism implemented to come back to old configuration\n");
   } else if (req->ReconfigComplOutcome == RRCreconf_success) {
     LOG_I(NR_MAC, "DU received confirmation of successful RRC Reconfiguration\n");
+    if (UE->reconfigSpCellConfig) {
+      // in case of reestablishment, the spCellConfig had to be released
+      // temporarily. Reapply now before doing the reconfiguration.
+      UE->CellGroup->spCellConfig = UE->reconfigSpCellConfig;
+      UE->reconfigSpCellConfig = NULL;
+    }
     // we re-configure the BWP to apply the CellGroup and to use UE specific Search Space with DCIX1
     nr_mac_clean_cellgroup(UE->CellGroup);
     configure_UE_BWP(mac, scc, UE, false, NR_SearchSpace__searchSpaceType_PR_ue_Specific, -1, -1);
     for (int i = 1; i < seq_arr_size(&UE->UE_sched_ctrl.lc_config); ++i) {
       nr_lc_config_t *c = seq_arr_at(&UE->UE_sched_ctrl.lc_config, i);
       c->suspended = false;
+      nr_rlc_reestablish_entity(req->gNB_DU_ue_id, c->lcid);
     }
   }
 
@@ -945,14 +952,6 @@ void dl_rrc_message_transfer(const f1ap_dl_rrc_message_t *dl_rrc)
     DevAssert(success);
   }
 
-  if (UE->reestablish_rlc && dl_rrc->srb_id == 1) {
-    // we expected a reconfiguration to re-establish RLC, and this is on DCCH. We assume this is the reconfiguration.
-    for (int i = 1; i < seq_arr_size(&UE->UE_sched_ctrl.lc_config); ++i) {
-      nr_lc_config_t *lc_config = seq_arr_at(&UE->UE_sched_ctrl.lc_config, i);
-      nr_rlc_reestablish_entity(dl_rrc->gNB_DU_ue_id, lc_config->lcid);
-    }
-    UE->reestablish_rlc = false;
-  }
 
   /* if we get the old-gNB-DU-UE-ID, this means there is a reestablishment
    * ongoing. */
@@ -980,9 +979,9 @@ void dl_rrc_message_transfer(const f1ap_dl_rrc_message_t *dl_rrc)
     oldUE->CellGroup = NULL;
     UE->mac_stats = oldUE->mac_stats;
     /* 38.331 5.3.7.2 says that the UE releases the spCellConfig, so we drop it
-     * from the current configuration. Also, expect the reconfiguration from
-     * the CU, so save the old UE's CellGroup for the new UE */
-    ASN_STRUCT_FREE(asn_DEF_NR_SpCellConfig, UE->CellGroup->spCellConfig);
+     * from the current configuration. It will be reapplied when the
+     * reconfiguration has succeeded (indicated by the CU) */
+    UE->reconfigSpCellConfig = UE->CellGroup->spCellConfig;
     UE->CellGroup->spCellConfig = NULL;
     mac_remove_nr_ue(mac, *dl_rrc->old_gNB_DU_ue_id);
     pthread_mutex_unlock(&mac->sched_lock);
@@ -990,9 +989,6 @@ void dl_rrc_message_transfer(const f1ap_dl_rrc_message_t *dl_rrc)
     nr_rlc_update_id(*dl_rrc->old_gNB_DU_ue_id, dl_rrc->gNB_DU_ue_id);
     /* 38.331 clause 5.3.7.4: apply the specified configuration defined in 9.2.1 for SRB1 */
     nr_rlc_reconfigure_entity(dl_rrc->gNB_DU_ue_id, 1, NULL);
-    /* Set flag to trigger RLC re-establishment
-     * for remaining RBs in next RRCReconfiguration */
-    UE->reestablish_rlc = true;
     instance_t f1inst = get_f1_gtp_instance();
     if (f1inst >= 0) // we actually use F1-U
       gtpv1u_update_ue_id(f1inst, *dl_rrc->old_gNB_DU_ue_id, dl_rrc->gNB_DU_ue_id);

openair2/LAYER2/NR_MAC_gNB/nr_mac_gNB.h

@@ -746,8 +746,9 @@ typedef struct {
   NR_mac_stats_t mac_stats;
   /// currently active CellGroupConfig
   NR_CellGroupConfig_t *CellGroup;
-  /// reestablishRLC has to be signaled in RRCreconfiguration
-  bool reestablish_rlc;
+  /// in case of reestablishment, old spCellConfig to apply after
+  /// reconfiguration
+  NR_SpCellConfig_t *reconfigSpCellConfig;
   interrupt_followup_action_t interrupt_action;
   NR_UE_NR_Capability_t *capability;
   // UE selected beam index