Simplify RRC DRB handling code

Prior to this commit, the handling of DRBs is complex: first the RRC "guessed" a DRB ID when setting up DRBs via E1AP (in rrc_gNB_process_NGAP_PDUSESSION_SETUP_REQ()), and later chose one for real in fill_DRB_Configlist() (called in rrc_gNB_generate_dedicatedRRCReconfiguration()). To simplify, remove fill_DRB_Configlist(), and instead allocate the DRB using generateDRB() before sending the message via E1AP, in rrc_gNB_generate_dedicatedRRCReconfiguration(). The rest of the logic is the same. For PDU sessions, always mark PDU sessions as "done" to match pdu session state logic.
2024-02-03 11:28:43 +01:00
parent a47eab5262
commit f81ec9c2cc
4 changed files with 136 additions and 183 deletions
@@ -121,73 +121,6 @@ mui_t rrc_gNB_mui = 0;
 ///---------------------------------------------------------------------------------------------------------------///
 ///---------------------------------------------------------------------------------------------------------------///

-NR_DRB_ToAddModList_t *fill_DRB_configList(gNB_RRC_UE_t *ue)
-{
-  gNB_RRC_INST *rrc = RC.nrrrc[0];
-  if (ue->nb_of_pdusessions == 0)
-    return NULL;
-  int nb_drb_to_setup = rrc->configuration.drbs;
-  long drb_priority[MAX_DRBS_PER_UE] = {0};
-  uint8_t drb_id_to_setup_start = 0;
-  NR_DRB_ToAddModList_t *DRB_configList = CALLOC(sizeof(*DRB_configList), 1);
-  for (int i = 0; i < ue->nb_of_pdusessions; i++) {
-    if (ue->pduSession[i].status >= PDU_SESSION_STATUS_DONE) {
-      continue;
-    }
-    LOG_I(NR_RRC, "adding rnti %x pdusession %d, nb drb %d\n", ue->rnti, ue->pduSession[i].param.pdusession_id, nb_drb_to_setup);
-    for (long drb_id_add = 1; drb_id_add <= nb_drb_to_setup; drb_id_add++) {
-      uint8_t drb_id;
-      // Reference TS23501 Table 5.7.4-1: Standardized 5QI to QoS characteristics mapping
-      for (int qos_flow_index = 0; qos_flow_index < ue->pduSession[i].param.nb_qos; qos_flow_index++) {
-        switch (ue->pduSession[i].param.qos[qos_flow_index].fiveQI) {
-          case 1 ... 4: /* GBR */
-            drb_id = next_available_drb(ue, &ue->pduSession[i], GBR_FLOW);
-            break;
-          case 5 ... 9: /* Non-GBR */
-            if (rrc->configuration.drbs > 1) { /* Force the creation from gNB Conf file */
-              LOG_W(NR_RRC, "Adding %d DRBs, from gNB config file (not decided by 5GC\n", rrc->configuration.drbs);
-              drb_id = next_available_drb(ue, &ue->pduSession[i], GBR_FLOW);
-            } else {
-              drb_id = next_available_drb(ue, &ue->pduSession[i], NONGBR_FLOW);
-            }
-            break;
-
-          default:
-            LOG_E(NR_RRC, "not supported 5qi %lu\n", ue->pduSession[i].param.qos[qos_flow_index].fiveQI);
-            ue->pduSession[i].status = PDU_SESSION_STATUS_FAILED;
-            continue;
-        }
-        drb_priority[drb_id - 1] = ue->pduSession[i].param.qos[qos_flow_index].allocation_retention_priority.priority_level;
-        if (drb_priority[drb_id - 1] < 0 || drb_priority[drb_id - 1] > NGAP_PRIORITY_LEVEL_NO_PRIORITY) {
-          LOG_E(NR_RRC, "invalid allocation_retention_priority.priority_level %ld set to _NO_PRIORITY\n", drb_priority[drb_id - 1]);
-          drb_priority[drb_id - 1] = NGAP_PRIORITY_LEVEL_NO_PRIORITY;
-        }
-
-        if (drb_is_active(ue, drb_id)) { /* Non-GBR flow using the same DRB or a GBR flow with no available DRBs*/
-          nb_drb_to_setup--;
-        } else {
-          generateDRB(ue,
-                      drb_id,
-                      &ue->pduSession[i],
-                      rrc->configuration.enable_sdap,
-                      rrc->security.do_drb_integrity,
-                      rrc->security.do_drb_ciphering);
-          NR_DRB_ToAddMod_t *DRB_config = generateDRB_ASN1(&ue->established_drbs[drb_id - 1]);
-          if (drb_id_to_setup_start == 0)
-            drb_id_to_setup_start = DRB_config->drb_Identity;
-          asn1cSeqAdd(&DRB_configList->list, DRB_config);
-        }
-        LOG_D(RRC, "DRB Priority %ld\n", drb_priority[drb_id]); // To supress warning for now
-      }
-    }
-  }
-  if (DRB_configList->list.count == 0) {
-    free(DRB_configList);
-    return NULL;
-  }
-  return DRB_configList;
-}
-
 static void freeDRBlist(NR_DRB_ToAddModList_t *list)
 {
  //ASN_STRUCT_FREE(asn_DEF_NR_DRB_ToAddModList, list);
@@ -579,10 +512,12 @@ static void rrc_gNB_generate_defaultRRCReconfiguration(const protocol_ctxt_t *co
    if (ue_p->pduSession[i].param.nas_pdu.buffer != NULL) {
      asn1cSequenceAdd(dedicatedNAS_MessageList->list, NR_DedicatedNAS_Message_t, msg);
      OCTET_STRING_fromBuf(msg, (char *)ue_p->pduSession[i].param.nas_pdu.buffer, ue_p->pduSession[i].param.nas_pdu.length);
-    }

-    ue_p->pduSession[i].status = PDU_SESSION_STATUS_DONE;
-    LOG_D(NR_RRC, "setting the status for the default DRB (index %d) to (%d,%s)\n", i, ue_p->pduSession[i].status, "PDU_SESSION_STATUS_DONE");
+    }
+    if (ue_p->pduSession[i].status < PDU_SESSION_STATUS_ESTABLISHED) {
+      ue_p->pduSession[i].status = PDU_SESSION_STATUS_DONE;
+      LOG_D(NR_RRC, "setting the status for the default DRB (index %d) to (%d,%s)\n", i, ue_p->pduSession[i].status, "PDU_SESSION_STATUS_DONE");
+    }
  }

  if (ue_p->nas_pdu.length) {
@@ -659,34 +594,29 @@ void rrc_gNB_generate_dedicatedRRCReconfiguration(const protocol_ctxt_t *const c

  uint8_t xid = rrc_gNB_get_next_transaction_identifier(ctxt_pP->module_id);
  gNB_RRC_UE_t *ue_p = &ue_context_pP->ue_context;
-  NR_DRB_ToAddModList_t *DRB_configList = fill_DRB_configList(ue_p);
  ue_p->xids[xid] = RRC_PDUSESSION_ESTABLISH;
-  struct NR_RRCReconfiguration_v1530_IEs__dedicatedNAS_MessageList *dedicatedNAS_MessageList = NULL;
-  NR_DedicatedNAS_Message_t *dedicatedNAS_Message = NULL;
-  dedicatedNAS_MessageList = CALLOC(1, sizeof(struct NR_RRCReconfiguration_v1530_IEs__dedicatedNAS_MessageList));
+  struct NR_RRCReconfiguration_v1530_IEs__dedicatedNAS_MessageList *dedicatedNAS_MessageList = CALLOC(1, sizeof(*dedicatedNAS_MessageList));

-  int nb_drb_to_setup = DRB_configList ? DRB_configList->list.count : 0;
-  for (int i=0; i < nb_drb_to_setup; i++) {
-    int j = ue_p->nb_of_pdusessions - 1;
-    AssertFatal(j >= 0, "");
-    if (ue_p->pduSession[j].param.nas_pdu.buffer != NULL) {
-      dedicatedNAS_Message = CALLOC(1, sizeof(NR_DedicatedNAS_Message_t));
-      memset(dedicatedNAS_Message, 0, sizeof(OCTET_STRING_t));
-      OCTET_STRING_fromBuf(dedicatedNAS_Message,
-                           (char *)ue_p->pduSession[j].param.nas_pdu.buffer,
-                           ue_p->pduSession[j].param.nas_pdu.length);
-      ue_p->pduSession[j].status = PDU_SESSION_STATUS_DONE;
-      asn1cSeqAdd(&dedicatedNAS_MessageList->list, dedicatedNAS_Message);
+  for (int i = 0; i < ue_p->nb_of_pdusessions; i++) {
+    if (ue_p->pduSession[i].param.nas_pdu.buffer != NULL) {
+      asn1cSequenceAdd(dedicatedNAS_MessageList->list, NR_DedicatedNAS_Message_t, msg);
+      OCTET_STRING_fromBuf(msg,
+                           (char *)ue_p->pduSession[i].param.nas_pdu.buffer,
+                           ue_p->pduSession[i].param.nas_pdu.length);
+      asn1cSeqAdd(&dedicatedNAS_MessageList->list, msg);

-      LOG_I(NR_RRC, "add NAS info with size %d (pdusession idx %d)\n", ue_p->pduSession[j].param.nas_pdu.length, j);
-    } else {
-      // TODO
-      LOG_E(NR_RRC, "no NAS info (pdusession idx %d)\n", j);
+      LOG_D(NR_RRC, "add NAS info with size %d (pdusession idx %d)\n", ue_p->pduSession[i].param.nas_pdu.length, i);
+      ue_p->pduSession[i].xid = xid;
+    }
+    if (ue_p->pduSession[i].status < PDU_SESSION_STATUS_ESTABLISHED) {
+      ue_p->pduSession[i].status = PDU_SESSION_STATUS_DONE;
    }
-
-    ue_p->pduSession[j].xid = xid;
  }
-  freeDRBlist(DRB_configList);
+
+  if (ue_p->nas_pdu.length) {
+    asn1cSequenceAdd(dedicatedNAS_MessageList->list, NR_DedicatedNAS_Message_t, msg);
+    OCTET_STRING_fromBuf(msg, (char *)ue_p->nas_pdu.buffer, ue_p->nas_pdu.length);
+  }

  /* If list is empty free the list and reset the address */
  if (dedicatedNAS_MessageList->list.count == 0) {
@@ -748,7 +678,6 @@ rrc_gNB_modify_dedicatedRRCReconfiguration(
 //-----------------------------------------------------------------------------
 {
  gNB_RRC_UE_t *ue_p = &ue_context_pP->ue_context;
-  NR_DRB_ToAddModList_t *DRB_configList = fill_DRB_configList(ue_p);
  int qos_flow_index = 0;
  uint8_t xid = rrc_gNB_get_next_transaction_identifier(ctxt_pP->module_id);
  ue_p->xids[xid] = RRC_PDUSESSION_MODIFY;
@@ -819,8 +748,6 @@ rrc_gNB_modify_dedicatedRRCReconfiguration(
            ue_p->pduSession[i].param.qos[qos_flow_index].fiveQI);
    }

-    asn1cSeqAdd(&DRB_configList->list, DRB_config);
-
    ue_p->pduSession[i].status = PDU_SESSION_STATUS_DONE;
    ue_p->pduSession[i].xid = xid;

@@ -839,19 +766,21 @@ rrc_gNB_modify_dedicatedRRCReconfiguration(
    dedicatedNAS_MessageList = NULL;
  }

+  NR_DRB_ToAddModList_t *DRBs = createDRBlist(ue_p, false);
  uint8_t buffer[RRC_BUF_SIZE];
  int size = do_RRCReconfiguration(ue_p,
                                   buffer,
                                   RRC_BUF_SIZE,
                                   xid,
                                   NULL,
-                                   DRB_configList,
+                                   DRBs,
                                   NULL,
                                   NULL,
                                   NULL,
                                   dedicatedNAS_MessageList,
                                   NULL);
  LOG_DUMPMSG(NR_RRC, DEBUG_RRC, (char *)buffer, size, "[MSG] RRC Reconfiguration\n");
+  freeDRBlist(DRBs);

  /* Free all NAS PDUs */
  for (int i = 0; i < ue_p->nb_of_pdusessions; i++) {
@@ -2442,7 +2371,7 @@ rrc_gNB_generate_SecurityModeCommand(
  NR_IntegrityProtAlgorithm_t integrity_algorithm = (NR_IntegrityProtAlgorithm_t)ue_p->integrity_algorithm;
  size = do_NR_SecurityModeCommand(ctxt_pP, buffer, rrc_gNB_get_next_transaction_identifier(ctxt_pP->module_id), ue_p->ciphering_algorithm, integrity_algorithm);
  LOG_DUMPMSG(NR_RRC,DEBUG_RRC,(char *)buffer,size,"[MSG] RRC Security Mode Command\n");
-  LOG_I(NR_RRC, "UE %04x Logical Channel DL-DCCH, Generate SecurityModeCommand (bytes %d)\n", ue_p->rnti, size);
+  LOG_I(NR_RRC, "UE %u Logical Channel DL-DCCH, Generate SecurityModeCommand (bytes %d)\n", ue_p->rrc_ue_id, size);

  gNB_RRC_INST *rrc = RC.nrrrc[ctxt_pP->module_id];
  AssertFatal(!NODE_IS_DU(rrc->node_type), "illegal node type DU!\n");
@@ -795,24 +795,35 @@ void rrc_gNB_process_NGAP_PDUSESSION_SETUP_REQ(MessageDef *msg_p, instance_t ins
    pdu->confidentialityProtectionIndication = rrc->security.do_drb_ciphering ? E1AP_ConfidentialityProtectionIndication_required : E1AP_ConfidentialityProtectionIndication_not_needed;
    pdu->teId = session->gtp_teid;
    memcpy(&pdu->tlAddress, session->upf_addr.buffer, 4); // Fixme: dirty IPv4 target
+
+    /* we assume for the moment one DRB per PDU session. Activate the bearer,
+     * and configure in RRC. */
+    int drb_id = get_next_available_drb_id(UE);
+    drb_t *rrc_drb = generateDRB(UE,
+                                 drb_id,
+                                 pduSession,
+                                 rrc->configuration.enable_sdap,
+                                 rrc->security.do_drb_integrity,
+                                 rrc->security.do_drb_ciphering);
+
    pdu->numDRB2Setup = 1; // One DRB per PDU Session. TODO: Remove hardcoding
    for (int j=0; j < pdu->numDRB2Setup; j++) {
      DRB_nGRAN_to_setup_t *drb = pdu->DRBnGRanList + j;

-      drb->id = i + j + UE->nb_of_pdusessions;
+      drb->id = rrc_drb->drb_id;

-      drb->defaultDRB = true;
+      struct sdap_config_s *sdap_config = &rrc_drb->cnAssociation.sdap_config;
+      drb->defaultDRB = sdap_config->defaultDRB ? E1AP_DefaultDRB_true : E1AP_DefaultDRB_false;
+      drb->sDAP_Header_UL = sdap_config->sdap_HeaderUL;
+      drb->sDAP_Header_DL = sdap_config->sdap_HeaderDL;

-      drb->sDAP_Header_UL = !(rrc->configuration.enable_sdap);
-      drb->sDAP_Header_DL = !(rrc->configuration.enable_sdap);
+      struct pdcp_config_s *pdcp_config = &rrc_drb->pdcp_config;
+      drb->pDCP_SN_Size_UL = pdcp_config->pdcp_SN_SizeUL;
+      drb->pDCP_SN_Size_DL = pdcp_config->pdcp_SN_SizeDL;
+      drb->discardTimer = pdcp_config->discardTimer;
+      drb->reorderingTimer = pdcp_config->t_Reordering;

-      drb->pDCP_SN_Size_UL = E1AP_PDCP_SN_Size_s_18;
-      drb->pDCP_SN_Size_DL = E1AP_PDCP_SN_Size_s_18;
-
-      drb->discardTimer = E1AP_DiscardTimer_infinity;
-      drb->reorderingTimer = E1AP_T_Reordering_ms100;
-
-      drb->rLC_Mode = E1AP_RLC_Mode_rlc_am;
+      drb->rLC_Mode = rrc->configuration.um_on_default_drb ? E1AP_RLC_Mode_rlc_um_bidirectional : E1AP_RLC_Mode_rlc_am;

      drb->numCellGroups = 1; // assume one cell group associated with a DRB

@@ -37,62 +37,71 @@ rrc_pdu_session_param_t *find_pduSession(gNB_RRC_UE_t *ue, int id, bool create)
  return ue->pduSession + j;
 }

-void generateDRB(gNB_RRC_UE_t *ue,
-                 uint8_t drb_id,
-                 rrc_pdu_session_param_t *pduSession,
-                 bool enable_sdap,
-                 int do_drb_integrity,
-                 int do_drb_ciphering)
+drb_t *get_drb(gNB_RRC_UE_t *ue, uint8_t drb_id)
 {
-  int i;
-  int qos_flow_index;
+  DevAssert(drb_id > 0 && drb_id < 32);
+  DevAssert(ue != NULL);
+
+  return &ue->established_drbs[drb_id - 1];
+}
+
+drb_t *generateDRB(gNB_RRC_UE_t *ue,
+                   uint8_t drb_id,
+                   const rrc_pdu_session_param_t *pduSession,
+                   bool enable_sdap,
+                   int do_drb_integrity,
+                   int do_drb_ciphering)
+{
+  DevAssert(ue != NULL);
+
+  LOG_I(NR_RRC, "UE %d: configure DRB ID %d for PDU session ID %d\n", ue->rrc_ue_id, drb_id, pduSession->param.pdusession_id);
+
  drb_t *est_drb = &ue->established_drbs[drb_id - 1];
-  if (est_drb->status == DRB_INACTIVE) {
-    /* DRB Management */
-    est_drb->drb_id = drb_id;
-    est_drb->reestablishPDCP = -1;
-    est_drb->recoverPDCP = -1;
-    for (i = 0; i < MAX_DRBS_PER_UE; i++) {
-      if ((est_drb->cnAssociation.sdap_config.pdusession_id == 0
-           || est_drb->cnAssociation.sdap_config.pdusession_id == pduSession->param.pdusession_id)
-          && est_drb->defaultDRBid == 0) {
-        est_drb->cnAssociation.sdap_config.defaultDRB = true;
-        est_drb->defaultDRBid = drb_id;
-      }
-    }
-    /* SDAP Configuration */
-    est_drb->cnAssociation.present = NR_DRB_ToAddMod__cnAssociation_PR_sdap_Config;
-    est_drb->cnAssociation.sdap_config.pdusession_id = pduSession->param.pdusession_id;
-    if (enable_sdap) {
-      est_drb->cnAssociation.sdap_config.sdap_HeaderDL = NR_SDAP_Config__sdap_HeaderDL_present;
-      est_drb->cnAssociation.sdap_config.sdap_HeaderUL = NR_SDAP_Config__sdap_HeaderUL_present;
-    } else {
-      est_drb->cnAssociation.sdap_config.sdap_HeaderDL = NR_SDAP_Config__sdap_HeaderDL_absent;
-      est_drb->cnAssociation.sdap_config.sdap_HeaderUL = NR_SDAP_Config__sdap_HeaderUL_absent;
-    }
-    for (qos_flow_index = 0; qos_flow_index < pduSession->param.nb_qos; qos_flow_index++) {
-      est_drb->cnAssociation.sdap_config.mappedQoS_FlowsToAdd[qos_flow_index] = pduSession->param.qos[qos_flow_index].qfi;
-      if (pduSession->param.qos[qos_flow_index].fiveQI > 5)
-        est_drb->status = DRB_ACTIVE_NONGBR;
-      else
-        est_drb->status = DRB_ACTIVE;
-    }
-    /* PDCP Configuration */
-    est_drb->pdcp_config.discardTimer = NR_PDCP_Config__drb__discardTimer_infinity;
-    est_drb->pdcp_config.pdcp_SN_SizeDL = NR_PDCP_Config__drb__pdcp_SN_SizeDL_len18bits;
-    est_drb->pdcp_config.pdcp_SN_SizeUL = NR_PDCP_Config__drb__pdcp_SN_SizeUL_len18bits;
-    est_drb->pdcp_config.t_Reordering = NR_PDCP_Config__t_Reordering_ms100;
-    est_drb->pdcp_config.headerCompression.present = NR_PDCP_Config__drb__headerCompression_PR_notUsed;
-    est_drb->pdcp_config.headerCompression.NotUsed = 0;
-    if (do_drb_integrity)
-      est_drb->pdcp_config.integrityProtection = NR_PDCP_Config__drb__integrityProtection_enabled;
-    else
-      est_drb->pdcp_config.integrityProtection = 1;
-    if (do_drb_ciphering)
-      est_drb->pdcp_config.ext1.cipheringDisabled = 1;
-    else
-      est_drb->pdcp_config.ext1.cipheringDisabled = NR_PDCP_Config__ext1__cipheringDisabled_true;
+  DevAssert(est_drb->status == DRB_INACTIVE);
+
+  est_drb->status = DRB_ACTIVE;
+  est_drb->drb_id = drb_id;
+  est_drb->reestablishPDCP = -1;
+  est_drb->recoverPDCP = -1;
+  est_drb->cnAssociation.sdap_config.defaultDRB = true;
+  est_drb->defaultDRBid = drb_id;
+
+  /* SDAP Configuration */
+  est_drb->cnAssociation.present = NR_DRB_ToAddMod__cnAssociation_PR_sdap_Config;
+  est_drb->cnAssociation.sdap_config.pdusession_id = pduSession->param.pdusession_id;
+  if (enable_sdap) {
+    est_drb->cnAssociation.sdap_config.sdap_HeaderDL = NR_SDAP_Config__sdap_HeaderDL_present;
+    est_drb->cnAssociation.sdap_config.sdap_HeaderUL = NR_SDAP_Config__sdap_HeaderUL_present;
+  } else {
+    est_drb->cnAssociation.sdap_config.sdap_HeaderDL = NR_SDAP_Config__sdap_HeaderDL_absent;
+    est_drb->cnAssociation.sdap_config.sdap_HeaderUL = NR_SDAP_Config__sdap_HeaderUL_absent;
  }
+  for (int qos_flow_index = 0; qos_flow_index < pduSession->param.nb_qos; qos_flow_index++) {
+    est_drb->cnAssociation.sdap_config.mappedQoS_FlowsToAdd[qos_flow_index] = pduSession->param.qos[qos_flow_index].qfi;
+    if (pduSession->param.qos[qos_flow_index].fiveQI > 5)
+      est_drb->status = DRB_ACTIVE_NONGBR;
+    else
+      est_drb->status = DRB_ACTIVE;
+  }
+  /* PDCP Configuration */
+  est_drb->pdcp_config.discardTimer = NR_PDCP_Config__drb__discardTimer_infinity;
+  est_drb->pdcp_config.pdcp_SN_SizeDL = NR_PDCP_Config__drb__pdcp_SN_SizeDL_len18bits;
+  est_drb->pdcp_config.pdcp_SN_SizeUL = NR_PDCP_Config__drb__pdcp_SN_SizeUL_len18bits;
+  est_drb->pdcp_config.t_Reordering = NR_PDCP_Config__t_Reordering_ms100;
+  est_drb->pdcp_config.headerCompression.present = NR_PDCP_Config__drb__headerCompression_PR_notUsed;
+  est_drb->pdcp_config.headerCompression.NotUsed = 0;
+  if (do_drb_integrity)
+    est_drb->pdcp_config.integrityProtection = NR_PDCP_Config__drb__integrityProtection_enabled;
+  else
+    est_drb->pdcp_config.integrityProtection = 1;
+  if (do_drb_ciphering)
+    est_drb->pdcp_config.ext1.cipheringDisabled = 1;
+  else
+    est_drb->pdcp_config.ext1.cipheringDisabled = NR_PDCP_Config__ext1__cipheringDisabled_true;
+
+  drb_t *rrc_drb = get_drb(ue, drb_id);
+  DevAssert(rrc_drb == est_drb); /* to double check that we create the same which we would retrieve */
+  return rrc_drb;
 }

 NR_DRB_ToAddMod_t *generateDRB_ASN1(const drb_t *drb_asn1)
@@ -143,17 +152,9 @@ NR_DRB_ToAddMod_t *generateDRB_ASN1(const drb_t *drb_asn1)
  return DRB_config;
 }

-uint8_t next_available_drb(gNB_RRC_UE_t *ue, rrc_pdu_session_param_t *pdusession, bool is_gbr)
+uint8_t get_next_available_drb_id(gNB_RRC_UE_t *ue)
 {
-  uint8_t drb_id;
-
-  if (0 /*!is_gbr*/) { /* Find if Non-GBR DRB exists in the same PDU Session */
-    for (drb_id = 0; drb_id < MAX_DRBS_PER_UE; drb_id++)
-      if (pdusession->param.used_drbs[drb_id] == DRB_ACTIVE_NONGBR)
-        return drb_id + 1;
-  }
-  /* GBR Flow  or a Non-GBR DRB does not exist in the same PDU Session, find an available DRB */
-  for (drb_id = 0; drb_id < MAX_DRBS_PER_UE; drb_id++)
+  for (uint8_t drb_id = 0; drb_id < MAX_DRBS_PER_UE; drb_id++)
    if (ue->established_drbs[drb_id].status == DRB_INACTIVE)
      return drb_id + 1;
  /* From this point, we need to handle the case that all DRBs are already used by the UE. */
@@ -163,6 +164,8 @@ uint8_t next_available_drb(gNB_RRC_UE_t *ue, rrc_pdu_session_param_t *pdusession

 bool drb_is_active(gNB_RRC_UE_t *ue, uint8_t drb_id)
 {
-  DevAssert(drb_id > 0);
-  return ue->established_drbs[drb_id - 1].status == DRB_ACTIVE;
+  drb_t *drb = get_drb(ue, drb_id);
+  if (drb == NULL)
+    return DRB_INACTIVE;
+  return drb->status != DRB_INACTIVE;
 }
@@ -39,23 +39,33 @@
 /// @param drb_t drb_asn1
 /// @return Returns the ASN1 DRB-ToAddMod structs.
 NR_DRB_ToAddMod_t *generateDRB_ASN1(const drb_t *drb_asn1);
-/// @brief Creates and stores a DRB in the gNB_RRC_UE_t struct, it doesn't create the actual entity,
-/// to create the actual entity use the generateDRB_ASN1.
+
+/// @brief retrieve the data structure representing DRB with ID drb_id of UE ue
+drb_t *get_drb(gNB_RRC_UE_t *ue, uint8_t drb_id);
+
+/// @brief Creates and stores a DRB in the gNB_RRC_UE_t struct
 /// @param ue The gNB_RRC_UE_t struct that holds information for the UEs
 /// @param drb_id The Data Radio Bearer Identity to be created for the established DRB.
 /// @param pduSession The PDU Session that the DRB is created for.
 /// @param enable_sdap If true the SDAP header will be added to the packet, else it will not add or search for SDAP header.
 /// @param do_drb_integrity
 /// @param do_drb_ciphering
-void generateDRB(gNB_RRC_UE_t *ue,
-                 uint8_t drb_id,
-                 rrc_pdu_session_param_t *pduSession,
-                 bool enable_sdap,
-                 int do_drb_integrity,
-                 int do_drb_ciphering);
-uint8_t next_available_drb(gNB_RRC_UE_t *ue, rrc_pdu_session_param_t *pdusession, bool is_gbr);
+/// @return returns a pointer to the generated DRB structure
+drb_t *generateDRB(gNB_RRC_UE_t *ue,
+                   uint8_t drb_id,
+                   const rrc_pdu_session_param_t *pduSession,
+                   bool enable_sdap,
+                   int do_drb_integrity,
+                   int do_drb_ciphering);
+
+/// @brief return the next available (inactive) DRB ID of UE ue
+uint8_t get_next_available_drb_id(gNB_RRC_UE_t *ue);
+
+/// @brief check if DRB with ID drb_id of UE ue is active
 bool drb_is_active(gNB_RRC_UE_t *ue, uint8_t drb_id);

+/// @brief retrieve PDU session of UE ue with ID id, optionally creating it if
+/// create is true
 rrc_pdu_session_param_t *find_pduSession(gNB_RRC_UE_t *ue, int id, bool create);

 #endif