Send NAS PDU in E-RAB Release Command and issue RRCConnectionReconfiguration to UE

This commit addresses the following points

- If a NAS-PDU IE is contained in the E-RAB RELEASE COMMAND message, the eNB shall pass it to the UE.
- Issue RRCConnectionReconfiguration for the DRB to be removed
- Cleaning of DRB in RLC and GTP-U
- Fix for Malformed E-RAB Setup Response upon reaching max. DRBs

srsenb/hdr/stack/rrc/rrc_bearer_cfg.h

@@ -96,6 +96,7 @@ public:
                            uint32_t                                teid_out,
                            uint32_t                                addr,
                            const gtpu_interface_rrc::bearer_props* props = nullptr);
+  void     rem_gtpu_bearer(gtpu_interface_rrc* gtpu, uint32_t erab_id);
   void     fill_pending_nas_info(asn1::rrc::rrc_conn_recfg_r8_ies_s* msg);
 
   const std::map<uint8_t, erab_t>&        get_erabs() const { return erabs; }

srsenb/hdr/stack/rrc/rrc_ue.h

@@ -47,7 +47,9 @@ public:
   void send_connection_reject();
   void send_connection_release();
   void send_connection_reest_rej();
-  void send_connection_reconf(srslte::unique_byte_buffer_t sdu = {}, bool phy_cfg_updated = true);
+  void send_connection_reconf(srslte::unique_byte_buffer_t           sdu             = {},
+                              bool                                   phy_cfg_updated = true,
+                              const asn1::unbounded_octstring<true>* nas_pdu         = nullptr);
   void send_security_mode_command();
   void send_ue_cap_enquiry();
   void send_ue_info_req();

srsenb/src/stack/rrc/rrc.cc

@@ -334,6 +334,10 @@ void rrc::release_erabs(uint32_t                              rnti,
       erabs_failed_to_release->push_back(erab_to_release.erab_id);
     }
   }
+  const asn1::unbounded_octstring<true>* nas_pdu =
+      msg.protocol_ies.nas_pdu_present ? &msg.protocol_ies.nas_pdu.value : nullptr;
+  user_it->second->send_connection_reconf(nullptr, false, nas_pdu);
+
   return;
 }
 

srsenb/src/stack/rrc/rrc_bearer_cfg.cc

@@ -339,6 +339,17 @@ uint32_t bearer_cfg_handler::add_gtpu_bearer(uint32_t
   return bearer.teid_in;
 }
 
+void bearer_cfg_handler::rem_gtpu_bearer(srsenb::gtpu_interface_rrc* gtpu, uint32_t erab_id)
+{
+  auto it = erabs.find(erab_id);
+  if (it != erabs.end()) {
+    // Map e.g. E-RAB 5 to LCID 3 (==DRB1)
+    gtpu->rem_bearer(rnti, erab_id - 2);
+  } else {
+    logger.error("Removing erab_id=%d to GTPU\n", erab_id);
+  }
+}
+
 void bearer_cfg_handler::fill_pending_nas_info(asn1::rrc::rrc_conn_recfg_r8_ies_s* msg)
 {
   // Add space for NAS messages

srsenb/src/stack/rrc/rrc_ue.cc

@@ -506,7 +506,9 @@ void rrc::ue::send_connection_reest_rej()
 /*
  * Connection Reconfiguration
  */
-void rrc::ue::send_connection_reconf(srslte::unique_byte_buffer_t pdu, bool phy_cfg_updated)
+void rrc::ue::send_connection_reconf(srslte::unique_byte_buffer_t           pdu,
+                                     bool                                   phy_cfg_updated,
+                                     const asn1::unbounded_octstring<true>* nas_pdu)
 {
   parent->logger.debug("RRC state %d", state);
 
@@ -545,6 +547,17 @@ void rrc::ue::send_connection_reconf(srslte::unique_byte_buffer_t pdu, bool phy_
   // UE MAC scheduler updates
   mac_ctrl.handle_con_reconf(recfg_r8, ue_capabilities);
 
+  // Fill in NAS PDU - Only for RRC Connection Reconfiguration during E-RAB Release Command
+  if (nas_pdu != nullptr and nas_pdu->size() > 0 and !recfg_r8.ded_info_nas_list_present) {
+    recfg_r8.ded_info_nas_list_present = true;
+    recfg_r8.ded_info_nas_list.resize(recfg_r8.rr_cfg_ded.drb_to_release_list.size());
+    // Add NAS PDU
+    for (uint32_t idx = 0; idx < recfg_r8.rr_cfg_ded.drb_to_release_list.size(); idx++) {
+      recfg_r8.ded_info_nas_list[idx].resize(nas_pdu->size());
+      memcpy(recfg_r8.ded_info_nas_list[idx].data(), nas_pdu->data(), nas_pdu->size());
+    }
+  }
+
   // Reuse same PDU
   if (pdu != nullptr) {
     pdu->clear();
@@ -932,6 +945,7 @@ void rrc::ue::notify_s1ap_ue_erab_setup_response(const asn1::s1ap::erab_to_be_se
       res.protocol_ies.erab_failed_to_setup_list_bearer_su_res_present = true;
       res.protocol_ies.erab_failed_to_setup_list_bearer_su_res.value.push_back({});
       auto& item                     = res.protocol_ies.erab_failed_to_setup_list_bearer_su_res.value.back();
+      item.load_info_obj(ASN1_S1AP_ID_ERAB_ITEM);
       item.value.erab_item().erab_id = id;
       item.value.erab_item().cause.set_radio_network().value =
           asn1::s1ap::cause_radio_network_opts::invalid_qos_combination;
@@ -1206,7 +1220,9 @@ void rrc::ue::apply_rlc_rb_updates(const rr_cfg_ded_s& pending_rr_cfg)
     parent->rlc->add_bearer(rnti, srb.srb_id, srslte::rlc_config_t::srb_config(srb.srb_id));
   }
   if (pending_rr_cfg.drb_to_release_list.size() > 0) {
-    parent->logger.error("Removing DRBs not currently supported");
+    for (uint8_t drb_id : pending_rr_cfg.drb_to_release_list) {
+      parent->rlc->del_bearer(rnti, drb_id + 2);
+    }
   }
   for (const drb_to_add_mod_s& drb : pending_rr_cfg.drb_to_add_mod_list) {
     if (not drb.rlc_cfg_present) {