nr,gnb,rrc&ngap: implementation of NGAP UE Context Release Request and RRC Release for the case RRC_CONNECTED->RRC_IDLE

lib/include/srsran/interfaces/gnb_ngap_interfaces.h

@@ -47,7 +47,7 @@ public:
   virtual void write_pdu(uint16_t rnti, srsran::const_byte_span pdu)                                 = 0;
   virtual bool user_exists(uint16_t rnti)                                                            = 0;
   virtual void user_mod(uint16_t old_rnti, uint16_t new_rnti)                                        = 0;
-  virtual bool user_release(uint16_t rnti, asn1::ngap_nr::cause_radio_network_e cause_radio) = 0;
+  virtual void user_release_request(uint16_t rnti, asn1::ngap_nr::cause_radio_network_e cause_radio) = 0;
   virtual bool is_amf_connected()                                                                    = 0;
   virtual void ue_notify_rrc_reconf_complete(uint16_t rnti, bool outcome)                            = 0;
 };

lib/include/srsran/interfaces/gnb_rrc_nr_interfaces.h

@@ -29,6 +29,7 @@ public:
                establish_rrc_bearer(uint16_t rnti, uint16_t pdu_session_id, srsran::const_byte_span nas_pdu, uint32_t lcid) = 0;
   virtual int  allocate_lcid(uint16_t rnti)                                   = 0;
   virtual int  release_bearers(uint16_t rnti)                                 = 0;
+  virtual void release_user(uint16_t rnti)                                    = 0;
   virtual void write_dl_info(uint16_t rnti, srsran::unique_byte_buffer_t sdu) = 0;
 };
 

srsgnb/hdr/stack/common/test/dummy_nr_classes.h

@@ -36,7 +36,7 @@ class ngap_dummy : public ngap_interface_rrc_nr
   void write_pdu(uint16_t rnti, srsran::const_byte_span pdu) {}
   bool user_exists(uint16_t rnti) { return true; }
   void user_mod(uint16_t old_rnti, uint16_t new_rnti) {}
-  bool user_release(uint16_t rnti, asn1::ngap_nr::cause_radio_network_e cause_radio) { return true; }
+  void user_release_request(uint16_t rnti, asn1::ngap_nr::cause_radio_network_e cause_radio) {}
   bool is_amf_connected() { return true; }
   void ue_notify_rrc_reconf_complete(uint16_t rnti, bool outcome) {}
 };

srsgnb/hdr/stack/ngap/ngap.h

@@ -51,22 +51,25 @@ public:
   void initial_ue(uint16_t                                rnti,
                   uint32_t                                gnb_cc_idx,
                   asn1::ngap_nr::rrcestablishment_cause_e cause,
-                  srsran::const_byte_span                 pdu);
+                  srsran::const_byte_span                 pdu) override;
   void initial_ue(uint16_t                                rnti,
                   uint32_t                                gnb_cc_idx,
                   asn1::ngap_nr::rrcestablishment_cause_e cause,
                   srsran::const_byte_span                 pdu,
-                  uint32_t                                s_tmsi);
+                  uint32_t                                s_tmsi) override;
 
-  void write_pdu(uint16_t rnti, srsran::const_byte_span pdu);
+  void write_pdu(uint16_t rnti, srsran::const_byte_span pdu) override;
-  bool user_exists(uint16_t rnti) { return true; };
+  bool user_exists(uint16_t rnti) override { return true; };
-  void user_mod(uint16_t old_rnti, uint16_t new_rnti){};
+  void user_mod(uint16_t old_rnti, uint16_t new_rnti) override {}
-  bool user_release(uint16_t rnti, asn1::ngap_nr::cause_radio_network_e cause_radio) { return true; };
+
-  bool is_amf_connected();
+  // TS 38.413 - Section 8.3.2 - UE Context Release Request
+  void user_release_request(uint16_t rnti, asn1::ngap_nr::cause_radio_network_e cause_radio) override;
+
+  bool is_amf_connected() override;
   bool send_error_indication(const asn1::ngap_nr::cause_c& cause,
                              srsran::optional<uint32_t>    ran_ue_ngap_id = {},
                              srsran::optional<uint32_t>    amf_ue_ngap_id = {});
-  void ue_notify_rrc_reconf_complete(uint16_t rnti, bool outcome);
+  void ue_notify_rrc_reconf_complete(uint16_t rnti, bool outcome) override;
   bool send_pdu_session_resource_setup_response();
 
   // Stack interface

srsgnb/hdr/stack/ngap/ngap_ue.h

@@ -48,6 +48,8 @@ public:
   bool send_ue_ctxt_release_complete();
   // TS 38.413 - Section 9.2.2.1 - Initial Context Setup Request
   bool handle_initial_ctxt_setup_request(const asn1::ngap_nr::init_context_setup_request_s& msg);
+  // TS 38.413 - Section 9.2.2.4 - UE Context Release Request
+  bool send_ue_context_release_request(asn1::ngap_nr::cause_c cause);
   // TS 38.413 - Section 9.2.2.5 - UE Context Release Command
   bool handle_ue_ctxt_release_cmd(const asn1::ngap_nr::ue_context_release_cmd_s& msg);
   // TS 38.413 - Section 9.2.1.1 - PDU Session Resource Setup Request

srsgnb/hdr/stack/ngap/ngap_ue_bearer_manager.h

@@ -56,6 +56,8 @@ public:
 
   int reset_pdu_sessions(uint16_t rnti);
 
+  const std::map<uint8_t, pdu_session_t>& pdu_sessions() const { return pdu_session_list; }
+
 private:
   gtpu_interface_rrc*              gtpu = nullptr;
   std::map<uint8_t, pdu_session_t> pdu_session_list;

srsgnb/hdr/stack/rrc/rrc_nr.h

@@ -103,6 +103,7 @@ public:
                             srsran::const_byte_span nas_pdu,
                             uint32_t                lcid) final;
   int  release_bearers(uint16_t rnti) final;
+  void release_user(uint16_t rnti) final;
   void write_dl_info(uint16_t rnti, srsran::unique_byte_buffer_t sdu) final;
   int  set_aggregate_max_bitrate(uint16_t rnti, const asn1::ngap_nr::ue_aggregate_maximum_bit_rate_s& rates) final;
   int  allocate_lcid(uint16_t rnti) final;

srsgnb/hdr/stack/rrc/rrc_nr_ue.h

@@ -90,7 +90,7 @@ private:
   int send_dl_ccch(const asn1::rrc_nr::dl_ccch_msg_s& dl_ccch_msg);
   int send_dl_dcch(srsran::nr_srb srb, const asn1::rrc_nr::dl_dcch_msg_s& dl_dcch_msg);
 
-  /* TS 38.331 - 5.3.3 RRC connection establishment */
+  /** TS 38.331 - 5.3.3 RRC connection establishment */
   void send_rrc_setup();
   void send_rrc_reject(uint8_t reject_wait_time_secs);
 

srsgnb/src/stack/ngap/ngap.cc

@@ -265,6 +265,23 @@ void ngap::write_pdu(uint16_t rnti, srsran::const_byte_span pdu)
   u->send_ul_nas_transport(pdu);
 }
 
+void ngap::user_release_request(uint16_t rnti, asn1::ngap_nr::cause_radio_network_e cause_radio)
+{
+  ue* u = users.find_ue_rnti(rnti);
+  if (u == nullptr) {
+    logger.warning("Released UE rnti=0x%x not found.", rnti);
+    return;
+  }
+
+  cause_c cause;
+  cause.set_radio_network().value = cause_radio;
+  if (not u->send_ue_context_release_request(cause)) {
+    logger.error("Failed to initiate RRC Release for rnti=0x%x. Removing user", rnti);
+    rrc->release_user(rnti);
+    users.erase(u);
+  }
+}
+
 /*********************************************************
  *              ngap::user_list class
  *********************************************************/

srsgnb/src/stack/ngap/ngap_ue.cc

@@ -244,6 +244,43 @@ bool ngap::ue::send_ue_ctxt_release_complete()
   return ngap_ptr->sctp_send_ngap_pdu(tx_pdu, ctxt.rnti, "UEContextReleaseComplete");
 }
 
+bool ngap::ue::send_ue_context_release_request(asn1::ngap_nr::cause_c cause)
+{
+  if (not ngap_ptr->amf_connected) {
+    logger.warning("AMF not connected");
+    return false;
+  }
+
+  if (was_uectxtrelease_requested()) {
+    // let timeout auto-remove user.
+    return false;
+  }
+  release_requested = true;
+
+  ngap_pdu_c tx_pdu;
+  tx_pdu.set_init_msg().load_info_obj(ASN1_NGAP_NR_ID_UE_CONTEXT_RELEASE_REQUEST);
+  ue_context_release_request_s& container = tx_pdu.init_msg().value.ue_context_release_request();
+
+  container.protocol_ies.cause.value = cause;
+
+  // PDU Session Resource List
+  auto& session_lst = container.protocol_ies.pdu_session_res_list_cxt_rel_req.value;
+  for (const auto& pdu_pair : bearer_manager.pdu_sessions()) {
+    const ngap_ue_bearer_manager::pdu_session_t& session = pdu_pair.second;
+
+    pdu_session_res_item_cxt_rel_req_s obj;
+    obj.pdu_session_id = session.id;
+    session_lst.push_back(obj);
+  }
+  container.protocol_ies.pdu_session_res_list_cxt_rel_req_present = session_lst.size() > 0;
+
+  container.protocol_ies.ran_ue_ngap_id.value = ctxt.ran_ue_ngap_id;
+  container.protocol_ies.amf_ue_ngap_id.value = ctxt.amf_ue_ngap_id.value();
+
+  // TODO: Implement timeout
+  return ngap_ptr->sctp_send_ngap_pdu(tx_pdu, ctxt.rnti, "UEContextReleaseRequest");
+}
+
 /*******************************************************************************
 /* NGAP message handler
 ********************************************************************************/

srsgnb/src/stack/ngap/ngap_ue_proc.cc

@@ -81,9 +81,8 @@ ngap_ue_ue_context_release_proc::ngap_ue_ue_context_release_proc(ngap_interface_
 proc_outcome_t ngap_ue_ue_context_release_proc::init(const asn1::ngap_nr::ue_context_release_cmd_s& msg)
 {
   logger.info("Started %s", name());
-  // TODO: How to approach erasing users ?
   bearer_manager->reset_pdu_sessions(ue_ctxt->rnti);
-  rrc->release_bearers(ue_ctxt->rnti);
+  rrc->release_user(ue_ctxt->rnti);
   parent->send_ue_ctxt_release_complete();
   return proc_outcome_t::success;
 }

srsgnb/src/stack/ngap/test/ngap_test.cc

@@ -115,6 +115,7 @@ public:
   }
 
   int  release_bearers(uint16_t rnti) { return SRSRAN_SUCCESS; }
+  void release_user(uint16_t rnti) {}
   int  allocate_lcid(uint16_t rnti) { return SRSRAN_SUCCESS; }
   void write_dl_info(uint16_t rnti, srsran::unique_byte_buffer_t sdu) {}
 

srsgnb/src/stack/rrc/rrc_nr.cc

@@ -629,6 +629,16 @@ int rrc_nr::release_bearers(uint16_t rnti)
   return SRSRAN_SUCCESS;
 }
 
+void rrc_nr::release_user(uint16_t rnti)
+{
+  if (not users.contains(rnti)) {
+    logger.warning("User rnti=0x%x has already been released", rnti);
+    return;
+  }
+
+  users[rnti]->send_rrc_release();
+}
+
 int rrc_nr::allocate_lcid(uint16_t rnti)
 {
   return SRSRAN_SUCCESS;

srsgnb/src/stack/rrc/rrc_nr_ue.cc

@@ -96,8 +96,8 @@ void rrc_nr::ue::activity_timer_expired(const activity_timeout_type_t type)
     case UE_INACTIVITY_TIMEOUT: {
       state = rrc_nr_state_t::RRC_INACTIVE;
       if (parent->cfg.is_standalone) {
-        // TODO: This procedure needs to be defined
+        // Start NGAP Release UE context
-        parent->rrc_release(rnti);
+        parent->ngap->user_release_request(rnti, asn1::ngap_nr::cause_radio_network_opts::user_inactivity);
       } else {
         parent->rrc_eutra->sgnb_inactivity_timeout(eutra_rnti);
       }
@@ -1017,7 +1017,7 @@ void rrc_nr::ue::send_security_mode_command(srsran::unique_byte_buffer_t nas_pdu
   ies.security_cfg_smc.security_algorithm_cfg                                  = sec_ctx.get_security_algorithm_cfg();
 
   if (send_dl_dcch(srsran::nr_srb::srb1, dl_dcch_msg) != SRSRAN_SUCCESS) {
-    send_rrc_release();
+    parent->ngap->user_release_request(rnti, asn1::ngap_nr::cause_radio_network_opts::radio_res_not_available);
   }
 }
 
@@ -1061,7 +1061,7 @@ void rrc_nr::ue::send_rrc_reconfiguration()
     // Pack masterCellGroup into container
     srsran::unique_byte_buffer_t pdu = parent->pack_into_pdu(master_cell_group, __FUNCTION__);
     if (pdu == nullptr) {
-      send_rrc_release();
+      parent->ngap->user_release_request(rnti, asn1::ngap_nr::cause_radio_network_opts::radio_res_not_available);
       return;
     }
     ies.non_crit_ext.master_cell_group.resize(pdu->N_bytes);
@@ -1097,7 +1097,7 @@ void rrc_nr::ue::send_rrc_reconfiguration()
   ies.non_crit_ext_present = ies.non_crit_ext.master_cell_group_present or ies.non_crit_ext.ded_nas_msg_list_present;
 
   if (send_dl_dcch(srsran::nr_srb::srb1, dl_dcch_msg) != SRSRAN_SUCCESS) {
-    send_rrc_release();
+    parent->ngap->user_release_request(rnti, asn1::ngap_nr::cause_radio_network_opts::radio_res_not_available);
   }
 }
 
@@ -1112,7 +1112,21 @@ void rrc_nr::ue::handle_rrc_reconfiguration_complete(const asn1::rrc_nr::rrc_rec
 
 void rrc_nr::ue::send_rrc_release()
 {
-  // TODO
+  static const uint32_t release_delay = 60; // Taken from TS 38.331, 5.3.8.3
+
+  dl_dcch_msg_s  dl_dcch_msg;
+  rrc_release_s& release = dl_dcch_msg.msg.set_c1().set_rrc_release();
+
+  release.rrc_transaction_id = (uint8_t)((transaction_id++) % 4);
+  rrc_release_ies_s& ies     = release.crit_exts.set_rrc_release();
+
+  ies.suspend_cfg_present = false; // goes to RRC_IDLE
+
+  send_dl_dcch(srsran::nr_srb::srb1, dl_dcch_msg);
+  state = rrc_nr_state_t::RRC_IDLE;
+
+  // TODO: Obtain acknowledgment from lower layers that RRC Release was received
+  parent->task_sched.defer_callback(release_delay, [this]() { parent->rem_user(rnti); });
 }
 
 void rrc_nr::ue::send_dl_information_transfer(srsran::unique_byte_buffer_t sdu)
@@ -1126,7 +1140,7 @@ void rrc_nr::ue::send_dl_information_transfer(srsran::unique_byte_buffer_t sdu)
   memcpy(ies.ded_nas_msg.data(), sdu->data(), ies.ded_nas_msg.size());
 
   if (send_dl_dcch(srsran::nr_srb::srb1, dl_dcch_msg) != SRSRAN_SUCCESS) {
-    send_rrc_release();
+    parent->ngap->user_release_request(rnti, asn1::ngap_nr::cause_radio_network_opts::radio_res_not_available);
   }
 }