cu-cp: implementation of class for handing paging messages

Author: frankist

lib/cu_cp/CMakeLists.txt

@@ -47,6 +47,7 @@ set(SOURCES
       ue_manager/cu_cp_ue_impl.cpp
       ue_manager/ue_manager_impl.cpp
       ue_manager/ue_task_scheduler_impl.cpp
+      paging/paging_message_handler.cpp
 )
 
 add_library(srsran_cu_cp STATIC ${SOURCES})

lib/cu_cp/adapters/ngap_adapters.h

@@ -12,6 +12,7 @@
 
 #include "../cu_cp_impl_interface.h"
 #include "../du_processor/du_processor.h"
+#include "../paging/paging_message_handler.h"
 #include "../ue_manager/cu_cp_ue_impl_interface.h"
 #include "srsran/cu_cp/ue_task_scheduler.h"
 #include "srsran/ngap/ngap.h"
@@ -26,16 +27,16 @@ class ngap_cu_cp_adapter : public ngap_cu_cp_du_repository_notifier, public ngap
 public:
   explicit ngap_cu_cp_adapter() = default;
 
-  void connect_cu_cp(du_repository_ngap_handler& du_repository_handler_, cu_cp_ngap_handler& cu_cp_handler_)
+  void connect_cu_cp(cu_cp_ngap_handler& cu_cp_handler_, paging_message_handler& paging_handler_)
   {
-    du_repository_handler = &du_repository_handler_;
-    cu_cp_handler         = &cu_cp_handler_;
+    cu_cp_handler  = &cu_cp_handler_;
+    paging_handler = &paging_handler_;
   }
 
   void on_paging_message(cu_cp_paging_message& msg) override
   {
-    srsran_assert(du_repository_handler != nullptr, "CU-CP Paging handler must not be nullptr");
-    du_repository_handler->handle_paging_message(msg);
+    srsran_assert(paging_handler != nullptr, "CU-CP Paging handler must not be nullptr");
+    paging_handler->handle_paging_message(msg);
   }
 
   async_task<ngap_handover_resource_allocation_response>
@@ -117,8 +118,8 @@ class ngap_cu_cp_adapter : public ngap_cu_cp_du_repository_notifier, public ngap
   }
 
 private:
-  du_repository_ngap_handler* du_repository_handler = nullptr;
-  cu_cp_ngap_handler*         cu_cp_handler         = nullptr;
+  cu_cp_ngap_handler*     cu_cp_handler  = nullptr;
+  paging_message_handler* paging_handler = nullptr;
 };
 
 /// Adapter between NGAP and CU-CP UE

lib/cu_cp/cu_cp_impl.cpp

@@ -65,13 +65,14 @@ cu_cp_impl::cu_cp_impl(const cu_cp_configuration& config_) :
                              conn_notifier,
                              srslog::fetch_basic_logger("CU-CP")}),
   cu_up_db(cu_up_repository_config{cfg, e1ap_ev_notifier, srslog::fetch_basic_logger("CU-CP")}),
+  paging_handler(du_db),
   metrics_hdlr(
       std::make_unique<metrics_handler_impl>(*cfg.services.cu_cp_executor, *cfg.services.timers, ue_mng, du_db))
 {
   assert_cu_cp_configuration_valid(cfg);
 
   // connect event notifiers to layers
-  ngap_cu_cp_ev_notifier.connect_cu_cp(du_db, *this);
+  ngap_cu_cp_ev_notifier.connect_cu_cp(*this, paging_handler);
   mobility_manager_ev_notifier.connect_cu_cp(get_cu_cp_mobility_manager_handler());
   e1ap_ev_notifier.connect_cu_cp(get_cu_cp_e1ap_handler());
   rrc_du_cu_cp_notifier.connect_cu_cp(get_cu_cp_measurement_config_handler());

lib/cu_cp/cu_cp_impl.h

@@ -22,6 +22,7 @@
 #include "cu_cp_impl_interface.h"
 #include "cu_up_processor/cu_up_processor_repository.h"
 #include "du_processor/du_processor_repository.h"
+#include "paging/paging_message_handler.h"
 #include "routine_managers/cu_cp_routine_manager.h"
 #include "ue_manager/ue_manager_impl.h"
 #include "srsran/cu_cp/cu_cp_configuration.h"
@@ -192,6 +193,9 @@ class cu_cp_impl final : public cu_cp,
   // CU-UP connections being managed by the CU-CP.
   cu_up_processor_repository cu_up_db;
 
+  // Handler of paging messages.
+  paging_message_handler paging_handler;
+
   // Handler of the CU-CP connections to other remote nodes (e.g. AMF, CU-UPs, DUs).
   std::unique_ptr<cu_cp_controller> controller;
 

lib/cu_cp/du_processor/du_processor.h

@@ -10,6 +10,7 @@
 
 #pragma once
 
+#include "du_configuration_handler.h"
 #include "du_metrics_handler.h"
 #include "srsran/adt/static_vector.h"
 #include "srsran/f1ap/cu_cp/f1ap_cu.h"
@@ -68,6 +69,9 @@ class du_processor_cell_info_interface
 
   /// \brief Checks whether a cell with the specified NR cell global id is served by the DU.
   virtual bool has_cell(nr_cell_global_id_t cgi) = 0;
+
+  /// \brief Get DU configuration context.
+  virtual const du_configuration_context& get_context() const = 0;
 };
 
 /// Interface to notify RRC DU about UE management procedures.

lib/cu_cp/du_processor/du_processor_impl.h

@@ -57,8 +57,9 @@ class du_processor_impl : public du_processor,
   void handle_paging_message(cu_cp_paging_message& msg) override;
 
   // du_processor_cell_info_interface
-  bool has_cell(pci_t pci) override;
-  bool has_cell(nr_cell_global_id_t cgi) override;
+  bool                            has_cell(pci_t pci) override;
+  bool                            has_cell(nr_cell_global_id_t cgi) override;
+  const du_configuration_context& get_context() const override { return cfg.du_cfg_hdlr->get_context(); }
 
   metrics_report::du_info handle_du_metrics_report_request() const override;
 

lib/cu_cp/paging/paging_message_handler.cpp

@@ -0,0 +1,85 @@
+/*
+ *
+ * Copyright 2021-2024 Software Radio Systems Limited
+ *
+ * By using this file, you agree to the terms and conditions set
+ * forth in the LICENSE file which can be found at the top level of
+ * the distribution.
+ *
+ */
+
+#include "paging_message_handler.h"
+#include "../du_processor/du_processor_repository.h"
+#include "srsran/cu_cp/cu_cp_types.h"
+
+using namespace srsran;
+using namespace srs_cu_cp;
+
+paging_message_handler::paging_message_handler(du_processor_repository& dus_) :
+  dus(dus_), logger(srslog::fetch_basic_logger("CU-CP"))
+{
+}
+
+void paging_message_handler::handle_paging_message(const cu_cp_paging_message& msg)
+{
+  // Forward paging message to all DU processors
+  bool paging_sent = false;
+  for (unsigned i = 0; i != dus.get_nof_dus(); ++i) {
+    paging_sent |= handle_du_paging_message(uint_to_du_index(i), msg);
+  }
+
+  if (not paging_sent) {
+    logger.warning("No DU processor was able to handle the paging message");
+  }
+}
+
+bool paging_message_handler::handle_du_paging_message(du_index_t du_index, const cu_cp_paging_message& msg_before)
+{
+  du_processor&                   du     = dus.get_du_processor(du_index);
+  const du_configuration_context& du_cfg = du.get_context();
+
+  // Recommended cells will be added to the original paging message.
+  cu_cp_paging_message msg_expanded{msg_before};
+  if (not msg_expanded.assist_data_for_paging.has_value()) {
+    msg_expanded.assist_data_for_paging.emplace();
+  }
+  if (not msg_expanded.assist_data_for_paging.value().assist_data_for_recommended_cells.has_value()) {
+    msg_expanded.assist_data_for_paging.value().assist_data_for_recommended_cells.emplace();
+  }
+  auto& recommended_cells = msg_expanded.assist_data_for_paging.value()
+                                .assist_data_for_recommended_cells.value()
+                                .recommended_cells_for_paging.recommended_cell_list;
+
+  for (const auto& tai_list_item : msg_expanded.tai_list_for_paging) {
+    for (const du_cell_configuration& cell : du_cfg.served_cells) {
+      if (cell.tac != tai_list_item.tai.tac) {
+        // Only add cells with matching TAC.
+        continue;
+      }
+
+      // Check if cell already exists in the list of recommended.
+      for (auto& recommended_cell : recommended_cells) {
+        if (recommended_cell.ngran_cgi == cell.cgi) {
+          // NR CGI for TAC is already present. Continue with next cell.
+          continue;
+          break;
+        }
+      }
+
+      // Setup recommended cell item to add in case it doesn't exist
+      cu_cp_recommended_cell_item cell_item;
+      cell_item.ngran_cgi = cell.cgi;
+      recommended_cells.push_back(cell_item);
+    }
+  }
+
+  if (recommended_cells.empty()) {
+    logger.info("du={}: No cells with matching TAC available at this DU", du_index);
+    return false;
+  }
+
+  // Forward message to F1AP of the respective DU.
+  du.get_f1ap_handler().get_f1ap_paging_manager().handle_paging(msg_expanded);
+
+  return true;
+}

lib/cu_cp/paging/paging_message_handler.h

@@ -0,0 +1,37 @@
+/*
+ *
+ * Copyright 2021-2024 Software Radio Systems Limited
+ *
+ * By using this file, you agree to the terms and conditions set
+ * forth in the LICENSE file which can be found at the top level of
+ * the distribution.
+ *
+ */
+
+#pragma once
+
+#include "srsran/cu_cp/cu_cp_types.h"
+
+namespace srsran {
+namespace srs_cu_cp {
+
+class du_processor_repository;
+struct cu_cp_paging_message;
+
+/// Class responsible for handling incoming paging messages and forwarding them to the appropriate DUs.
+class paging_message_handler
+{
+public:
+  paging_message_handler(du_processor_repository& dus_);
+
+  void handle_paging_message(const cu_cp_paging_message& msg);
+
+private:
+  bool handle_du_paging_message(du_index_t du_index, const cu_cp_paging_message& msg);
+
+  du_processor_repository& dus;
+  srslog::basic_logger&    logger;
+};
+
+} // namespace srs_cu_cp
+} // namespace srsran