enb: signal user activity to EUTRA RRC when doing NR DL traffic

to avoid releasing the UE when only NR DL traffic is done.
similar to the EUTRA solution.

lib/include/srsran/interfaces/enb_x2_interfaces.h

@@ -81,6 +81,13 @@ public:
    * @param nr_rnti    The RNTI that has been assigned to the UE on the SgNB
    */
   virtual void sgnb_addition_complete(uint16_t eutra_rnti, uint16_t nr_rnti) = 0;
+
+  /**
+   * @brief Signal user activity (i.e. DL/UL traffic) for given RNTI
+   *
+   * @param eutra_rnti The RNTI that the EUTRA RRC uses
+   */
+  virtual void set_activity_user(uint16_t eutra_rnti) = 0;
 };
 
 class stack_nr_interface_stack_eutra

lib/include/srsran/interfaces/gnb_interfaces.h

@@ -136,6 +136,7 @@ public:
   /// User management
   virtual int  add_user(uint16_t rnti)                           = 0;
   virtual int  update_user(uint16_t new_rnti, uint16_t old_rnti) = 0;
+  virtual void set_activity_user(uint16_t rnti)                  = 0;
 };
 
 // NR interface is almost identical to EUTRA version

srsenb/hdr/stack/enb_stack_lte.h

@@ -118,6 +118,7 @@ public:
   {
     rrc.sgnb_addition_complete(eutra_rnti, nr_rnti);
   }
+  void set_activity_user(uint16_t eutra_rnti) final { rrc.set_activity_user(eutra_rnti); }
 
   // gtpu_interface_pdcp
   void write_pdu(uint16_t rnti, uint32_t lcid, srsran::unique_byte_buffer_t pdu);

srsenb/hdr/stack/rrc/rrc_nr.h

@@ -62,15 +62,18 @@ public:
   void get_metrics(srsenb::rrc_metrics_t& m);
 
   rrc_nr_cfg_t update_default_cfg(const rrc_nr_cfg_t& rrc_cfg);
-  int          add_user(uint16_t rnti);
-  void         rem_user(uint16_t rnti);
-  int          update_user(uint16_t new_rnti, uint16_t old_rnti);
   void         config_phy();
   void         config_mac();
   int32_t      generate_sibs();
   int          read_pdu_bcch_bch(const uint32_t tti, srsran::unique_byte_buffer_t& buffer) final;
   int          read_pdu_bcch_dlsch(uint32_t sib_index, srsran::unique_byte_buffer_t& buffer) final;
 
+  /// User manegement
+  int  add_user(uint16_t rnti);
+  void rem_user(uint16_t rnti);
+  int  update_user(uint16_t new_rnti, uint16_t old_rnti);
+  void set_activity_user(uint16_t rnti);
+
   // RLC interface
   // TODO
   void        read_pdu_pcch(uint8_t* payload, uint32_t payload_size) {}
@@ -112,6 +115,7 @@ public:
     bool is_idle() { return state == rrc_nr_state_t::RRC_IDLE; }
     bool is_inactive() { return state == rrc_nr_state_t::RRC_INACTIVE; }
     bool is_endc() { return endc; }
+    uint16_t get_eutra_rnti() { return eutra_rnti; }
 
     // setters
 

srsenb/hdr/x2_adapter.h

@@ -85,6 +85,14 @@ public:
     eutra_stack->sgnb_addition_complete(eutra_rnti, nr_rnti);
   }
 
+  void set_activity_user(uint16_t eutra_rnti)
+  {
+    if (eutra_stack == nullptr) {
+      return;
+    }
+    eutra_stack->set_activity_user(eutra_rnti);
+  }
+
   // stack_nr_interface_stack_eutra
   void tti_clock()
   {

srsenb/src/stack/mac/nr/ue_nr.cc

@@ -143,6 +143,12 @@ int ue_nr::generate_pdu(srsran::byte_buffer_t* pdu, uint32_t grant_size)
 
     // add to MAC PDU and pack
     mac_pdu_dl.add_sdu(lcid, ue_rlc_buffer->msg, ue_rlc_buffer->N_bytes);
+
+    // Indicate DRB activity in DL to RRC
+    if (lcid > 3) {
+      rrc->set_activity_user(rnti);
+      logger.debug("DL activity rnti=0x%x, n_bytes=%d", rnti, ue_rlc_buffer->N_bytes);
+    }
   }
 
   mac_pdu_dl.pack();

srsenb/src/stack/rrc/rrc_nr.cc

@@ -201,6 +201,22 @@ int rrc_nr::update_user(uint16_t new_rnti, uint16_t old_rnti)
   return SRSRAN_SUCCESS;
 }
 
+void rrc_nr::set_activity_user(uint16_t rnti)
+{
+  auto it = users.find(rnti);
+  if (it == users.end()) {
+    logger.info("rnti=0x%x not found. Can't set activity", rnti);
+    return;
+  }
+  ue* ue_ptr = it->second.get();
+
+  // inform EUTRA RRC about user activity
+  if (ue_ptr->is_endc()) {
+    // inform EUTRA RRC about user activity
+    rrc_eutra->set_activity_user(ue_ptr->get_eutra_rnti());
+  }
+}
+
 void rrc_nr::config_phy()
 {
   static const srsran::phy_cfg_nr_t default_phy_cfg =

srsenb/test/common/dummy_classes_nr.h

@@ -25,6 +25,7 @@ public:
   int  read_pdu_bcch_dlsch(uint32_t sib_index, srsran::unique_byte_buffer_t& buffer) { return SRSRAN_SUCCESS; }
   int  add_user(uint16_t rnti) { return SRSRAN_SUCCESS; }
   int  update_user(uint16_t new_rnti, uint16_t old_rnti) { return SRSRAN_SUCCESS; }
+  void set_activity_user(uint16_t rnti) {}
 };
 
 class rlc_nr_dummy : public rlc_interface_mac_nr