Added NAS timer functionality to the EPC. This entails:

* Adding timer creation at NAS using timerfd_create
  * Adding the ability to add and remove the timer file descriptor to the MME main select loop
  * Adding the ability to the MME for the NAS to check if a timer is running
  * Adding the timer expiry handling functionality at the MME

lib/include/srslte/interfaces/epc_interfaces.h

@@ -29,6 +29,10 @@ namespace srsepc {
 
 class nas;
 
+enum nas_timer_type {
+  T_3413,
+};
+
 /******************
  * MME Interfaces *
  ******************/
@@ -74,6 +78,20 @@ public:
   virtual bool resync_sqn(uint64_t imsi, uint8_t* auts)                                                          = 0;
 };
 
+class mme_interface_nas   //NAS -> MME
+{
+public:
+  virtual bool add_nas_timer(int timer_fd, enum nas_timer_type type, uint64_t imsi) = 0;
+  virtual bool is_nas_timer_running(enum nas_timer_type type, uint64_t imsi)        = 0;
+  virtual bool remove_nas_timer(enum nas_timer_type type, uint64_t imsi)            = 0;
+};
+
+class s1ap_interface_mme   //MME -> S1AP
+{
+public:
+  virtual bool expire_nas_timer(enum nas_timer_type type, uint64_t imsi) = 0;
+};
+
 /*******************
  * SPGW Interfaces *
  *******************/

srsepc/epc.conf.example

@@ -17,6 +17,7 @@
 #                   (default: EEA0, support: EEA1, EEA2)
 # integrity_algo:   Preferred integrity protection algorithm for NAS 
 #                   (default: EIA1, support: EIA1, EIA2 (EIA0 not support)
+# paging_timer:     Value of paging timer in seconds (T3413)
 #
 #####################################################################
 [mme]
@@ -30,6 +31,7 @@ apn = srsapn
 dns_addr = 8.8.8.8
 encryption_algo = EEA0
 integrity_algo = EIA1
+paging_timer = 2
 
 #####################################################################
 # HSS configuration

srsepc/hdr/mme/mme.h

@@ -49,7 +49,13 @@ typedef struct {
   // gtpc_args_t gtpc_args;
 } mme_args_t;
 
-class mme : public thread
+typedef struct {
+  int fd;
+  uint64_t imsi;
+  enum nas_timer_type type;
+} mme_timer_t;
+
+class mme : public thread, public mme_interface_nas
 {
 public:
   static mme* get_instance(void);
@@ -63,6 +69,11 @@ public:
   int  get_s1_mme();
   void run_thread();
 
+  // Timer Methods
+  virtual bool add_nas_timer(int timer_fd, enum nas_timer_type type, uint64_t imsi);
+  virtual bool is_nas_timer_running(enum nas_timer_type type, uint64_t imsi);
+  virtual bool remove_nas_timer(enum nas_timer_type type, uint64_t imsi);
+
 private:
   mme();
   virtual ~mme();
@@ -74,7 +85,13 @@ private:
   srslte::byte_buffer_pool* m_pool;
   fd_set                    m_set;
 
-  /*Logs*/
+  // Timer map
+  std::vector<mme_timer_t> m_timers;
+
+  // Timer Methods
+  void handle_timer_expire(int timer_fd);
+
+  // Logs
   srslte::log_filter* m_nas_log;
   srslte::log_filter* m_s1ap_log;
   srslte::log_filter* m_mme_gtpc_log;

srsepc/hdr/mme/nas.h

@@ -131,6 +131,7 @@ typedef struct {
   uint8_t                             mme_code;
   uint16_t                            mme_group;
   uint16_t                            tac;
+  uint16_t                            paging_timer;
   std::string                         apn;
   std::string                         dns;
   srslte::CIPHERING_ALGORITHM_ID_ENUM cipher_algo;
@@ -141,6 +142,7 @@ typedef struct {
   s1ap_interface_nas* s1ap;
   gtpc_interface_nas* gtpc;
   hss_interface_nas*  hss;
+  mme_interface_nas*  mme;
 } nas_if_t;
 
 class nas
@@ -250,6 +252,10 @@ public:
   void cipher_decrypt(srslte::byte_buffer_t* pdu);
   void cipher_encrypt(srslte::byte_buffer_t* pdu);
 
+  /*Timer functions*/
+  bool start_timer(enum nas_timer_type type);
+  bool expire_timer(enum nas_timer_type type);
+
   /* UE Context */
   emm_ctx_t m_emm_ctx;
   ecm_ctx_t m_ecm_ctx;
@@ -262,6 +268,7 @@ private:
   gtpc_interface_nas*       m_gtpc;
   s1ap_interface_nas*       m_s1ap;
   hss_interface_nas*        m_hss;
+  mme_interface_nas*        m_mme;
 
   uint16_t    m_mcc;
   uint16_t    m_mnc;
@@ -270,6 +277,13 @@ private:
   uint16_t    m_tac;
   std::string m_apn;
   std::string m_dns;
+
+  // Timers timeout values
+  uint16_t    m_t3413;
+
+  // Timer functions
+  bool start_t3413();
+  bool expire_t3413();
 };
 
 } // namespace srsepc

srsepc/hdr/mme/s1ap.h

@@ -52,7 +52,7 @@ namespace srsepc {
 
 const uint16_t S1MME_PORT = 36412;
 
-class s1ap : public s1ap_interface_nas, public s1ap_interface_gtpc
+class s1ap : public s1ap_interface_nas, public s1ap_interface_gtpc, public s1ap_interface_mme
 {
 public:
   static s1ap* get_instance();
@@ -113,6 +113,8 @@ public:
                                            srslte::byte_buffer_t* nas_msg,
                                            struct sctp_sndrcvinfo enb_sri);
 
+  virtual bool expire_nas_timer(enum nas_timer_type type, uint64_t imsi);
+
 private:
   s1ap();
   virtual ~s1ap();

srsepc/hdr/mme/s1ap_common.h

@@ -38,6 +38,7 @@ typedef struct{
   uint16_t                            tac;          // 16-bit tac
   uint16_t                            mcc;          // BCD-coded with 0xF filler
   uint16_t                            mnc;          // BCD-coded with 0xF filler
+  uint16_t                            paging_timer; // Paging timer in sec (T3413)
   std::string                         mme_bind_addr;
   std::string                         mme_name;
   std::string                         dns_addr;

srsepc/src/main.cc

@@ -91,6 +91,7 @@ void parse_args(all_args_t* args, int argc, char* argv[])
   string   mme_apn;
   string   encryption_algo;
   string   integrity_algo;
+  uint16_t paging_timer;
   string   spgw_bind_addr;
   string   sgi_if_addr;
   string   sgi_if_name;
@@ -120,6 +121,7 @@ void parse_args(all_args_t* args, int argc, char* argv[])
     ("mme.apn",             bpo::value<string>(&mme_apn)->default_value(""),                 "Set Access Point Name (APN) for data services")
     ("mme.encryption_algo", bpo::value<string>(&encryption_algo)->default_value("EEA0"),     "Set preferred encryption algorithm for NAS layer ")
     ("mme.integrity_algo",  bpo::value<string>(&integrity_algo)->default_value("EIA1"),      "Set preferred integrity protection algorithm for NAS")
+    ("mme.paging_timer",    bpo::value<uint16_t>(&paging_timer)->default_value(2),           "Set paging timer value in seconds (T3413)")
     ("hss.db_file",         bpo::value<string>(&hss_db_file)->default_value("ue_db.csv"),    ".csv file that stores UE's keys")
     ("hss.auth_algo",       bpo::value<string>(&hss_auth_algo)->default_value("milenage"),   "HSS uthentication algorithm.")
     ("spgw.gtpu_bind_addr", bpo::value<string>(&spgw_bind_addr)->default_value("127.0.0.1"), "IP address of SP-GW for the S1-U connection")
@@ -262,6 +264,7 @@ void parse_args(all_args_t* args, int argc, char* argv[])
   args->mme_args.s1ap_args.mme_name      = mme_name;
   args->mme_args.s1ap_args.dns_addr      = dns_addr;
   args->mme_args.s1ap_args.mme_apn       = mme_apn;
+  args->mme_args.s1ap_args.paging_timer  = paging_timer;
   args->spgw_args.gtpu_bind_addr         = spgw_bind_addr;
   args->spgw_args.sgi_if_addr            = sgi_if_addr;
   args->spgw_args.sgi_if_name            = sgi_if_name;

srsepc/src/mme/mme.cc

@@ -136,6 +136,13 @@ void mme::run_thread()
     FD_SET(s1mme, &m_set);
     FD_SET(s11, &m_set);
 
+    // Add timers to select
+    for (std::vector<mme_timer_t>::iterator it = m_timers.begin(); it != m_timers.end(); ++it) {
+      FD_SET(it->fd, &m_set);
+      max_fd = std::max(max_fd, it->fd);
+      m_s1ap_log->debug("Adding Timer fd %d to fd_set\n", it->fd);
+    }
+
     m_s1ap_log->debug("Waiting for S1-MME or S11 Message\n");
     int n = select(max_fd + 1, &m_set, NULL, NULL, NULL);
     if (n == -1) {
@@ -171,10 +178,71 @@ void mme::run_thread()
         pdu->N_bytes = recvfrom(s11, pdu->msg, SRSLTE_MAX_BUFFER_SIZE_BYTES, 0, NULL, NULL);
         m_mme_gtpc->handle_s11_pdu(pdu);
       }
+      // Handle NAS Timers
+      for (std::vector<mme_timer_t>::iterator it = m_timers.begin(); it != m_timers.end();) {
+        if (FD_ISSET(it->fd, &m_set)) {
+          m_s1ap_log->info("Timer expired\n");
+          uint64_t exp;
+          rd_sz = read(it->fd, &exp, sizeof(uint64_t));
+          m_s1ap->expire_nas_timer(it->type, it->imsi);
+          close(it->fd);
+          m_timers.erase(it);
+        } else {
+          ++it;
+        }
+      }
     } else {
       m_s1ap_log->debug("No data from select.\n");
     }
   }
   return;
 }
+
+/*
+ * Timer Handling
+ */
+bool mme::add_nas_timer(int timer_fd, nas_timer_type type, uint64_t imsi)
+{
+  m_s1ap_log->debug("Adding NAS timer to MME. IMSI %" PRIu64 ", Type %d, Fd: %d\n", imsi, type, timer_fd);
+  mme_timer_t timer;
+  timer.fd   = timer_fd;
+  timer.type = type;
+  timer.imsi = imsi;
+
+  m_timers.push_back(timer);
+  return true;
+}
+
+bool mme::is_nas_timer_running(nas_timer_type type, uint64_t imsi)
+{
+  std::vector<mme_timer_t>::iterator it;
+  for (it = m_timers.begin(); it != m_timers.end(); ++it) {
+    if (it->type == type && it->imsi == imsi) {
+      return true; // found timer
+    }
+  }
+  return false;
+}
+
+bool mme::remove_nas_timer(nas_timer_type type, uint64_t imsi)
+{
+  std::vector<mme_timer_t>::iterator it;
+  for (it = m_timers.begin(); it != m_timers.end(); ++it) {
+    if (it->type == type && it->imsi == imsi) {
+      break; // found timer to remove
+    }
+  }
+  if (it == m_timers.end()) {
+    m_s1ap_log->warning("Could not find timer to remove. IMSI %" PRIu64 ", Type %d\n", imsi, type);
+    return false;
+  }
+
+  // removing timer
+  m_s1ap_log->debug("Removing NAS timer from MME. IMSI %" PRIu64 ", Type %d, Fd: %d\n", imsi, type, it->fd);
+  FD_CLR(it->fd, &m_set);
+  close(it->fd);
+  m_timers.erase(it);
+  return true;
+}
+
 } // namespace srsepc

srsepc/src/mme/nas.cc

@@ -47,6 +47,7 @@ void nas::init(nas_init_t args, nas_if_t itf, srslte::log* nas_log)
   m_tac       = args.tac;
   m_apn       = args.apn;
   m_dns       = args.dns;
+  m_t3413     = args.paging_timer;
 
   m_sec_ctx.integ_algo  = args.integ_algo;
   m_sec_ctx.cipher_algo = args.cipher_algo;
@@ -54,6 +55,7 @@ void nas::init(nas_init_t args, nas_if_t itf, srslte::log* nas_log)
   m_s1ap    = itf.s1ap;
   m_gtpc    = itf.gtpc;
   m_hss     = itf.hss;
+  m_mme     = itf.mme;
   m_nas_log = nas_log;
   m_nas_log->info("NAS Context Initialized. MCC: 0x%x, MNC 0x%x\n", m_mcc, m_mnc);
 }
@@ -1565,4 +1567,79 @@ void nas::cipher_encrypt(srslte::byte_buffer_t* pdu)
       break;
   }
 }
+
+/**************************
+ *
+ * Timer related functions
+ *
+ **************************/
+bool nas::start_timer(enum nas_timer_type type)
+{
+  m_nas_log->debug("Starting NAS timer\n");
+  bool err = false;
+  switch (type) {
+    case T_3413:
+      err = start_t3413();
+      break;
+    default:
+      m_nas_log->error("Invalid timer type\n");
+  }
+  return err;
+}
+
+bool nas::expire_timer(enum nas_timer_type type)
+{
+  m_nas_log->debug("NAS timer expired\n");
+  bool err = false;
+  switch (type) {
+    case T_3413:
+      err = expire_t3413();
+      break;
+    default:
+      m_nas_log->error("Invalid timer type\n");
+  }
+  return err;
+}
+
+// T3413 -> Paging timer
+bool nas::start_t3413()
+{
+  m_nas_log->info("Starting T3413 Timer: Timeout value %d\n", m_t3413);
+  if (m_emm_ctx.state != EMM_STATE_REGISTERED) {
+    m_nas_log->error("EMM invalid status to start T3413\n");
+    return false;
+  }
+
+  int fdt = timerfd_create(CLOCK_MONOTONIC, 0);
+  if (fdt < 0) {
+    m_nas_log->error("Error creating timer. %s\n", strerror(errno));
+    return false;
+  }
+  struct itimerspec t_value;
+  t_value.it_value.tv_sec     = m_t3413;
+  t_value.it_value.tv_nsec    = 0;
+  t_value.it_interval.tv_sec  = 0;
+  t_value.it_interval.tv_nsec = 0;
+
+  if (timerfd_settime(fdt, 0, &t_value, NULL) == -1) {
+    m_nas_log->error("Could not set timer\n");
+    close(fdt);
+    return false;
+  }
+
+  m_mme->add_nas_timer(fdt, T_3413, m_emm_ctx.imsi); // TODO timers without IMSI?
+  return true;
+}
+
+bool nas::expire_t3413()
+{
+  m_nas_log->info("T3413 expired -- Could not page the ue.\n");
+  if (m_emm_ctx.state != EMM_STATE_REGISTERED) {
+    m_nas_log->error("EMM invalid status upon T3413 expiration\n");
+    return false;
+  }
+  // Send Paging Failure to the SPGW (TODO)
+  return true;
+}
+
 } // namespace srsepc

srsepc/src/mme/s1ap.cc

@@ -627,4 +627,16 @@ bool s1ap::send_downlink_nas_transport(uint32_t               enb_ue_s1ap_id,
 {
   return m_s1ap_nas_transport->send_downlink_nas_transport(enb_ue_s1ap_id, mme_ue_s1ap_id, nas_msg, enb_sri);
 }
+
+bool s1ap::expire_nas_timer(enum nas_timer_type type, uint64_t imsi)
+{
+  nas* nas_ctx = find_nas_ctx_from_imsi(imsi);
+  if (nas_ctx == NULL) {
+    m_s1ap_log->error("Error finding NAS context to handle timer\n");
+    return false;
+  }
+  bool err = nas_ctx->expire_timer(type);
+  return err;
+}
+
 } // namespace srsepc

srsepc/src/mme/s1ap_nas_transport.cc

@@ -25,6 +25,7 @@
  */
 
 #include "srsepc/hdr/mme/s1ap_nas_transport.h"
+#include "srsepc/hdr/mme/mme.h"
 #include "srsepc/hdr/mme/s1ap.h"
 #include "srslte/common/int_helpers.h"
 #include "srslte/common/liblte_security.h"
@@ -81,6 +82,7 @@ void s1ap_nas_transport::init()
   m_nas_init.tac          = m_s1ap->m_s1ap_args.tac;
   m_nas_init.apn          = m_s1ap->m_s1ap_args.mme_apn;
   m_nas_init.dns          = m_s1ap->m_s1ap_args.dns_addr;
+  m_nas_init.paging_timer = m_s1ap->m_s1ap_args.paging_timer;
   m_nas_init.integ_algo   = m_s1ap->m_s1ap_args.integrity_algo;
   m_nas_init.cipher_algo  = m_s1ap->m_s1ap_args.encryption_algo;
 
@@ -88,6 +90,7 @@ void s1ap_nas_transport::init()
   m_nas_if.s1ap = s1ap::get_instance();
   m_nas_if.gtpc = mme_gtpc::get_instance();
   m_nas_if.hss  = hss::get_instance();
+  m_nas_if.mme  = mme::get_instance();
 }
 
 bool s1ap_nas_transport::handle_initial_ue_message(LIBLTE_S1AP_MESSAGE_INITIALUEMESSAGE_STRUCT* init_ue,