srsue/extnas: add a possibility to enable the external NAS interface

The new configuration section '[extnas]' allows to disable the
built-in NAS implementation, and provide the interface (UNIX
domain socket) to an external entity. The interface itself will
be implemented in the follow up commits.

srsue/hdr/stack/ue_stack_base.h

@@ -68,6 +68,7 @@ typedef struct {
   usim_args_t      usim;
   rrc_args_t       rrc;
   std::string      ue_category_str;
+  nas_ext_args_t   nas_ext;
   nas_args_t       nas;
   gw_args_t        gw;
   uint32_t         sync_queue_size; // Max allowed difference between PHY and Stack clocks (in TTI)

srsue/hdr/stack/ue_stack_lte.h

@@ -37,6 +37,7 @@
 #include "srslte/upper/pdcp.h"
 #include "srslte/upper/rlc.h"
 #include "upper/nas.h"
+#include "upper/nas_ext.h"
 #include "upper/usim.h"
 
 #include "srslte/common/buffer_pool.h"

srsue/src/main.cc

@@ -139,6 +139,9 @@ static int parse_args(all_args_t* args, int argc, char* argv[])
     ("nas.eia",               bpo::value<string>(&args->stack.nas.eia)->default_value("1,2,3"),  "List of integrity algorithms included in UE capabilities")
     ("nas.eea",               bpo::value<string>(&args->stack.nas.eea)->default_value("0,1,2,3"),  "List of ciphering algorithms included in UE capabilities")
 
+    ("extnas.enable", bpo::value<bool>(&args->stack.nas_ext.enable)->default_value(false), "Disable the built-in NAS implementation, provide external interface")
+    ("extnas.sock_path", bpo::value<string>(&args->stack.nas_ext.sock_path)->default_value("/tmp/ue_extnas.sock"), "UNIX socket path of the external interface")
+
     ("pcap.enable", bpo::value<bool>(&args->stack.pcap.enable)->default_value(false), "Enable MAC packet captures for wireshark")
     ("pcap.filename", bpo::value<string>(&args->stack.pcap.filename)->default_value("ue.pcap"), "MAC layer capture filename")
     ("pcap.nas_enable",   bpo::value<bool>(&args->stack.pcap.nas_enable)->default_value(false), "Enable NAS packet captures for wireshark")

srsue/src/stack/ue_stack_lte.cc

@@ -106,9 +106,13 @@ int ue_stack_lte::init(const stack_args_t& args_, srslte::logger* logger_)
   extif_log->set_hex_limit(args.log.extif_hex_limit);
 
   // Should we use the built-in NAS implementation
-  // TODO: or provide an external interface (RRCTL)?
-  std::unique_ptr<srsue::nas> nas_impl(new srsue::nas(&task_sched, args.nas));
-  nas = std::move(nas_impl);
+  if (!args.nas_ext.enable) {
+    std::unique_ptr<srsue::nas> nas_impl(new srsue::nas(&task_sched, args.nas));
+    nas = std::move(nas_impl);
+  } else { // ... or provide an external interface (RRCTL)?
+    std::unique_ptr<srsue::nas_ext> nas_impl(new srsue::nas_ext(&task_sched, args.nas_ext));
+    nas = std::move(nas_impl);
+  }
 
   // Set up pcap
   if (args.pcap.enable) {

srsue/ue.conf.example

@@ -163,6 +163,16 @@ imei = 353490069873319
 #eia = 1,2
 #eea = 0,1,2
 
+#####################################################################
+# External NAS interface configuration
+#
+# enable:               Disable the built-in NAS implementation, provide external interface
+# sock_path:            UNIX socket path of the external interface
+#####################################################################
+[extnas]
+#enable = false
+#sock_path = /tmp/ue_extnas.sock
+
 #####################################################################
 # GW configuration
 #