diff --git a/cmake_targets/CMakeLists.txt b/cmake_targets/CMakeLists.txt
index e62b13462b..5bf01edf12 100644
--- a/cmake_targets/CMakeLists.txt
+++ b/cmake_targets/CMakeLists.txt
@@ -2380,6 +2380,124 @@ if(NAS_UE)
 endif()
 
 
+if(ITTI_SIM)
+  set(libnas_ue_api_OBJS
+    ${NAS_SRC}UE/API/USER/at_command.c
+    ${NAS_SRC}UE/API/USER/at_error.c
+    ${NAS_SRC}UE/API/USER/at_response.c
+    ${NAS_SRC}UE/API/USER/user_api.c
+    ${NAS_SRC}UE/API/USER/user_indication.c
+    ${NAS_SRC}UE/API/USIM/aka_functions.c
+    ${NAS_SRC}UE/API/USIM/usim_api.c
+  )
+  set(libnas_ue_emm_OBJS
+    ${NAS_SRC}UE/EMM/Attach.c
+    ${NAS_SRC}UE/EMM/Authentication.c
+    ${NAS_SRC}UE/EMM/Detach.c
+    ${NAS_SRC}UE/EMM/emm_main.c
+    ${NAS_SRC}UE/EMM/EmmStatusHdl.c
+    ${NAS_SRC}UE/EMM/Identification.c
+    ${NAS_SRC}UE/EMM/IdleMode.c
+    ${NAS_SRC}UE/EMM/LowerLayer.c
+    ${NAS_SRC}UE/EMM/SecurityModeControl.c
+    ${NAS_SRC}UE/EMM/ServiceRequestHdl.c
+    ${NAS_SRC}UE/EMM/TrackingAreaUpdate.c
+  )
+  set(libnas_ue_emm_sap_OBJS
+    ${NAS_SRC}UE/EMM/SAP/emm_as.c
+    ${NAS_SRC}UE/EMM/SAP/EmmDeregisteredAttachNeeded.c
+    ${NAS_SRC}UE/EMM/SAP/EmmDeregisteredAttemptingToAttach.c
+    ${NAS_SRC}UE/EMM/SAP/EmmDeregistered.c
+    ${NAS_SRC}UE/EMM/SAP/EmmDeregisteredInitiated.c
+    ${NAS_SRC}UE/EMM/SAP/EmmDeregisteredLimitedService.c
+    ${NAS_SRC}UE/EMM/SAP/EmmDeregisteredNoCellAvailable.c
+    ${NAS_SRC}UE/EMM/SAP/EmmDeregisteredNoImsi.c
+    ${NAS_SRC}UE/EMM/SAP/EmmDeregisteredNormalService.c
+    ${NAS_SRC}UE/EMM/SAP/EmmDeregisteredPlmnSearch.c
+    ${NAS_SRC}UE/EMM/SAP/emm_esm.c
+    ${NAS_SRC}UE/EMM/SAP/emm_fsm.c
+    ${NAS_SRC}UE/EMM/SAP/EmmNull.c
+    ${NAS_SRC}UE/EMM/SAP/emm_recv.c
+    ${NAS_SRC}UE/EMM/SAP/emm_reg.c
+    ${NAS_SRC}UE/EMM/SAP/EmmRegisteredAttemptingToUpdate.c
+    ${NAS_SRC}UE/EMM/SAP/EmmRegistered.c
+    ${NAS_SRC}UE/EMM/SAP/EmmRegisteredImsiDetachInitiated.c
+    ${NAS_SRC}UE/EMM/SAP/EmmRegisteredInitiated.c
+    ${NAS_SRC}UE/EMM/SAP/EmmRegisteredLimitedService.c
+    ${NAS_SRC}UE/EMM/SAP/EmmRegisteredNoCellAvailable.c
+    ${NAS_SRC}UE/EMM/SAP/EmmRegisteredNormalService.c
+    ${NAS_SRC}UE/EMM/SAP/EmmRegisteredPlmnSearch.c
+    ${NAS_SRC}UE/EMM/SAP/EmmRegisteredUpdateNeeded.c
+    ${NAS_SRC}UE/EMM/SAP/emm_sap.c
+    ${NAS_SRC}UE/EMM/SAP/emm_send.c
+    ${NAS_SRC}UE/EMM/SAP/EmmServiceRequestInitiated.c
+    ${NAS_SRC}UE/EMM/SAP/EmmTrackingAreaUpdatingInitiated.c
+  )
+  set (libnas_ue_esm_OBJS
+    ${NAS_SRC}UE/ESM/DedicatedEpsBearerContextActivation.c
+    ${NAS_SRC}UE/ESM/DefaultEpsBearerContextActivation.c
+    ${NAS_SRC}UE/ESM/EpsBearerContextDeactivation.c
+    ${NAS_SRC}UE/ESM/esm_ebr.c
+    ${NAS_SRC}UE/ESM/esm_ebr_context.c
+    ${NAS_SRC}UE/ESM/esm_ip.c
+    ${NAS_SRC}UE/ESM/esm_main.c
+    ${NAS_SRC}UE/ESM/esm_pt.c
+    ${NAS_SRC}UE/ESM/EsmStatusHdl.c
+    ${NAS_SRC}UE/ESM/PdnConnectivity.c
+    ${NAS_SRC}UE/ESM/PdnDisconnect.c
+  )
+  set(libnas_ue_esm_sap_OBJS
+    ${NAS_SRC}UE/ESM/SAP/esm_recv.c
+    ${NAS_SRC}UE/ESM/SAP/esm_send.c
+    ${NAS_SRC}UE/ESM/SAP/esm_sap.c
+  )
+
+  set(libnrnas_emm_msg_OBJS
+    ${NAS_SRC}COMMON/EMM/MSG/RegistrationRequest.c
+  )
+
+  set(libnrnas_ies_OBJS
+    ${NAS_SRC}COMMON/IES/ExtendedProtocolDiscriminator.c
+    ${NAS_SRC}COMMON/IES/FGSMobileIdentity.c
+    ${NAS_SRC}COMMON/IES/FGSRegistrationType.c
+    ${NAS_SRC}COMMON/IES/SpareHalfOctet.c
+    ${NAS_SRC}COMMON/IES/FGMMCapability.c
+    ${NAS_SRC}COMMON/IES/NrUESecurityCapability.c
+  )
+
+  add_library(LIB_NAS_SIMUE
+    ${NAS_SRC}UE/nas_itti_messaging.c
+    ${NAS_SRC}UE/nas_network.c
+    ${NAS_SRC}UE/nas_parser.c
+    ${NAS_SRC}UE/nas_proc.c
+    ${NAS_SRC}UE/nas_user.c
+    ${NAS_SRC}NR_UE/nr_nas_msg_sim.c
+    ${libnas_api_OBJS}
+    ${libnas_ue_api_OBJS}
+    ${libnas_emm_msg_OBJS}
+    ${libnas_esm_msg_OBJS}
+    ${libnas_ies_OBJS}
+    ${libnas_utils_OBJS}
+    ${libnas_ue_emm_OBJS}
+    ${libnas_ue_emm_sap_OBJS}
+    ${libnas_ue_esm_OBJS}
+    ${libnas_ue_esm_sap_OBJS}
+    ${libnrnas_emm_msg_OBJS}
+    ${libnrnas_ies_OBJS}
+  )
+  add_dependencies(LIB_NAS_SIMUE rrc_flag)
+  set(NAS_SIM_LIB LIB_NAS_SIMUE)
+
+  include_directories(${NAS_SRC}NR_UE)
+  include_directories(${NAS_SRC}UE)
+  include_directories(${NAS_SRC}UE/API/USER)
+  include_directories(${NAS_SRC}UE/API/USIM)
+  include_directories(${NAS_SRC}UE/EMM)
+  include_directories(${NAS_SRC}UE/EMM/SAP)
+  include_directories(${NAS_SRC}UE/ESM)
+  include_directories(${NAS_SRC}UE/ESM/SAP)
+endif()
+
 # nbiot
 add_definitions("-DNUMBER_OF_UE_MAX_NB_IoT=16")
 set (NBIOT_SOURCES
@@ -3332,7 +3450,7 @@ add_executable(nr-ittisim
 target_link_libraries (nr-ittisim
   -Wl,--start-group
   UTIL HASHTABLE SCTP_CLIENT UDP SCHED_LIB SCHED_RU_LIB SCHED_NR_LIB PHY_NR PHY PHY_COMMON PHY_NR_COMMON PHY_RU LFDS NR_GTPV1U SECU_CN SECU_OSA
-  ${ITTI_LIB} ${FLPT_MSG_LIB} ${ASYNC_IF_LIB} ${FLEXRAN_AGENT_LIB} LFDS7 ${MSC_LIB} ${RAL_LIB} ${NAS_UE_LIB} RRC_LIB NR_RRC_LIB 
+  ${ITTI_LIB} ${FLPT_MSG_LIB} ${ASYNC_IF_LIB} ${FLEXRAN_AGENT_LIB} LFDS7 ${MSC_LIB} ${RAL_LIB} ${NAS_SIM_LIB} RRC_LIB NR_RRC_LIB 
   NGAP_LIB NGAP_GNB S1AP_LIB S1AP_ENB L2_LTE_NR L2_NR MAC_NR_COMMON NFAPI_COMMON_LIB NFAPI_LIB NFAPI_VNF_LIB NFAPI_PNF_LIB NFAPI_USER_LIB
   X2AP_LIB X2AP_ENB F1AP_LIB F1AP M2AP_LIB M2AP_ENB M3AP_LIB M3AP_ENB ${PROTO_AGENT_LIB} ${FSPT_MSG_LIB}
   NR_L2_UE
diff --git a/openair2/RRC/NR_UE/rrc_UE.c b/openair2/RRC/NR_UE/rrc_UE.c
index 949cf5bf08..0e3c59d02e 100755
--- a/openair2/RRC/NR_UE/rrc_UE.c
+++ b/openair2/RRC/NR_UE/rrc_UE.c
@@ -68,6 +68,10 @@
 #include "RRC/NAS/rb_config.h"
 #include "SIMULATION/TOOLS/sim.h" // for taus
 
+#if ITTI_SIM
+#include "nr_nas_msg_sim.h"
+#endif
+
 /* NAS Attach request with IMSI */
 static const char  nr_nas_attach_req_imsi[] = {
   0x07, 0x41,
@@ -1351,8 +1355,15 @@ static void rrc_ue_generate_RRCSetupComplete(
         const char *nas_msg;
         int   nas_msg_length;
        if (AMF_MODE_ENABLED) {
+#if ITTI_SIM
+          as_nas_info_t initialNasMsg;
+          generateRegistrationRequest(&initialNasMsg);
+          nas_msg = (char*)initialNasMsg.data;
+          nas_msg_length = initialNasMsg.length;
+#else
           nas_msg         = (char *) NR_UE_rrc_inst[ctxt_pP->module_id].initialNasMsg.data;
           nas_msg_length  = NR_UE_rrc_inst[ctxt_pP->module_id].initialNasMsg.length;
+#endif
            } else {
           nas_msg         = nr_nas_attach_req_imsi;
           nas_msg_length  = sizeof(nr_nas_attach_req_imsi);
diff --git a/openair3/NAS/COMMON/EMM/MSG/RegistrationRequest.c b/openair3/NAS/COMMON/EMM/MSG/RegistrationRequest.c
index 4d449168d5..23404e0ed1 100644
--- a/openair3/NAS/COMMON/EMM/MSG/RegistrationRequest.c
+++ b/openair3/NAS/COMMON/EMM/MSG/RegistrationRequest.c
@@ -65,7 +65,30 @@ int encode_registration_request(registration_request_msg *registration_request,
   else
     encoded += encode_result;
 
-  // TODO, Eecoding optional fields
+  if ((registration_request->presencemask & REGISTRATION_REQUEST_5GMM_CAPABILITY_PRESENT)
+      == REGISTRATION_REQUEST_5GMM_CAPABILITY_PRESENT) {
+    if ((encode_result = encode_5gmm_capability(&registration_request->fgmmcapability,
+                         REGISTRATION_REQUEST_5GMM_CAPABILITY_IEI, buffer + encoded, len -
+                         encoded)) < 0)
+      // Return in case of error
+      return encode_result;
+    else
+      encoded += encode_result;
+  }
+
+  if ((registration_request->presencemask & REGISTRATION_REQUEST_UE_SECURITY_CAPABILITY_PRESENT)
+      == REGISTRATION_REQUEST_UE_SECURITY_CAPABILITY_PRESENT) {
+    if ((encode_result = encode_nrue_security_capability(&registration_request->nruesecuritycapability,
+                         REGISTRATION_REQUEST_UE_SECURITY_CAPABILITY_IEI, buffer + encoded, len -
+                         encoded)) < 0)
+      // Return in case of error
+      return encode_result;
+    else
+      encoded += encode_result;
+  }
+
+
+  // TODO, Encoding optional fields
   return encoded;
 }
 
diff --git a/openair3/NAS/COMMON/EMM/MSG/RegistrationRequest.h b/openair3/NAS/COMMON/EMM/MSG/RegistrationRequest.h
index 4d023e05e9..fdc70fa57d 100644
--- a/openair3/NAS/COMMON/EMM/MSG/RegistrationRequest.h
+++ b/openair3/NAS/COMMON/EMM/MSG/RegistrationRequest.h
@@ -18,6 +18,8 @@
 #include "NasKeySetIdentifier.h"
 #include "FGSRegistrationType.h"
 #include "MessageType.h"
+#include "FGMMCapability.h"
+#include "NrUESecurityCapability.h"
 
 #ifndef REGISTRATION_REQUEST_H_
 #define REGISTRATION_REQUEST_H_
@@ -89,6 +91,9 @@ typedef struct registration_request_msg_tag {
   FGSMobileIdentity                       fgsmobileidentity;
 
   /* Optional fields */
+  uint32_t                                presencemask;
+  FGMMCapability                          fgmmcapability;
+  NrUESecurityCapability                  nruesecuritycapability;
 } registration_request_msg;
 
 int decode_registration_request(registration_request_msg *registrationrequest, uint8_t *buffer, uint32_t len);
diff --git a/openair3/NAS/COMMON/IES/FGMMCapability.c b/openair3/NAS/COMMON/IES/FGMMCapability.c
new file mode 100644
index 0000000000..b0796478f0
--- /dev/null
+++ b/openair3/NAS/COMMON/IES/FGMMCapability.c
@@ -0,0 +1,34 @@
+/*! \file FGSMobileIdentity.c
+
+\brief 5GS Mobile Identity for registration request procedures
+\author Yoshio INOUE, Masayuki HARADA
+\email: yoshio.inoue@fujitsu.com,masayuki.harada@fujitsu.com
+\date 2020
+\version 0.1
+*/
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdint.h>
+
+
+#include "TLVEncoder.h"
+#include "TLVDecoder.h"
+#include "FGMMCapability.h"
+
+
+
+int encode_5gmm_capability(FGMMCapability *fgmmcapability, uint8_t iei, uint8_t *buffer, uint32_t len)
+{
+  int encoded = 0;
+  if(iei){
+    *buffer = fgmmcapability->iei;
+     encoded++;
+     *(buffer+encoded) = fgmmcapability->length;
+     encoded++;
+     *(buffer+encoded) = fgmmcapability->value;
+     encoded++;
+  }
+  return encoded;
+}
+
diff --git a/openair3/NAS/COMMON/IES/FGMMCapability.h b/openair3/NAS/COMMON/IES/FGMMCapability.h
new file mode 100644
index 0000000000..c8cc238c80
--- /dev/null
+++ b/openair3/NAS/COMMON/IES/FGMMCapability.h
@@ -0,0 +1,30 @@
+/*! \file FGSMobileIdentity.h
+
+\brief 5GS Mobile Identity for registration request procedures
+\author Yoshio INOUE, Masayuki HARADA
+\email: yoshio.inoue@fujitsu.com,masayuki.harada@fujitsu.com
+\date 2020
+\version 0.1
+*/
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdint.h>
+
+#include "OctetString.h"
+
+#ifndef FGMM_CAPABILITY_H_
+#define FGMM_CAPABILITY_H_
+
+
+typedef struct {
+  uint8_t iei;
+  uint8_t length;
+  uint8_t value;
+} FGMMCapability;
+
+
+int encode_5gmm_capability(FGMMCapability *fgmmcapability, uint8_t iei, uint8_t *buffer, uint32_t len);
+
+#endif /* FGMM_CAPABILITY_H_ */
+
diff --git a/openair3/NAS/COMMON/IES/FGSMobileIdentity.c b/openair3/NAS/COMMON/IES/FGSMobileIdentity.c
index 77551c3eed..dfe19b4a35 100644
--- a/openair3/NAS/COMMON/IES/FGSMobileIdentity.c
+++ b/openair3/NAS/COMMON/IES/FGSMobileIdentity.c
@@ -51,7 +51,6 @@ int decode_5gs_mobile_identity(FGSMobileIdentity *fgsmobileidentity, uint8_t iei
 
 int encode_5gs_mobile_identity(FGSMobileIdentity *fgsmobileidentity, uint8_t iei, uint8_t *buffer, uint32_t len)
 {
-  uint8_t *lenPtr;
   int encoded_rc = TLV_ENCODE_VALUE_DOESNT_MATCH;
   uint32_t encoded = 0;
 
@@ -60,8 +59,7 @@ int encode_5gs_mobile_identity(FGSMobileIdentity *fgsmobileidentity, uint8_t iei
     encoded++;
   }
 
-  lenPtr  = (buffer + encoded);
-  encoded ++;
+  encoded = encoded + 2;
 
   if (fgsmobileidentity->guti.typeofidentity == FGS_MOBILE_IDENTITY_5G_GUTI) {
     encoded_rc = encode_guti_5gs_mobile_identity(&fgsmobileidentity->guti,
@@ -72,7 +70,7 @@ int encode_5gs_mobile_identity(FGSMobileIdentity *fgsmobileidentity, uint8_t iei
     return encoded_rc;
   }
 
-  *lenPtr = encoded  + encoded_rc - 1 - ((iei > 0) ? 1 : 0);
+  *(uint16_t*) buffer = htons(encoded  + encoded_rc - 2 - ((iei > 0) ? 1 : 0));
   return (encoded + encoded_rc);
 }
 
diff --git a/openair3/NAS/COMMON/IES/FGSRegistrationType.c b/openair3/NAS/COMMON/IES/FGSRegistrationType.c
index 4202e9c65f..9760238f10 100644
--- a/openair3/NAS/COMMON/IES/FGSRegistrationType.c
+++ b/openair3/NAS/COMMON/IES/FGSRegistrationType.c
@@ -15,9 +15,10 @@
 #include "TLVDecoder.h"
 #include "FGSRegistrationType.h"
 
-int decode_5gs_registration_type(FGSRegistrationType *fgsregistrationtype, uint8_t iei, uint8_t *buffer, uint32_t len)
+int decode_5gs_registration_type(FGSRegistrationType *fgsregistrationtype, uint8_t iei, uint8_t value, uint32_t len)
 {
   int decoded = 0;
+  uint8_t *buffer = &value;
   if (iei > 0) {
     CHECK_IEI_DECODER((*buffer & 0xf0), iei);
   }
@@ -34,7 +35,7 @@ int encode_5gs_registration_type(FGSRegistrationType *fgsregistrationtype)
   uint8_t *buffer = &bufferReturn;
   uint8_t encoded = 0;
   uint8_t iei = 0;
-  *(buffer + encoded) = 0x00 | (iei & 0xf0) |
+  *(buffer + encoded) = 0x00 | (iei & 0xf0) | 0x8|
                         (*fgsregistrationtype & 0x7);
   encoded++;
 
diff --git a/openair3/NAS/COMMON/IES/FGSRegistrationType.h b/openair3/NAS/COMMON/IES/FGSRegistrationType.h
index b9fee868fb..5e6e3ebc6e 100644
--- a/openair3/NAS/COMMON/IES/FGSRegistrationType.h
+++ b/openair3/NAS/COMMON/IES/FGSRegistrationType.h
@@ -28,7 +28,7 @@ typedef uint8_t FGSRegistrationType;
 
 int encode_5gs_registration_type(FGSRegistrationType *fgsregistrationtype);
 
-int decode_5gs_registration_type(FGSRegistrationType *fgsregistrationtype, uint8_t iei, uint8_t *buffer, uint32_t len);
+int decode_5gs_registration_type(FGSRegistrationType *fgsregistrationtype, uint8_t iei, uint8_t value, uint32_t len);
 
 
 #endif /* FGS_REGISTRATION_TYPE_H_*/
diff --git a/openair3/NAS/COMMON/IES/NrUESecurityCapability.c b/openair3/NAS/COMMON/IES/NrUESecurityCapability.c
new file mode 100644
index 0000000000..964e226835
--- /dev/null
+++ b/openair3/NAS/COMMON/IES/NrUESecurityCapability.c
@@ -0,0 +1,42 @@
+/*! \file FGSMobileIdentity.c
+
+\brief 5GS Mobile Identity for registration request procedures
+\author Yoshio INOUE, Masayuki HARADA
+\email: yoshio.inoue@fujitsu.com,masayuki.harada@fujitsu.com
+\date 2020
+\version 0.1
+*/
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdint.h>
+
+
+#include "TLVEncoder.h"
+#include "TLVDecoder.h"
+#include "NrUESecurityCapability.h"
+
+
+
+int encode_nrue_security_capability(NrUESecurityCapability *nruesecuritycapability, uint8_t iei, uint8_t *buffer, uint32_t len)
+{
+  int encoded = 0;
+  if(iei){
+    *buffer = nruesecuritycapability->iei;
+     encoded++;
+     *(buffer+encoded) = nruesecuritycapability->length;
+     encoded++;
+     *(buffer+encoded) = nruesecuritycapability->fg_EA;
+     encoded++;
+     *(buffer+encoded) = nruesecuritycapability->fg_IA;
+     encoded++;
+     *(buffer+encoded) = nruesecuritycapability->EEA;
+     encoded++;
+     *(buffer+encoded) = nruesecuritycapability->EIA;
+     encoded++;
+     if((nruesecuritycapability->length - 4) > 0)
+       encoded = encoded + nruesecuritycapability->length - 4;
+  }
+  return encoded;
+}
+
diff --git a/openair3/NAS/COMMON/IES/NrUESecurityCapability.h b/openair3/NAS/COMMON/IES/NrUESecurityCapability.h
new file mode 100644
index 0000000000..a16b7c1c5c
--- /dev/null
+++ b/openair3/NAS/COMMON/IES/NrUESecurityCapability.h
@@ -0,0 +1,33 @@
+/*! \file FGSMobileIdentity.h
+
+\brief 5GS Mobile Identity for registration request procedures
+\author Yoshio INOUE, Masayuki HARADA
+\email: yoshio.inoue@fujitsu.com,masayuki.harada@fujitsu.com
+\date 2020
+\version 0.1
+*/
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdint.h>
+
+#include "OctetString.h"
+
+#ifndef NRUE_SECURITY_CAPABILITY_H_
+#define NRUE_SECURITY_CAPABILITY_H_
+
+
+typedef struct {
+  uint8_t iei;
+  uint8_t length;
+  uint8_t fg_EA;
+  uint8_t fg_IA;
+  uint8_t EEA;
+  uint8_t EIA;
+} NrUESecurityCapability;
+
+
+int encode_nrue_security_capability(NrUESecurityCapability *nruesecuritycapability, uint8_t iei, uint8_t *buffer, uint32_t len);
+
+#endif /* NRUE_SECURITY_CAPABILITY_H_ */
+
diff --git a/openair3/NAS/NR_UE/nr_nas_msg_sim.c b/openair3/NAS/NR_UE/nr_nas_msg_sim.c
new file mode 100644
index 0000000000..29203dbc47
--- /dev/null
+++ b/openair3/NAS/NR_UE/nr_nas_msg_sim.c
@@ -0,0 +1,148 @@
+
+/*! \file nr_nas_msg_sim.c
+
+\brief simulator for nr nas message
+\author Yoshio INOUE, Masayuki HARADA
+\email: yoshio.inoue@fujitsu.com,masayuki.harada@fujitsu.com
+\date 2020
+\version 0.1
+*/
+
+#include <string.h> // memset
+#include <stdlib.h> // malloc, free
+
+#include "nas_log.h"
+#include "TLVDecoder.h"
+#include "TLVEncoder.h"
+#include "nr_nas_msg_sim.h"
+
+
+static int _nas_mm_msg_encode_header(const mm_msg_header_t *header,
+                                  uint8_t *buffer, uint32_t len) {
+  int size = 0;
+
+  /* Check the buffer length */
+  if (len < sizeof(mm_msg_header_t)) {
+    return (TLV_ENCODE_BUFFER_TOO_SHORT);
+  }
+
+  /* Check the protocol discriminator */
+  if (header->ex_protocol_discriminator != FGS_MOBILITY_MANAGEMENT_MESSAGE) {
+    LOG_TRACE(ERROR, "ESM-MSG   - Unexpected extened protocol discriminator: 0x%x",
+              header->ex_protocol_discriminator);
+    return (TLV_ENCODE_PROTOCOL_NOT_SUPPORTED);
+  }
+
+  /* Encode the extendedprotocol discriminator */
+  ENCODE_U8(buffer + size, header->ex_protocol_discriminator, size);
+  /* Encode the security header type */
+  ENCODE_U8(buffer + size, (header->security_header_type & 0xf), size);
+  /* Encode the message type */
+  ENCODE_U8(buffer + size, header->message_type, size);
+  return (size);
+}
+
+
+int mm_msg_encode(MM_msg *mm_msg, uint8_t *buffer, uint32_t len) {
+  LOG_FUNC_IN;
+  int header_result;
+  int encode_result;
+  uint8_t msg_type = mm_msg->header.message_type;
+
+
+  /* First encode the EMM message header */
+  header_result = _nas_mm_msg_encode_header(&mm_msg->header, buffer, len);
+
+  if (header_result < 0) {
+    LOG_TRACE(ERROR, "EMM-MSG   - Failed to encode EMM message header "
+              "(%d)", header_result);
+    LOG_FUNC_RETURN(header_result);
+  }
+
+  buffer += header_result;
+  len -= header_result;
+
+  switch(msg_type) {
+    case REGISTRATION_REQUEST:
+      encode_result = encode_registration_request(&mm_msg->registration_request, buffer, len);
+      break;
+
+    default:
+      LOG_TRACE(ERROR, "EMM-MSG   - Unexpected message type: 0x%x",
+    		  mm_msg->header.message_type);
+      encode_result = TLV_ENCODE_WRONG_MESSAGE_TYPE;
+      break;
+      /* TODO: Handle not standard layer 3 messages: SERVICE_REQUEST */
+  }
+
+  if (encode_result < 0) {
+    LOG_TRACE(ERROR, "EMM-MSG   - Failed to encode L3 EMM message 0x%x "
+              "(%d)", mm_msg->header.message_type, encode_result);
+  }
+
+  if (encode_result < 0)
+    LOG_FUNC_RETURN (encode_result);
+
+  LOG_FUNC_RETURN (header_result + encode_result);
+}
+
+
+
+void generateRegistrationRequest(as_nas_info_t *initialNasMsg) {
+  int size = sizeof(mm_msg_header_t);
+  fgs_nas_message_t nas_msg;
+  memset(&nas_msg, 0, sizeof(fgs_nas_message_t));
+  MM_msg *mm_msg;
+
+  mm_msg = &nas_msg.plain.mm_msg;
+  // set header
+  mm_msg->header.ex_protocol_discriminator = FGS_MOBILITY_MANAGEMENT_MESSAGE;
+  mm_msg->header.security_header_type = PLAIN_5GS_MSG;
+  mm_msg->header.message_type = REGISTRATION_REQUEST;
+
+
+  // set registration request
+  mm_msg->registration_request.protocoldiscriminator = FGS_MOBILITY_MANAGEMENT_MESSAGE;
+  size += 1;
+  mm_msg->registration_request.securityheadertype = PLAIN_5GS_MSG;
+  size += 1;
+  mm_msg->registration_request.messagetype = REGISTRATION_REQUEST;
+  size += 1;
+  mm_msg->registration_request.fgsregistrationtype = INITIAL_REGISTRATION;
+  mm_msg->registration_request.naskeysetidentifier.naskeysetidentifier = NAS_KEY_SET_IDENTIFIER_NOT_AVAILABLE;
+  size += 1;
+  mm_msg->registration_request.fgsmobileidentity.guti.typeofidentity = FGS_MOBILE_IDENTITY_5G_GUTI;
+//  mm_msg->registration_request.fgsmobileidentity.guti.amfregionid = 1;
+//  mm_msg->registration_request.fgsmobileidentity.guti.amfpointer = 1;
+//  mm_msg->registration_request.fgsmobileidentity.guti.amfsetid = 1;
+  mm_msg->registration_request.fgsmobileidentity.guti.tmsi = 10;
+  mm_msg->registration_request.fgsmobileidentity.guti.mncdigit1 = 9;
+  mm_msg->registration_request.fgsmobileidentity.guti.mncdigit2 = 3;
+  mm_msg->registration_request.fgsmobileidentity.guti.mccdigit1 = 2;
+  mm_msg->registration_request.fgsmobileidentity.guti.mccdigit2 = 0;
+  mm_msg->registration_request.fgsmobileidentity.guti.mccdigit3 = 8;
+
+  size += 13;
+
+  mm_msg->registration_request.presencemask |= REGISTRATION_REQUEST_5GMM_CAPABILITY_PRESENT;
+  mm_msg->registration_request.fgmmcapability.iei = REGISTRATION_REQUEST_5GMM_CAPABILITY_IEI;
+  mm_msg->registration_request.fgmmcapability.length = 1;
+  mm_msg->registration_request.fgmmcapability.value = 0x7;
+  size += 3;
+
+  mm_msg->registration_request.presencemask |= REGISTRATION_REQUEST_UE_SECURITY_CAPABILITY_PRESENT;
+  mm_msg->registration_request.nruesecuritycapability.iei = REGISTRATION_REQUEST_UE_SECURITY_CAPABILITY_IEI;
+  mm_msg->registration_request.nruesecuritycapability.length = 8;
+  mm_msg->registration_request.nruesecuritycapability.fg_EA = 0x80;
+  mm_msg->registration_request.nruesecuritycapability.fg_IA = 0x20;
+  mm_msg->registration_request.nruesecuritycapability.EEA = 0;
+  mm_msg->registration_request.nruesecuritycapability.EIA = 0;
+  size += 10;
+
+  // encode the message
+  initialNasMsg->data = (Byte_t *)malloc(size * sizeof(Byte_t));
+
+  initialNasMsg->length = mm_msg_encode(mm_msg, (uint8_t*)(initialNasMsg->data), size);
+
+
+}
diff --git a/openair3/NAS/NR_UE/nr_nas_msg_sim.h b/openair3/NAS/NR_UE/nr_nas_msg_sim.h
new file mode 100644
index 0000000000..c5ec902c4a
--- /dev/null
+++ b/openair3/NAS/NR_UE/nr_nas_msg_sim.h
@@ -0,0 +1,73 @@
+/*! \file nr_nas_msg_sim.h
+
+\brief simulator for nr nas message
+\author Yoshio INOUE, Masayuki HARADA
+\email: yoshio.inoue@fujitsu.com,masayuki.harada@fujitsu.com
+\date 2020
+\version 0.1
+*/
+
+
+#ifndef __NR_NAS_MSG_SIM_H__
+#define __NR_NAS_MSG_SIM_H__
+
+#include "RegistrationRequest.h"
+#include "as_message.h"
+
+
+#define PLAIN_5GS_MSG                                      0b0000
+#define INTEGRITY_PROTECTED                                0b0001
+
+#define REGISTRATION_REQUEST                               0b01000001 /* 65 = 0x41 */
+#define INITIAL_REGISTRATION                               0b001
+
+
+typedef enum fgs_protocol_discriminator_e {
+  /* Protocol discriminator identifier for 5GS Mobility Management */
+  FGS_MOBILITY_MANAGEMENT_MESSAGE =   0x7E,
+
+  /* Protocol discriminator identifier for 5GS Session Management */
+  FGS_SESSION_MANAGEMENT_MESSAGE =    0x2E,
+} fgs_protocol_discriminator_t;
+
+
+typedef struct {
+  uint8_t ex_protocol_discriminator;
+  uint8_t security_header_type;
+  uint8_t message_type;
+} mm_msg_header_t;
+
+/* Structure of security protected header */
+typedef struct {
+  fgs_protocol_discriminator_t    protocol_discriminator;
+  uint8_t                         security_header_type;
+  uint32_t                        message_authentication_code;
+  uint8_t                         sequence_number;
+} fgs_nas_message_security_header_t;
+
+typedef union {
+  mm_msg_header_t                        header;
+  registration_request_msg               registration_request;
+} MM_msg;
+
+
+
+typedef struct {
+  MM_msg mm_msg;    /* 5GS Mobility Management messages */
+} fgs_nas_message_plain_t;
+
+typedef struct {
+  fgs_nas_message_security_header_t header;
+  fgs_nas_message_plain_t plain;
+} fgs_nas_message_security_protected_t;
+
+
+typedef union {
+  fgs_nas_message_security_header_t header;
+  fgs_nas_message_security_protected_t security_protected;
+  fgs_nas_message_plain_t plain;
+} fgs_nas_message_t;
+
+void generateRegistrationRequest(as_nas_info_t *initialNasMsg);
+
+#endif /* __NR_NAS_MSG_SIM_H__*/