diff --git a/include/common/s1ap_structs.h b/include/common/s1ap_structs.h
new file mode 100644
index 0000000..d61e13f
--- /dev/null
+++ b/include/common/s1ap_structs.h
@@ -0,0 +1,761 @@
+/*
+ * Copyright (c) 2003-2018, Great Software Laboratory Pvt. Ltd.
+ * Copyright (c) 2017 Intel Corporation
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef __S1AP_STRUCTS_H_
+#define __S1AP_STRUCTS_H_
+
+#include <stdint.h>
+#include <stdbool.h>
+
+#include "sec.h"
+#include "ProcedureCode.h"
+#include "Criticality.h"
+#include "S1AP-PDU.h"
+#include "InitiatingMessage.h"
+
+#define NAS_RAND_SIZE 16
+#define NAS_AUTN_SIZE 16
+
+#define AUTH_REQ_NO_OF_IES 3
+#define SEC_MODE_NO_OF_IES 3
+#define ESM_REQ_NO_OF_IES 3
+#define ICS_REQ_NO_OF_IES 6
+#define DTCH_ACCEPT_NO_OF_IES 3
+#define UE_CTX_RELEASE_NO_OF_IES 3
+#define ATTACH_REJECT_NO_OF_IES 3
+
+#define ATTACH_ID_REQUEST_NO_OF_IES 3
+#define TAU_RSP_NO_OF_IES 3
+
+#define NI_UE_CTX_RELEASE_NO_OF_IES 3
+#define NI_DTCH_REQUEST_NO_OF_IES 3
+
+
+#define AUTH_REQ_NO_OF_NAS_IES 2
+#define SEC_MODE_NO_OF_NAS_IES 1
+#define ICS_REQ_NO_OF_NAS_IES 5
+#define TAU_RSP_NO_OF_NAS_IES 2
+
+#define SERVICE_REQ_SECURITY_HEADER 12
+#define SHORT_MAC_SIZE 2
+
+#define AUTHREQ_NAS_SECURITY_PARAM 0x01
+
+#define MSISDN_STR_LEN 10
+
+#define EMM_MAX_TAI_LIST 16
+
+#define SECURITY_KEY_SIZE 32
+
+#define MAC_SIZE 4
+#define AUTH_SYNC_FAILURE 21
+#define AUTH_RESPONSE 53
+/* ESM messages */
+ #define ESM_MSG_ACTV_DEF_BEAR__CTX_REQ 0xc1
+
+/*24.008 - 10.5.6.1
+APN name can be in range of min 3 octets to max 102 octets
+*/
+#define MAX_APN_LEN 102
+
+
+struct apn_name {
+	unsigned char len;
+	unsigned char val[MAX_APN_LEN];/*TODO: Make dynamic as range is big 3-102*/
+};
+
+/*TODO: Needed fro paging. Ignoring for now*/
+struct proto_conf {
+	int placeholder;
+};
+
+struct esm_sec_info {
+	struct proto_conf proto_config;
+};
+
+/*NAS MSG IE CODES */
+/* Message content : 
+   3gpp 24.301
+   Table 8.2.4.1: IEI Column.*/
+typedef enum
+{
+    NAS_IE_TYPE_EPS_MOBILE_ID_IMSI=0x1,
+    NAS_IE_TYPE_UE_NETWORK_CAPABILITY=0x2,
+    NAS_IE_TYPE_ESM_MSG=0x3,
+    NAS_IE_TYPE_TMSI_STATUS=0x09,
+    NAS_IE_TYPE_MS_NETWORK_FEATURE_SUPPORT=0x0C,
+    NAS_IE_TYPE_GUTI_TYPE=0x0E,
+    NAS_IE_TYPE_ADDITIONAL_UPDATE_TYPE=0xF,
+    NAS_IE_TYPE_MS_CLASSMARK_2=0x11,
+    NAS_IE_TYPE_LAI=0x13,
+    NAS_IE_TYPE_PTMSI_SIGNATURE=0x19,
+    NAS_IE_TYPE_MS_CLASSMARK_3=0x20,
+    NAS_IE_TYPE_APN=0x28,
+    NAS_IE_TYPE_AUTH_FAIL_PARAM=0x30,
+    NAS_IE_TYPE_MS_NETWORK_CAPABILITY=0x31,
+    NAS_IE_TYPE_DRX_PARAM=0x5C,
+    NAS_IE_TYPE_TAI=0x52,
+    NAS_IE_TYPE_VOICE_DOMAIN_PREF_UE_USAGE_SETTING=0x5D,
+    NAS_IE_TYPE_TX_FLAG=0xAA,
+    NAS_IE_TYPE_PCO=0xAB,
+    NAS_IE_TYPE_PTI=0xAC,
+}nas_ie_type;
+typedef struct MS_net_capab {
+    bool          pres;
+	unsigned char element_id;
+	unsigned char len;
+	unsigned char capab[6];
+}MS_net_capab;
+
+#if 0
+/* MS Network capability */
+typedef struct MS_net_capab {
+   unsigned char pres;
+   unsigned char len;
+   unsigned char gea1;
+   unsigned char smCapViaDdctdChan;
+   unsigned char smCapViaGprsChan;
+   unsigned char ucs2Supp;
+   unsigned char ssScrInd;
+   unsigned char soLsaCap;
+   unsigned char revLvlInd;
+   unsigned char pfcFeatMode;
+   unsigned char gea2;
+   unsigned char gea3;
+   unsigned char gea4;
+   unsigned char gea5;
+   unsigned char gea6;
+   unsigned char gea7;
+   unsigned char lcsVaCap;
+   unsigned char psInterRATho2UtranIuModeCap;
+   unsigned char psInterRATho2EutranS1ModeCap;
+   unsigned char csfbCap;
+   unsigned char isrSupp;
+   unsigned char srvcc2UtranCap;
+   unsigned char epcCap;
+}MS_net_capab;
+#endif
+
+struct UE_net_capab {
+	unsigned char len;
+	unsigned char capab[6];
+};
+#if 0
+/* UE Network capability */
+typedef struct UE_net_capab {
+   unsigned char pres;
+   unsigned char len;
+
+   unsigned char eea7;
+   unsigned char eea6;
+   unsigned char eea5;
+   unsigned char eea4;
+   unsigned char eea3;
+   unsigned char eea2_128;
+   unsigned char eea1_128;
+   unsigned char eea0;
+
+   unsigned char eia7;
+   unsigned char eia6;
+   unsigned char eia5;
+   unsigned char eia4;
+   unsigned char eia3;
+   unsigned char eia2_128;
+   unsigned char eia1_128;
+   unsigned char eia0;
+
+   unsigned char uea7;
+   unsigned char uea6;
+   unsigned char uea5;
+   unsigned char uea4;
+   unsigned char uea3;
+   unsigned char uea2;
+   unsigned char uea1;
+   unsigned char uea0;
+
+   unsigned char uia7;
+   unsigned char uia6;
+   unsigned char uia5;
+   unsigned char uia4;
+   unsigned char uia3;
+   unsigned char uia2;
+   unsigned char uia1;
+   unsigned char ucs2;
+
+   unsigned char vcc_1xsr;
+
+} UE_net_capab;
+#endif
+
+enum drx_params {
+	PAGINX_DRX32,
+	PAGINX_DRX64,
+	PAGINX_DRX128,
+	PAGINX_DRX256,
+	PAGINX_DRX512,
+};
+
+enum s1ap_cn_domain
+{
+    CN_DOMAIN_PS,
+    CN_DOMAIN_CS,
+    CN_DOMAIN_NONE
+};
+
+struct s1ap_header{
+	unsigned short procedure_code;
+	unsigned char criticality;
+};
+
+#pragma pack(1)
+
+/*36.413: 9.2.3.8 - MCC, MCN : Only 3 bytes are used*/
+struct PLMN {
+	unsigned char  idx[3];
+};
+
+struct TAI {
+	struct PLMN plmn_id;
+	short tac; /*2 bytes. 36.413: 9.2.3.7*/
+};
+
+struct STMSI {
+	uint8_t mme_code;
+    uint32_t m_TMSI;
+};
+
+
+typedef struct tai_list {
+	uint8_t spare :1;
+	uint8_t type :2;
+	uint8_t num_of_elements :4;
+	struct TAI partial_list[EMM_MAX_TAI_LIST];
+} tai_list;
+
+typedef struct pdn_address {
+	uint8_t spare :5;
+	uint8_t type :3;
+	uint32_t ipv4; /* TODO: Revisit 24.301 - 9.9.4.9.1 */
+} pdn_address;
+
+typedef struct linked_transcation_id {
+	uint8_t flag :1;
+	uint8_t val :7;
+} linked_transcation_id;
+
+typedef struct esm_qos
+{
+	uint8_t reliability_class :3;
+	uint8_t delay_class :3;
+	uint8_t spare1 :2;
+	uint8_t precedence_class :3;
+	uint8_t spare2 :1;
+	uint8_t peak_throughput :4;
+	uint8_t mean_throughput :5;
+	uint8_t spare3 :3;
+	uint8_t delivery_err_sdu :3;
+	uint8_t delivery_order :2;
+	uint8_t traffic_class :3;
+	uint8_t max_sdu_size;
+	uint8_t mbr_ul;
+	uint8_t mbr_dl;
+	uint8_t sdu_err_ratio :4;
+	uint8_t residual_ber :4;
+	uint8_t trffic_prio :2;
+	uint8_t transfer_delay :6;
+	uint8_t gbr_ul;
+	uint8_t gbr_dl;
+	uint8_t src_stat_desc :4;
+	uint8_t sig_ind :1;
+	uint8_t spare4 :3;
+	uint8_t mbr_dl_ext;
+	uint8_t gbr_dl_ext;
+	uint8_t mbr_ul_ext;
+	uint8_t gbr_ul_ext;
+
+} esm_qos;
+
+/* TODO : Revisit 24.301 - 9.9.4.2.1 */
+typedef struct ESM_APN_AMBR {
+	uint8_t dl;
+	uint8_t reserved;
+	uint8_t dlext;
+	uint8_t ulext;
+	uint8_t dlext2;
+	/* uint8_t dl_total; */
+	uint8_t ulext2;
+	/* uint8_t ul_total; */
+} ESM_APN_AMBR;
+
+typedef struct guti {
+	uint8_t spare :4;
+	uint8_t odd_even_indication :1;
+	uint8_t id_type :3;
+	struct PLMN plmn_id;
+	uint16_t mme_grp_id;
+	uint8_t mme_code;
+	uint32_t m_TMSI;
+} guti;
+
+typedef struct esm_msg_container {
+	uint8_t eps_bearer_id :4;
+	uint8_t proto_discriminator :4;
+	uint8_t procedure_trans_identity;
+	uint8_t session_management_msgs;
+	uint8_t eps_qos;  /* TODO: Revisit 24.301 - 9.9.4.3.1 */
+	struct apn_name apn;
+	pdn_address pdn_addr;
+	linked_transcation_id linked_ti;
+	esm_qos negotiated_qos;
+	ESM_APN_AMBR apn_ambr;
+} esm_msg_container;
+
+typedef struct ue_sec_capabilities {
+	uint8_t eea1 :1;
+	uint8_t eea2 :1;
+	uint8_t eea3 :1;
+	uint8_t eea4 :1;
+	uint8_t eea5 :1;
+	uint8_t eea6_128 :1;
+	uint8_t eea7_128 :1;
+	uint8_t eea8 :1;
+
+	uint8_t eia1 :1;
+	uint8_t eia2 :1;
+	uint8_t eia3 :1;
+	uint8_t eia4 :1;
+	uint8_t eia5 :1;
+	uint8_t eia6_128 :1;
+	uint8_t eia8_128 :1;
+	uint8_t eia8 :1;
+
+	uint8_t uea1 :1;
+	uint8_t uea2 :1;
+	uint8_t uea3 :1;
+	uint8_t uea4 :1;
+	uint8_t uea5 :1;
+	uint8_t uea6 :1;
+	uint8_t uea7 :1;
+	uint8_t uea8 :1;
+
+	uint8_t uia1 :1;
+	uint8_t uia2 :1;
+	uint8_t uia3 :1;
+	uint8_t uia4 :1;
+	uint8_t uia5 :1;
+	uint8_t uia6 :1;
+	uint8_t uia7 :1;
+	uint8_t spare1 :1;
+
+	uint8_t gea1 :1;
+	uint8_t gea2 :1;
+	uint8_t gea3 :1;
+	uint8_t gea4 :1;
+	uint8_t gea5 :1;
+	uint8_t gea6 :1;
+	uint8_t gea7 :1;
+	uint8_t spare2 :1;
+} ue_sec_capabilities;
+
+typedef struct nas_pdu_header {
+	unsigned char security_header_type:4;
+	unsigned char proto_discriminator:4;
+	unsigned char message_type;
+	unsigned char security_encryption_algo:4;
+	unsigned char security_integrity_algo:4;
+	unsigned char nas_security_param;
+	unsigned char mac[MAC_SIZE];
+	unsigned char short_mac[SHORT_MAC_SIZE];
+	unsigned char ksi;
+	unsigned char seq_no;
+	unsigned char eps_bearer_identity;
+	unsigned char procedure_trans_identity;
+	unsigned char detach_type;
+} nas_pdu_header;
+
+#pragma pack()
+
+/****Information elements presentations **/
+#define BINARY_IMSI_LEN 8 /*same as packet capture. TODO: Write macros*/
+#define BCD_IMSI_STR_LEN 15
+
+/*36.413 - 9.2.1.38*/
+struct CGI {
+	struct PLMN plmn_id;
+	int cell_id;
+};
+/*36.413: 9.2.1.37*/
+#define MACRO_ENB_ID_SIZE 20
+struct ie_global_enb_id {
+	int plmn;
+	char macro_enb_id[MACRO_ENB_ID_SIZE];
+	/*TODO: make union of enb IDs*/
+};
+
+/*36.413: 9.1.8.4*/
+#define ENB_NAME_SIZE 150
+struct ie_enb_name {
+	char enb_name[ENB_NAME_SIZE];
+};
+
+/*36.413: 9.2.1.3a*/
+enum ie_RRC_est_cause {
+	EMERGENCY,
+	HIGHPRIORITYACCESS,
+	MT_ACCESS,
+	MO_SIGNALLING,
+	MO_DATA,
+	DELAYTOLERANTACCESS,
+	MO_VOICECALL,
+	MO_EXCEPTIONDATA
+};
+
+/**E-RAB structure declarations**/
+struct eRAB_header { //TODO: making provision, chec -is it needed?
+	unsigned char criticality;
+};
+
+struct eRAB_setup_ctx_SU {
+	unsigned short eRAB_id;
+	unsigned short dont_know_byte;
+	unsigned int transp_layer_addr;
+	unsigned int gtp_teid;
+};
+
+union eRAB_IE {
+	struct eRAB_setup_ctx_SU su_res;
+};
+
+typedef struct eRAB_elements {
+	struct eRAB_header header;
+	unsigned char no_of_elements;
+	union eRAB_IE *elements;
+}eRAB_elements;
+/**eRAB structures end**/
+
+/**Information elements structs end**/
+typedef union nas_pdu_elements_union {
+	unsigned char rand[NAS_RAND_SIZE];
+	unsigned char autn[NAS_AUTN_SIZE];
+	unsigned char IMSI[BINARY_IMSI_LEN];
+	unsigned char short_mac[SHORT_MAC_SIZE];
+	struct esm_sec_info esm_info;
+	enum drx_params drx;
+	struct MS_net_capab ms_network;
+	struct UE_net_capab ue_network;
+
+	struct XRES   auth_resp; /*Authentication response*/
+	struct AUTS   auth_fail_resp; /*Authentication response*/
+
+	struct apn_name apn;
+
+	unsigned char attach_res;
+	unsigned char t3412;
+	tai_list tailist;
+	esm_msg_container esm_msg;
+	guti mi_guti;
+	bool esm_info_tx_required;
+	unsigned char pti;
+    unsigned char eps_res;
+    unsigned char spare;
+    unsigned short int pco_options[10];
+}nas_pdu_elements_union;
+typedef struct nas_pdu_elements {
+   nas_ie_type msgType;
+   nas_pdu_elements_union pduElement;
+}nas_pdu_elements;
+
+
+#define NAS_MSG_UE_IE_GUTI  0x00000001
+#define NAS_MSG_UE_IE_IMSI  0x00000002
+#define UE_ID_IMSI(flags)   ((flags & NAS_MSG_UE_IE_IMSI) == NAS_MSG_UE_IE_IMSI)
+#define UE_ID_GUTI(flags)   ((flags & NAS_MSG_UE_IE_GUTI) == NAS_MSG_UE_IE_GUTI)
+typedef struct nasPDU {
+	nas_pdu_header header;
+	unsigned char elements_len;
+	nas_pdu_elements *elements;
+    unsigned int flags;
+} nasPDU;
+
+#pragma pack(1)
+/* TODO : Change type */
+typedef struct ue_aggregate_maximum_bitrate {
+	uint32_t uEaggregateMaxBitRateDL;
+	uint32_t uEaggregateMaxBitRateUL;
+} ue_aggregate_maximum_bitrate;
+
+typedef struct allocation_retention_prio {
+	uint8_t prioLevel :4;
+	uint8_t preEmptionCapab :1;
+	uint8_t preEmptionVulnebility :1;
+	uint8_t spare :2;
+} allocation_retention_prio;
+
+typedef struct E_RAB_Level_QoS_Params {
+	uint8_t qci;
+	//uint8_t ext;
+    allocation_retention_prio arPrio;
+} E_RAB_Level_QoS_Params;
+
+typedef struct ERABSetup {
+	uint8_t e_RAB_ID;
+	E_RAB_Level_QoS_Params e_RAB_QoS_Params;
+	uint32_t transportLayerAddress;
+	uint32_t gtp_teid;
+	struct nasPDU nas;
+} ERABSetup;
+
+#pragma pack()
+/* Dependencies */
+typedef enum s1apCause_PR {
+    s1apCause_PR_NOTHING,   /* No components present */
+    s1apCause_PR_radioNetwork,
+    s1apCause_PR_transport,
+    s1apCause_PR_nas,
+    s1apCause_PR_protocol,
+    s1apCause_PR_misc
+
+} s1apCause_PR;
+
+typedef enum s1apCause_PR_transporauseRadioNetwork {
+    s1apCauseRadioNetwork_unspecified   = 0,
+    s1apCauseRadioNetwork_tx2relocoverall_expiry    = 1,
+    s1apCauseRadioNetwork_successful_handover   = 2,
+    s1apCauseRadioNetwork_release_due_to_eutran_generated_reason    = 3,
+    s1apCauseRadioNetwork_handover_cancelled    = 4,
+    s1apCauseRadioNetwork_partial_handover  = 5,
+    s1apCauseRadioNetwork_ho_failure_in_target_EPC_eNB_or_target_system = 6,
+    s1apCauseRadioNetwork_ho_target_not_allowed = 7,
+    s1apCauseRadioNetwork_tS1relocoverall_expiry    = 8,
+    s1apCauseRadioNetwork_tS1relocprep_expiry   = 9,
+    s1apCauseRadioNetwork_cell_not_available    = 10,
+    s1apCauseRadioNetwork_unknown_targetID  = 11,
+    s1apCauseRadioNetwork_no_radio_resources_available_in_target_cell   = 12,
+    s1apCauseRadioNetwork_unknown_mme_ue_s1ap_id    = 13,
+    s1apCauseRadioNetwork_unknown_enb_ue_s1ap_id    = 14,
+    s1apCauseRadioNetwork_unknown_pair_ue_s1ap_id   = 15,
+    s1apCauseRadioNetwork_handover_desirable_for_radio_reason   = 16,
+    s1apCauseRadioNetwork_time_critical_handover    = 17,
+    s1apCauseRadioNetwork_resource_optimisation_handover    = 18,
+    s1apCauseRadioNetwork_reduce_load_in_serving_cell   = 19,
+    s1apCauseRadioNetwork_user_inactivity   = 20,
+    s1apCauseRadioNetwork_radio_connection_with_ue_lost = 21,
+    s1apCauseRadioNetwork_load_balancing_tau_required   = 22,
+    s1apCauseRadioNetwork_cs_fallback_triggered = 23,
+    s1apCauseRadioNetwork_ue_not_available_for_ps_service   = 24,
+    s1apCauseRadioNetwork_radio_resources_not_available = 25,
+    s1apCauseRadioNetwork_failure_in_radio_interface_procedure  = 26,
+    s1apCauseRadioNetwork_invalid_qos_combination   = 27,
+    s1apCauseRadioNetwork_interrat_redirection  = 28,
+    s1apCauseRadioNetwork_interaction_with_other_procedure  = 29,
+    s1apCauseRadioNetwork_unknown_E_RAB_ID  = 30,
+    s1apCauseRadioNetwork_multiple_E_RAB_ID_instances   = 31,
+    s1apCauseRadioNetwork_encryption_and_or_integrity_protection_algorithms_not_supported   = 32,
+    s1apCauseRadioNetwork_s1_intra_system_handover_triggered    = 33,
+    s1apCauseRadioNetwork_s1_inter_system_handover_triggered    = 34,
+    s1apCauseRadioNetwork_x2_handover_triggered = 35,
+    s1apCauseRadioNetwork_redirection_towards_1xRTT = 36,
+    s1apCauseRadioNetwork_not_supported_QCI_value   = 37,
+    s1apCauseRadioNetwork_invalid_CSG_Id    = 38,
+    s1apCauseRadioNetwork_release_due_to_pre_emption    = 39
+} e_s1apCauseRadioNetwork;
+
+typedef enum s1apCauseTransport {
+    s1apCauseTransport_transport_resource_unavailable   = 0,
+    s1apCauseTransport_unspecified  = 1
+} e_s1apCauseTransport;
+
+typedef enum s1apCauseNas {
+    s1apCauseNas_normal_release = 0,
+    s1apCauseNas_authentication_failure = 1,
+    s1apCauseNas_detach = 2,
+    s1apCauseNas_unspecified    = 3,
+    s1apCauseNas_csg_subscription_expiry    = 4
+} e_s1apCauseNas;
+
+typedef enum s1apCauseProtocol {
+    s1apCauseProtocol_transfer_syntax_error = 0,
+    s1apCauseProtocol_abstract_syntax_error_reject  = 1,
+    s1apCauseProtocol_abstract_syntax_error_ignore_and_notify   = 2,
+    s1apCauseProtocol_message_not_compatible_with_receiver_state    = 3,
+    s1apCauseProtocol_semantic_error    = 4,
+    s1apCauseProtocol_abstract_syntax_error_falsely_constructed_message = 5,
+    s1apCauseProtocol_unspecified   = 6
+} e_s1apCauseProtocol;
+
+typedef enum s1apCauseMisc {
+    s1apCauseMisc_control_processing_overload   = 0,
+    s1apCauseMisc_not_enough_user_plane_processing_resources    = 1,
+    s1apCauseMisc_hardware_failure  = 2,
+    s1apCauseMisc_om_intervention   = 3,
+    s1apCauseMisc_unspecified   = 4,
+    s1apCauseMisc_unknown_PLMN  = 5
+} e_s1apCauseMisc;
+
+/* s1apCauseMisc */
+typedef long     s1apCauseMisc_t;
+/* s1apCauseProtocol */
+typedef long     s1apCauseProtocol_t;
+/* s1apCauseNas */
+typedef long     s1apCauseNas_t;
+/* s1apCauseTransport */
+typedef long     s1apCauseTransport_t;
+/* s1apCauseRadioNetwork */
+typedef long     s1apCauseRadioNetwork_t;
+
+typedef struct s1apCause {
+    s1apCause_PR present;
+    union s1apCause_u {
+        s1apCauseRadioNetwork_t  radioNetwork;
+        s1apCauseTransport_t     transport;
+        s1apCauseNas_t   nas;
+        s1apCauseProtocol_t  protocol;
+        s1apCauseMisc_t  misc;
+    } choice;
+} s1apCause_t;
+
+
+typedef struct proto_IE_data {
+	int 			IE_type;
+    union value{
+        struct ie_enb_name 	enb_name;
+        struct ie_global_enb_id global_enb_id;
+        long			enb_ue_s1ap_id;
+        long			mme_ue_s1ap_id;
+        struct 			nasPDU nas;
+        struct s1apCause cause;
+        struct TAI 		 tai;
+        struct CGI 		 utran_cgi;
+        struct STMSI	 s_tmsi;
+        enum ie_RRC_est_cause 	rrc_est_cause;
+        struct eRAB_elements 	erab;
+        ue_aggregate_maximum_bitrate ue_aggrt_max_bit_rate;
+        ERABSetup E_RABToBeSetupItemCtxtSUReq;
+        ue_sec_capabilities ue_sec_capab;
+        uint8_t sec_key[SECURITY_KEY_SIZE];
+    }val;
+}proto_IEs;
+
+struct proto_IE {
+    ProcedureCode_t  procedureCode;
+    Criticality_t    criticality;
+	short 		no_of_IEs;
+	proto_IEs	*data;
+	uint8_t     ie_nas_index;
+    uint8_t     ie_tai_index;
+    uint8_t     ie_cgi_index;
+};
+
+enum protocolie_id {
+	id_MME_UE_S1AP_ID = 0,
+	id_Cause = 2,
+	id_eNB_UE_S1AP_ID = 8,
+	id_ERABToBeSetupListCtxtSUReq = 24,
+	id_NAS_PDU = 26,
+	id_ERABToBeSetupItemCtxtSUReq = 52,
+	id_uEaggregatedMaximumBitrate = 66,
+	id_SecurityKey = 73,
+	id_UE_S1AP_IDs = 99,
+	id_UESecurityCapabilities = 107,
+};
+
+enum protocol_discriminator{
+	EPSSessionManagementMessage = 2,
+    EPSMobilityManagementMessages = 7,
+};
+
+enum criticality{
+	CRITICALITY_REJECT = 0x0,
+	CRITICALITY_IGNORE = 0x40,
+	CRITICALITY_NOTIFY,
+};
+
+enum eps_nas_mesage_type {
+	AttachAccept = 0x42,
+	AttachReject = 0x44,
+	DetachAccept = 0x46,
+	DetachRequest = 0x45,
+	TauAccept    = 0x49,
+    TauReject    = 0x4b,
+	AuthenticationRequest = 0x52,
+    IdentityRequest       = 0x55,
+	SecurityModeCommand = 0x5d,
+	ESMInformationRequest = 0xd9,
+};
+
+enum procedure_code {
+	id_InitialContextSetup = 9,
+	id_downlinkNASTransport = 11,
+	id_errorIndication = 15,
+	id_UEContexRelease = 23,
+};
+
+typedef struct s1ap_PDU {
+	unsigned char procedurecode;
+	unsigned char criticality;
+	struct proto_IE value;
+}s1ap_PDU;
+
+/* NAS Security Header */
+typedef enum security_header_type {
+    Plain = 0,
+    IntegrityProtected,
+    IntegrityProtectedCiphered,
+    IntegrityProtectedEPSSecCntxt,
+}security_header_type;
+
+typedef struct nas_pdu_header_sec {
+        unsigned char security_header_type:4;
+        unsigned char proto_discriminator:4;
+        unsigned char mac[MAC_SIZE];
+        unsigned char seq_no;
+}nas_pdu_header_sec;
+
+typedef struct nas_pdu_header_short {
+        unsigned char security_header_type:4;
+        unsigned char proto_discriminator:4;
+        unsigned char message_type;
+}nas_pdu_header_short;
+
+typedef struct nas_pdu_header_long {
+        unsigned char security_header_type:4;
+        unsigned char proto_discriminator:4;
+        unsigned char procedure_trans_identity;
+        unsigned char message_type;
+}nas_pdu_header_long;
+
+/* NAS Security Encryption Algorithm */
+typedef enum security_encryption_algo {
+	Algo_EEA0 = 0,
+
+}security_encryption_algo;
+
+/* NAS Security Integrity Algorithm */
+typedef enum security_integrity_algo {
+	Algo_EIA0 = 0,
+	Algo_128EIA1 = 1,
+}security_integrity_algo;
+
+
+#define BUFFER_SIZE 255
+
+typedef struct Buffer {
+	unsigned char buf[BUFFER_SIZE];
+	unsigned char pos;
+}Buffer;
+
+#endif /*__S1AP_STRUCTS_H*/