diff --git a/sysinfo/GSM_SystemInformation.ttcn b/sysinfo/GSM_SystemInformation.ttcn
new file mode 100644
index 0000000..01565c1
--- /dev/null
+++ b/sysinfo/GSM_SystemInformation.ttcn
@@ -0,0 +1,267 @@
+/* Encoding/Decoding routines for GSM System Information messages
+ * according to 3GPP TS 44.018 Version 12.3.0 Release 12 */
+
+/* (C) 2017 by Harald Welte <laforge@gnumonks.org> */
+
+module GSM_SystemInformation {
+
+	import from General_Types all;
+
+	type integer uint32_t (0..4294967295) with { variant "unsigned 32 bit" };
+	type integer uint16_t (0..65535) with { variant "unsigned 16 bit" };
+	type integer uint2_t (0..3) with { variant "unsigned 2 bit" };
+	type integer uint3_t (0..7) with { variant "unsigned 3 bit" };
+	type integer uint4_t (0..15) with { variant "unsigned 4 bit" };
+	type integer uint5_t (0..31) with { variant "unsigned 5 bit" };
+	type integer uint6_t (0..63) with { variant "unsigned 6 bit" };
+	type integer uint7_t (0..127) with { variant "unsigned 7 bit" };
+	type integer uint8_t (0..255) with { variant "unsigned 8 bit" };
+	type integer uint9_t (0..511) with { variant "unsigned 9 bit" };
+	type integer uint10_t (0..1023) with { variant "unsigned 10 bit" };
+	type integer uint11_t (0..2047) with { variant "unsigned 11 bit" };
+	type integer uint12_t (0..4095) with { variant "unsigned 12 bit" };
+
+	type record L2PseudoLength {
+		uint6_t		l2_plen,
+		BIT2		zero_one
+	} with { variant "" };
+
+	template L2PseudoLength t_L2Pseudolength(uint6_t len) := {
+		l2_plen := len,
+		zero_one := '01'B
+	};
+
+	type octetstring RestOctets  with { variant "PADDING(yes), PADDING_PATTERN('00101011'B)" };
+
+	type record MaioHsn {
+	} with { variant "" };
+
+	type union ArfcnOrMaio {
+		uint12_t	arfcn,
+		MaioHsn		maio_hsn
+	} with { variant "" };
+
+	type record SystemInformationHeader {
+		L2PseudoLength	l2_plen,
+		uint4_t		skip_indicator,
+		uint4_t		rr_protocol_discriminator,
+		OCT1		message_type
+	} with { variant "" };
+
+	template SystemInformationHeader t_SiHeader(OCT1 msg_type, uint6_t len) := {
+		l2_plen := t_L2Pseudolength(len),
+		rr_protocol_discriminator := 6,
+		message_type := msg_type
+	};
+
+	external function enc_SystemInformationHeader(in SystemInformationHeader si) return octetstring
+		with { extension "prototype(convert) encode(RAW)" };
+	external function dec_SystemInformationHeader(in octetstring stream) return SystemInformationHeader
+		with { extension "prototype(convert) decode(RAW)" };
+
+	type hexstring GsmBcdString with { variant "HEXORDER(low)" };
+	type GsmBcdString BcdMccMnc with { variant "FIELDLENGTH(6)" };
+
+	/* 24.008 10.5.1.1 */
+	type uint16_t CellIdentity;
+
+	/* 24.008 10.5.1.3 */
+	type record LocationAreaIdentification {
+		BcdMccMnc	mcc_mnc,
+		uint16_t	lac
+	} with { variant "" };
+
+	/* 44.018 10.5.2.1b */
+	type octetstring CellChannelDescription with { variant "FIELDLENGTH(16)" };
+
+	/* 44.018 10.5.2.3 */
+	type record CellOptions {
+		boolean		dn_ind,
+		boolean		pwrc,
+		BIT2		dtx,
+		BIT4		radio_link_timeout
+	} with { variant "" };
+
+	/* 44.018 10.5.2.3a */
+	type record CellOptionsSacch {
+		BIT1		dtx_ext,
+		boolean		pwrc,
+		BIT2		dtx,
+		BIT4		radio_link_timeout
+	} with { variant "" };
+
+	/* 44.018 10.5.2.4 */
+	type record CellSelectionParameters {
+		uint3_t		cell_resel_hyst,
+		uint5_t		ms_txpwr_max_cch,
+		boolean		acs,
+		boolean		neci,
+		uint6_t		rxlev_access_min
+	} with { variant "" };
+
+	/* 44.018 10.5.2.5 */
+	type record ChannelDescription {
+		OCT1		iei,
+		BIT5		chan_type_tdma_offset,
+		uint3_t		tn,
+		uint3_t		tsc,
+		boolean		h,
+		uint12_t	arfcn optional,
+		MaioHsn		maio_hsn optional
+	} with { variant (arfcn) "PRESENCE(h = true)"
+		 variant (maio_hsn) "PRESENCE(h = false)" };
+
+	/* 44.018 10.5.2.11 */
+	type record ControlChannelDescription {
+		boolean		mscrr,
+		boolean		att,
+		uint3_t		bs_ag_blks_res,
+		uint3_t		ccch_conf,
+		boolean		si22ind,
+		uint2_t		cbq3,
+		BIT2		spare,
+		uint3_t		bs_pa_mfrms,
+		uint8_t		t3212
+	} with { variant "" };
+
+	/* 44.018 10.5.2.21 */
+	type record MobileAllocation {
+		OCT1		iei,
+		uint8_t		len,
+		bitstring	ma
+	} with { variant "" };
+
+	/* 44.018 10.5.2.22 */
+	type octetstring NeighbourCellDescription with { variant "FIELDLENGTH(16)" };
+
+	/* 44.018 10.5.2.22a */
+	type octetstring NeighbourCellDescription2 with { variant "FIELDLENGTH(16)" };
+
+	type bitstring AccessControlClass with { variant "FIELDLENGTH(16), BYTEORDER(last)" };
+
+	/* 44.018 10.5.2.29 */
+	type record RachControlParameters {
+		BIT2		max_retrans,
+		BIT4		tx_integer,
+		boolean		cell_barr_access,
+		boolean		re,
+		AccessControlClass ac
+	} with { variant (ac) "FIELDLENGTH(16)" };
+
+	/* 44.018 10.5.2.32 */
+	type RestOctets Si1RestOctets with { variant "FIELDLENGTH(1)" };
+	type RestOctets Si3RestOctets with { variant "FIELDLENGTH(4)" };
+
+	/* 44.018 9.1.31 */
+	type record SystemInformationType1 {
+		SystemInformationHeader	header,
+		CellChannelDescription	cell_chan_desc,
+		RachControlParameters	rach_control,
+		Si1RestOctets		rest_octets
+	} with { variant "" };
+
+	/* 44.018 9.1.32 */
+	type record SystemInformationType2 {
+		SystemInformationHeader	header,
+		NeighbourCellDescription bcch_freq_list,
+		BIT8			ncc_permitted,
+		RachControlParameters	rach_control
+	} with { variant "" };
+
+	/* 44.018 9.1.33 */
+	type record SystemInformationType2bis {
+		SystemInformationHeader		header,
+		NeighbourCellDescription	extd_bcch_freq_list,
+		RachControlParameters		rach_control,
+		OCT1				rest_octets
+	} with { variant "" };
+
+	/* 44.018 9.1.34 */
+	type record SystemInformationType2ter {
+		SystemInformationHeader		header,
+		NeighbourCellDescription2	extd_bcch_freq_list,
+		RachControlParameters		rach_control,
+		OCT4				rest_octets
+	} with { variant "" };
+
+	/* 44.018 9.1.35 */
+	type record SystemInformationType3 {
+		SystemInformationHeader		header,
+		CellIdentity			cell_id,
+		LocationAreaIdentification	lai,
+		ControlChannelDescription	ctrl_chan_desc,
+		CellOptions			cell_options,
+		CellSelectionParameters		cell_sel_par,
+		RachControlParameters		rach_control,
+		Si3RestOctets			rest_octets
+	} with { variant "" };
+
+	/* 44.018 9.1.36 */
+	type record SystemInformationType4 {
+		SystemInformationHeader		header,
+		LocationAreaIdentification	lai,
+		CellSelectionParameters		cell_sel_par,
+		RachControlParameters		rach_control,
+		ChannelDescription		cbch_chan_desc optional,
+		MobileAllocation		cbch_mobile_alloc optional,
+		RestOctets			rest_octets
+	} with { variant "TAG(cbch_chan_desc, iei = '64'O; cbch_mobile_alloc, iei = '72'O)" };
+
+	/* 44.018 9.1.37 */
+	type record SystemInformationType5 {
+		SystemInformationHeader		header,
+		NeighbourCellDescription	bcch_freq_list
+	} with { variant "" };
+
+	/* 44.018 9.1.38 */
+	type record SystemInformationType5bis {
+		SystemInformationHeader		header,
+		NeighbourCellDescription	extd_bcch_freq_list
+	} with { variant "" };
+
+	/* 44.018 9.1.39 */
+	type record SystemInformationType5ter {
+		SystemInformationHeader		header,
+		NeighbourCellDescription2	extd_bcch_freq_list
+	} with { variant "" };
+
+	/* 44.018 9.1.40 */
+	type record SystemInformationType6 {
+		SystemInformationHeader		header,
+		CellIdentity			cell_id,
+		LocationAreaIdentification	lai,
+		CellOptionsSacch		cell_options,
+		BIT8				ncc_permitted,
+		OCT7				rest_octets
+	} with { variant "" };
+
+
+	type union SystemInformation {
+		SystemInformationType1		si1,
+		SystemInformationType2		si2,
+		SystemInformationType2bis	si2bis,
+		SystemInformationType2ter	si2ter,
+		SystemInformationType3		si3,
+		SystemInformationType4		si4,
+		SystemInformationType5		si5,
+		SystemInformationType5bis	si5bis,
+		SystemInformationType5ter	si5ter,
+		SystemInformationType6		si6
+	} with { variant "TAG(si1, header.message_type = '19'O;
+			      si2, header.message_type = '1A'O;
+			      si2bis, header.message_type = '02'O;
+			      si2ter, header.message_type = '03'O;
+			      si3, header.message_type = '1B'O;
+			      si4, header.message_type = '1C'O;
+			      si5, header.message_type = '1D'O;
+			      si5bis, header.message_type = '05'O;
+			      si5ter, header.message_type = '06'O;
+			      si6, header.message_type = '1E'O;
+			)" };
+
+	external function enc_SystemInformation(in SystemInformation si) return octetstring
+		with { extension "prototype(convert) encode(RAW)" };
+	external function dec_SystemInformation(in octetstring stream) return SystemInformation
+		with { extension "prototype(convert) decode(RAW)" };
+
+} with { encode "RAW"; variant "FIELDORDER(msb)" }