diff --git a/src/mgw_nat.erl b/src/mgw_nat.erl
new file mode 100644
index 0000000..39c8abe
--- /dev/null
+++ b/src/mgw_nat.erl
@@ -0,0 +1,294 @@
+% 
+
+% (C) 2011 by Harald Welte <laforge@gnumonks.org>
+% (C) 2011 OnWaves
+%
+% All Rights Reserved
+%
+% This program is free software; you can redistribute it and/or modify
+% it under the terms of the GNU Affero General Public License as
+% published by the Free Software Foundation; either version 3 of the
+% License, or (at your option) any later version.
+%
+% This program is distributed in the hope that it will be useful,
+% but WITHOUT ANY WARRANTY; without even the implied warranty of
+% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+% GNU General Public License for more details.
+%
+% You should have received a copy of the GNU Affero General Public License
+% along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+-module(mgw_nat).
+-author("Harald Welte <laforge@gnumonks.org>").
+-export([mangle_rx_data/3]).
+
+%-include_lib("kernel/include/inet.hrl").
+%-include_lib("kernel/include/inet_sctp.hrl").
+
+-include("m2ua.hrl").
+-include("mtp3.hrl").
+-include("isup.hrl").
+-include("sccp.hrl").
+
+% mangle the received data
+mangle_rx_data(L, From, Data) when is_binary(Data) ->
+	{ok, M2ua} = m2ua_codec:parse_m2ua_msg(Data),
+	%io:format("M2UA Decode: ~p~n", [M2ua]),
+	case M2ua of
+		#m2ua_msg{msg_class = ?M2UA_MSGC_MAUP,
+			  msg_type = ?M2UA_MAUP_MSGT_DATA} ->
+			M2ua_out = mangle_rx_m2ua_maup(L, From, M2ua);
+		#m2ua_msg{} ->
+			% simply pass it along unmodified
+			M2ua_out = M2ua
+	end,
+	% re-encode the data
+	%io:format("M2UA Encode: ~p~n", [M2ua_out]),
+	m2ua_codec:encode_m2ua_msg(M2ua_out).
+
+% mangle the received M2UA
+mangle_rx_m2ua_maup(L, From, M2ua = #m2ua_msg{parameters = Params}) ->
+	{_Len, M2uaPayload} = proplists:get_value(16#300, Params),
+	Mtp3 = mtp3_codec:parse_mtp3_msg(M2uaPayload),
+	%io:format("MTP3 Decode: ~p~n", [Mtp3]),
+	Mtp3_out = mangle_rx_mtp3(L, From, Mtp3),
+	%io:format("MTP3 Encode: ~p~n", [Mtp3_out]),
+	Mtp3OutBin = mtp3_codec:encode_mtp3_msg(Mtp3_out),
+	Params2 = proplists:delete(16#300, Params),
+	ParamsNew = Params2 ++ [{16#300, {byte_size(Mtp3OutBin), Mtp3OutBin}}],
+	% return mangled parsed m2ua msg
+	M2ua#m2ua_msg{parameters = ParamsNew}.
+
+% mangle the MTP3 payload
+mangle_rx_mtp3(L, From, Mtp3 = #mtp3_msg{service_ind = Service}) ->
+	mangle_rx_mtp3_serv(L, From, Service, Mtp3).
+
+% mangle the ISUP content
+mangle_rx_mtp3_serv(_L, From, ?MTP3_SERV_ISUP, Mtp3 = #mtp3_msg{payload = Payload}) ->
+	io:format("ISUP In: ~p~n", [Payload]),
+	Isup = isup_codec:parse_isup_msg(Payload),
+	io:format("ISUP Decode: ~p~n", [Isup]),
+	% FIXME
+	IsupMangled = mangle_rx_isup(From, Isup#isup_msg.msg_type, Isup),
+	if IsupMangled == Isup ->
+		Mtp3;
+	   true ->
+		io:format("ISUP Encode In: ~p~n", [IsupMangled]),
+		Payload_out = isup_codec:encode_isup_msg(IsupMangled),
+		io:format("ISUP Encode Out: ~p~n", [Payload_out]),
+		% return modified MTP3 payload
+		Mtp3#mtp3_msg{payload = Payload_out}
+	end;
+% mangle the SCCP content
+mangle_rx_mtp3_serv(_L, From, ?MTP3_SERV_SCCP, Mtp3 = #mtp3_msg{payload = Payload}) ->
+	io:format("SCCP In: ~p~n", [Payload]),
+	{ok, Sccp} = sccp_codec:parse_sccp_msg(Payload),
+	io:format("SCCP Decode: ~p~n", [Sccp]),
+	SccpMangled = mangle_rx_sccp(From, Sccp#sccp_msg.msg_type, Sccp),
+	SccpMasqued = sccp_masq:sccp_masq_msg(From, SccpMangled#sccp_msg.msg_type,
+					      SccpMangled),
+	if SccpMasqued == Sccp ->
+		Mtp3;
+	   true ->
+		io:format("SCCP Encode In: ~p~n", [SccpMasqued]),
+		Payload_out = sccp_codec:encode_sccp_msg(SccpMasqued),
+		io:format("SCCP Encode Out: ~p~n", [Payload_out]),
+		% return modified MTP3 payload
+		Mtp3#mtp3_msg{payload = Payload_out}
+	end;
+% default: do nothing
+mangle_rx_mtp3_serv(_L, _From, _, Mtp3) ->
+	Mtp3.
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+% Actual mangling of the decoded SCCP messages
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+
+% iterate over list of rewrite tuples and apply translation if there is a match
+do_sccp_gt_rewrite(GT, _From, []) ->
+	GT;
+do_sccp_gt_rewrite(GT = #global_title{phone_number = PhoneNum}, from_stp, [Head|List]) ->
+	{MscSide, StpSide, Comment} = Head,
+	if PhoneNum == StpSide ->
+		NewPhoneNum = MscSide,
+		io:format("SCCP STP->MSC rewrite (~p) ~p -> ~p~n",
+			  [Comment, PhoneNum, NewPhoneNum]),
+		GT#global_title{phone_number = NewPhoneNum};
+	   true ->
+		do_sccp_gt_rewrite(GT, from_stp, List)
+	end;
+do_sccp_gt_rewrite(GT = #global_title{phone_number = PhoneNum}, from_msc, [Head|List]) ->
+	{MscSide, StpSide, Comment} = Head,
+	if PhoneNum == MscSide ->
+		NewPhoneNum = StpSide,
+		io:format("SCCP MSC->STP rewrite (~p) ~p -> ~p~n",
+			  [Comment, PhoneNum, NewPhoneNum]),
+		GT#global_title{phone_number = NewPhoneNum};
+	   true ->
+		do_sccp_gt_rewrite(GT, from_msc, List)
+	end.
+
+% mangle called address
+mangle_rx_called(from_stp, Addr = #sccp_addr{global_title = GT}) ->
+	{ok, RewriteTbl} = application:get_env(sccp_rewrite_tbl),
+	GTout = do_sccp_gt_rewrite(GT, from_stp, RewriteTbl),
+	Addr#sccp_addr{global_title = GTout};
+mangle_rx_called(_From, Addr) ->
+	Addr.
+
+% mangle calling address
+mangle_rx_calling(from_msc, Addr = #sccp_addr{global_title = GT}) ->
+	{ok, RewriteTbl} = application:get_env(sccp_rewrite_tbl),
+	GTout = do_sccp_gt_rewrite(GT, from_msc, RewriteTbl),
+	Addr#sccp_addr{global_title = GTout};
+mangle_rx_calling(_From, Addr) ->
+	Addr.
+
+mangle_rx_sccp(From, ?SCCP_MSGT_UDT, Msg = #sccp_msg{parameters = Opts}) ->
+	CalledParty = proplists:get_value(called_party_addr, Opts),
+	CalledPartyNew = mangle_rx_called(From, CalledParty),
+	CallingParty = proplists:get_value(calling_party_addr, Opts),
+	CallingPartyNew = mangle_rx_calling(From, CallingParty),
+	Opts1 = lists:keyreplace(called_party_addr, 1, Opts,
+				 {called_party_addr, CalledPartyNew}),
+	Opts2 = lists:keyreplace(calling_party_addr, 1, Opts1,
+				 {calling_party_addr, CallingPartyNew}),
+	Msg#sccp_msg{parameters = Opts2};
+mangle_rx_sccp(_From, _MsgType, Msg) ->
+	Msg.
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+% Actual mangling of the decoded ISUP messages 
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+
+% iterate over list of parameters and call mangle_rx_isup_par() for each one
+mangle_rx_isup_params(_From, _MsgType, _Msg, ParListOut, []) ->
+	ParListOut;
+mangle_rx_isup_params(From, MsgType, Msg, ParListOut, [Par|ParList]) ->
+	ParOut = mangle_rx_isup_par(From, MsgType, Msg, Par),
+	mangle_rx_isup_params(From, MsgType, Msg, ParListOut++[ParOut], ParList).
+
+% manipulate phone numbers
+mangle_rx_isup_par(From, MsgType, _Msg, {ParType, ParBody}) when
+					ParType == ?ISUP_PAR_CALLED_P_NUM;
+					ParType == ?ISUP_PAR_CONNECTED_NUM;
+					ParType == ?ISUP_PAR_CALLING_P_NUM ->
+	NewParBody = mangle_isup_number(From, MsgType, ParType, ParBody),
+	{ParType, NewParBody};
+% defauly case: do not mangle this parameter
+mangle_rx_isup_par(_From, _MsgType, _Msg, Par) ->
+	Par.
+
+% mangle an incoming ISUP message
+mangle_rx_isup(From, MsgType, Msg = #isup_msg{parameters = Params}) ->
+	ParamsOut = mangle_rx_isup_params(From, MsgType, Msg, [], Params),
+	% return message with modified parameter list
+	Msg#isup_msg{parameters = ParamsOut}.
+
+% STP->MSC: Mangle a Party Number in IAM
+mangle_isup_number(from_stp, ?ISUP_MSGT_IAM, NumType, PartyNum) ->
+	case NumType of
+		?ISUP_PAR_CALLED_P_NUM ->
+			% First convert to international number, if it is national
+			Num1 = isup_party_internationalize(PartyNum,
+						application:get_env(intern_pfx)),
+			io:format("IAM MSRN rewrite (STP->MSC): "),
+			isup_party_replace_prefix(Num1,
+						application:get_env(msrn_pfx_stp),
+						application:get_env(msrn_pfx_msc));
+		_ ->
+			PartyNum
+	end;
+% MSC->STP: Mangle connected number in response to IAM
+mangle_isup_number(from_msc, MsgT, NumType, PartyNum) when MsgT == ?ISUP_MSGT_CON;
+							   MsgT == ?ISUP_MSGT_ANM ->
+	case NumType of
+		?ISUP_PAR_CONNECTED_NUM ->
+			io:format("CON MSRN rewrite (MSC->STP): "),
+			Num1 = isup_party_replace_prefix(PartyNum,
+						application:get_env(msrn_pfx_msc),
+						application:get_env(msrn_pfx_stp)),
+			% Second: convert to national number, if it is international
+			isup_party_nationalize(Num1,
+						application:get_env(intern_pfx));
+		_ ->
+			PartyNum
+	end;
+% MAC->STP: Mangle IAM international -> national
+mangle_isup_number(from_msc, ?ISUP_MSGT_IAM, NumType, PartyNum) ->
+	case NumType of
+		?ISUP_PAR_CALLED_P_NUM ->
+			isup_party_nationalize(PartyNum,
+						applicaiton:get_env(intern_pfx));
+		_ ->
+			PartyNum
+	end;
+% STP->MSC: Mangle connected number in response to IAM (national->international)
+mangle_isup_number(from_stp, MsgT, NumType, PartyNum) when MsgT == ?ISUP_MSGT_CON;
+							   MsgT == ?ISUP_MSGT_ANM ->
+	case NumType of
+		?ISUP_PAR_CONNECTED_NUM ->
+			isup_party_internationalize(PartyNum,
+						application:get_env(intern_pfx));
+		_ ->
+			PartyNum
+	end;
+% default case: no rewrite
+mangle_isup_number(from_msc, _, _, PartyNum) ->
+	PartyNum.
+
+% replace the prefix of PartyNum with NewPfx _if_ the current prefix matches MatchPfx
+isup_party_replace_prefix(PartyNum, MatchPfx, NewPfxInt) ->
+	IntIn = PartyNum#party_number.phone_number,
+	DigitsIn = osmo_util:int2digit_list(IntIn),
+	NewPfx = osmo_util:int2digit_list(NewPfxInt),
+	MatchPfxLen = length(MatchPfx),
+	Pfx = lists:sublist(DigitsIn, 1, MatchPfxLen),
+	if Pfx == MatchPfx ->
+		Trailer = lists:sublist(DigitsIn, MatchPfxLen+1, length(DigitsIn)-MatchPfxLen),
+		DigitsOut = NewPfx ++ Trailer,
+		io:format("Prefix rewrite: ~p -> ~p~n", [DigitsIn, DigitsOut]);
+	   true ->
+		io:format("Prefix rewrite: NO MATCH (~p != ~p)~n", [Pfx, MatchPfx]),
+		DigitsOut = DigitsIn
+	end,
+	IntOut = osmo_util:digit_list2int(DigitsOut),
+	PartyNum#party_number{phone_number = IntOut}.
+
+isup_party_internationalize(PartyNum, CountryCode) ->
+	#party_number{phone_number = IntIn, nature_of_addr_ind = Nature} = PartyNum,
+	DigitsIn = osmo_util:int2digit_list(IntIn),
+	case Nature of
+		?ISUP_ADDR_NAT_NATIONAL ->
+			DigitsOut = CountryCode ++ DigitsIn,
+			NatureOut = ?ISUP_ADDR_NAT_INTERNATIONAL,
+			io:format("Internationalize: ~p -> ~p~n", [DigitsIn, DigitsOut]);
+		_ ->
+			DigitsOut = DigitsIn,
+			NatureOut = Nature
+	end,
+	IntOut = osmo_util:digit_list2int(DigitsOut),
+	PartyNum#party_number{phone_number = IntOut, nature_of_addr_ind = NatureOut}.
+
+isup_party_nationalize(PartyNum, CountryCode) ->
+	#party_number{phone_number = IntIn, nature_of_addr_ind = Nature} = PartyNum,
+	DigitsIn = osmo_util:int2digit_list(IntIn),
+	CountryCodeLen = length(CountryCode),
+	case Nature of
+		?ISUP_ADDR_NAT_INTERNATIONAL ->
+			Pfx = lists:sublist(DigitsIn, CountryCodeLen),
+			if Pfx == CountryCode ->
+				DigitsOut = lists:sublist(DigitsIn, CountryCodeLen+1,
+							  length(DigitsIn)-CountryCodeLen),
+				NatureOut = ?ISUP_ADDR_NAT_NATIONAL,
+				io:format("Nationalize: ~p -> ~p~n", [DigitsIn, DigitsOut]);
+			   true ->
+				DigitsOut = DigitsIn,
+				NatureOut = Nature
+			end;
+		_ ->
+			DigitsOut = DigitsIn,
+			NatureOut = Nature
+	end,
+	IntOut = osmo_util:digit_list2int(DigitsOut),
+	PartyNum#party_number{phone_number = IntOut, nature_of_addr_ind = NatureOut}.
diff --git a/src/mgw_nat_app.erl b/src/mgw_nat_app.erl
new file mode 100644
index 0000000..c4e32ea
--- /dev/null
+++ b/src/mgw_nat_app.erl
@@ -0,0 +1,16 @@
+-module(mgw_nat_app).
+-behavior(application).
+-export([start/2, stop/1]).
+
+-export([reload_config/0]).
+
+start(_Type, _Args) ->
+	Sup = mgw_nat_sup:start_link(),
+	io:format("Sup ~p~n", [Sup]),
+	Sup.
+
+stop(_State) ->
+	ok.
+
+reload_config() ->
+	osmo_util:reload_config().
diff --git a/src/mgw_nat_sup.erl b/src/mgw_nat_sup.erl
new file mode 100644
index 0000000..2dfe245
--- /dev/null
+++ b/src/mgw_nat_sup.erl
@@ -0,0 +1,40 @@
+% OTP Supervisor for MGW NAT
+
+% (C) 2011 by Harald Welte <laforge@gnumonks.org>
+% (C) 2011 OnWaves
+%
+% All Rights Reserved
+%
+% This program is free software; you can redistribute it and/or modify
+% it under the terms of the GNU Affero General Public License as
+% published by the Free Software Foundation; either version 3 of the
+% License, or (at your option) any later version.
+%
+% This program is distributed in the hope that it will be useful,
+% but WITHOUT ANY WARRANTY; without even the implied warranty of
+% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+% GNU General Public License for more details.
+%
+% You should have received a copy of the GNU Affero General Public License
+% along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+-module(mgw_nat_sup).
+-behavior(supervisor).
+
+-export([start_link/0]).
+-export([init/1]).
+
+start_link() ->
+	supervisor:start_link({local, ?MODULE}, ?MODULE, []).
+
+init(_Arg) ->
+	{ok, MscLocalIp} = application:get_env(msc_local_ip),
+	{ok, MscLocalPort} = application:get_env(msc_local_port),
+	{ok, MscRemoteIp} = application:get_env(msc_remote_ip),
+	{ok, StpRemoteIp} = application:get_env(stp_remote_ip),
+	{ok, StpRemotePort} = application:get_env(stp_remote_port),
+	SctpHdlrArgs =	[MscLocalIp, MscLocalPort, MscRemoteIp,
+			 StpRemoteIp, StpRemotePort],
+	MgwChild = {mgw_nat_usr, {mgw_nat_usr, start_link, [SctpHdlrArgs]},
+		    permanent, 2000, worker, [mgw_nat_usr, sctp_handler, mgw_nat]},
+	{ok,{{one_for_all,1,1}, [MgwChild]}}.
diff --git a/src/mgw_nat_usr.erl b/src/mgw_nat_usr.erl
new file mode 100644
index 0000000..f738f7e
--- /dev/null
+++ b/src/mgw_nat_usr.erl
@@ -0,0 +1,59 @@
+% Wrapper code, wrapping sctp_handler.erl into OTP gen_server
+
+% (C) 2011 by Harald Welte <laforge@gnumonks.org>
+% (C) 2011 OnWaves
+%
+% All Rights Reserved
+%
+% This program is free software; you can redistribute it and/or modify
+% it under the terms of the GNU Affero General Public License as
+% published by the Free Software Foundation; either version 3 of the
+% License, or (at your option) any later version.
+%
+% This program is distributed in the hope that it will be useful,
+% but WITHOUT ANY WARRANTY; without even the implied warranty of
+% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+% GNU General Public License for more details.
+%
+% You should have received a copy of the GNU Affero General Public License
+% along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+-module(mgw_nat_usr).
+-author("Harald Welte <laforge@gnumonks.org>").
+
+-behavior(gen_server).
+
+-export([start_link/1, stop/0, sccp_masq_reset/0]).
+-export([init/1, handle_cast/2, handle_info/2, terminate/2]).
+
+
+start_link(Params) ->
+	gen_server:start_link({local, ?MODULE}, ?MODULE, Params, []).
+
+stop() ->
+	gen_server:cast(?MODULE, stop).
+
+sccp_masq_reset() ->
+	gen_server:cast(?MODULE, sccp_masq_reset).
+
+
+%% Callback functions of the OTP behavior
+
+init(Params) ->
+	sccp_masq:init(),
+	apply(sctp_handler, init, Params).
+
+handle_cast(stop, LoopData) ->
+	{stop, normal, LoopData};
+
+handle_cast(sccp_masq_reset, LoopData) ->
+	sccp_masq:reset(),
+	{noreply, LoopData}.
+
+terminate(_Reason, _LoopData) ->
+	ok.
+
+% callback for other events like incoming SCTP message
+handle_info({sctp, Sock, Ip, Port, Data}, LoopData) ->
+	NewL = sctp_handler:handle_sctp(LoopData, {sctp, Sock, Ip, Port, Data}),
+	{noreply, NewL}.
diff --git a/src/sccp_masq.erl b/src/sccp_masq.erl
new file mode 100644
index 0000000..2739307
--- /dev/null
+++ b/src/sccp_masq.erl
@@ -0,0 +1,132 @@
+% ITU-T Q.71x SCCP UDT stateful masquerading
+
+% (C) 2011 by Harald Welte <laforge@gnumonks.org>
+%
+% All Rights Reserved
+%
+% This program is free software; you can redistribute it and/or modify
+% it under the terms of the GNU Affero General Public License as
+% published by the Free Software Foundation; either version 3 of the
+% License, or (at your option) any later version.
+%
+% This program is distributed in the hope that it will be useful,
+% but WITHOUT ANY WARRANTY; without even the implied warranty of
+% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+% GNU General Public License for more details.
+%
+% You should have received a copy of the GNU Affero General Public License
+% along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+-module(sccp_masq).
+-author('Harald Welte <laforge@gnumonks.org>').
+-include("sccp.hrl").
+
+-export([sccp_masq_msg/3, init/0, reset/0]).
+
+-compile([export_all]).
+
+-record(sccp_masq_rec, {
+	  digits_in,	% list of GT digits
+	  digits_out,	% list of GT digits
+	  last_access	% timestamp of last usage
+	}).
+
+% alloc + insert a new masquerade state record in our tables
+masq_alloc(DigitsOrig) ->
+	{ok, Base} = application:get_env(sccp_masq_gt_base),
+	{ok, Max} = application:get_env(sccp_masq_gt_max),
+	masq_try_alloc(DigitsOrig, Base, Max, 0).
+masq_try_alloc(_DigitsOrig, _Base, Max, Offset) when Offset > Max ->
+	undef;
+masq_try_alloc(DigitsOrig, Base, Max, Offset) ->
+	Try = Base + Offset,
+	EtsRet = ets:insert_new(get(sccp_masq_orig),
+				#sccp_masq_rec{digits_in = DigitsOrig,
+					       digits_out = Try}),
+	case EtsRet of
+		false ->
+			masq_try_alloc(DigitsOrig, Base, Max, Offset+1);
+		_ ->
+			ets:insert(get(sccp_masq_rev),
+				   #sccp_masq_rec{digits_in = Try,
+						  digits_out = DigitsOrig}),
+			Try
+	end.
+
+% lookup a masqerade state record
+lookup_masq_addr(orig, GtDigits) ->
+	case ets:lookup(get(sccp_masq_orig), GtDigits) of
+		[#sccp_masq_rec{digits_out = DigitsOut}] ->
+			DigitsOut;
+		_ ->
+			% allocate a new masq GT
+			masq_alloc(GtDigits)
+	end;
+lookup_masq_addr(rev, GtDigits) ->
+	case ets:lookup(get(sccp_masq_rev), GtDigits) of
+		[#sccp_masq_rec{digits_out = DigitsOut}] ->
+			DigitsOut;
+		_ ->
+			% we do not allocate entries in the reverse direction
+			undef
+	end.
+
+
+% Masquerade the CALLING address in first STP(G-MSC) -> HLR/VLR/MSC dir
+mangle_rx_calling(from_stp, Addr = #sccp_addr{global_title = GT}) ->
+	GtOrig = GT#global_title.phone_number,
+	GtReplace = lookup_masq_addr(orig, GtOrig),
+	case GtReplace of
+		undef ->
+			io:format("SCCP MASQ: Unable to rewrite in original direction (out of GT addrs?)~n"),
+			Addr;
+		_ ->
+			io:format("SCCP MASQ (STP->MSC) rewrite ~p->~p~n", [GtOrig, GtReplace]),
+			GTout = GT#global_title{phone_number = GtReplace},
+			Addr#sccp_addr{global_title = GTout}
+	end;
+mangle_rx_calling(_From, Addr) ->
+	Addr.
+
+mangle_rx_called(from_msc, Addr = #sccp_addr{global_title = GT}) ->
+	GtOrig = GT#global_title.phone_number,
+	GtReplace = lookup_masq_addr(rev, GtOrig),
+	case GtReplace of
+		undef ->
+			io:format("SCCP MASQ: Unable to rewrite in original direction (unknown GT ~p)~n", [GT]),
+			Addr;
+		_ ->
+			io:format("SCCP MASQ (MSC->STP) rewrite ~p->~p~n", [GtOrig, GtReplace]),
+			GTout = GT#global_title{phone_number = GtReplace},
+			Addr#sccp_addr{global_title = GTout}
+	end;
+mangle_rx_called(_From, Addr) ->
+	Addr.
+
+
+sccp_masq_msg(From, ?SCCP_MSGT_UDT, Msg = #sccp_msg{parameters = Opts}) ->
+	CalledParty = proplists:get_value(called_party_addr, Opts),
+	CalledPartyNew = mangle_rx_called(From, CalledParty),
+	CallingParty = proplists:get_value(calling_party_addr, Opts),
+	CallingPartyNew = mangle_rx_calling(From, CallingParty),
+	Opts1 = lists:keyreplace(called_party_addr, 1, Opts,
+				 {called_party_addr, CalledPartyNew}),
+	Opts2 = lists:keyreplace(calling_party_addr, 1, Opts1,
+				 {calling_party_addr, CallingPartyNew}),
+	Msg#sccp_msg{parameters = Opts2};
+sccp_masq_msg(_From, _MsgType, Msg) ->
+	Msg.
+
+init() ->
+	Orig = ets:new(sccp_masq_orig, [ordered_set,
+					{keypos, #sccp_masq_rec.digits_in}]),
+	Rev  = ets:new(sccp_masq_rev, [ordered_set,
+					{keypos, #sccp_masq_rec.digits_in}]),
+	put(sccp_masq_orig, Orig),
+	put(sccp_masq_rev, Rev),
+	ok.
+
+reset() ->
+	io:format("SCCP MASQ: Deleting all MASQ state records~n"),
+	ets:delete_all_objects(get(sccp_masq_orig)),
+	ets:delete_all_objects(get(sccp_masq_rev)).