diff --git a/src/mtp3_sltc.erl b/src/mtp3_sltc.erl
new file mode 100644
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+++ b/src/mtp3_sltc.erl
@@ -0,0 +1,211 @@
+% MTP3 Signalling Link Test Control (SLTC) according to Q.707
+
+% (C) 2011-2012 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(mtp3_sltc).
+-author('Harald Welte <laforge@gnumonks.org>').
+-behaviour(gen_fsm).
+
+-include("mtp3.hrl").
+
+% gen_fsm exports 
+-export([init/1, terminate/3, code_change/4, handle_event/3, handle_info/3]).
+
+% individual FSM states
+-export([idle/2, first_attempt/2, second_attempt/2]).
+
+-record(sltc_state, {
+		hmrt_pid,
+		mgmt_pid,
+		lsac_pid,
+		sls,
+		opc,
+		adj_dpc,
+		t1,
+		t1_timeout,
+		x
+	}).
+
+-define(SLTC_T1_DEF,	10000).
+-define(SLTC_T2_DEF,	60000).
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+% gen_fsm callbacks
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+
+init([Hmrt, Mgmt, Lsac, Sls, AdjDpc, Opc]) when
+		is_pid(Hmrt), is_pid(Mgmt), is_pid(Lsac), is_integer(Sls) ->
+	SltState = #sltc_state{hmrt_pid = Hmrt,
+			       mgmt_pid = Mgmt,
+			       lsac_pid = Lsac,
+			       sls = Sls,
+			       adj_dpc = AdjDpc,
+			       opc = Opc,
+			       t1_timeout = ?SLTC_T1_DEF,
+			       x = 16#2342},
+	{ok, idle, SltState}.
+
+terminate(Reason, State, _LoopDat) ->
+	io:format("Terminating ~p in State ~p (Reason: ~p)~n",
+		  [?MODULE, State, Reason]),
+	ok.
+
+code_change(_OldVsn, StateName, LoopDat, _Extra) ->
+	{ok, StateName, LoopDat}.
+
+handle_event(Event, State, LoopDat) ->
+	io:format("Unknown Event ~p in state ~p~n", [Event, State]),
+	{next_state, State, LoopDat}.
+
+handle_info(Info, State, LoopDat) ->
+	io:format("Unknown Info ~p in state ~p~n", [Info, State]),
+	{next_state, State, LoopDat}.
+
+% See Figure 2 of Q.707
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+% STATE: idle
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+
+idle(M=#mtp3_msg{service_ind = ?MTP3_SERV_MGMT,
+		 payload = #mtp3mg_msg{h0 = ?MTP3MG_H0_TEST,
+			 		h1 = ?MTP3MG_H1_SLTM}}, LoopDat) ->
+	Slta = slta_from_sltm(M),
+	send_to(hmrt, Slta, LoopDat),
+	{next_state, idle, LoopDat};
+
+idle(start, LoopDat) ->
+	Sltm = generate_sltm(LoopDat),
+	send_to(hmrt, Sltm, LoopDat),
+	{ok, T1} = timer:apply_after(gen_fsm, send_event,
+				     [self(), {timer_expired, t1}]),
+	{next_state, first_attempt, LoopDat#sltc_state{t1 = T1}}.
+
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+% STATE: first_attempt
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+
+first_attempt(M=#mtp3_msg{service_ind = ?MTP3_SERV_MGMT,
+			  payload = #mtp3mg_msg{h0 = ?MTP3MG_H0_TEST,
+						h1 = ?MTP3MG_H1_SLTM}}, LoopDat) ->
+	Slta = slta_from_sltm(M),
+	send_to(hmrt, Slta, LoopDat),
+	{next_state, first_attempt, LoopDat};
+
+first_attempt(M = #mtp3_msg{service_ind = ?MTP3_SERV_MGMT,
+			    payload = #mtp3mg_msg{h0 = ?MTP3MG_H0_TEST,
+						  h1 = ?MTP3MG_H1_SLTA}}, LoopDat) ->
+	timer:cancel(LoopDat#sltc_state.t1),
+	case slt_matches(M, LoopDat) of
+	    true ->
+		send_to(lsac, slt_successful, LoopDat),
+		{next_state, idle, LoopDat};
+	    false ->
+		Sltm = generate_sltm(LoopDat),
+		send_to(hmrt, Sltm, LoopDat),
+		{ok, T1} = timer:apply_after(gen_fsm, send_event,
+					     [self(), {timer_expired, t1}]),
+		{next_state, second_attempt, LoopDat#sltc_state{t1 = T1}}
+	end.
+
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+% STATE: second_attempt
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+
+second_attempt(M=#mtp3_msg{service_ind = ?MTP3_SERV_MGMT,
+			  payload = #mtp3mg_msg{h0 = ?MTP3MG_H0_TEST,
+						h1 = ?MTP3MG_H1_SLTM}}, LoopDat) ->
+	Slta = slta_from_sltm(M),
+	send_to(hmrt, Slta, LoopDat),
+	{next_state, second_attempt, LoopDat};
+
+second_attempt(M = #mtp3_msg{service_ind = ?MTP3_SERV_MGMT,
+			     payload = #mtp3mg_msg{h0 = ?MTP3MG_H0_TEST,
+						   h1 = ?MTP3MG_H1_SLTA}}, LoopDat) ->
+	timer:cancel(LoopDat#sltc_state.t1),
+	case slt_matches(M, LoopDat) of
+	    true ->
+		send_to(lsac, slt_successful, LoopDat);
+	    false ->
+		send_to(mgmt, slt_failed, LoopDat),
+		send_to(lsac, slt_failed, LoopDat)
+	end,
+	{next_state, idle, LoopDat};
+
+second_attempt({timer_expired, t1}, LoopDat) ->
+	send_to(mgmt, slt_failed, LoopDat),
+	send_to(lsac, slt_failed, LoopDat),
+	{next_state, idle, LoopDat}.
+
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+% helper functions
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+send_to(hmrt, What, #sltc_state{hmrt_pid = Txc}) ->
+	Txc ! {sltc_hmrt, What};
+send_to(mgmt, What, #sltc_state{mgmt_pid = Txc}) ->
+	Txc ! {sltc_mgmt, What};
+send_to(lsac, What, #sltc_state{lsac_pid = Txc}) ->
+	Txc ! {sltc_lsac, What}.
+
+slta_from_sltm(M = #mtp3_msg{service_ind = ?MTP3_SERV_MGMT,
+			     routing_label = RoutLbl,
+			     payload = #mtp3mg_msg{h0 = ?MTP3MG_H0_TEST,
+						   h1 = ?MTP3MG_H1_SLTM,
+					   	   test_pattern = TP}}) ->
+	InvRoutLbl = invert_rout_lbl(RoutLbl),
+	M#mtp3_msg{routing_label = InvRoutLbl,
+		   payload = #mtp3mg_msg{h0 = ?MTP3MG_H0_TEST,
+			   		 h1 = ?MTP3MG_H1_SLTA,
+					 test_pattern = TP}}.
+
+generate_sltm(LoopDat) ->
+	Mg = #mtp3mg_msg{h0 = ?MTP3MG_H0_TEST, h1 = ?MTP3MG_H1_SLTM,
+			 test_pattern = LoopDat#sltc_state.x},
+	Lbl = #mtp3_routing_label{sig_link_sel = LoopDat#sltc_state.sls,
+				  origin_pc = LoopDat#sltc_state.opc,
+				  dest_pc = LoopDat#sltc_state.adj_dpc},
+
+	#mtp3_msg{network_ind = ?MTP3_NETIND_INTERNATIONAL,
+		  service_ind = ?MTP3_SERV_MGMT,
+		  routing_label = Lbl, payload = Mg}.
+
+rout_lbl_matches(#mtp3_routing_label{sig_link_sel = SlsLocal,
+				     origin_pc = OPC}, LoopDat) ->
+	#sltc_state{adj_dpc = AdjDpc, sls = SLS} = LoopDat,
+	if SLS == SlsLocal, OPC == AdjDpc ->
+		true;
+	   true ->
+		false
+	end.
+
+slt_matches(#mtp3_msg{routing_label = RoutLbl,
+		      payload = #mtp3mg_msg{test_pattern = TP}}, LoopDat) ->
+	case LoopDat#sltc_state.x of
+	    TP ->
+		rout_lbl_matches(RoutLbl, LoopDat);
+	    _ ->
+		false
+	end.
+
+
+
+invert_rout_lbl(L = #mtp3_routing_label{origin_pc = Opc, dest_pc = Dpc}) ->
+	L#mtp3_routing_label{origin_pc = Dpc, dest_pc = Opc}.