94 lines
3.9 KiB
Erlang
94 lines
3.9 KiB
Erlang
% ITU-T Q.704 (MTP Level 3) coding / decoding
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% (C) 2011 by Harald Welte <laforge@gnumonks.org>
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%
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% All Rights Reserved
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%
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% This program is free software; you can redistribute it and/or modify
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% it under the terms of the GNU Affero General Public License as
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% published by the Free Software Foundation; either version 3 of the
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% License, or (at your option) any later version.
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%
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% This program is distributed in the hope that it will be useful,
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% but WITHOUT ANY WARRANTY; without even the implied warranty of
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% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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% GNU General Public License for more details.
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%
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% You should have received a copy of the GNU Affero General Public License
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% along with this program. If not, see <http://www.gnu.org/licenses/>.
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%
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% Additional Permission under GNU AGPL version 3 section 7:
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%
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% If you modify this Program, or any covered work, by linking or
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% combining it with runtime libraries of Erlang/OTP as released by
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% Ericsson on http://www.erlang.org (or a modified version of these
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% libraries), containing parts covered by the terms of the Erlang Public
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% License (http://www.erlang.org/EPLICENSE), the licensors of this
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% Program grant you additional permission to convey the resulting work
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% without the need to license the runtime libraries of Erlang/OTP under
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% the GNU Affero General Public License. Corresponding Source for a
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% non-source form of such a combination shall include the source code
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% for the parts of the runtime libraries of Erlang/OTP used as well as
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% that of the covered work.
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-module(mtp3_codec).
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-author('Harald Welte <laforge@gnumonks.org>').
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-include("mtp3.hrl").
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-export([parse_mtp3_msg/1, encode_mtp3_msg/1, invert_rout_lbl/1]).
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-compile({parse_transform, exprecs}).
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-export_records([mtp3_routing_label, mtp3_msg]).
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% Parse standard routing label according to Section 2.2 of ITU-T Q.704
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parse_mtp3_routing_label(_, LabelBin) when is_binary(LabelBin) ->
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% we need to swap the four bytes and then parse the fields
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<<Label32:32/little, Remain/binary>> = LabelBin,
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LabelRev = <<Label32:32/big>>,
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<<Sls:4/big, Opc:14/big, Dpc:14/big>> = LabelRev,
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{ok, #mtp3_routing_label{sig_link_sel = Sls, origin_pc = Opc, dest_pc = Dpc}, Remain}.
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parse_mtp3_msg(DataBin) when is_binary(DataBin) ->
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<<NetInd:2, 0:2, ServiceInd:4, Remain/binary>> = DataBin,
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{ok, RoutLbl, Payload} = parse_mtp3_routing_label(ServiceInd, Remain),
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PayloadDec = decode_payload(ServiceInd, Payload),
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#mtp3_msg{network_ind = NetInd, service_ind = ServiceInd, routing_label = RoutLbl,
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payload = PayloadDec}.
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encode_mtp3_routing_label(#mtp3_routing_label{sig_link_sel = Sls, origin_pc = OpcIn,
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dest_pc = DpcIn}) ->
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Opc = osmo_util:pointcode2int(OpcIn),
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Dpc = osmo_util:pointcode2int(DpcIn),
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% we need to swap the four bytes after encoding the fields
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<<Label32:32/little>> = <<Sls:4/big, Opc:14/big, Dpc:14/big>>,
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<<Label32:32/big>>.
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encode_mtp3_msg(#mtp3_msg{network_ind = NetInd, service_ind = ServiceInd,
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routing_label = RoutLbl, payload = Payload}) ->
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RoutLblBin = encode_mtp3_routing_label(RoutLbl),
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PayloadBin = payload_to_binary(ServiceInd, Payload),
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<<NetInd:2, 0:2, ServiceInd:4, RoutLblBin/binary, PayloadBin/binary>>.
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decode_payload(?MTP3_SERV_MTN, Payload) ->
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<<H1:4, H0:4, Len:4, 0:4, TP/binary>> = Payload,
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#mtp3mg_msg{h0 = H0, h1 = H1, payload = TP};
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decode_payload(?MTP3_SERV_MGMT, Payload) ->
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<<H1:4, H0:4, Remain/binary>> = Payload,
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#mtp3mg_msg{h0 = H0, h1 = H1, payload = Remain};
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decode_payload(_, Payload) ->
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Payload.
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payload_to_binary(?MTP3_SERV_MTN, #mtp3mg_msg{h0=H0, h1=H1, payload=TP}) ->
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Len = byte_size(TP),
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<<H1:4, H0:4, Len:4, 0:4, TP/binary>>;
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payload_to_binary(?MTP3_SERV_MGMT, #mtp3mg_msg{h0=H0, h1=H1, payload=Payload}) ->
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<<H1:4, H0:4, Payload/binary>>;
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payload_to_binary(_, Whatever) ->
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Whatever.
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invert_rout_lbl(L = #mtp3_routing_label{origin_pc = Opc, dest_pc = Dpc}) ->
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L#mtp3_routing_label{origin_pc = Dpc, dest_pc = Opc}.
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