summaryrefslogtreecommitdiffstats
path: root/lib/edioutput/PFT.cpp
blob: 7e0e8e943c3bf5f250306bbe88a6f9fabd6008c8 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
/*
   Copyright (C) 2021
   Matthias P. Braendli, matthias.braendli@mpb.li

    http://www.opendigitalradio.org

   EDI output,
   Protection, Fragmentation and Transport. (PFT)

   Are supported:
    Reed-Solomon and Fragmentation

   This implements part of PFT as defined ETSI TS 102 821.

   */
/*
   This file is part of the ODR-mmbTools.

   This program is free software: you can redistribute it and/or modify
   it under the terms of the GNU 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 General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#include <vector>
#include <list>
#include <cstdio>
#include <cstring>
#include <cstdint>
#include <arpa/inet.h>
#include <stdexcept>
#include <sstream>
#include "PFT.h"
#include "crc.h"
#include "ReedSolomon.h"

namespace edi {

using namespace std;

// An integer division that rounds up, i.e. ceil(a/b)
#define CEIL_DIV(a, b) (a % b == 0  ? a / b : a / b + 1)

PFT::PFT() { }

PFT::PFT(const configuration_t &conf) :
    m_k(conf.chunk_len),
    m_m(conf.fec),
    m_pseq(0),
    m_num_chunks(0),
    m_verbose(conf.verbose)
    {
        if (m_k > 207) {
            etiLog.level(warn) <<
                "EDI PFT: maximum chunk size is 207.";
            throw std::out_of_range("EDI PFT Chunk size too large.");
        }

        if (m_m > 5) {
            etiLog.level(warn) <<
                "EDI PFT: high number of recoverable fragments"
                " may lead to large overhead";
            // See TS 102 821, 7.2.1 Known values, list entry for 'm'
        }
    }

RSBlock PFT::Protect(AFPacket af_packet)
{
    RSBlock rs_block;

    // number of chunks is ceil(afpacketsize / m_k)
    // TS 102 821 7.2.2: c = ceil(l / k_max)
    m_num_chunks = CEIL_DIV(af_packet.size(), m_k);

    if (m_verbose) {
        fprintf(stderr, "Protect %zu chunks of size %zu\n",
                m_num_chunks, af_packet.size());
    }

    // calculate size of chunk:
    // TS 102 821 7.2.2: k = ceil(l / c)
    // chunk_len does not include the 48 bytes of protection.
    const size_t chunk_len = CEIL_DIV(af_packet.size(), m_num_chunks);
    if (chunk_len > 207) {
        std::stringstream ss;
        ss << "Chunk length " << chunk_len << " too large (>207)";
        throw std::runtime_error(ss.str());
    }

    // The last RS chunk is zero padded
    // TS 102 821 7.2.2: z = c*k - l
    const size_t zero_pad = m_num_chunks * chunk_len - af_packet.size();

    // Create the RS(k+p,k) encoder
    const int firstRoot = 1; // Discovered by analysing EDI dump
    const int gfPoly = 0x11d;
    const bool reverse = false;
    // The encoding has to be 255, 207 always, because the chunk has to
    // be padded at the end, and not at the beginning as libfec would
    // do
    ReedSolomon rs_encoder(255, 207, reverse, gfPoly, firstRoot);

    // add zero padding to last chunk
    for (size_t i = 0; i < zero_pad; i++) {
        af_packet.push_back(0);
    }

    if (m_verbose) {
        fprintf(stderr, "        add %zu zero padding\n", zero_pad);
    }

    // Calculate RS for each chunk and assemble RS block
    for (size_t i = 0; i < af_packet.size(); i+= chunk_len) {
        vector<uint8_t> chunk(207);
        vector<uint8_t> protection(PARITYBYTES);

        // copy chunk_len bytes into new chunk
        memcpy(&chunk.front(), &af_packet[i], chunk_len);

        // calculate RS for chunk with padding
        rs_encoder.encode(&chunk.front(), &protection.front(), 207);

        // Drop the padding
        chunk.resize(chunk_len);

        // append new chunk and protection to the RS Packet
        rs_block.insert(rs_block.end(), chunk.begin(), chunk.end());
        rs_block.insert(rs_block.end(), protection.begin(), protection.end());
    }

    return rs_block;
}

vector< vector<uint8_t> > PFT::ProtectAndFragment(AFPacket af_packet)
{
    const bool enable_RS = (m_m > 0);

    if (enable_RS) {
        RSBlock rs_block = Protect(af_packet);

#if 0
        fprintf(stderr, "  af_packet (%zu):", af_packet.size());
        for (size_t i = 0; i < af_packet.size(); i++) {
            fprintf(stderr, "%02x ", af_packet[i]);
        }
        fprintf(stderr, "\n");

        fprintf(stderr, "  rs_block (%zu):", rs_block.size());
        for (size_t i = 0; i < rs_block.size(); i++) {
            fprintf(stderr, "%02x ", rs_block[i]);
        }
        fprintf(stderr, "\n");
#endif

        // TS 102 821 7.2.2: s_max = MIN(floor(c*p/(m+1)), MTU - h))
        const size_t max_payload_size = ( m_num_chunks * PARITYBYTES ) / (m_m + 1);

        // Calculate fragment count and size
        // TS 102 821 7.2.2: ceil((l + c*p + z) / s_max)
        // l + c*p + z = length of RS block
        const size_t num_fragments = CEIL_DIV(rs_block.size(), max_payload_size);

        // TS 102 821 7.2.2: ceil((l + c*p + z) / f)
        const size_t fragment_size = CEIL_DIV(rs_block.size(), num_fragments);

        if (m_verbose)
            fprintf(stderr, "  PnF fragment_size %zu, num frag %zu\n",
                    fragment_size, num_fragments);

        vector< vector<uint8_t> > fragments(num_fragments);

        for (size_t i = 0; i < num_fragments; i++) {
            fragments[i].resize(fragment_size);
            for (size_t j = 0; j < fragment_size; j++) {
                const size_t ix = j*num_fragments + i;
                if (ix < rs_block.size()) {
                    fragments[i][j] = rs_block[ix];
                }
                else {
                    fragments[i][j] = 0;
                }
            }
        }

        return fragments;
    }
    else { // No RS, only fragmentation
        // TS 102 821 7.2.2: s_max = MTU - h
        // Ethernet MTU is 1500, but maybe you are routing over a network which
        // has some sort of packet encapsulation. Add some margin.
        const size_t max_payload_size = 1400;

        // Calculate fragment count and size
        // TS 102 821 7.2.2: ceil((l + c*p + z) / s_max)
        // l + c*p + z = length of AF packet
        const size_t num_fragments = CEIL_DIV(af_packet.size(), max_payload_size);

        // TS 102 821 7.2.2: ceil((l + c*p + z) / f)
        const size_t fragment_size = CEIL_DIV(af_packet.size(), num_fragments);
        vector< vector<uint8_t> > fragments(num_fragments);

        for (size_t i = 0; i < num_fragments; i++) {
            fragments[i].reserve(fragment_size);

            for (size_t j = 0; j < fragment_size; j++) {
                const size_t ix = i*fragment_size + j;
                if (ix < af_packet.size()) {
                    fragments[i].push_back(af_packet.at(ix));
                }
                else {
                    break;
                }
            }
        }

        return fragments;
    }
}

std::vector< PFTFragment > PFT::Assemble(AFPacket af_packet)
{
    vector< vector<uint8_t> > fragments = ProtectAndFragment(af_packet);
    vector< vector<uint8_t> > pft_fragments; // These contain PF headers

    const bool enable_RS = (m_m > 0);

    unsigned int findex = 0;

    unsigned fcount = fragments.size();

    // calculate size of chunk:
    // TS 102 821 7.2.2: k = ceil(l / c)
    // chunk_len does not include the 48 bytes of protection.
    const size_t chunk_len = enable_RS ?
        CEIL_DIV(af_packet.size(), m_num_chunks) : 0;

    // The last RS chunk is zero padded
    // TS 102 821 7.2.2: z = c*k - l
    const size_t zero_pad = enable_RS ?
        m_num_chunks * chunk_len - af_packet.size() : 0;

    for (const auto &fragment : fragments) {
        // Psync
        std::string psync("PF");
        std::vector<uint8_t> packet(psync.begin(), psync.end());

        // Pseq
        packet.push_back(m_pseq >> 8);
        packet.push_back(m_pseq & 0xFF);

        // Findex
        packet.push_back(findex >> 16);
        packet.push_back(findex >> 8);
        packet.push_back(findex & 0xFF);
        findex++;

        // Fcount
        packet.push_back(fcount >> 16);
        packet.push_back(fcount >> 8);
        packet.push_back(fcount & 0xFF);

        // RS (1 bit), transport (1 bit) and Plen (14 bits)
        unsigned int plen = fragment.size();
        if (enable_RS) {
            plen |= 0x8000; // Set FEC bit
        }

        if (m_transport_header) {
            plen |= 0x4000; // Set ADDR bit
        }

        packet.push_back(plen >> 8);
        packet.push_back(plen & 0xFF);

        if (enable_RS) {
            packet.push_back(chunk_len);   // RSk
            packet.push_back(zero_pad);    // RSz
        }

        if (m_transport_header) {
            // Source (16 bits)
            packet.push_back(m_addr_source >> 8);
            packet.push_back(m_addr_source & 0xFF);

            // Dest (16 bits)
            packet.push_back(m_dest_port >> 8);
            packet.push_back(m_dest_port & 0xFF);
        }

        // calculate CRC over AF Header and payload
        uint16_t crc = 0xffff;
        crc = crc16(crc, &(packet.front()), packet.size());
        crc ^= 0xffff;

        packet.push_back((crc >> 8) & 0xFF);
        packet.push_back(crc & 0xFF);

        // insert payload, must have a length multiple of 8 bytes
        packet.insert(packet.end(), fragment.begin(), fragment.end());

        pft_fragments.push_back(packet);

#if 0
        fprintf(stderr, "* PFT pseq %d, findex %d, fcount %d, plen %d\n",
                m_pseq, findex, fcount, plen & ~0xC000);
#endif
    }

    m_pseq++;

    return pft_fragments;
}

void PFT::OverridePSeq(uint16_t pseq)
{
    m_pseq = pseq;
}

}