1 files changed, 327 insertions, 0 deletions
diff --git a/lib/edi/PFT.cpp b/lib/edi/PFT.cpp
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+/*
+   Copyright (C) 2019
+   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 "config.h"
+#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_dest_port(conf.dest_port),
+    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);
+    const bool enable_transport = true;
+
+    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 (enable_transport) {
+            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 (enable_transport) {
+            // Source (16 bits)
+            uint16_t addr_source = 0;
+            packet.push_back(addr_source >> 8);
+            packet.push_back(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;
+}
+
+}
+