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diff --git a/libtransport/src/core/rs.h b/libtransport/src/core/rs.h
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+
+/*
+ * Copyright (c) 2021 Cisco and/or its affiliates.
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at:
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <arpa/inet.h>
+#include <hicn/transport/utils/membuf.h>
+#include <protocols/fec_base.h>
+
+#include <array>
+#include <cstdint>
+#include <map>
+#include <unordered_set>
+#include <vector>
+
+namespace transport {
+namespace core {
+
+namespace fec {
+
+static const constexpr uint16_t MAX_SOURCE_BLOCK_SIZE = 128;
+
+using buffer = typename utils::MemBuf::Ptr;
+/**
+ * We use a std::array in place of std::vector to avoid to allocate a new vector
+ * in the heap every time we build a new source block, which would be bad if
+ * the decoder has to allocate several source blocks for many concurrent bases.
+ * std::array allows to be constructed in place, saving the allocation at the
+ * price os knowing in advance its size.
+ */
+using Packets = std::array<std::pair<uint32_t, buffer>, MAX_SOURCE_BLOCK_SIZE>;
+
+/**
+ * FEC Header, prepended to symbol packets.
+ */
+struct fec_header {
+  /**
+   * The base source packet seq_number this FES symbol refers to
+   */
+  uint32_t seq_number;
+
+  /**
+   * The index of the symbol inside the source block, between k and n - 1
+   */
+  uint8_t encoded_symbol_id;
+
+  /**
+   * Total length of source block (n)
+   */
+  uint8_t source_block_len;
+
+  /**
+   * Total number of symbols (n - k)
+   */
+  uint8_t n_fec_symbols;
+
+  /**
+   * Align header to 64 bits
+   */
+  uint8_t padding;
+
+  void setSeqNumberBase(uint32_t suffix) { seq_number = htonl(suffix); }
+  uint32_t getSeqNumberBase() { return ntohl(seq_number); }
+  void setEncodedSymbolId(uint8_t esi) { encoded_symbol_id = esi; }
+  uint8_t getEncodedSymbolId() { return encoded_symbol_id; }
+  void setSourceBlockLen(uint8_t k) { source_block_len = k; }
+  uint8_t getSourceBlockLen() { return source_block_len; }
+  void setNFecSymbols(uint8_t n_r) { n_fec_symbols = n_r; }
+  uint8_t getNFecSymbols() { return n_fec_symbols; }
+};
+
+/**
+ * This class models the source block itself.
+ */
+class BlockCode : public Packets {
+  /**
+   * For variable length packet we need to prepend to the padded payload the
+   * real length of the packet. This is *not* sent over the network.
+   */
+  static constexpr std::size_t LEN_SIZE_BYTES = 2;
+
+ public:
+  BlockCode(uint32_t k, uint32_t n, struct fec_parms *code);
+
+  /**
+   * Add a repair symbol to the dource block.
+   */
+  bool addRepairSymbol(const fec::buffer &packet, uint32_t i);
+
+  /**
+   * Add a source symbol to the source block.
+   */
+  bool addSourceSymbol(const fec::buffer &packet, uint32_t i);
+
+  /**
+   * Get current length of source block.
+   */
+  std::size_t length() { return current_block_size_; }
+
+  /**
+   * Get N
+   */
+  uint32_t getN() { return n_; }
+
+  /**
+   * Get K
+   */
+  uint32_t getK() { return k_; }
+
+  /**
+   * Clear source block
+   */
+  void clear();
+
+ private:
+  /**
+   * Add symbol to source block
+   **/
+  bool addSymbol(const fec::buffer &packet, uint32_t i, std::size_t size);
+
+  /**
+   * Starting from k source symbols, get the n - k repair symbols
+   */
+  void encode();
+
+  /**
+   * Starting from k symbols (mixed repair and source), get k source symbols.
+   * NOTE: It does not make sense to retrieve the k source symbols using the
+   * very same k source symbols. With the current implementation that case can
+   * never happen.
+   */
+  void decode();
+
+ private:
+  uint32_t k_;
+  uint32_t n_;
+  struct fec_parms *code_;
+  std::size_t max_buffer_size_;
+  std::size_t current_block_size_;
+  std::vector<uint32_t> sorted_index_;
+  bool to_decode_;
+};
+
+/**
+ * This class contains common parameters between the fec encoder and decoder.
+ * In particular it contains:
+ *  - The callback to be called when symbols are encoded / decoded
+ *  - The reference to the static reed-solomon parameters, allocated at program
+ * startup
+ *  - N and K. Ideally they are useful only for the encoder (the decoder can
+ * retrieve them from the FEC header). However right now we assume sender and
+ * receiver agreed on the parameters k and n to use. We will introduce a control
+ * message later to negotiate them, so that decoder cah dynamically change them
+ * during the download.
+ */
+class rs {
+  /**
+   * Deleter for static preallocated reed-solomon parameters.
+   */
+  struct MatrixDeleter {
+    void operator()(struct fec_parms *params);
+  };
+
+  /**
+   * unique_ptr to reed-solomon parameters, with custom deleter to call fec_free
+   * at the end of the program
+   */
+  using Matrix = std::unique_ptr<struct fec_parms, MatrixDeleter>;
+
+  /**
+   * Key to retrieve static preallocated reed-solomon parameters. It is pair of
+   * k and n
+   */
+  using Code = std::pair<std::uint32_t /* k */, std::uint32_t /* n */>;
+
+  /**
+   * Custom hash function for (k, n) pair.
+   */
+  struct CodeHasher {
+    std::size_t operator()(const transport::core::fec::rs::Code &code) const {
+      uint64_t ret = uint64_t(code.first) << 32 | uint64_t(code.second);
+      return std::hash<uint64_t>{}(ret);
+    }
+  };
+
+ protected:
+  /**
+   * Callback to be called after the encode or the decode operations. In the
+   * former case it will contain the symbols, while in the latter the sources.
+   */
+  using PacketsReady = std::function<void(std::vector<buffer> &)>;
+
+  /**
+   * The sequence number base.
+   */
+  using SNBase = std::uint32_t;
+
+  /**
+   * The map of source blocks, used at the decoder side. For the encoding
+   * operation we can use one source block only, since packet are produced in
+   * order.
+   */
+  using SourceBlocks = std::unordered_map<SNBase, BlockCode>;
+
+  /**
+   * Map (k, n) -> reed-solomon parameter
+   */
+  using Codes = std::unordered_map<Code, Matrix, CodeHasher>;
+
+ public:
+  rs(uint32_t k, uint32_t n);
+  ~rs() = default;
+
+  /**
+   * Set callback to call after packet encoding / decoding
+   */
+  void setFECCallback(const PacketsReady &callback);
+
+  virtual void clear() { processed_source_blocks_.clear(); }
+
+ private:
+  /**
+   * Create reed-solomon codes at program startup.
+   */
+  static Codes createCodes();
+
+ protected:
+  bool processed(SNBase seq_base) {
+    return processed_source_blocks_.find(seq_base) !=
+           processed_source_blocks_.end();
+  }
+
+  std::uint32_t k_;
+  std::uint32_t n_;
+  PacketsReady fec_callback_;
+
+  /**
+   * Keep track of processed source blocks
+   */
+  std::unordered_set<SNBase> processed_source_blocks_;
+
+  static Codes codes_;
+};
+
+/**
+ * The reed-solomon encoder. It is feeded with source symbols and it provide
+ * repair-symbols through the fec_callback_
+ */
+class encoder : public rs {
+ public:
+  encoder(uint32_t k, uint32_t n);
+  /**
+   * Always consume source symbols.
+   */
+  void consume(const fec::buffer &packet, uint32_t index);
+
+  void clear() override {
+    rs::clear();
+    source_block_.clear();
+  }
+
+ private:
+  struct fec_parms *current_code_;
+  /**
+   * The source block. As soon as it is filled with k source symbols, the
+   * encoder calls the callback fec_callback_ and the resets the block 0, ready
+   * to accept another batch of k source symbols.
+   */
+  BlockCode source_block_;
+};
+
+/**
+ * The reed-solomon encoder. It is feeded with source/repair symbols and it
+ * provides the original source symbols through the fec_callback_
+ */
+class decoder : public rs {
+ public:
+  decoder(uint32_t k, uint32_t n);
+
+  /**
+   * Consume source symbol
+   */
+  void consume(const fec::buffer &packet, uint32_t i);
+
+  /**
+   * Consume repair symbol
+   */
+  void consume(const fec::buffer &packet);
+
+  /**
+   * Clear decoder to reuse
+   */
+  void clear() override {
+    rs::clear();
+    src_blocks_.clear();
+    parked_packets_.clear();
+  }
+
+ private:
+  void recoverPackets(SourceBlocks::iterator &src_block_it);
+
+ private:
+  /**
+   * Map of source blocks. We use a map because we may receive symbols belonging
+   * to diffreent source blocks at the same time, so we need to be able to
+   * decode many source symbols at the same time.
+   */
+  SourceBlocks src_blocks_;
+
+  /**
+   * Unordered Map of source symbols for which we did not receive any repair
+   * symbol in the same source block. Notably this happens when:
+   *
+   * - We receive the source symbols first and the repair symbols after
+   * - We received only source symbols for a given block. In that case it does
+   * not make any sense to build the source block, since we received all the
+   * source packet of the block.
+   */
+  std::unordered_map<uint32_t, std::vector<std::pair<buffer, uint32_t>>>
+      parked_packets_;
+};
+
+}  // namespace fec
+
+}  // namespace core
+
+}  // namespace transport