diff --git a/libuavcan/include/uavcan/internal/transport/transfer.hpp b/libuavcan/include/uavcan/internal/transport/transfer.hpp
new file mode 100644
index 0000000000..e5609ed9e6
--- /dev/null
+++ b/libuavcan/include/uavcan/internal/transport/transfer.hpp
@@ -0,0 +1,90 @@
+/*
+ * Copyright (C) 2014 <pavel.kirienko@gmail.com>
+ */
+
+#pragma once
+
+#include <cassert>
+#include <algorithm>
+#include <uavcan/internal/transport/can_io.hpp>
+
+namespace uavcan
+{
+
+enum TransferType
+{
+    SERVICE_RESPONSE  = 0,
+    SERVICE_REQUEST   = 1,
+    MESSAGE_BROADCAST = 2,
+    MESSAGE_UNICAST   = 3
+};
+
+struct Frame
+{
+    enum { MAX_TRANSFER_ID = 15 };
+
+    uint8_t payload[8];
+    TransferType transfer_type;
+    uint_fast16_t data_type_id;
+    uint_fast8_t payload_len;
+    uint_fast8_t source_node_id;
+    uint_fast8_t frame_index;
+    uint_fast8_t transfer_id;
+    bool last_frame;
+
+    Frame(const uint8_t* payload, uint_fast8_t payload_len, uint_fast16_t data_type_id, TransferType transfer_type,
+          uint_fast8_t source_node_id, uint_fast8_t frame_index, uint_fast8_t transfer_id, bool last_frame)
+    : transfer_type(transfer_type)
+    , data_type_id(data_type_id)
+    , payload_len(payload_len)
+    , source_node_id(source_node_id)
+    , frame_index(frame_index)
+    , transfer_id(transfer_id)
+    , last_frame(last_frame)
+    {
+        assert(payload && payload_len <= 8);
+        std::copy(payload, payload + payload_len, this->payload);
+    }
+
+    static Frame parse(const CanFrame& can_frame);
+
+    /**
+     * Difference computed from (this.transfer_id - rhs.transfer_id) with proper overflow handling.
+     */
+    int subtractTransferID(const Frame& rhs) const { return subtractTransferID(rhs.transfer_id); }
+    int subtractTransferID(int rhs) const;
+
+    bool operator!=(const Frame& rhs) const { return !operator==(rhs); }
+    bool operator==(const Frame& rhs) const
+    {
+        return
+            (transfer_type == rhs.transfer_type) &&
+            (data_type_id == rhs.data_type_id) &&
+            (source_node_id == rhs.source_node_id) &&
+            (frame_index == rhs.frame_index) &&
+            (transfer_id == rhs.transfer_id) &&
+            (last_frame == rhs.last_frame) &&
+            (payload_len == rhs.payload_len) &&
+            std::equal(payload, payload + payload_len, rhs.payload);
+    }
+};
+
+struct RxFrame
+{
+    uint_fast64_t timestamp;
+    Frame frame;
+    uint_fast8_t iface_index;
+
+    RxFrame(const Frame& frame, uint_fast64_t timestamp, uint_fast8_t iface_index)
+    : timestamp(timestamp)
+    , frame(frame)
+    , iface_index(iface_index)
+    { }
+
+    static RxFrame parse(const CanRxFrame& can_frame)
+    {
+        return RxFrame(Frame::parse(can_frame.frame), can_frame.timestamp, can_frame.iface_index);
+    }
+};
+
+}
diff --git a/libuavcan/src/transport/transfer.cpp b/libuavcan/src/transport/transfer.cpp
new file mode 100644
index 0000000000..21dd7b263f
--- /dev/null
+++ b/libuavcan/src/transport/transfer.cpp
@@ -0,0 +1,28 @@
+/*
+ * Copyright (C) 2014 <pavel.kirienko@gmail.com>
+ */
+
+#include <uavcan/internal/transport/transfer.hpp>
+
+namespace uavcan
+{
+
+//static Frame Frame::parse(const CanFrame& can_frame)
+//{
+//}
+
+int Frame::subtractTransferID(int rhs) const
+{
+    static const int RANGE = MAX_TRANSFER_ID + 1;  //  16  256
+    static const int NEGATIVE = -RANGE / 2;        // -8  -128 (two's complement)
+    static const int POSITIVE = (-NEGATIVE) - 1;   //  7   127
+
+    const int d = int(this->transfer_id) - rhs;
+    if (d <= NEGATIVE)
+        return RANGE + d;
+    else if (d >= POSITIVE)
+        return d - RANGE;
+    return d;
+}
+
+}