diff --git a/lib/trx/trx_burst_if_impl.cc b/lib/trx/trx_burst_if_impl.cc
new file mode 100644
index 0000000..e3fcc89
--- /dev/null
+++ b/lib/trx/trx_burst_if_impl.cc
@@ -0,0 +1,231 @@
+/* -*- c++ -*- */
+/* @file
+ * @author Vadim Yanitskiy <axilirator@gmail.com>
+ * @section LICENSE
+ * 
+ * Gr-gsm 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, or (at your option)
+ * any later version.
+ * 
+ * Gr-gsm 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 gr-gsm; see the file COPYING.  If not, write to
+ * the Free Software Foundation, Inc., 51 Franklin Street,
+ * Boston, MA 02110-1301, USA.
+ * 
+ */
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include <gnuradio/io_signature.h>
+#include <boost/lexical_cast.hpp>
+
+#include "grgsm/misc_utils/udp_socket.h"
+#include "trx_burst_if_impl.h"
+
+#define BURST_SIZE     148
+#define DATA_IF_MTU    160
+
+/**
+ * 41-bit RACH synchronization sequence
+ * GSM 05.02 Chapter 5.2.7 Access burst (AB)
+ */
+static uint8_t rach_synch_seq[] = {
+  0, 1, 0, 0, 1, 0, 1, 1, 0, 1, 1, 1, 1, 1,
+  1, 1, 1, 0, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0,
+  1, 0, 1, 0, 0, 0, 1, 1, 1, 1, 0, 0, 0,
+};
+
+namespace gr {
+  namespace gsm {
+
+    trx_burst_if::sptr
+    trx_burst_if::make(
+      const std::string &remote_addr,
+      const std::string &base_port)
+    {
+      int base_port_int = boost::lexical_cast<int> (base_port);
+
+      return gnuradio::get_initial_sptr
+        (new trx_burst_if_impl(remote_addr, base_port_int));
+    }
+
+    /*
+     * The private constructor
+     */
+    trx_burst_if_impl::trx_burst_if_impl(
+      const std::string &remote_addr,
+      int base_port
+    ) : gr::block("trx_burst_if",
+        gr::io_signature::make(0, 0, 0),
+        gr::io_signature::make(0, 0, 0))
+    {
+        message_port_register_in(pmt::mp("bursts"));
+        message_port_register_out(pmt::mp("bursts"));
+
+        // Bind a port handler
+        set_msg_handler(pmt::mp("bursts"),
+          boost::bind(&trx_burst_if_impl::handle_dl_burst, this, _1));
+
+        // Prepare port numbers
+        std::string data_src_port = boost::lexical_cast<std::string> (base_port + 2);
+        std::string data_dst_port = boost::lexical_cast<std::string> (base_port + 102);
+
+        // Init DATA interface
+        d_data_sock = new udp_socket(remote_addr,
+          data_src_port, data_dst_port, DATA_IF_MTU);
+
+        // Bind DATA interface handler
+        d_data_sock->udp_rx_handler = boost::bind(
+          &trx_burst_if_impl::handle_ul_burst, this, _1, _2);
+    }
+
+    /*
+     * Our virtual destructor.
+     */
+    trx_burst_if_impl::~trx_burst_if_impl()
+    {
+        // Release all UDP sockets and free memory
+        delete d_data_sock;
+    }
+
+    /*
+     * Check if burst is a RACH burst
+     */
+    bool trx_burst_if_impl::detect_rach(uint8_t *burst)
+    {
+      // Compare synchronization sequence
+      for (int i = 0; i < 41; i++)
+        if (burst[i + 8] != rach_synch_seq[i])
+          return false;
+
+      // Make sure TB and GP are filled by 0x00
+      for (int i = 0; i < 63; i++)
+        if (burst[i + 85] != 0x00)
+          return false;
+
+      return true;
+    }
+
+    /*
+     * Create an UDP payload with burst bits
+     * and some channel data.
+     */
+    void
+    trx_burst_if_impl::burst_pack(pmt::pmt_t msg, uint8_t *buf)
+    {
+      pmt::pmt_t header_plus_burst = pmt::cdr(msg);
+
+      // Extract GSMTAP header from message
+      gsmtap_hdr *header = (gsmtap_hdr *)
+        pmt::blob_data(header_plus_burst);
+
+      // Pack timeslot index
+      buf[0] = header->timeslot;
+
+      // Extract frame number
+      uint32_t frame_nr = be32toh(header->frame_number);
+
+      // Pack frame number
+      buf[1] = (frame_nr >> 24) & 0xff;
+      buf[2] = (frame_nr >> 16) & 0xff;
+      buf[3] = (frame_nr >>  8) & 0xff;
+      buf[4] = (frame_nr >>  0) & 0xff;
+
+      // Pack RSSI (-dBm)
+      buf[5] = -(uint8_t) header->signal_dbm;
+
+      // Pack correlator timing offset (TOA)
+      // FIXME: where to find this value?
+      buf[6] = 0;
+      buf[7] = 0;
+
+      // Extract bits {0..1} from message
+      // Despite GR-GSM uses int8_t, they are not real sbits {-127..127}
+      uint8_t *burst = (uint8_t *)
+        (pmt::blob_data(header_plus_burst)) + sizeof(gsmtap_hdr);
+
+      // Convert to transceiver interface specific bits {255..0}
+      for (int i = 0; i < 148; i++)
+        buf[8 + i] = burst[i] ? 255 : 0;
+
+      // Fill two unused bytes
+      buf[156] = 0x00;
+      buf[157] = 0x00;
+    }
+
+    void
+    trx_burst_if_impl::handle_dl_burst(pmt::pmt_t msg)
+    {
+      // 8 bytes of header + 148 bytes of burst
+      // + two unused, but required bytes
+      // otherwise bursts would be rejected
+      uint8_t buf[158];
+
+      // Compose a new UDP payload with burst
+      burst_pack(msg, buf);
+
+      // Send a burst
+      d_data_sock->udp_send(buf, 158);
+    }
+
+    void
+    trx_burst_if_impl::handle_ul_burst(uint8_t *payload, size_t len)
+    {
+      // Check length according to the protocol
+      if (len != 154)
+        return;
+
+      /* Make sure TS index is correct */
+      if (payload[0] >= 8)
+        return;
+
+      /* Unpack and check frame number */
+      uint32_t fn = (payload[1] << 24)
+        | (payload[2] << 16)
+        | (payload[3] << 8)
+        | payload[4];
+
+      if (fn >= 2715648)
+        return;
+
+      // Prepare a buffer for GSMTAP header and burst
+      uint8_t buf[sizeof(gsmtap_hdr) + BURST_SIZE];
+
+      // Set up pointer to GSMTAP header structure
+      struct gsmtap_hdr *header = (struct gsmtap_hdr *) buf;
+      memset(header, 0x00, sizeof(struct gsmtap_hdr));
+
+      // Fill in basic info
+      header->version = GSMTAP_VERSION;
+      header->hdr_len = sizeof(gsmtap_hdr) / 4;
+      header->type = GSMTAP_TYPE_UM_BURST;
+
+      // Set timeslot index and frame number
+      header->timeslot = payload[0];
+      header->frame_number = htobe32(fn);
+
+      // Check if one is a RACH burst
+      header->sub_type = detect_rach(payload + 6) ?
+        GSMTAP_BURST_ACCESS : GSMTAP_BURST_NORMAL;
+
+      // Copy burst bits (0 & 1) for source message
+      memcpy(buf + sizeof(gsmtap_hdr), payload + 6, BURST_SIZE);
+
+      // Create a pmt blob
+      pmt::pmt_t blob = pmt::make_blob(buf, sizeof(gsmtap_hdr) + BURST_SIZE);
+      pmt::pmt_t msg = pmt::cons(pmt::PMT_NIL, blob);
+
+      /* Send a message to the output */
+      message_port_pub(pmt::mp("bursts"), msg);
+    }
+
+  } /* namespace gsm */
+} /* namespace gr */