diff --git a/lib/CMakeLists.txt b/lib/CMakeLists.txt
index 680c41f..5d3f461 100644
--- a/lib/CMakeLists.txt
+++ b/lib/CMakeLists.txt
@@ -69,6 +69,8 @@
     qa_utils/message_source_impl.cc
     qa_utils/message_sink_impl.cc
     decryption/decryption_impl.cc
+    trx_interface/udp_socket.cc
+    trx_interface/trx_impl.cc
 )
 
 
diff --git a/lib/trx_interface/trx_impl.cc b/lib/trx_interface/trx_impl.cc
new file mode 100644
index 0000000..9b9c484
--- /dev/null
+++ b/lib/trx_interface/trx_impl.cc
@@ -0,0 +1,154 @@
+/* -*- 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 "udp_socket.h"
+#include "trx_impl.h"
+
+namespace gr {
+  namespace grgsm {
+
+    trx::sptr
+    trx::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_impl(remote_addr, base_port_int));
+    }
+
+    /*
+     * The private constructor
+     */
+    trx_impl::trx_impl(const std::string &remote_addr, int base_port)
+    : gr::block("trx",
+        gr::io_signature::make(0, 0, 0),
+        gr::io_signature::make(0, 0, 0))
+    {
+        message_port_register_in(pmt::mp("bursts"));
+        set_msg_handler(pmt::mp("bursts"),
+          boost::bind(&trx_impl::handle_dl_burst, this, _1));
+
+        // Prepare port numbers
+        std::string clck_src_port = boost::lexical_cast<std::string> (base_port + 0);
+        std::string clck_dst_port = boost::lexical_cast<std::string> (base_port + 100);
+        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);
+        d_clck_sock = new udp_socket(remote_addr, clck_src_port, clck_dst_port);
+    }
+
+    /*
+     * Our virtual destructor.
+     */
+    trx_impl::~trx_impl()
+    {
+        // Release all UDP sockets and free memory
+        delete d_data_sock;
+        delete d_clck_sock;
+    }
+
+    /*
+     * Create an UDP payload with clock indication
+     */
+    void
+    trx_impl::clck_ind_send(uint32_t frame_nr)
+    {
+      char buf[20];
+      size_t n;
+
+      n = snprintf(buf, 20, "IND CLOCK %u", frame_nr);
+      d_clck_sock->udp_send((uint8_t *) buf, n + 1);
+    }
+
+    /*
+     * Create an UDP payload with burst bits
+     * and some channel data.
+     */
+    void
+    trx_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);
+
+      // HACK: send clock indications every 51-th frame
+      if (frame_nr % 51 == 0)
+        clck_ind_send(frame_nr);
+
+      // 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;
+    }
+
+    void
+    trx_impl::handle_dl_burst(pmt::pmt_t msg)
+    {
+      // 8 bytes of header + 148 bytes of burst
+      uint8_t buf[156];
+
+      // Compose a new UDP payload with burst
+      burst_pack(msg, buf);
+
+      // Send a burst
+      d_data_sock->udp_send(buf, 156);
+    }
+
+  } /* namespace grgsm */
+} /* namespace gr */
diff --git a/lib/trx_interface/trx_impl.h b/lib/trx_interface/trx_impl.h
new file mode 100644
index 0000000..41a4788
--- /dev/null
+++ b/lib/trx_interface/trx_impl.h
@@ -0,0 +1,54 @@
+/* -*- 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.
+ * 
+ */
+
+#ifndef INCLUDED_GRGSM_TRX_IMPL_H
+#define INCLUDED_GRGSM_TRX_IMPL_H
+
+#include <stddef.h>
+
+#include <grgsm/gsmtap.h>
+#include <grgsm/trx_interface/trx.h>
+
+namespace gr {
+  namespace grgsm {
+
+    class trx_impl : public trx
+    {
+     private:
+      udp_socket *d_data_sock;
+      udp_socket *d_clck_sock;
+
+      void clck_ind_send(uint32_t frame_nr);
+      void burst_pack(pmt::pmt_t msg, uint8_t *buf);
+
+     public:
+      trx_impl(const std::string &remote_addr, int base_port);
+      ~trx_impl();
+
+      void handle_dl_burst(pmt::pmt_t msg);
+    };
+
+  } // namespace grgsm
+} // namespace gr
+
+#endif /* INCLUDED_GRGSM_TRX_IMPL_H */
+
diff --git a/lib/trx_interface/udp_socket.cc b/lib/trx_interface/udp_socket.cc
new file mode 100644
index 0000000..4bbf206
--- /dev/null
+++ b/lib/trx_interface/udp_socket.cc
@@ -0,0 +1,117 @@
+/* -*- c++ -*- */
+/*
+ * Copyright 2013 Free Software Foundation, Inc.
+ *
+ * This file is part of GNU Radio
+ *
+ * GNU Radio 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.
+ *
+ * GNU Radio 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 GNU Radio; 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/thread/thread.h>
+#include <gnuradio/io_signature.h>
+#include <gnuradio/blocks/pdu.h>
+#include <pmt/pmt.h>
+
+#include <boost/lexical_cast.hpp>
+#include "udp_socket.h"
+
+using boost::asio::ip::udp;
+
+namespace gr {
+  namespace grgsm {
+
+    udp_socket::udp_socket(
+      const std::string &remote_addr,
+      const std::string &src_port,
+      const std::string &dst_port)
+    {
+      // Resolve remote host address
+      udp::resolver resolver(d_io_service);
+
+      udp::resolver::query rx_query(
+        udp::v4(), remote_addr, src_port,
+        boost::asio::ip::resolver_query_base::passive);
+      udp::resolver::query tx_query(
+        udp::v4(), remote_addr, dst_port,
+        boost::asio::ip::resolver_query_base::passive);
+
+      d_udp_endpoint_rx = *resolver.resolve(rx_query);
+      d_udp_endpoint_tx = *resolver.resolve(tx_query);
+
+      // Create a socket
+      d_udp_socket.reset(new udp::socket(d_io_service, d_udp_endpoint_rx));
+
+      // Setup read handler
+      d_udp_socket->async_receive_from(
+        boost::asio::buffer(d_rxbuf), d_udp_endpoint_rx,
+        boost::bind(&udp_socket::handle_udp_read, this,
+          boost::asio::placeholders::error,
+          boost::asio::placeholders::bytes_transferred));
+
+      // Start server
+      d_thread = gr::thread::thread(
+        boost::bind(&udp_socket::run_io_service, this));
+    }
+
+    udp_socket::~udp_socket()
+    {
+      // Stop server
+      d_io_service.stop();
+      d_thread.interrupt();
+      d_thread.join();
+    }
+
+    void
+    udp_socket::run_io_service(void)
+    {
+      d_io_service.run();
+    }
+
+    void
+    udp_socket::udp_send(uint8_t *data, size_t len)
+    {
+      d_udp_socket->send_to(
+        boost::asio::buffer(data, len),
+        d_udp_endpoint_tx);
+    }
+
+    void
+    udp_socket::handle_udp_read(
+      const boost::system::error_code& error,
+      size_t bytes_transferred)
+    {
+      if (error)
+        return;
+
+      pmt::pmt_t vector = pmt::init_u8vector(bytes_transferred,
+        (const uint8_t *) &d_rxbuf[0]);
+      pmt::pmt_t pdu = pmt::cons(pmt::PMT_NIL, vector);
+
+      // TODO: call handler here
+
+      d_udp_socket->async_receive_from(
+        boost::asio::buffer(d_rxbuf), d_udp_endpoint_rx,
+        boost::bind(&udp_socket::handle_udp_read, this,
+          boost::asio::placeholders::error,
+          boost::asio::placeholders::bytes_transferred));
+    }
+
+  } /* namespace blocks */
+}/* namespace gr */
diff --git a/lib/trx_interface/udp_socket.h b/lib/trx_interface/udp_socket.h
new file mode 100644
index 0000000..2f424c9
--- /dev/null
+++ b/lib/trx_interface/udp_socket.h
@@ -0,0 +1,65 @@
+/* -*- c++ -*- */
+/*
+ * Copyright 2013 Free Software Foundation, Inc.
+ *
+ * This file is part of GNU Radio
+ *
+ * GNU Radio 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.
+ *
+ * GNU Radio 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 GNU Radio; see the file COPYING.  If not, write to
+ * the Free Software Foundation, Inc., 51 Franklin Street,
+ * Boston, MA 02110-1301, USA.
+ */
+
+#ifndef INCLUDED_GRGSM_TRX_UDP_SOCKET_H
+#define INCLUDED_GRGSM_TRX_UDP_SOCKET_H
+
+#include <gnuradio/thread/thread.h>
+
+#include <boost/array.hpp>
+#include <boost/asio.hpp>
+#include <pmt/pmt.h>
+
+namespace gr {
+  namespace grgsm {
+
+    class udp_socket
+    {
+    private:
+      boost::asio::io_service d_io_service;
+      std::vector<char> d_rxbuf;
+      gr::thread::thread d_thread;
+      bool d_started;
+      bool d_finished;
+
+      boost::asio::ip::udp::endpoint d_udp_endpoint_rx;
+      boost::asio::ip::udp::endpoint d_udp_endpoint_tx;
+      boost::shared_ptr<boost::asio::ip::udp::socket> d_udp_socket;
+
+      void handle_udp_read(const boost::system::error_code& error,
+        size_t bytes_transferred);
+      void run_io_service(void);
+
+    public:
+      udp_socket(
+        const std::string &remote_addr,
+        const std::string &src_port,
+        const std::string &dst_port);
+      ~udp_socket();
+
+      void udp_send(uint8_t *data, size_t len);
+    };
+
+  } /* namespace blocks */
+} /* namespace gr */
+
+#endif /* INCLUDED_GRGSM_TRX_UDP_SOCKET_H */