diff --git a/apps/trx/ctrl_if.py b/apps/trx/ctrl_if.py
new file mode 100644
index 0000000..0129d7f
--- /dev/null
+++ b/apps/trx/ctrl_if.py
@@ -0,0 +1,82 @@
+#!/usr/bin/env python2
+# -*- coding: utf-8 -*-
+
+# GR-GSM based transceiver
+# CTRL interface implementation
+#
+# (C) 2016-2017 by Vadim Yanitskiy <axilirator@gmail.com>
+#
+# All Rights Reserved
+#
+# 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 2 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, write to the Free Software Foundation, Inc.,
+# 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+
+from udp_link import UDPLink
+
+class CTRLInterface(UDPLink):
+	def handle_rx(self, data):
+		if self.verify_req(data):
+			request = self.prepare_req(data)
+			rc = self.parse_cmd(request)
+
+			if type(rc) is tuple:
+				self.send_response(request, rc[0], rc[1])
+			else:
+				self.send_response(request, rc)
+		else:
+			print("[!] Wrong data on CTRL interface")
+
+	def verify_req(self, data):
+		# Verify command signature
+		return data.startswith("CMD")
+
+	def prepare_req(self, data):
+		# Strip signature, paddings and \0
+		request = data[4:].strip().strip("\0")
+		# Split into a command and arguments
+		request = request.split(" ")
+		# Now we have something like ["TXTUNE", "941600"]
+		return request
+
+	def verify_cmd(self, request, cmd, argc):
+		# Check if requested command matches
+		if request[0] != cmd:
+			return False
+
+		# And has enough arguments
+		if len(request) - 1 != argc:
+			return False
+
+		# Check if all arguments are numeric
+		for v in request[1:]:
+			if not v.isdigit():
+				return False
+
+		return True
+
+	def send_response(self, request, response_code, params = None):
+		# Include status code, for example ["TXTUNE", "0", "941600"]
+		request.insert(1, str(response_code))
+
+		# Optionally append command specific parameters
+		if params is not None:
+			request += params
+
+		# Add the response signature, and join back to string
+		response = "RSP " + " ".join(request) + "\0"
+		# Now we have something like "RSP TXTUNE 0 941600"
+		self.send(response)
+
+	def parse_cmd(self, request):
+		raise NotImplementedError
diff --git a/apps/trx/ctrl_if_bb.py b/apps/trx/ctrl_if_bb.py
new file mode 100644
index 0000000..b0d54f9
--- /dev/null
+++ b/apps/trx/ctrl_if_bb.py
@@ -0,0 +1,142 @@
+#!/usr/bin/env python2
+# -*- coding: utf-8 -*-
+
+# GR-GSM based transceiver
+# CTRL interface for OsmocomBB
+#
+# (C) 2016-2017 by Vadim Yanitskiy <axilirator@gmail.com>
+#
+# All Rights Reserved
+#
+# 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 2 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, write to the Free Software Foundation, Inc.,
+# 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+
+from ctrl_if import CTRLInterface
+
+class CTRLInterfaceBB(CTRLInterface):
+	def __init__(self, remote_addr, remote_port, bind_port, tb, pm):
+		print("[i] Init CTRL interface")
+		CTRLInterface.__init__(self, remote_addr, remote_port, bind_port)
+
+		# Set link to the follow graph (top block)
+		self.tb = tb
+		# Power measurement
+		self.pm = pm
+
+	def shutdown(self):
+		print("[i] Shutdown CTRL interface")
+		CTRLInterface.shutdown(self)
+
+	def parse_cmd(self, request):
+		# Power control
+		if self.verify_cmd(request, "POWERON", 0):
+			print("[i] Recv POWERON CMD")
+
+			# Ensure transceiver isn't working
+			if self.tb.trx_started:
+				print("[!] Transceiver already started")
+				return -1
+
+			# Ensure transceiver is ready to start
+			if not self.tb.check_available():
+				print("[!] Transceiver isn't ready to start")
+				return -1
+
+			print("[i] Starting transceiver...")
+			self.tb.trx_started = True
+			self.tb.start()
+
+			return 0
+
+		elif self.verify_cmd(request, "POWEROFF", 0):
+			print("[i] Recv POWEROFF cmd")
+
+			# TODO: flush all buffers between blocks
+			if self.tb.trx_started:
+				print("[i] Stopping transceiver...")
+				self.tb.trx_started = False
+				self.tb.stop()
+				self.tb.wait()
+
+			return 0
+
+		elif self.verify_cmd(request, "SETRXGAIN", 1):
+			print("[i] Recv SETRXGAIN cmd")
+
+			# TODO: check gain value
+			gain = int(request[1])
+			self.tb.set_gain(gain)
+
+			return 0
+
+		# Tuning Control
+		elif self.verify_cmd(request, "RXTUNE", 1):
+			print("[i] Recv RXTUNE cmd")
+
+			# TODO: check freq range
+			freq = int(request[1]) * 1000
+			self.tb.set_fc(freq)
+
+			return 0
+
+		elif self.verify_cmd(request, "TXTUNE", 1):
+			print("[i] Recv TXTUNE cmd")
+
+			# TODO: is not implemented yet
+			return 0
+
+		# Timeslot management
+		elif self.verify_cmd(request, "SETSLOT", 2):
+			print("[i] Recv SETSLOT cmd")
+
+			# Obtain TS index
+			tn = int(request[1])
+			if tn not in range(0, 8):
+				print("[!] TS index should be in range: 0..7")
+				return -1
+
+			# Ignore timeslot type for now
+			# Value 0 means 'drop all'
+			config = -1 if int(request[2]) == 0 else tn
+
+			print("[i] Configure timeslot filter to: %s"
+				% ("drop all" if config == -1 else "TS %d" % tn))
+
+			# HACK: configure built-in timeslot filter
+			self.tb.gsm_trx_if.ts_filter_set_tn(config)
+
+			return 0
+
+		# Power measurement
+		elif self.verify_cmd(request, "MEASURE", 1):
+			print("[i] Recv MEASURE cmd")
+
+			# TODO: check freq range
+			meas_freq = int(request[1]) * 1000
+
+			# HACK: send fake low power values
+			# until actual power measurement is implemented
+			meas_dbm = str(self.pm.measure(meas_freq))
+
+			return (0, [meas_dbm])
+
+		# Misc
+		elif self.verify_cmd(request, "ECHO", 0):
+			print("[i] Recv ECHO cmd")
+			return 0
+
+		# Wrong / unknown command
+		else:
+			print("[!] Wrong request on CTRL interface")
+			return -1
diff --git a/apps/trx/fake_pm.py b/apps/trx/fake_pm.py
new file mode 100644
index 0000000..1d76916
--- /dev/null
+++ b/apps/trx/fake_pm.py
@@ -0,0 +1,53 @@
+#!/usr/bin/env python2
+# -*- coding: utf-8 -*-
+
+# Virtual Um-interface (fake transceiver)
+# Power measurement emulation for BB
+#
+# (C) 2017 by Vadim Yanitskiy <axilirator@gmail.com>
+#
+# All Rights Reserved
+#
+# 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 2 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, write to the Free Software Foundation, Inc.,
+# 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+
+from random import randint
+
+class FakePM:
+	# Freq. list for good power level
+	bts_list = []
+
+	def __init__(self, noise_min, noise_max, bts_min, bts_max):
+		# Save power level ranges
+		self.noise_min = noise_min
+		self.noise_max = noise_max
+		self.bts_min = bts_min
+		self.bts_max = bts_max
+
+	def measure(self, bts):
+		if bts in self.bts_list:
+			return randint(self.bts_min, self.bts_max)
+		else:
+			return randint(self.noise_min, self.noise_max)
+
+	def update_bts_list(self, new_list):
+		self.bts_list = new_list
+
+	def add_bts_list(self, add_list):
+		self.bts_list += add_list
+
+	def del_bts_list(self, del_list):
+		for item in del_list:
+			if item in self.bts_list:
+				self.bts_list.remove(item)
diff --git a/apps/trx/grgsm_trx.py b/apps/trx/grgsm_trx.py
new file mode 100755
index 0000000..fbc9350
--- /dev/null
+++ b/apps/trx/grgsm_trx.py
@@ -0,0 +1,155 @@
+#!/usr/bin/env python2
+# -*- coding: utf-8 -*-
+
+# GR-GSM based transceiver
+#
+# (C) 2016-2017 by Vadim Yanitskiy <axilirator@gmail.com>
+#
+# All Rights Reserved
+#
+# 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 2 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, write to the Free Software Foundation, Inc.,
+# 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+
+import signal
+import getopt
+import sys
+
+from ctrl_if_bb import CTRLInterfaceBB
+from radio_if import RadioInterface
+from fake_pm import FakePM
+
+COPYRIGHT = \
+	"Copyright (C) 2016-2017 by Vadim Yanitskiy <axilirator@gmail.com>\n" \
+	"License GPLv2+: GNU GPL version 2 or later " \
+	"<http://gnu.org/licenses/gpl.html>\n" \
+	"This is free software: you are free to change and redistribute it.\n" \
+	"There is NO WARRANTY, to the extent permitted by law.\n"
+
+class Application:
+	# Application variables
+	remote_addr = "127.0.0.1"
+	base_port = 5700
+
+	# PHY specific
+	phy_sample_rate = 2000000
+	phy_subdev_spec = False
+	phy_gain = 30
+	phy_args = ""
+	phy_ppm = 0
+
+	def __init__(self):
+		self.print_copyright()
+		self.parse_argv()
+
+		# Set up signal handlers
+		signal.signal(signal.SIGINT, self.sig_handler)
+
+	def run(self):
+		# Init Radio interface
+		self.radio = RadioInterface(self.phy_args, self.phy_subdev_spec,
+			self.phy_sample_rate, self.phy_gain, self.phy_ppm,
+			self.remote_addr, self.base_port)
+
+		# Power measurement emulation
+		# Noise: -120 .. -105
+		# BTS: -75 .. -50
+		self.pm = FakePM(-120, -105, -75, -50)
+
+		# Init TRX CTRL interface
+		self.server = CTRLInterfaceBB(self.remote_addr,
+			self.base_port + 101, self.base_port + 1,
+			self.radio, self.pm)
+
+		print("[i] Init complete")
+
+		# Enter main loop
+		while True:
+			self.server.loop()
+
+	def shutdown(self):
+		print("[i] Shutting down...")
+		self.server.shutdown()
+		self.radio.shutdown()
+
+	def print_copyright(self):
+		print(COPYRIGHT)
+
+	def print_help(self):
+		s  = " Usage: " + sys.argv[0] + " [options]\n\n" \
+			 " Some help...\n" \
+			 "  -h --help         this text\n\n"
+
+		# TRX specific
+		s += " TRX interface specific\n" \
+			 "  -s --remote-addr  Set remote address (default 127.0.0.1)\n" \
+			 "  -p --base-port    Set base port number (default 5700)\n\n"
+
+		# PHY specific
+		s += " Radio interface specific\n" \
+			 "  -a --device-args  Set device arguments\n" \
+			 "  -s --sample-rate  Set PHY sample rate (default 2000000)\n" \
+			 "  -S --subdev-spec  Set PHY sub-device specification\n" \
+			 "  -g --gain         Set PHY gain (default 30)\n" \
+			 "     --ppm          Set PHY frequency correction (default 0)\n"
+
+		print(s)
+
+	def parse_argv(self):
+		try:
+			opts, args = getopt.getopt(sys.argv[1:],
+				"a:p:i:s:S:g:h",
+				["help", "remote-addr=", "base-port=", "device-args=",
+				"gain=", "subdev-spec=", "sample-rate=", "ppm="])
+		except getopt.GetoptError as err:
+			# Print(help and exit)
+			self.print_help()
+			print("[!] " + str(err))
+			sys.exit(2)
+
+		for o, v in opts:
+			if o in ("-h", "--help"):
+				self.print_help()
+				sys.exit(2)
+
+			# TRX specific
+			elif o in ("-i", "--remote-addr"):
+				self.remote_addr = v
+			elif o in ("-p", "--base-port"):
+				if int(v) >= 0 and int(v) <= 65535:
+					self.base_port = int(v)
+				else:
+					print("[!] The port number should be in range [0-65536]")
+					sys.exit(2)
+
+			# PHY specific
+			elif o in ("-a", "--device-args"):
+				self.phy_args = v
+			elif o in ("-g", "--gain"):
+				self.phy_gain = int(v)
+			elif o in ("-S", "--subdev-spec"):
+				self.phy_subdev_spec = v
+			elif o in ("-s", "--sample-rate"):
+				self.phy_sample_rate = int(v)
+			elif o in ("--ppm"):
+				self.phy_ppm = int(v)
+
+	def sig_handler(self, signum, frame):
+		print("Signal %d received" % signum)
+		if signum is signal.SIGINT:
+			self.shutdown()
+			sys.exit(0)
+
+if __name__ == '__main__':
+	app = Application()
+	app.run()
diff --git a/apps/trx/radio_if.py b/apps/trx/radio_if.py
new file mode 100644
index 0000000..c162f69
--- /dev/null
+++ b/apps/trx/radio_if.py
@@ -0,0 +1,175 @@
+#!/usr/bin/env python2
+# -*- coding: utf-8 -*-
+
+# GR-GSM based transceiver
+# Follow graph implementation
+#
+# (C) 2016-2017 by Vadim Yanitskiy <axilirator@gmail.com>
+#
+# All Rights Reserved
+#
+# 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 2 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, write to the Free Software Foundation, Inc.,
+# 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+
+import pmt
+import time
+import grgsm
+import osmosdr
+
+from math import pi
+
+from gnuradio import blocks
+from gnuradio import gr
+
+class RadioInterface(gr.top_block):
+	# PHY specific variables
+	samp_rate = 2000000
+	shiftoff = 400e3
+	subdev_spec = "" # TODO: use it
+	device_args = ""
+	fc = 941.6e6 # TODO: set ARFCN to 0?
+	gain = 30
+	ppm = 0
+
+	# Application state flags
+	trx_started = False
+	fc_set = False
+
+	def __init__(self, phy_args, phy_subdev_spec,
+				phy_sample_rate, phy_gain, phy_ppm,
+				trx_remote_addr, trx_base_port):
+		print("[i] Init Radio interface")
+
+		# TRX block specific variables
+		self.trx_remote_addr = trx_remote_addr
+		self.trx_base_port = trx_base_port
+
+		# PHY specific variables
+		self.subdev_spec = phy_subdev_spec
+		self.samp_rate = phy_sample_rate
+		self.device_args = phy_args
+		self.gain = phy_gain
+		self.ppm = phy_ppm
+
+		gr.top_block.__init__(self, "GR-GSM TRX")
+		shift_fc = self.fc - self.shiftoff
+
+		##################################################
+		# PHY Definition
+		##################################################
+		self.phy = osmosdr.source(
+			args = "numchan=%d %s" % (1, self.device_args))
+
+		self.phy.set_bandwidth(250e3 + abs(self.shiftoff), 0)
+		self.phy.set_center_freq(shift_fc, 0)
+		self.phy.set_sample_rate(self.samp_rate)
+		self.phy.set_freq_corr(self.ppm, 0)
+		self.phy.set_iq_balance_mode(2, 0)
+		self.phy.set_dc_offset_mode(2, 0)
+		self.phy.set_gain_mode(False, 0)
+		self.phy.set_gain(self.gain, 0)
+		self.phy.set_if_gain(20, 0)
+		self.phy.set_bb_gain(20, 0)
+		self.phy.set_antenna("", 0)
+
+		##################################################
+		# GR-GSM Magic
+		##################################################
+		self.blocks_rotator = blocks.rotator_cc(
+			-2 * pi * self.shiftoff / self.samp_rate)
+
+		self.gsm_input = grgsm.gsm_input(
+			ppm = self.ppm, osr = 4, fc = self.fc,
+			samp_rate_in = self.samp_rate)
+
+		self.gsm_receiver = grgsm.receiver(4, ([0]), ([]))
+
+		self.gsm_clck_ctrl = grgsm.clock_offset_control(
+			shift_fc, self.samp_rate, osr = 4)
+
+		self.gsm_trx_if = grgsm.trx(self.trx_remote_addr,
+			str(self.trx_base_port))
+
+		##################################################
+		# Connections
+		##################################################
+		self.connect((self.phy, 0), (self.blocks_rotator, 0))
+		self.connect((self.blocks_rotator, 0), (self.gsm_input, 0))
+		self.connect((self.gsm_input, 0), (self.gsm_receiver, 0))
+
+		self.msg_connect((self.gsm_receiver, 'measurements'),
+			(self.gsm_clck_ctrl, 'measurements'))
+
+		self.msg_connect((self.gsm_clck_ctrl, 'ctrl'),
+			(self.gsm_input, 'ctrl_in'))
+
+		self.msg_connect((self.gsm_receiver, 'C0'),
+			(self.gsm_trx_if, 'bursts'))
+
+	def check_available(self):
+		return self.fc_set
+
+	def shutdown(self):
+		print("[i] Shutdown Radio interface")
+		self.stop()
+		self.wait()
+
+	def get_args(self):
+		return self.args
+
+	def set_args(self, args):
+		self.args = args
+
+	def get_fc(self):
+		return self.fc
+
+	def set_fc(self, fc):
+		self.phy.set_center_freq(fc - self.shiftoff, 0)
+		self.gsm_input.set_fc(fc)
+		self.fc_set = True
+		self.fc = fc
+
+	def get_gain(self):
+		return self.gain
+
+	def set_gain(self, gain):
+		self.phy.set_gain(gain, 0)
+		self.gain = gain
+
+	def get_ppm(self):
+		return self.ppm
+
+	def set_ppm(self, ppm):
+		self.rtlsdr_source_0.set_freq_corr(ppm, 0)
+		self.ppm = ppm
+
+	def get_samp_rate(self):
+		return self.samp_rate
+
+	def set_samp_rate(self, samp_rate):
+		self.blocks_rotator.set_phase_inc(
+			-2 * pi * self.shiftoff / samp_rate)
+		self.gsm_input.set_samp_rate_in(samp_rate)
+		self.phy.set_sample_rate(samp_rate)
+		self.samp_rate = samp_rate
+
+	def get_shiftoff(self):
+		return self.shiftoff
+
+	def set_shiftoff(self, shiftoff):
+		self.blocks_rotator.set_phase_inc(
+			-2 * pi * shiftoff / self.samp_rate)
+		self.phy.set_bandwidth(250e3 + abs(shiftoff), 0)
+		self.phy.set_center_freq(self.fc - shiftoff, 0)
+		self.shiftoff = shiftoff
diff --git a/apps/trx/udp_link.py b/apps/trx/udp_link.py
new file mode 100644
index 0000000..0d90ec9
--- /dev/null
+++ b/apps/trx/udp_link.py
@@ -0,0 +1,56 @@
+#!/usr/bin/env python2
+# -*- coding: utf-8 -*-
+
+# GR-GSM based transceiver
+# UDP link implementation
+#
+# (C) 2017 by Vadim Yanitskiy <axilirator@gmail.com>
+#
+# All Rights Reserved
+#
+# 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 2 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, write to the Free Software Foundation, Inc.,
+# 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+
+import socket
+import select
+
+class UDPLink:
+	def __init__(self, remote_addr, remote_port, bind_port):
+		self.sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
+		self.sock.bind(('0.0.0.0', bind_port))
+		self.sock.setblocking(0)
+
+		# Save remote info
+		self.remote_addr = remote_addr
+		self.remote_port = remote_port
+
+	def loop(self):
+		r_event, w_event, x_event = select.select([self.sock], [], [])
+
+		# Check for incoming data
+		if self.sock in r_event:
+			data, addr = self.sock.recvfrom(128)
+			self.handle_rx(data.decode())
+
+	def shutdown(self):
+		self.sock.close();
+
+	def send(self, data):
+		if type(data) not in [bytearray, bytes]:
+			data = data.encode()
+
+		self.sock.sendto(data, (self.remote_addr, self.remote_port))
+
+	def handle_rx(self, data):
+		raise NotImplementedError
diff --git a/grc/CMakeLists.txt b/grc/CMakeLists.txt
index 2b94539..045d6a5 100644
--- a/grc/CMakeLists.txt
+++ b/grc/CMakeLists.txt
@@ -23,6 +23,7 @@
 add_subdirectory(receiver)
 add_subdirectory(flow_control)
 add_subdirectory(misc_utils)
+add_subdirectory(trx_interface)
 install(FILES
     gsm_block_tree.xml DESTINATION share/gnuradio/grc/blocks
 )
diff --git a/grc/trx_interface/CMakeLists.txt b/grc/trx_interface/CMakeLists.txt
new file mode 100644
index 0000000..752b7a7
--- /dev/null
+++ b/grc/trx_interface/CMakeLists.txt
@@ -0,0 +1,22 @@
+# Copyright 2011,2012 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.
+
+install(FILES
+    gsm_trx.xml DESTINATION share/gnuradio/grc/blocks
+)
diff --git a/grc/trx_interface/gsm_trx.xml b/grc/trx_interface/gsm_trx.xml
new file mode 100644
index 0000000..cbe268c
--- /dev/null
+++ b/grc/trx_interface/gsm_trx.xml
@@ -0,0 +1,75 @@
+<?xml version="1.0"?>
+<block>
+  <name>TRX Interface</name>
+  <key>grgsm_trx_interface</key>
+  <import>import grgsm</import>
+  <make>grgsm.trx($remote_addr, $base_port)</make>
+
+  <param>
+    <name>base_port</name>
+    <key>base_port</key>
+    <value>5700</value>
+    <type>string</type>
+  </param>
+
+  <param>
+    <name>remote_addr</name>
+    <key>remote_addr</key>
+    <value>127.0.0.1</value>
+    <type>string</type>
+  </param>
+
+  <sink>
+    <name>bursts</name>
+    <type>message</type>
+    <optional>1</optional>
+  </sink>
+
+  <source>
+    <name>bursts</name>
+    <type>message</type>
+    <optional>1</optional>
+  </source>
+
+  <doc>
+      OsmoTRX like UDP interface for external applications.
+
+      There are three UDP sockets: CLCK, CTRL and DATA.
+      Give a base port B (5700 by default), the SCH clock
+      interface is at port P=B. The TRX-side control interface
+      is on port P=B+100+1 and the data interface is on an odd
+      numbered port P=B+100+2.
+
+      Indications on the SCH Clock Interface (CLCK)
+      The SCH clock interface is output only (from the radio).
+      CLOCK gives the current value of the BTS clock to
+      be used by external applications. The indications are
+      sent whenever a transmission packet arrives that is too
+      late or too early.
+
+      Commands on Control Interface (CTRL)
+      The control interface uses a command-response protocol.
+      Commands are NULL-terminated ASCII strings. Each command
+      has a corresponding response. This interface isn't handled
+      by this particular block, and should be implemented outside.
+
+      Messages on the Data Interface
+      Messages on the data interface carry one radio burst per
+      UDP message.
+
+      Received Data Burst:
+      1 byte timeslot index
+      4 bytes GSM frame number, big endian
+      1 byte RSSI in -dBm
+      2 bytes correlator timing offset in 1/256 symbol steps,
+          2's-comp, big endian
+      148 bytes soft symbol estimates, 0 -&gt; definite "0",
+          255 -&gt; definite "1"
+
+      Transmit Data Burst:
+      1 byte timeslot index
+      4 bytes GSM frame number, big endian
+      1 byte transmit level wrt ARFCN max, -dB (attenuation)
+      148 bytes output symbol values, 0 &amp; 1
+  </doc>
+</block>
diff --git a/include/grgsm/CMakeLists.txt b/include/grgsm/CMakeLists.txt
index d9b032d..1ce9134 100644
--- a/include/grgsm/CMakeLists.txt
+++ b/include/grgsm/CMakeLists.txt
@@ -35,3 +35,4 @@
 add_subdirectory(misc_utils)
 add_subdirectory(qa_utils)
 add_subdirectory(flow_control)
+add_subdirectory(trx_interface)
diff --git a/include/grgsm/trx_interface/CMakeLists.txt b/include/grgsm/trx_interface/CMakeLists.txt
new file mode 100644
index 0000000..8d35ef7
--- /dev/null
+++ b/include/grgsm/trx_interface/CMakeLists.txt
@@ -0,0 +1,25 @@
+# Copyright 2011,2012 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.
+
+########################################################################
+# Install public header files
+########################################################################
+install(FILES
+    trx.h DESTINATION include/grgsm/trx_interface
+)
diff --git a/include/grgsm/trx_interface/trx.h b/include/grgsm/trx_interface/trx.h
new file mode 100644
index 0000000..997ef62
--- /dev/null
+++ b/include/grgsm/trx_interface/trx.h
@@ -0,0 +1,63 @@
+/* -*- 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_H
+#define INCLUDED_GRGSM_TRX_H
+
+#include <grgsm/api.h>
+#include <gnuradio/sync_block.h>
+
+namespace gr {
+  namespace grgsm {
+
+    /*!
+     * \brief <+description of block+>
+     * \ingroup grgsm
+     *
+     */
+    class GRGSM_API trx : virtual public gr::block
+    {
+     public:
+      typedef boost::shared_ptr<trx> sptr;
+
+      /*!
+       * \brief Return a shared_ptr to a new instance of grgsm::trx.
+       *
+       * To avoid accidental use of raw pointers, grgsm::trx's
+       * constructor is in a private implementation
+       * class. grgsm::trx::make is the public interface for
+       * creating new instances.
+       */
+      static sptr make(
+        const std::string &remote_addr,
+        const std::string &base_port);
+
+      /* Expose internal timeslot filter API */
+      virtual void ts_filter_set_tn(int tn) = 0;
+      virtual int ts_filter_get_tn(void) = 0;
+    };
+
+  } // namespace grgsm
+} // namespace gr
+
+#endif /* INCLUDED_GRGSM_TRX_H */
+
diff --git a/lib/CMakeLists.txt b/lib/CMakeLists.txt
index e6dd115..c6bba6e 100644
--- a/lib/CMakeLists.txt
+++ b/lib/CMakeLists.txt
@@ -70,6 +70,8 @@
 add_subdirectory(misc_utils)
 add_subdirectory(qa_utils)
 add_subdirectory(receiver)
+add_subdirectory(transmitter)
+add_subdirectory(trx_interface)
 
 ########################################################################
 # Setup library
diff --git a/lib/trx_interface/trx_impl.cc b/lib/trx_interface/trx_impl.cc
new file mode 100644
index 0000000..2068da3
--- /dev/null
+++ b/lib/trx_interface/trx_impl.cc
@@ -0,0 +1,273 @@
+/* -*- 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"
+
+#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 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"));
+        message_port_register_out(pmt::mp("bursts"));
+
+        // Bind a port handler
+        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 & CLCK interfaces
+        d_data_sock = new udp_socket(remote_addr,
+          data_src_port, data_dst_port, DATA_IF_MTU);
+        d_clck_sock = new udp_socket(remote_addr,
+          clck_src_port, clck_dst_port, DATA_IF_MTU);
+
+        // Bind DATA interface handler
+        d_data_sock->udp_rx_handler = boost::bind(
+          &trx_impl::handle_ul_burst, this, _1, _2);
+
+        // Init timeslot filter
+        d_ts_filter_tn = -1;
+    }
+
+    /*
+     * Our virtual destructor.
+     */
+    trx_impl::~trx_impl()
+    {
+        // Release all UDP sockets and free memory
+        delete d_data_sock;
+        delete d_clck_sock;
+    }
+
+    /*
+     * Timeslot filter API (getter and setter)
+     */
+    void
+    trx_impl::ts_filter_set_tn(int tn)
+    {
+      d_ts_filter_tn = (tn >= 0 && tn <= 7) ? tn : -1;
+    }
+
+    int
+    trx_impl::ts_filter_get_tn(void)
+    {
+      return d_ts_filter_tn;
+    }
+
+    /*
+     * Check if burst is a RACH burst
+     */
+    bool trx_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 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;
+
+      // Fill two unused bytes
+      buf[156] = 0x00;
+      buf[157] = 0x00;
+    }
+
+    void
+    trx_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);
+
+      // Timeslot filter
+      if (d_ts_filter_tn != -1 && buf[0] != d_ts_filter_tn)
+        return;
+
+      // Send a burst
+      d_data_sock->udp_send(buf, 158);
+    }
+
+    void
+    trx_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 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..19e4848
--- /dev/null
+++ b/lib/trx_interface/trx_impl.h
@@ -0,0 +1,61 @@
+/* -*- 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;
+      int d_ts_filter_tn;
+
+      bool detect_rach(uint8_t *burst);
+      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();
+
+      /* Timeslot filter API */
+      void ts_filter_set_tn(int tn);
+      int ts_filter_get_tn(void);
+
+      void handle_dl_burst(pmt::pmt_t msg);
+      void handle_ul_burst(uint8_t *payload, size_t len);
+    };
+
+  } // 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..be4bb66
--- /dev/null
+++ b/lib/trx_interface/udp_socket.cc
@@ -0,0 +1,119 @@
+/* -*- 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,
+      size_t mtu)
+    {
+      // Resize receive buffer according to MTU value
+      d_rxbuf.resize(mtu);
+
+      // 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;
+
+      // Call incoming data handler
+      if (udp_rx_handler != NULL)
+        udp_rx_handler((uint8_t *) &d_rxbuf[0], bytes_transferred);
+
+      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..5bcc42b
--- /dev/null
+++ b/lib/trx_interface/udp_socket.h
@@ -0,0 +1,69 @@
+/* -*- 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/function.hpp>
+#include <boost/array.hpp>
+#include <boost/asio.hpp>
+#include <boost/bind.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,
+        size_t mtu);
+      ~udp_socket();
+
+      void udp_send(uint8_t *data, size_t len);
+      boost::function<void (uint8_t *, size_t)> udp_rx_handler;
+    };
+
+  } /* namespace blocks */
+} /* namespace gr */
+
+#endif /* INCLUDED_GRGSM_TRX_UDP_SOCKET_H */
diff --git a/swig/grgsm_swig.i b/swig/grgsm_swig.i
index 66615e6..a67e264 100644
--- a/swig/grgsm_swig.i
+++ b/swig/grgsm_swig.i
@@ -64,6 +64,7 @@
 #include "grgsm/misc_utils/message_file_source.h"
 #include "grgsm/misc_utils/msg_to_tag.h"
 #include "grgsm/misc_utils/controlled_fractional_resampler_cc.h"
+#include "grgsm/trx_interface/trx.h"
 %}
 
 %include "constants.i"
@@ -143,4 +144,5 @@
 GR_SWIG_BLOCK_MAGIC2(gsm, message_source);
 %include "grgsm/qa_utils/message_sink.h"
 GR_SWIG_BLOCK_MAGIC2(gsm, message_sink);
-
+%include "grgsm/trx_interface/trx.h"
+GR_SWIG_BLOCK_MAGIC2(grgsm, trx);