diff --git a/apps/trx/ctrl_if.py b/apps/trx/ctrl_if.py
new file mode 100644
index 0000000..43fc185
--- /dev/null
+++ b/apps/trx/ctrl_if.py
@@ -0,0 +1,157 @@
+#!/usr/bin/env python2
+# -*- coding: utf-8 -*-
+
+# GR-GSM based transceiver
+# Transceiver UDP interface
+#
+# (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 socket
+import select
+
+class UDPServer:
+	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)
+
+	def shutdown(self):
+		self.sock.close();
+
+	def send(self, data):
+		self.sock.sendto(data, (self.remote_addr, self.remote_port))
+
+	def handle_rx(self, data):
+		raise NotImplementedError
+
+class CTRLInterface(UDPServer):
+	def __init__(self, remote_addr, remote_port, bind_port, radio_if):
+		print("[i] Init TRX CTRL interface")
+		UDPServer.__init__(self, remote_addr, remote_port, bind_port)
+		self.tb = radio_if
+
+	def shutdown(self):
+		print("[i] Shutdown TRX CTRL interface")
+		UDPServer.shutdown(self)
+
+	def handle_rx(self, data):
+		if self.verify_req(data):
+			request = self.prepare_req(data)
+			self.parse_cmd(request)
+		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 parse_cmd(self, request):
+		response_code = "0"
+
+		# Power control
+		if self.verify_cmd(request, "POWERON", 0):
+			print("[i] Recv POWERON cmd")
+			if not self.tb.trx_started:
+				if self.tb.check_available():
+					print("[i] Starting transceiver...")
+					self.tb.trx_started = True
+					self.tb.start()
+				else:
+					print("[!] Transceiver isn't ready to start")
+					response_code = "-1"
+			else:
+				print("[!] Transceiver already started!")
+				response_code = "-1"
+		elif self.verify_cmd(request, "POWEROFF", 0):
+			print("[i] Recv POWEROFF cmd")
+			print("[i] Stopping transceiver...")
+			self.tb.trx_started = False
+			# TODO: flush all buffers between blocks
+			self.tb.stop()
+		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)
+
+		# 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)
+		elif self.verify_cmd(request, "TXTUNE", 1):
+			print("[i] Recv TXTUNE cmd")
+			# TODO: is not implemented yet
+
+		# Misc
+		elif self.verify_cmd(request, "ECHO", 0):
+			print("[i] Recv ECHO cmd")
+
+		# Wrong / unknown command
+		else:
+			print("[!] Wrong request on CTRL interface")
+			response_code = "-1"
+
+		# Anyway, we need to respond
+		self.send_response(request, response_code)
+
+	def send_response(self, request, response_code):
+		# Include status code, for example ["TXTUNE", "0", "941600"]
+		request.insert(1, response_code)
+		# 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)
diff --git a/apps/trx/radio_if.py b/apps/trx/radio_if.py
new file mode 100644
index 0000000..41eb3e8
--- /dev/null
+++ b/apps/trx/radio_if.py
@@ -0,0 +1,184 @@
+#!/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.eng_option import eng_option
+from gnuradio import eng_notation
+from gnuradio.filter import firdes
+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)
+
+		# TODO: implement configurable TS filter
+		self.gsm_ts_filter = grgsm.burst_timeslot_filter(0)
+
+		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_ts_filter, 'in'))
+
+		self.msg_connect((self.gsm_ts_filter, 'out'),
+			(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/trx.py b/apps/trx/trx.py
new file mode 100755
index 0000000..25f76cf
--- /dev/null
+++ b/apps/trx/trx.py
@@ -0,0 +1,150 @@
+#!/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 import CTRLInterface
+from radio_if import RadioInterface
+
+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)
+
+		# Init TRX CTRL interface
+		self.server = CTRLInterface(self.remote_addr,
+			self.base_port + 101, self.base_port + 1, self.radio)
+
+		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)
+
+def main():
+	Application().run()
+
+if __name__ == '__main__':
+	main()