diff --git a/tnc/data_handler.py b/tnc/data_handler.py
index 52cba795..f96492eb 100644
--- a/tnc/data_handler.py
+++ b/tnc/data_handler.py
@@ -218,8 +218,18 @@ def arq_data_received(data_in:bytes, bytes_per_frame:int):
         else:
             static.INFO.append("ARQ;RECEIVING;FAILED")
             structlog.get_logger("structlog").warning("[TNC] ARQ | RX | DATA FRAME NOT SUCESSFULLY RECEIVED!", e="wrong crc", expected=data_frame_crc, received=data_frame_crc_received)
-     
-        
+
+            # BUILDING NACK FRAME FOR DATA FRAME
+            nack_frame       = bytearray(14)
+            nack_frame[:1]   = bytes([63])
+            nack_frame[1:2]  = static.DXCALLSIGN_CRC8
+            nack_frame[2:3]  = static.MYCALLSIGN_CRC8     
+            
+            # TRANSMIT NACK FRAME FOR BURST
+            txbuffer = [nack_frame]
+            modem.transmit(mode=14, repeats=1, repeat_delay=0, frames=txbuffer)    
+            
+                
         # And finally we do a cleanup of our buffers and states
         arq_cleanup()        
         
@@ -260,10 +270,8 @@ def arq_transmit(data_out:bytes, mode:int, n_frames_per_burst:int):
     static.ARQ_COMPRESSION_FACTOR = len(data_out) / len(data_frame_compressed)
     data_out = data_frame_compressed    
 
-
-
-    tx_start_of_transmission = time.time()
     # reset statistics
+    tx_start_of_transmission = time.time()
     calculate_transfer_rate_tx(tx_start_of_transmission, 0, len(data_out))
 
     # append a crc and beginn and end of file indicators
@@ -403,6 +411,12 @@ def frame_ack_received():
         DATA_CHANNEL_LAST_RECEIVED = int(time.time()) # we need to update our timeout timestamp
 
 
+def frame_nack_received():
+    static.INFO.append("ARQ;TRANSMITTING;FAILED")
+    arq_cleanup()
+
+
+
 def burst_rpt_received(data_in:bytes):
     global RPT_REQUEST_RECEIVED
     global RPT_REQUEST_BUFFER
diff --git a/tnc/modem.py b/tnc/modem.py
index fc548c3f..817e9703 100644
--- a/tnc/modem.py
+++ b/tnc/modem.py
@@ -396,6 +396,11 @@ class RF():
                 logging.debug("REPEAT REQUEST RECEIVED....")
                 data_handler.burst_rpt_received(bytes_out[:-2])
 
+            # FRAME NACK
+            elif frametype == 63:
+                logging.debug("FRAME NOT ACK RECEIVED....")
+                data_handler.frame_nack_received(bytes_out[:-2])
+
             # CQ FRAME
             elif frametype == 200:
                 logging.debug("CQ RECEIVED....")
@@ -435,10 +440,12 @@ class RF():
                 data_handler.arq_received_channel_is_open(bytes_out[:-2])
 
             # ARQ CONNECT ACK / KEEP ALIVE
+            # this is outdated and we may remove it
             elif frametype == 230:
                 logging.debug("BEACON RECEIVED")
                 data_handler.received_beacon(bytes_out[:-2])
 
+            # TESTFRAMES
             elif frametype == 255:
                 structlog.get_logger("structlog").debug("TESTFRAME RECEIVED", frame=bytes_out[:])
                 
@@ -448,6 +455,7 @@ class RF():
 
             
             # DO UNSYNC AFTER LAST BURST by checking the frame nums against the total frames per burst
+            # this should be changed to a timeout based unsync
             if frame == n_frames_per_burst:
                 logging.info("LAST FRAME ---> UNSYNC")
                 self.c_lib.freedv_set_sync(freedv, 0)  # FORCE UNSYNC