diff --git a/modem/arq_session.py b/modem/arq_session.py
index d9f695d0..b8ab0655 100644
--- a/modem/arq_session.py
+++ b/modem/arq_session.py
@@ -51,9 +51,9 @@ class ARQSession():
     def get_mode_by_speed_level(self, speed_level):
         return self.SPEED_LEVEL_DICT[speed_level]["mode"]
 
-    def transmit_frame(self, frame: bytearray, mode = False):
+    def transmit_frame(self, frame: bytearray, mode='auto'):
         self.log("Transmitting frame")
-        if not mode:
+        if mode in ['auto']:
             self.get_mode_by_speed_level(self.speed_level)
 
         modem_queue_item = {
diff --git a/modem/arq_session_iss.py b/modem/arq_session_iss.py
index 602a9c0a..abe005e7 100644
--- a/modem/arq_session_iss.py
+++ b/modem/arq_session_iss.py
@@ -85,7 +85,7 @@ class ARQSessionISS(arq_session.ARQSession):
         info_frame = self.frame_factory.build_arq_session_info(self.id, len(self.data), 
                                                                helpers.get_crc_32(self.data), 
                                                                self.snr[0])
-        self.launch_twr(info_frame, self.TIMEOUT_CONNECT_ACK, self.RETRIES_CONNECT)
+        self.launch_twr(info_frame, self.TIMEOUT_CONNECT_ACK, self.RETRIES_CONNECT, mode=FREEDV_MODE.datac13)
         self.set_state(self.STATE_INFO_SENT)
 
     def send_data(self, irs_frame):
@@ -109,5 +109,5 @@ class ARQSessionISS(arq_session.ARQSession):
                 self.id, self.confirmed_bytes, payload)
             burst.append(data_frame)
 
-        self.launch_twr(burst, self.TIMEOUT_CONNECT_ACK, self.RETRIES_CONNECT)
+        self.launch_twr(burst, self.TIMEOUT_CONNECT_ACK, self.RETRIES_CONNECT, mode='auto')
         self.set_state(self.STATE_BURST_SENT)