diff --git a/modem/arq_session.py b/modem/arq_session.py
index 7653140c..298b8ada 100644
--- a/modem/arq_session.py
+++ b/modem/arq_session.py
@@ -1,18 +1,14 @@
 import queue, threading
-from codec2 import FREEDV_MODE
+import codec2
 import data_frame_factory
 import structlog
 
 class ARQSession():
 
     MODE_BY_SPEED = [
-        FREEDV_MODE.datac4.value,
-        FREEDV_MODE.datac3.value,
-        FREEDV_MODE.datac1.value,
-    ]
-
-    SIZE_BY_SPEED = [
-
+        codec2.FREEDV_MODE.datac4.value,
+        codec2.FREEDV_MODE.datac3.value,
+        codec2.FREEDV_MODE.datac1.value,
     ]
 
     def __init__(self, config: dict, tx_frame_queue: queue.Queue, dxcall: str):
@@ -44,3 +40,7 @@ class ARQSession():
     def setState(self, state):
         self.state = state
         self.logger.info(f"state changed to {state}")
+
+    def get_payload_size(self, speed_level):
+        mode = self.MODE_BY_SPEED[speed_level]
+        return codec2.get_bytes_per_frame(mode)
diff --git a/modem/arq_session_iss.py b/modem/arq_session_iss.py
index 20e30b8a..4a801e64 100644
--- a/modem/arq_session_iss.py
+++ b/modem/arq_session_iss.py
@@ -76,7 +76,7 @@ class ARQSessionISS(arq_session.ARQSession):
     def send_data(self):
         offset = 0
         while offset < len(self.data):
-            max_size = self.get_max_size_for_speed_level(self.speed_level)
+            max_size = self.get_payload_size(self.speed_level)
             end_offset = min(len(self.data), max_size)
             frame_payload = self.data[offset:end_offset]
             data_frame = self.frame_factory.build_arq_session_send(self.speed_level, 
diff --git a/tests/test_arq_session.py b/tests/test_arq_session.py
index 4f9fc0e0..e3de109c 100644
--- a/tests/test_arq_session.py
+++ b/tests/test_arq_session.py
@@ -51,9 +51,9 @@ class TestARQSession(unittest.TestCase):
             transmission_item = modem_transmit_queue.get()
             frame_bytes = bytes(transmission_item['frame'])
             if random.randint(0, 100) < self.loss_probability:
-                self.logger.info("[TestChannel] Frame lost...")
+                self.logger.info(f"[{threading.current_thread().name}] Frame lost...")
                 continue
-            self.logger.info("[TestChannel] Redirecting frame")
+            self.logger.info(f"[{threading.current_thread().name}] Redirecting frame")
             frame_dispatcher.new_process_data(frame_bytes, None, len(frame_bytes), 0, 0)
 
     def establishChannels(self):