diff --git a/examples/ble_dual_node_echo.py b/examples/ble_dual_node_echo.py
index 38a7298..e441c97 100755
--- a/examples/ble_dual_node_echo.py
+++ b/examples/ble_dual_node_echo.py
@@ -38,6 +38,8 @@ import time
 
 APP_NAME = "ble_reticulum_poc"
 APP_ASPECT = "echo"
+DEFAULT_MESSAGE_CHUNK_SIZE = 300
+LINK_PAYLOAD_BUDGET = 420
 
 RNS = None
 running = True
@@ -46,7 +48,7 @@ active_links_lock = threading.Lock()
 temporary_config_dir = None
 message_file_text = None
 message_file_path = None
-message_chunk_size = 900
+message_chunk_size = DEFAULT_MESSAGE_CHUNK_SIZE
 
 
 
@@ -299,24 +301,46 @@ def utf8_chunks(text, max_bytes):
         yield chunk
 
 
+def file_chunk_prefix(index, total, chunk_bytes):
+    return (
+        f"file_chunk {index}/{total} from {NODE_NAME} "
+        f"bytes={chunk_bytes} file={os.path.basename(message_file_path)} data="
+    )
+
+
+def file_data_chunk_size(total, total_bytes):
+    prefix = file_chunk_prefix(total, total, total_bytes)
+    send_epoch_suffix = " send_epoch=1778951576.861234"
+    metadata_bytes = len(prefix.encode("utf-8")) + len(send_epoch_suffix.encode("utf-8"))
+    safe_size = max(1, LINK_PAYLOAD_BUDGET - metadata_bytes)
+    return min(message_chunk_size, safe_size)
+
+
 def send_message_file(link):
     if message_file_text is None:
         return
 
-    chunks = list(utf8_chunks(message_file_text, message_chunk_size))
-    total = max(1, len(chunks))
     total_bytes = len(message_file_text.encode("utf-8"))
+    estimated_total = max(1, (total_bytes + message_chunk_size - 1) // message_chunk_size)
+    data_chunk_size = file_data_chunk_size(estimated_total, total_bytes)
+    chunks = list(utf8_chunks(message_file_text, data_chunk_size))
+    total = max(1, len(chunks))
+    data_chunk_size = file_data_chunk_size(total, total_bytes)
+    chunks = list(utf8_chunks(message_file_text, data_chunk_size))
+    total = max(1, len(chunks))
+    if data_chunk_size < message_chunk_size:
+        log(
+            f"Requested message chunk size {message_chunk_size} exceeds Reticulum link budget; "
+            f"using {data_chunk_size} data bytes per chunk"
+        )
     log(f"Sending file {message_file_path} as {total} chunk(s), {total_bytes} bytes")
 
     for index, chunk_text in enumerate(chunks):
         if not running or link.status != RNS.Link.ACTIVE:
             return
 
-        send_link_packet(
-            link,
-            f"file_chunk {index + 1}/{total} from {NODE_NAME} "
-            f"bytes={len(chunk_text.encode('utf-8'))} file={os.path.basename(message_file_path)} data={chunk_text}",
-        )
+        chunk_bytes = len(chunk_text.encode("utf-8"))
+        send_link_packet(link, f"{file_chunk_prefix(index + 1, total, chunk_bytes)}{chunk_text}")
         time.sleep(0.1)
 
 
@@ -465,8 +489,8 @@ def parse_args():
     parser.add_argument(
         "--message-chunk-size",
         type=int,
-        default=900,
-        help="Maximum UTF-8 bytes per file chunk packet",
+        default=DEFAULT_MESSAGE_CHUNK_SIZE,
+        help="Requested maximum UTF-8 data bytes per file chunk packet",
     )
     parser.add_argument(
         "--announce-only-when-disconnected",