diff --git a/sw/airborne/downlink.h b/sw/airborne/downlink.h
index 4df1ee4166..cef7385d28 100644
--- a/sw/airborne/downlink.h
+++ b/sw/airborne/downlink.h
@@ -61,6 +61,9 @@ extern uint8_t telemetry_mode_Fbw;
 
 /** Counter of messages not sent because of unavailibity of the output buffer*/
 extern uint8_t downlink_nb_ovrn;
+extern uint16_t downlink_nb_bytes;
+extern uint16_t downlink_nb_msgs;
+
 
 #define __Transport(dev, _x) dev##_x
 #define _Transport(dev, _x) __Transport(dev, _x)
@@ -68,7 +71,9 @@ extern uint8_t downlink_nb_ovrn;
 
 
 /** Set of macros for generated code (messages.h) from messages.xml */
-#define DownlinkSizeOf(_x) Transport(SizeOf(_x))
+/** 2 = ac_id + msg_id */
+#define DownlinkIDsSize(_x) (_x+2)
+#define DownlinkSizeOf(_x) Transport(SizeOf(DownlinkIDsSize(_x)))
 
 #define DownlinkCheckFreeSpace(_x) Transport(CheckFreeSpace((uint8_t)(_x)))
 
@@ -87,10 +92,12 @@ extern uint8_t downlink_nb_ovrn;
 #define DownlinkPutUint16Array(_n, _x) Transport(PutUint16Array(_n, _x))
 #define DownlinkPutUint8Array(_n, _x) Transport(PutUint8Array(_n, _x))
 
-#define DonwlinkOverrun() downlink_nb_ovrn++;
+#define DownlinkOverrun() downlink_nb_ovrn++;
+#define DownlinkCountBytes(_n) downlink_nb_bytes += _n;
 
 #define DownlinkStartMessage(_name, msg_id, payload_len) { \
-  Transport(Header(payload_len)); \
+  downlink_nb_msgs++; \
+  Transport(Header(DownlinkIDsSize(payload_len))); \
   Transport(PutUint8(AC_ID)); \
   Transport(PutNamedUint8(_name, msg_id)); \
 }
diff --git a/sw/airborne/pprz_transport.h b/sw/airborne/pprz_transport.h
index 36db7f1e28..0c501ae37d 100644
--- a/sw/airborne/pprz_transport.h
+++ b/sw/airborne/pprz_transport.h
@@ -33,8 +33,8 @@ extern uint8_t ck_a, ck_b;
 
 #define STX  0x99
 
-/** 6 = STX + len + ac_id + msg_id + ck_a + ck_b */
-#define PprzTransportSizeOf(_payload) (_payload+6)
+/** 4 = STX + len + ck_a + ck_b */
+#define PprzTransportSizeOf(_payload) (_payload+4)
 
 #define __Link(dev, _x) dev##_x
 #define _Link(dev, _x)  __Link(dev, _x)
diff --git a/sw/airborne/xbee.h b/sw/airborne/xbee.h
index 06d648febd..2069c762d7 100644
--- a/sw/airborne/xbee.h
+++ b/sw/airborne/xbee.h
@@ -57,7 +57,10 @@ void xbee_init( void );
 #define XBeePrintHex16(x) XBeeLink(PrintHex16(x))
 #define XBeeTransportPut1Byte(x) XBeeLink(Transmit(x))
 #define XBeeTransportCheckFreeSpace(x) XBeeLink(CheckFreeSpace(x))
-#define XBeeTransportSizeOf(_x) (_x+5)
+/* 5 = Start + len_msb + len_lsb + API_id + checksum */
+#define XBeeAPISizeOf(_x) (_x+5)
+/* 4 = frame_id + addr_msb + addr_lsb + options */
+#define XBeeTransportSizeOf(_x) XBeeAPISizeOf(_x+4)
 #define XBeeTransportSendMessage() XBeeLink(SendMessage())
 
 #define XBeeTransportPutUint8(_x) { \
@@ -129,7 +132,7 @@ void xbee_init( void );
 
 #define XBeeTransportHeader(_len) { \
   XBeeTransportPut1Byte(XBEE_START); \
-  uint8_t payload_len = XBeeTransportSizeOf(_len + 2); \
+  uint8_t payload_len = XBeeAPISizeOf(_len); \
   XBeeTransportPut2Bytes(payload_len); \
   xbee_cs = 0; \
   XBeeTransportPutTX16Header(); \