diff --git a/source/6LoWPAN/ws/ws_llc_data_service.c b/source/6LoWPAN/ws/ws_llc_data_service.c
index 240837620cf..f3352d65728 100644
--- a/source/6LoWPAN/ws/ws_llc_data_service.c
+++ b/source/6LoWPAN/ws/ws_llc_data_service.c
@@ -577,7 +577,7 @@ static uint16_t ws_mpx_header_size_get(llc_data_base_t *base, uint16_t user_id)
     //TODO add WS_WP_NESTED_IE support
     uint16_t header_size = 0;
     if (user_id == MPX_LOWPAN_ENC_USER_ID) {
-        header_size += 7+ 5 + 2; //UTT+ MPX + Padding
+        header_size += 7 + 8 + 5 + 2; //UTT+BTT+ MPX + Padding
         if (base->ie_params.vendor_header_length) {
             header_size += base->ie_params.vendor_header_length + 3;
         }
@@ -615,6 +615,7 @@ static void ws_llc_mpx_data_request(const mpx_api_t *api, const struct mcps_data
     wp_nested_ie_sub_list_t nested_wp_id;
     memset(&nested_wp_id, 0, sizeof(wp_nested_ie_sub_list_t));
     ie_header_mask.utt_ie = true;
+    ie_header_mask.bt_ie = true;
     if (base->ie_params.vendor_header_length && user_id == MPX_LOWPAN_ENC_USER_ID) {
         ie_header_mask.vh_ie = true;
     }
@@ -675,6 +676,7 @@ static void ws_llc_mpx_data_request(const mpx_api_t *api, const struct mcps_data
     //Write UTT
 
     ptr = ws_wh_utt_write(ptr, message->messsage_type);
+    ptr = ws_wh_bt_write(ptr);
 
     if (user_id == MPX_LOWPAN_ENC_USER_ID && ie_header_mask.vh_ie) {
         ptr = ws_wh_vh_write(ptr, base->ie_params.vendor_header_data, base->ie_params.vendor_header_length);