+An implementation of T-Frames and I-Frames can be found in
+tinyos-2.x/tos/chips/cc2420/. The components in
+tos/chips/cc2420/lowpan/ control which is used. By default, TinyOS
+802.15.4 stacks use I-Frames, and the 'tframe' make option configures
+them to use T-Frames. This make option defines a symbol named
+``TFRAMES_ENABLED``. In the case of the CC2420 stack, this causes
+``CC2420.h`` to define ``CC2420_IFRAME_TYPE``, which adds the extra
+byte to the message_t header structure.
+