Revised text in 3.2:

   D-mode uses UDP, as this is the only encapsulation which does not
   require per-message shared state to be maintained between the peers.
   It is an assumption that long-term evolution of GIST will preserve
   the simplicity of the current D-mode design.  Any extension to the
   security or transport capabilities of D-mode can be considered as the
   selection of a different protocol stack under the GIST messaging
   layer (either using existing protocols or a some specification
   developed specifically to support GIST).  This would then become
   another option within the overall C-mode framework.