{HEAD ~ System} for exchanging data between {TAIL ~ a portable payment terminal} and a stationary base terminal 
{ HEAD ~ System } for exchanging data between { TAIL ~ a portable payment terminal } and a stationary base terminal
HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH