A system for exchanging data between a portable payment terminal and a stationary base terminal in {HEAD ~ communication} with {TAIL ~ a payment center} 
with
A system for exchanging data between a portable payment terminal and a stationary base terminal in { HEAD ~ communication } with { TAIL ~ a payment center }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL