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