After {HEAD ~ the routing data} is added to {TAIL ~ the data frame}, the buffer transmits the data frame to the switching system 
is added to
After { HEAD ~ the routing data } is added to { TAIL ~ the data frame } , the buffer transmits the data frame to the switching system
OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH