{HEAD ~ Portion} of data stream or data block 200 is sent from {TAIL ~ one or more clients}  
is sent from
{ HEAD ~ Portion } of data stream or data block 200 is sent from { TAIL ~ one or more clients }
HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH