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