When the repair server detects that there are {HEAD ~ packets} missing from {TAIL ~ the session} it has received, it uses the ordered list to sequentially request the missing packets from respective ones of the plurality of retransmit servers 
When the repair server detects that there are { HEAD ~ packets } missing from { TAIL ~ the session } it has received , it uses the ordered list to sequentially request the missing packets from respective ones of the plurality of retransmit servers
OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH