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