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