A plurality of {HEAD ~ retransmit servers} in {TAIL ~ the network buffer portions} of the packets they respectively receive during the multicast session 
in
A plurality of { HEAD ~ retransmit servers } in { TAIL ~ the network buffer portions } of the packets they respectively receive during the multicast session
OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH