A network includes {HEAD ~ a source} of {TAIL ~ multicast packets} in a multicast session and a plurality of multicast recipients in that session 
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A network includes { HEAD ~ a source } of { TAIL ~ multicast packets } in a multicast session and a plurality of multicast recipients in that session
OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH