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