A repair server polls multiple transmit servers to accumulate as many of {TAIL ~ the packets} missing from {HEAD ~ the multicast session} as possible 
A repair server polls multiple transmit servers to accumulate as many of { TAIL ~ the packets } missing from { HEAD ~ the multicast session } as possible
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH