Two exemplary types of service level layers are {HEAD ~ peak signal} to noise {TAIL ~ ratio layers} and bitrate layers 
to noise
Two exemplary types of service level layers are { HEAD ~ peak signal } to noise { TAIL ~ ratio layers } and bitrate layers
OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH