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