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