One of the layers may be left unencrypted to allow {HEAD ~ free browsing} of {TAIL ~ a low quality service level} 
One of the layers may be left unencrypted to allow { HEAD ~ free browsing } of { TAIL ~ a low quality service level }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL