In the described embodiment, {TAIL ~ the ad selection process} is “decoupled” from {HEAD ~ the ad content delivery process} 
In the described embodiment , { TAIL ~ the ad selection process } is “ decoupled ” from { HEAD ~ the ad content delivery process }
OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD