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