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So far Google has purchased 16 ad networks, which include online as well as mobile ad networks .Google's double click acquisition was the most expensive , followed by Admeld .
Google acquired double click for $3,100,000,000, while Admeld was the second most expensive advertising network to be acquired by Google for $400,000,000
Google's purchase of ad networks gives it enormous reach in display advertising . While AdSense network enables publishers to run relevant ads - including text, image,rich media and video ads
across their websites, The ad networks plays a different role .The ad networks aggregates a large number of ad networks (over 65 at last count, including more than half of the largest 20 networks in the US) which competes in real time auction instead of using historical data, or trying to negotiate prices upfront (usually at a discount). It chooses the highest value ad from these competing networks at each moment,
Google acquisition of ad networks integrated its AdSense network to work with DoubleClick, Admeld , Invite media and other ad networks t help publishers more precise metrics which helps them to judge the effectiveness of their campaigns
