LinkedIn Demographic Data Jun08Click to viewBusiness networking site LinkedIn launched an online ad network today. The world doesn't need another online-ad network, which offers repackaged ad views from multiple websites, sold as a single buy to advertisers. There are already 300 or so. But LinkedIn may prove a survivor when the ad-network bubble bursts.The first reason an interactive agency buyer chooses an ad network for his clients is because the people who work there take him out to lunch. But the second reason buyers choose one ad network over the other 299 is that they can trust the ad network to carefully manage its audience and the publishing partners it includes. The first requirement LinkedIn has down: Its users are rich and easily targeted by industry, seniority, company size, geography, gender, and number of connections. If publishers sign up for its network, LinkedIn can detect when those users visit other websites, using its personalized information to target ads. But to meet the second requirement, LinkedIn needs to carefully restrict the publishers it allows into its ad network. This could prove more challenging for the startup. BusinessWeek , CNBC, and the New York Times already pipe content into LinkedIn, but it's unclear if they plan to carry LinkedIn's ads, too. There's some incentive for them to join up: LinkedIn says it charges advertisers between $30 and $76.50 per thousand ad impressions, an attractive rate for almost any publisher. LinkedIn might have trouble recruiting those types of publishers because they, too, want to start their own ad networks. Even though the world doesn't need another one.