1. A method of online advertising over a network comprising: receiving, at an ad server node, at least one generic ad request from a generic advertiser, the generic ad request including a number of requested impressions; an ad server of the ad server node providing availability information to one or more child advertisers of the generic advertiser based on the number of requested impressions for the generic ad request and a web site designation for the generic ad request; receiving, at the ad server node, targeted ad requests including target information from at least one of the one or more child advertisers; an ad server of the ad server node determining a media buy output based on the received targeted ad requests and the generic ad request.