The Transactional channel encompasses Supply Side Providers (SSPs) that serve as marketplaces for ads that haven’t been sold by humans via the Enterprise channel. It is dominated by the obvious heavyweight: Google’s Google Ad Manager. SSPs actually serve as ad exchanges between buyers of ad space (advertisers) and sellers of ad space (publishers). The rock-solid metric for publishers is CPM (cost per mille aka cost per thousand impressions). Know how can one improve CPM with Tellius.