At first glance it might seem confusing why Publishers and Marketers both maintain their own Ad Servers. After all, what’s the point of forcing a browser to make so many trips across the internet, bouncing from Ad Server to Ad Server when technically all you need is a single Ad Server to deliver an ad?
The answer is mostly convenience, but also so Marketers and Publishers can audit each other when it comes time to bill.
Ad Servers are convenient because they allow Publishers and Marketers to centralize the nuts and bolts of getting an ad on a web page. If a Marketer bought media across ten different sites for example, without and ad server every time they wanted to change their creative assets they would have to talk to ten different publishers. Not only that, but when it came time to report on how well their campaigns did, they would have to compile ten different data sources into a single report. For a sophisticated marketer advertising multiple products to multiple audiences with multiple messages, this quickly becomes unmanageable and is distasteful from the start.
However, with an Ad Server, a Marketer can update their creative in a single place, whenever they want, and do so without needing to contact a publisher. Moreover, they can pull reporting on-demand from one place that uses the same tracking methodology.
Publishers maintain an Ad Server for the same reasons – they have multiple clients running multiple creatives for varying amounts and with different targeting requirements. Publishers also want a single source for reporting, and where they can efficiently track that they are delivering on schedule so they can bill clients in full.
Lastly, separate Ad Servers allow both parties to maintain their own independent set of reports. This forces both parties to rely on the technology when it comes time to bill rather than each others honesty. Of course, using two Ad Server that count at different times, even milliseconds apart creates the possibility for Ad Serving Discrepancies, the bane of Publishers and Marketers alike.