AppNexus shared some interesting insights on what’s up and down regarding Server-to-Server Header Bidding on it’s blog recently.
Server-to-server header bidding allows publishers to include a greater number of demand partners in their header bidding auctions. The difference between server-to-server and client-side setups lies in where the header bidding auction takes place.
Client-side auction happens in the header of a publisher’s web page where publishers send ad calls back and forth between the user and each of the participating demand partners. This creates an additional load on the browser that is not designed to make so many simultaneous calls resulting in long load times and a terrible user experience.
In a server-to-server setup, the publisher only sends a single ad call to a high-powered server that calls all the different exchange partners. With the right setup, publishers call 200 ad exchanges without increasing latency.
But server-to-server header bidding decreases publishers’ cookie match rate and publishers risk seeing a decrease in both the number of bids they receive and the CPMs advertisers are willing to pay.
Also server-to-server header bidding is less transparent since all of this takes place inside a black 3rd party box, so you can’t see if they are taking an unfair cut or certain demand sources are ranked over others.