About AdMob Mediation
AdMob Mediation is a feature that lets you serve ads to your apps from multiple sources, including the AdMob network, the AdMob eCPM Floor Beta, third-party ad networks, and house ad campaigns. AdMob Mediation helps maximize your fill rate and increase your monetization by sending ad requests to multiple networks to ensure you find the best available network to serve ads.
There are two types of mediation you can use, independently or simultaneously, in AdMob:
Impression goal campaigns are house ad campaigns that serve ads to your app using your own inventory, free of charge. The impression goals that you set determine the target number of impressions that the campaign will serve during the duration of the campaign. You can use impression goal campaigns to promote your app or another advertiser's product. For example, you can work out a deal directly with an advertiser outside of AdMob to run their campaign in your app.
Impression goal campaigns are served via AdMob Mediation and take precedence over other ad sources in the mediation stack. If there are multiple impression goal campaigns, ad serving will rotate evenly through the campaigns. However, AdMob limits the number of impressions that can be served daily, based on the following calculation:
daily limit = impression goal / total number of days the campaign will run
After all impression goal campaigns are served (or the daily limit is reached), ad requests will be filled by eCPM-based ad sources, including the AdMob Network, the AdMob eCPM Floor Beta, third-party ad networks, and house ad campaigns. The eCPM value determines the order of the ad network to serve ads.
When you set up mediation, your settings tell AdMob how to choose between multiple ad sources. Currently, you can only allocate traffic based on the eCPM (effective cost per thousand impressions) value, which is an estimate of ad revenue. You can find the eCPM value of each ad network from the historical reports available through their websites or you can enable ad network optimization to allow AdMob to automatically obtain the eCPM value from each ad network.
The eCPM value determines the order of the ad network to serve ads. The ad network with the highest eCPM value is served first. If an ad network is unable to fill the request, AdMob tries the network with the next highest eCPM. It continues down the list until it finds a network to fill the request. Ad networks with the same eCPM value are distributed evenly. This list or ranking of ad networks is often called the mediation stack.
You can enable AdMob to bid alongside the other ad networks on a per-impression basis. That means, AdMob Network will be dynamically positioned in the mediation stack.