In Google AdMob SDK v6.0 and above, you can request ads from multiple ad networks, including AdMob, while controlling how the requests are allocated among those networks. With this new feature, called mediation, you configure a mediation placement at by assigning each network either an eCPM or a percentage value.

Some of you have asked how AdMob uses these values to determine the network order, so we'd like to take this opportunity to explain. We’d also like to discuss what happens when you add an ad network to an existing mediation placement.

Network Allocation Methods

There are two ways in which traffic is allocated across ad networks.

  1. eCPM values. Input the eCPM you expect to get paid from each ad network you work with. AdMob then sorts the ad networks by their eCPM values from highest to lowest, and the result becomes the network order used to request ads. The network with the highest eCPM value is the first network Admob goes to with an ad request.

  2. Percentages. Alternatively, you can assign percentage values to each ad network. Mediation randomly determines the first network using the given percentages, and then normalizes the remaining percentages to determine the next ad network. This process continues until all configured networks have been selected. Note that any ad network with 0% percentage allocation will be ignored.

Unlike AdWhirl, which refreshes its configuration on each ad refresh, AdMob Mediation refreshes its configuration once every 300 seconds. This means that the SDK uses the same network order until a new mediation configuration is fetched.

Adding a New Network to an Existing Application

It's important to know how your application will behave when you add a new ad network to it. Remember that anytime you add a new ad network, you need to include the corresponding ad network adapter in your app. If the adapter cannot be found, the AdMob SDK skips that network and moves on to the next one.

Don't worry if your application doesn’t include the ad network adapter. For placements with eCPM values, the added network doesn't affect existing versions of the application. Similarly, for placements using percentage configurations, percentages are effectively normalized across existing valid ad networks, as invalid networks are automatically thrown out.

Let us know on our forum if you have any questions about mediation placements or general questions about the Google AdMob SDK. You can also ask us questions at our next hangout session.