How mediation works

For each mediation request from a publisher's mobile app, Ad Manager uses yield groups targeting to determine which ad networks are eligible to compete and then assembles a list, or chain, of ad networks to receive that request in sequence.

Steps in the life cycle of a mediation request

1. Publisher's mobile app sends an ad request to Ad Manager
2. Ad Manager determines which line items and yield groups are eligible for the request
3. Ad Manager creates a chain of ad networks to call in mediation
4. Ad Manager compares the expected yield with other Ad Manager line items
5. Ad Manager sends the mediation chain to publisher's mobile app
6. Google Mobile Ads SDK sends a request to each ad network until an ad is returned
7. Google Mobile Ads SDK displays the returned ad

More details on each step

1. Publisher's mobile app sends an ad request to Ad Manager

An ad request is sent to the Ad Manager ad server using the Google Mobile Ads SDK and special third-party ad network adapters. Learn more about getting started with mediation.

2. Ad Manager determines which line items and yield groups are eligible for the request

Ad Manager assembles a list of eligible line items and yield groups based on inventory targeting. Learn more about the creation of lists for matching line items and yield groups.

3. Ad Manager creates a chain of ad networks to call in mediation

If one or more yield groups matches the ad request, a single, sequential list, or "chain," of mediation networks contained in the eligible yield groups is compiled, ordered from highest to lowest expected yield using historical performance data or user-entered CPM values. Ad Exchange uses real-time auction-winning bids.

Mediation sorts ad network tags by CPM in decreasing order, using the estimated CPM for each ad network tag and the real time Ad Exchange CPM.

The estimated CPM reflects either the "default CPM" entered for each mediation network, or the "dynamic CPM" if automatic data collection is activated. If Ad Manager collects data automatically, the estimated CPM reflects the historical CPM observed for that ad network tag adjusted for impression discrepancies with Ad Manager recorded impressions.

• If Ad Exchange has an eligible bid, the Ad Exchange creative will appear at the end of the mediation chain.
• Ad network tags with a lower expected yield than Ad Exchange are excluded from the chain.
• If the Ad Exchange ad's CPM is higher than all network tags, only the Ad Exchange ad is returned.

If you've setup fallback ads, we recommend you read an overview of mobile fallback ads to understand how it fits in the mediation chain.

4. Ad Manager compares the expected yield with other Ad Manager line items

Mediation chains are also able to take into account other Ad Manager line items based on their dynamic allocation.

If the best line item is a remnant line that beats the Ad Exchange winning bid, Ad Manager will include that line in the chain instead of the Ad Exchange bid.  

If the winning line item is a guaranteed line that beats the Ad Exchange winning bid, Ad Manager will include the guaranteed line item instead of Ad Exchange. 

Ad Manager line items that do not beat the Ad Exchange bid will not be included in the chain.

If there are no Ad Exchange eligible bids or eligible line items, the mediation chain will only contain ad network tags, and a reservation ad can be added to the end of the mediation chain.

5. Ad Manager sends the mediation chain to publisher's mobile app

The mediation chain is returned to the publisher's mobile app with an Ad Exchange, remnant, or guaranteed line item at the end when eligible.

6. Google Mobile Ads SDK sends a request to each ad network until an ad is returned

Using the returned mediation chain, the mobile app's SDK can then use the network adapters to send a request, or "callout," to each ad network until an ad is returned.

If none of the ad networks in the mediation chain are able to fill the ad request, the request will be unfilled and no automatic passback to the ad server is triggered.

Activate automatic data collection or ensure that each mediation network's CPM is adjusted periodically according to the bids actually received by each partner.

7. Google Mobile Ads SDK displays the returned ad

The Google Mobile Ads SDK displays the final returned ad in the publisher's mobile app.