How mediation works

Learn the life cycle of a mediation request

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.

Example

Ad network 1 has the highest CPM, and is therefore at the top of the chain.

  1. Ad network 1: CPM $5.75
  2. Ad Exchange: CPM $4.00
  3. Ad network 2: CPM $3.50
  4. Ad network 3: CPM $3.25
  5. Ad network 4: CPM $2.00

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.

  • Fill rate is only used to calculate the expected value of the entire mediation chain for competition in dynamic allocation. Fill rate is not used to discount estimated CPM for an ad network tag.
  • If the number of competing network tags in a mediation chain exceeds the system limit, Ad Manager uses ad network tag fill rate, CPM and calculated order to discard ad tags and meet the limit with a maximum possible expected value.
  • 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 there are no Ad Exchange eligible bids, the mediation chain will only contain ad network tags, and a reservation ad can be added to the end of the mediation chain.

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 in addition to the Ad Exchange bid.  

Example
Several yield partners have submitted bids with CPMs of different values, along with Ad Exchange and Ad Manager backfill:
  1. Ad network 1: CPM $5.75
  2. Ad Exchange: CPM $4.00
  3. Ad network 2: CPM $3.50
  4. Ad network 3: CPM $3.25
  5. Ad network 4: CPM $2.00
  6. Ad Manager price priority line item 1: CPM $5.00
  7. Ad Manager line item 2: CPM $4.00
Because the price priority line item beats the Ad Exchange bid, Ad Manager would return this mediation chain:
  1. Ad network 1: CPM $5.75
  2. Ad Manager price priority line item 1: CPM $5.00
  3. Ad Exchange: CPM $4.00

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. 

Example
Several yield partners have submitted bids with CPMs of different values, along with Ad Exchange and Ad Manager backfill:

8. Ad network 1: CPM $5.75

9. Ad Exchange: CPM $4.00

10. Ad network 2: CPM $3.50

11. Ad network 3: CPM $3.25

12. Ad network 4: CPM $2.00

13. Ad Manager standard line item 1: CPM $5.00

14. Ad Manager line item 2: CPM $4.00

 
Because the standard item beats the Ad Exchange bid, Ad Manager would return this mediation chain:

4. Ad network 1: CPM $5.75

5. Ad Manager standard line item 1: CPM $5.00

Ad Manager line items that do not beat the Ad Exchange bid will not be included in the 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 Ad Exchange or, when Ad Exchange is not eligible, a reservation ad the end of the chain. Any line items, except sponsorship line items, are 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.

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