Auction Dynamics

When an advertiser runs programmatic ads, their bids compete with hundreds of thousands of other bids for the same ad inventory in an auction. Advertisers need to have transparency into how such auctions are conducted, and winners are chosen.

Auction Type

InMobi Exchange runs all its auctions on a First Price Auction model.

A First Price Auction is an auction model where the buyer pays the price; they bid for a given ad opportunity or impression.

Identifying Auction Type in Bid Request

InMobi Exchange passes the auction type to a DSP within the oRTB bid request as recommended by IAB. Within the oRTB bid request, “auction type” is represented as “at:”. Since InMobi Exchange runs exclusively on First -Price auctions, the value passed in the request will be “at:1.”

Auction Notifications

InMobi sends demand partners real-time notifications to indicate when an impression has been served and billed and when a bid is lost, and the reason for the loss.

The following figure illustrates the OpenRTB interactions between an exchange and its bidders. For each inbound ad request, bid requests are broadcasted to bidders, responses are evaluated under prevailing auction rules (at InMobi), and a winner is selected.

  • The system notifies the winning bidder of the auction win through a win notification (NURL).
  • Ad markup can either be included in the bid prospectively or in response to the win notice.
  • A separate billing notice is also available to accommodate specific details like billing on device delivery, viewability, BURL, and so on.

The win notice is essential to inform the bidder’s pricing algorithms of success, whereas the billing notice indicates that spending should be applied.

  • Loss notification (LURL) is also available to inform the bidder of why their bid did not win. The loss reason code will follow the guidelines mentioned in oRTB spec v2.5.

The URLs for the win, billing, and loss notices and the ad markup itself can contain any of several standard macros that enable InMobi to communicate critical data to the bidder (e.g., clearing price).


It’s essential that the bidder is either oRTB 2.3 or oRTB 2.5 compliant and provide an HTTP/HTTPS endpoint to receive auction notification responses.

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Last Updated on: 09 Mar, 2022