Definition
Before RTB, inventory was bought in blocks: a thousand impressions on a site at a fixed CPM, regardless of who saw them. RTB prices each impression on its own: the buyer sees the GEO, device, placement and context, decides whether this one is worth bidding on, and names a price. The result is that two impressions on the same page can sell for very different amounts, and that a buyer can stop bidding on a source the moment its conversions fall.
How an RTB auction works
- The supply side (an SSP, an exchange or an ad network) builds a bid request: impression format and size, site or app, device, GEO, language, the floor price and the identifiers consent allows.
- The request is sent to connected demand platforms at the same time.
- Each DSP scores the impression against its advertisers' campaigns and returns a bid response with a price and the ad markup, or passes.
- Responses that arrive after the timeout are discarded; among the rest, the highest bid above the floor wins.
- The winner is notified at the clearing price and the creative is served. A click and any conversion are tracked as usual.
RTB for pop, push and redirect traffic
OpenRTB was designed for display and video, where the buyer returns markup to render. Pop, push, in-page push and direct click traffic are traded between networks and DSPs with a simpler mechanism: an XML or JSON feed that the supply side calls with the visitor's parameters, receiving a landing URL and a CPC price in return. The economics are the same, one auction per visitor, but the price is per click rather than per impression. Reacheffect runs both: OpenRTB on CPM for popunder, banner, video and native, and XML/JSON GET feeds on CPC for popunder, push, in-page push and direct click.
Who uses RTB
Demand-side platforms, agency trading desks and ad networks buying reach beyond their own publishers; on the other side, SSPs, exchanges and networks selling inventory their own advertisers do not fill. A single advertiser with a self-serve account does not see RTB at all; it happens behind the campaign wizard when the network buys or sells on its behalf.
Related terms
| Term | Relation | Where defined |
|---|---|---|
| Ad exchange | Where RTB auctions run | Term page |
| DSP | The bidder | Glossary entry |
| SSP | The seller | Glossary entry |
| CPM | The price unit for display RTB | Term page |
FAQ
Is RTB the same as programmatic advertising?
RTB is one kind of programmatic buying, the open-auction kind. Programmatic also includes private marketplaces, preferred deals and programmatic guaranteed, which use the same pipes with fixed or negotiated prices.
How fast does an RTB auction run?
The supply side gives bidders a timeout of roughly 100 to 300 milliseconds; the whole cycle fits inside the page load so the visitor never waits for it.
Can a DSP buy popunder traffic over RTB?
Yes. Popunder inventory is sold over OpenRTB on CPM and over XML/JSON feeds on CPC; the DSP chooses the integration that matches its pricing model.