What is real-time bidding?
Real-time bidding (RTB) is the sale of a single ad impression through an auction that runs while the page or app is loading. An exchange describes the impression in a bid request, sends it to many bidders at once, collects priced responses within a deadline of a few hundred milliseconds or less, and picks a winner. OpenRTB is the message format most of these auctions use.
Also called: RTB, real time bidding, RTB auction.
How it works
One RTB auction is a short sequence of HTTP calls. The exchange POSTs a BidRequest to each bidder it wants to hear from, with BidRequest.tmax stating how many milliseconds it will wait. Each bidder answers with a BidResponse holding priced bids for specific impressions, or with HTTP 204 when it passes. The exchange drops late or invalid responses, applies floors and blocks, ranks what is left under the auction type in BidRequest.at, and tells the winner through the win notice URL in Bid.nurl. Billing and loss notices (Bid.burl, Bid.lurl) report what happened afterwards.
What makes it real time is that every impression is priced on its own, from what the request says about the page or app, the device, the user's consent state, and the supply path. A guaranteed buy booked weeks ahead at a fixed price works the other way round. Deals sit between the two: a programmatic guaranteed deal still travels through an RTB request, but its price and obligation were settled in advance and the request only executes them.
Most RTB failures are silent. A bidder that cannot parse a request, or reads a field from the wrong version, simply returns no bid, and the exchange records a lower bid rate instead of an error. A response that arrives after BidRequest.tmax is thrown away regardless of price. Request quality and latency therefore decide how much of the market a bidder actually sees, as much as its bidding logic does.
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Related terms
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