How Does RTB Work? A Step-by-Step Example

RTB happens within 100 milliseconds of a user loading a webpage. Here is what happens during an RTB auction:

1. User Visits a Website — The user navigates to a publisher’s site. The page begins to load and the ad server detects an available ad slot.
2. Bid Request is Sent — The publisher’s SSP (such as TwinRed) sends a bid request to connected DSPs and advertisers. The request includes: ad slot specifications (size, format, position), publisher domain and page URL, user signals (device, browser, OS, location), and a unique auction ID.
3. Advertisers Evaluate and Bid — Each DSP evaluates the bid request against its advertisers’ campaign criteria (targeting, budgets, bid limits) and submits a bid if the impression matches.
4. Auction Winner is Determined — The highest bid wins. The winning price is typically determined by a second-price auction model (winner pays just above the second-highest bid).
5. Ad is Served — The winning creative is delivered to the user’s browser and rendered in the ad slot. The entire process takes under 100 milliseconds.