OpenRTB (Real-Time Bidding)

OpenRTB is the protocol maintained by the IAB that defines how DSPs and SSPs communicate during programmatic auctions. When an impression becomes available, the SSP sends a bid request: specifying the user, context, format, and constraints: to every connected DSP; each DSP evaluates the opportunity against its bidding rules and returns a bid; the highest qualifying bid wins; the ad is served. Every step completes in roughly 100–300 milliseconds.

OpenRTB standardisation is why programmatic scaled. Before OpenRTB, every DSP-to-SSP integration required bespoke engineering. With the standardised protocol, any compliant DSP can buy from any compliant SSP without custom work, which collapsed the cost of programmatic expansion and made global-scale ad exchanges practical. The protocol has evolved through multiple versions (2.x, 3.x) and now covers CTV, audio, and digital-out-of-home as well as traditional display.