Ad Exchange

An ad exchange is a real-time auction marketplace where DSPs bid on impressions exposed by SSPs. Historically, exchanges were a separate layer between DSP and SSP (Right Media, AdX, OpenX), but in modern programmatic the SSP-and-exchange roles have largely merged — Magnite is an SSP and an exchange; FreeWheel is an SSP and an exchange.

Mechanically, every exchange runs the same loop. A bid request lands describing the impression (publisher, format, dimensions, audience signals, floor price). The exchange fans the request out to N DSPs in parallel, waits up to ~80-100ms for responses, picks the highest bid above the floor, and returns the winning creative. The whole loop sits inside the RTB protocol; OpenRTB 2.6 is the current spec version.

Auction mechanics matter. First-price auctions (the buyer pays what it bid) are now the dominant DOOH and CTV format; second-price (pay one cent above the second-highest bid) used to dominate but was deprecated industry-wide circa 2019 because of trust-and-transparency concerns. Some exchanges support sealed first-price; others support hybrid models with soft floors.

Google's AdX is the largest exchange globally; on DOOH specifically, Vistar Media's exchange and Place Exchange are the dominant supply-side specialists. Trillboards integrates with multiple DOOH exchanges through its partner SDK.