The ad-exchange receives a constant stream of chances to place ads. This stream is generated by the "#SupplySidePlatform" (#SSP), a service that represents publishers who want to sell ads.

Meta/#Facebook and Google both the "full stack" of ads: they represent buyers *and* sellers, and they operate the marketplace. When the sale closes, #Googbook collects a commission from the advertiser, another from the publisher, *and* a fee for running the market.

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