SSP (supply-side platform)

An SSP (supply-side platform) is the software screen owners and publishers use to sell their advertising space automatically, to many buyers at once. It sits on the seller’s side of programmatic trading.

How does it work?

A network of digital out-of-home (DOOH) screens, in streets, malls or stations, connects its inventory to an SSP. The owner then sets the rules of sale:

• which screens and hours are offered,
• a floor price, below which a slot is not sold,
• which advertisers or categories are accepted or blocked,
• which buyers get private or guaranteed deals.

The SSP makes that inventory visible to buyers’ platforms, the DSPs. When a play is coming up, the SSP describes the opportunity (screen, location, time, audience estimate), collects bids or deal requests, and picks the winner. In an open auction, this happens through real-time bidding.

Before anything airs, the SSP also checks the creative’s format and duration, and the location’s content rules.

Example

Illustrative example: a mall network offers its 50 screens through an SSP, with a floor CPM of €8. On a Saturday afternoon, three DSPs bid for the same slot, at CPMs of €7, €9 and €12. The bid at €7 is under the floor and is rejected. The slot goes to the highest bidder and, depending on the auction rules, the price paid is €12 or just above €9.

Why it matters when you plan a DOOH campaign

As a buyer, you rarely touch an SSP directly, but its settings shape what you can buy. Floor prices decide whether your bids win. Deal settings decide whether a slot can be guaranteed to you or only won at auction. And the audience estimate the SSP attaches to each play decides what a CPM is really worth.

So when a plan runs through automated buying, ask which SSPs sit behind the screens, and how they count audiences. The same screen can look cheap or expensive depending on the impression multiplier it is sold with. Two plans with the same CPM are only comparable if their audiences were counted the same way.