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Fix the driver behind crashes, sound loss and screen glitchesFind Drivers →Clear out junk files and repair common Windows errorsFree Scan →Scan for outdated or missing drivers - takes under a minuteDriver Scan →A supply-side platform (SSP) helps publishers sell advertising inventory; a demand-side platform (DSP) helps advertisers and agencies choose and buy ad impressions. They can meet through programmatic auctions, but an SSP-to-exchange-to-DSP chain is only one common route—not a requirement for every online ad.
What is a supply-side platform (SSP)?
An SSP is software used by a publisher, app, or other media owner to manage and offer advertising inventory to potential buyers. Its role is on the selling side: it helps connect available ad space with sources of advertiser demand and supports the publisher’s effort to monetize that inventory. IAB Europe’s supply-chain Q&A describes the roles of the main participants.
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What is a demand-side platform (DSP)?
A DSP is software used by advertisers and agencies to evaluate and buy ad impressions across sources. It helps turn campaign goals and settings into buying decisions, including which opportunities to pursue and what to bid. The advertiser’s platform is therefore on the buying side, facing the publisher’s inventory and the systems that make it available.
SSP vs. DSP: the practical difference
| Role | Primary customer | Core job | Typical optimization focus | Direction in the ad ecosystem |
|---|---|---|---|---|
| SSP | Publisher, app, or media owner | Manage and sell advertising inventory | Inventory monetization and yield | Connects inventory to demand sources |
| DSP | Advertiser or agency | Select and buy ad impressions | Audience, placement, bid, budget, and campaign outcomes | Connects buying decisions to publishers, SSPs, and exchanges |
These are role-level definitions, not rigid company categories. Some adtech businesses operate at more than one point in the supply chain, so a company’s services may cross the line between the two roles. The UK government’s Online Advertising Programme consultation describes these overlapping arrangements and other ways inventory is bought and sold.
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How an SSP and DSP can work together
In a simplified open-display programmatic transaction, a page load creates an opportunity to show an ad. The publisher’s ad server signals available inventory through an SSP; demand sources receive or access the opportunity; DSPs assess it against advertiser goals and settings and may submit bids. An auction process selects an outcome, and the ad is delivered.
- A person loads a publisher’s page, creating an available ad impression.
- The publisher’s ad server signals the opportunity through its SSP.
- Demand sources make the opportunity available to buying systems.
- A DSP evaluates the impression for an advertiser and may submit a bid.
- The relevant auction process selects an outcome and the ad is served.
This is a teaching model, not a universal technical sequence. Auction forms and execution flows vary. IAB Tech Lab defines a programmatic auction as “part of the process to determine how an advertisement is delivered into a relevant ad placement”; its definitions page says they were finalized on June 24, 2026. IAB Tech Lab’s programmatic-auction definitions explains the terminology and variation.
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Does every online ad use both an SSP and a DSP?
No. Buying routes range from a multi-party programmatic chain to direct contracts between an advertiser and a publisher. Some publishers sell inventory without SSP or DSP involvement, and some adtech companies work across multiple supply-chain levels. The familiar SSP-and-DSP diagram is useful for understanding one route, but it should not be mistaken for a mandatory path for every ad. The UK government’s consultation outlines these alternatives.
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1Scan for outdated or missing drivers - takes under a minute2Repair Windows errors before they cause bigger problems3Fix the driver behind crashes, sound loss and screen glitchesHow buyers can assess the supply path
An impression may pass through multiple businesses before it reaches a buyer. Transparency mechanisms help buyers check who is authorized to sell a publisher’s inventory and understand the businesses involved in a supply path. IAB Europe identifies three tools that can contribute to these checks:
- ads.txt: a publisher’s public declaration of authorized sellers of its digital inventory.
- sellers.json: information that helps identify sellers participating in programmatic transactions.
- SupplyChain object: transaction information that helps buyers see the entities involved in selling an impression.
Used together, these mechanisms can help buyers assess authorization and supply-chain composition and reject counterfeit inventory before bidding. They provide visibility, but do not make every transaction path identical. IAB Europe’s Q&A on the digital advertising supply chain explains their purpose.
What the reported sample figures do—and do not—show
In figures reported by IAB Europe in 2025, at least 73% of 2,054 European online news publishers in its sample hosted ads.txt files. More than 99% of ads.txt lines checked in that sample were valid, and around 79% of the sellers.json relationships checked matched publisher declarations. These results describe that study’s population and checks; they are not global adoption rates or measurements of all publishers. IAB Europe’s 2025 Q&A provides the sample context.
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