DSPs and SSPs: the two sides of the trade

Every programmatic trade has two robots at its heart. One works for the buyer, one works for the seller. They never meet in person, they negotiate millions of times a second, and between them they move most open-web ad money. Understanding what each robot optimises for, and how each gets paid, explains most of the tension in the industry.

Think of a stock market. A DSP is like a brokerage app that places orders for investors. An SSP is like the broker who represents a company selling its shares and tries to get the best price. The exchange is the trading floor. In ad tech, one company often runs both the seller's broker and the trading floor.

The DSP: a buyer's autopilot

A DSP lets an agency or advertiser load campaigns, audiences, budgets and rules, then bids automatically on impressions from many exchanges. For each bid request it asks: does this match a campaign? Is it brand safe? Is the traffic likely human? How likely is this person to click, watch or buy? Then it computes a bid.

• Targeting and data: first-party audiences uploaded by the brand, third-party segments, contextual categories, location.
• Bidding algorithms: predict the value of each impression and bid to hit the campaign goal at the lowest cost.
• Controls: frequency caps, pacing, allow and block lists, pre-bid filtering for fraud and brand safety.
• Reporting: Win rate, spend, delivery and performance by site, app and supply path.

Well-known independent DSPs include The Trade Desk (US), plus regional and specialist players. Google's Display & Video 360 and Amazon DSP are the largest owned by big platforms. Some DSPs are self-serve platform: the agency operates it directly. Others offer a managed service, where the vendor's own team runs campaigns for the client.

The SSP: a seller's auctioneer

An SSP connects a publisher's inventory to as many buyers as possible and tries to maximise revenue for each impression. It packages bid requests, runs or joins auctions, enforces floors and blocks, screens out bad advertisers and malicious creatives, and pays the publisher. Major SSPs include Magnite, PubMatic, Index Exchange, Google AdX, Equativ, OpenX and Sovrn, with strong regional players in Japan, India and Latin America.

An ad exchange is the marketplace where the auction happens. Historically exchanges and SSPs were separate businesses; today nearly every SSP runs its own exchange, so "SSP" and "exchange" are often used interchangeably.

How they make money

Both sides typically earn a percentage of the money that passes through them, known as their take rate. A DSP adds its fee on top of the media cost it pays; an SSP deducts its fee from the clearing price before paying the publisher. Neither fee is visible to the other side unless contracts or log data reveal it, which is the heart of the transparency debate.

Some agencies add another layer through principal-based buying: the agency buys inventory in bulk on its own account and resells it to clients as a packaged product at a marked-up price, rather than acting as a transparent agent. It can be cheaper for the client, but it hides the true media cost.

Why the line is blurring

The neat buy-side versus sell-side split is fading. DSPs have built direct connections to publishers to skip SSP fees; The Trade Desk's OpenPath is the best-known example. SSPs have built tools to sell directly to brands and agencies and to package audiences for them. Amazon runs a DSP and also sells its own and partners' streaming inventory. Google has operated a DSP, an exchange and the leading publisher ad server all at once, which a US court found in April 2025 was used to unlawfully maintain monopoly power in publisher ad servers and exchanges.

What a DSP sees that you do not

Because a DSP bids across many exchanges, it builds a view of the bid landscape: what prices tend to win for each kind of impression, which sellers send duplicated requests, which paths deliver viewable human traffic. That knowledge makes the DSP powerful, and it is also why independent verification and log-level reporting matter to the advertiser paying the bill.