Supply-Side Platform

Almost every news site finances itself to a large extent through advertising. In the past, an ad sales department sold this space by hand, with phone calls and contracts. Today, software takes over. A supply-side platform is exactly this kind of program: it belongs to the supplier’s side, that is, the website or app operator, and automatically puts that operator’s available ad space up for sale. Every time someone visits the page, it announces the available slot to potential buyers and collects their price bids. The slot goes to the highest bid, and all of this takes less than a tenth of a second.

What publishers gain from it

A single news site often has millions of page views per month, but only a small ad sales department. This inventory could never be sold by hand. A supply-side platform makes even small leftover quantities usable, because it auctions off every single visit individually. Without such technology, a large portion of the ad space would simply remain empty.

The second advantage is competition. If there’s only one buyer, that buyer sets the price. If ten buyers are competing at once, the revenue rises. This is exactly what the platform is built for: it connects one supplier with many buyers at once. Publishers often express the resulting average revenue in euros per thousand impressions.

At the same time, the operator retains control. They can set minimum prices below which they will not sell. They can also exclude entire industries, such as gambling or political advertising. These rules are entered into the platform once, and they then apply automatically to every auction.

The course of an ad auction

The process begins when a page is loaded. The browser notifies the supply-side platform that a particular ad slot is available. Information such as country, device type, page topic, and size of the space is included. The platform sends this request to many buying systems simultaneously.

On the other side sit demand-side platforms, the buying systems used by advertisers. They check whether the slot fits an ongoing campaign and respond with a price. This exchange is called real-time bidding. The supply-side platform compares the incoming bids and selects the highest one. The winner then delivers their ad creative, which the user sees as a banner or video.

A common misconception is that the supply-side platform selects the ad based on content. It does not. It merely organizes the auction and enforces the operator’s rules. Which ad fits in terms of content is decided by the buyer on the other side. Artificial intelligence still plays a role, though: models predict, for instance, how high the achievable price of a slot is likely to be, and continuously adjust minimum prices.

SSPs in stock market news and in the browser

In everyday life, little of a supply-side platform is visible. At most, one notices that an ad space briefly remains empty and then fills in. In that millisecond, the auction described above took place. Anyone who looks at the network requests of a news site in their browser will find the names of providers such as Google Ad Manager, Magnite, PubMatic, or Xandr.

These companies regularly appear in financial news, since some are publicly traded. Their revenues are considered an early indicator for the entire advertising market. Just as often, the topic is regulation: data protection rules and antitrust proceedings against major providers concern exactly this technology. To understand such reports, it’s important to know the division of roles. The supply-side platform represents the seller, the demand-side platform represents the buyer, and both meet on a marketplace called an ad exchange.