Supply-side platform (SSP)

An SSP (supply-side platform) is software that publishers use to sell ad space on websites, apps or connected TV to many buyers at once, applying floor prices automatically and picking the winning bid for each impression.

What is an SSP?

The “supply side” is whoever has space to sell: a news site, a comic reading app, a free game. Each time someone opens a page, the SSP sends that impression out to multiple demand sources, including ad exchanges and DSPs, then picks the best price that meets the publisher’s conditions.

The main jobs an SSP does for a publisher:

• Setting floor prices by placement, format, country or buyer.
• Blocking categories, advertisers or creatives the publisher does not want to show.
• Managing deal types: open auctions, private auctions for a group of invited buyers, or guaranteed deals with a fixed number of impressions at a fixed price.
• Reporting revenue, fill rate and eCPM for each demand source.

Header bidding and Prebid

Header bidding lets a publisher collect bids from many demand sources at the same time and then have those bids compete directly with bids in the ad server (Prebid.org, Intro to Header Bidding, accessed October 2026). Prebid is an open-source toolkit for running header bidding on web, in apps and on servers. An SSP or buyer that wants to take part connects through a bidder adapter in Prebid. That way the publisher does not depend on the priority order the ad server assigns to each demand source.

Changes in 2025 and 2026

The remedies ruling in the Google ad tech case, issued in September 2026, requires DFP (Google’s ad server for publishers) to work with other exchanges, including Prebid, the same way it works with AdX. It also bars Google Ads from opening its own separate direct bidding channel into DFP, while it can still do so through Prebid (Tech Policy Press, September 2026). For independent SSPs, this opens up more chances to compete for the same impression on pages that use DFP. The real effect still depends on how the court-appointed monitor and technical committee oversee enforcement.

On transparency, IAB Tech Lab maintains a set of supply chain standards: ads.txt and app-ads.txt, which let publishers declare who is authorized to sell their inventory; sellers.json, which lets SSPs disclose who their sellers are; and the SupplyChain object in OpenRTB, which lets buyers see every link in a bid request (IAB Tech Lab, sellers.json, updated October 2026).

SSP vs. ad exchange vs. ad server

Example (hypothetical)

A news site gets 3 million pageviews a month, with 2 ad slots on each page, which makes 6 million ad requests. Through the SSP, 70% of those requests find a buyer, giving 4.2 million impressions. At an eCPM of 20,000 VND, monthly revenue is 4,200,000 / 1,000 × 20,000 = 84 million VND. If adding demand sources lifts the fill rate to 80% while eCPM holds steady, revenue rises to 96 million VND.

Frequently asked questions

Do advertisers need to care about SSPs?

Yes, at least enough to check. When you buy through a DSP, look at which SSP your impressions come from and whether the publisher lists that SSP in its ads.txt. Inventory resold through several layers of middlemen is harder to keep clean.

Is an SSP the same as an ad network?

Not quite. An ad network pools inventory and resells it in packages, while an SSP sells each impression at auction through RTB. Some companies run both models.

If you would like to review the supply sources in a display campaign you are running, the Adtek team can go through them with you via our contact page.