What is an SSP? A plain-English guide for publishers

By the MS Ads Network team · Published 14 October 2026 · 5 min read

If you have ever wondered what actually happens between "a visitor opens my page" and "an ad appears and I earn money", the answer usually involves a supply-side platform, or SSP. This guide explains what an SSP does, how an auction runs in a fraction of a second, how an SSP differs from an ad network and a DSP, and what to check before you pick one for your site.

What is an SSP?

A supply-side platform is software that publishers use to sell their advertising space automatically. "Supply" means the ad impressions your website or app can show. The SSP takes each available impression, describes it to many potential buyers at the same time, collects their bids, and lets the best valid bid win, all while your page is still loading.

Before programmatic advertising, selling ads meant emailing media kits, negotiating prices and inserting ads by hand. An SSP replaces that with an automated marketplace. You keep control through settings such as floor prices (the minimum you accept), blocked categories and allowed ad formats. The buyers compete for each impression instead of buying your traffic in bulk at a fixed rate.

How an SSP auction works, step by step

Most SSPs use the OpenRTB protocol published by IAB Tech Lab, so buyers and sellers speak the same language. A typical auction looks like this:

1. The page loads. Your ad tag (a small script you placed once) tells the SSP that an ad slot, say a 300×250 in the sidebar, is ready to be filled.
2. The SSP builds a bid request. It describes the impression: the page URL, ad size, device type, approximate country and other non-personal signals. It also applies your rules, for example your floor price.
3. Buyers bid. The request goes to connected demand partners, usually demand-side platforms (DSPs) that run campaigns for advertisers. Each decides in milliseconds whether the impression fits its campaigns and what it is worth.
4. The SSP picks a winner. Bids below your floor or from blocked advertisers are discarded. The highest remaining bid wins. In a first-price auction, the winner pays what it bid.
5. The ad renders. The winning creative is returned and shown in your slot. The impression is recorded for reporting.
6. Quality checks and payment. Good SSPs check traffic for invalid activity, such as bots, before crediting earnings. Your share of the revenue is added to your balance and paid on the platform's schedule.

The whole process usually takes well under a second. The visitor just sees the page load with an ad in it.

SSP vs ad network vs DSP

These terms are often mixed up, and many companies offer more than one of them, so it helps to separate the roles:

An ad network is a simpler model: the network buys your inventory and sells it on, so you depend on that one network's advertisers. An SSP opens your inventory to many buyers at once, which usually means more competition per impression. A DSP is the buyer-side mirror of an SSP; advertisers use it to bid. Some platforms, MS Ads Network included, run both an SSP for publishers and a self-serve DSP for advertisers.

Why publishers use an SSP

• Competition per impression. When several buyers bid on the same impression, prices are set by demand rather than by a fixed rate card.
• Control. Floor prices, category blocks and format choices let you balance revenue against user experience.
• Transparency. Bid-level reporting can show you how many bids arrived, what won and why a request went unfilled.
• Standards. OpenRTB, ads.txt and sellers.json make the supply chain verifiable, which serious advertisers increasingly require.
• Several formats from one integration. Banner, native, video and other formats can run through the same account.

How to choose an SSP: a practical checklist

Most comparisons focus only on CPM, but the CPM a platform advertises tells you little about your own site. Use questions you can check instead:

1. Revenue share. What percentage of gross auction revenue do you keep? Is it written in the terms?
2. Payment terms. What is the minimum payout, how often are you paid (for example monthly, Net-30), and which payout methods work in your country?
3. Approval requirements. Is there a minimum traffic level? Which content is not accepted?
4. Formats. Does it support the formats that fit your site, such as native for content sites or video for sites with a player?
5. Traffic quality handling. How is invalid traffic detected, and what happens to earnings from it? Clear rules protect honest publishers.
6. Supply-chain transparency. Does it publish a sellers.json file, and does it give you the exact ads.txt line to add?
7. Reporting. Can you see earnings by site, ad unit, country and format? Can you see why requests went unfilled?
8. Support. Can you reach a person when something breaks?

Then test. Run the SSP on part of your traffic for a few weeks and compare eCPM (earnings per 1,000 impressions), fill rate and page speed with your current setup. Your own numbers matter more than any published average.

What setting up an SSP usually involves

The steps are similar across platforms. With MS Ads Network they are:

1. Create a free publisher account and add your website.
2. Add the ads.txt line shown in your dashboard to the ads.txt file at the root of your domain. Our ads.txt and sellers.json guide walks through it.
3. Wait for the site review. We check content and traffic quality before approval.
4. Create ad units for the formats you want and paste the tags into your pages.
5. Watch reporting for the first days, then adjust placements and floors.

Common mistakes to avoid

• Floors set too high on day one. High floors can block most bids. Start moderate and raise them with data.
• Too many ad units. More units can lower viewability and page speed, which can reduce what buyers will pay.
• Missing or outdated ads.txt. Many buyers skip inventory they cannot verify.
• Judging after one day. Auctions need some time and volume to settle. Compare at least a few weeks.
• Buying traffic. Paid or incentivised traffic is a common source of invalid traffic and can lead to withheld earnings.

Frequently asked questions

Is an SSP the same as an ad exchange?

They are closely related. An ad exchange is the marketplace where the auction happens; an SSP is the publisher's tool for selling into exchanges and buyers. Many modern platforms combine both.

Do I need a lot of traffic to use an SSP?

Requirements vary by platform. Some focus on large publishers; others, including MS Ads Network, review smaller sites individually, focusing on content and traffic quality.

Can I use an SSP and Google AdSense together?

Often yes, if ads do not overlap or mislead users and each platform's policies are followed. Read the terms of both before combining them.

How do SSPs make money?

Usually through a revenue share: the platform keeps a percentage of the gross auction revenue and passes the rest to the publisher.