What is a Supply Side Platform? What you need to know

supply side platform

“What’s an SSP? It’s is a platform to publisher success”

The Supply Side Platform, or SSP, is a crucial part of the modern, programmatic online advertising ecosystem.

While most people surfing the web are unaware of it, Supply Side Platforms play a key role in today’s internet browsing experience. When you’re browsing your favorite sites, there is a good chance that an SSP is involved every time you open a new page.

How’s that work? Let’s find out.

It all begins with the publisher

Let’s quickly establish what a publisher is.

A publisher is anyone that has some kind of audience that they want to monetize by serving ads. So, a publisher might be a blog, a news site, a mobile game, a vlog, et cetera.

Publishers are incredibly diverse. The only thing that they all have in common is the desire to monetize by serving ads.

In many cases, these publishers, especially extremely large ones with well-developed brands, will work directly with Ad Agencies. The Ad Agency will buy space on a site straight from the publisher itself. Often, however, the publisher can’t sell all of its available ad space itself.

Or perhaps it’s a smaller publisher. Smaller publishers simply do not have the presence to work directly with Ad Agencies directly.

In this case, they’ll go to a Supply-Side Platform with their available ad space, or “inventory“.

The Gateway to the Publisher

When large publishers need to fill remaining ad space or small publishers need to fill all their ad space, Supply-Side Platforms are often their best option.

The SSP is essentially the publisher’s entry point into a vast array of advertisers that are looking to get their ads out in front of users.

A large number of publishers will use the same SSP, and their aggregate content then constitutes the SSP’s “inventory.” The goal of the SSP is to sell this inventory on the open market to advertisers.

It’s essential to keep in mind, though, that the publisher’s ad server is sending each impression to the SSP.

It’s not selling ad space for a certain period of time or something to that effect. Instead, the SSP sells each impression that it receives from the publisher’s ad server. And it sells them individually.

How does the SSP do that?

By rapidly conducting an auction and sale in real time for every single impression. To do this the SSP links into a much larger ecosystem.

Where does the SSP fit in?

The Supply-Side Platform is only one link in a long chain. But it’s generally the only one with which publishers interact.

But let’s look at how it fits into the broader online advertising ecosystem. For on its own, the Supply-Side Platform can’t achieve much.

In general, there are five major links in the chain of programmatic ad buying.

These are the Publisher, the Supply-Side Platform, the Ad Exchange, the Demand-Side Platform and the Advertiser.

Let’s look at exactly how this works.

First, a user starts loading a page on a publisher’s site. In the HTML code, there is a section that refers back to the URL of the site’s Ad Server.

The publisher’s Ad Server then checks to see if this inventory is already bought by a direct buyer, if it is, then the Server displays the corresponding ad. If not, then the impression is passed on to the Supply-Side Platform that the publisher uses.

Here the SSP can contact a third-party data service to learn more about the impression before it sends it off to an Ad Exchange.

The Ad Exchange is the meeting place where Supply-Side Platforms and Demand-Side Platforms buy and sell.

When the Ad Exchange receives the information from the SSP, it creates a bid request. This bid request is then sent out to all the DSPs (and Ad Networks) on the Exchange.

The DSPs then quickly analyze the information that came with the bid request and compare it to their own data. Based on how well the impression matches up with an active campaign that the DSP is running, it returns a bid.

Now, the impression often doesn’t match a given DSP’s active campaigns, and in this case it returns a “no bid.” (A DSP must respond to a bid request).

The Ad Exchange then determines who won the auction.

The information pertaining to the winning ad is then sent back down the line. From the Exchange to the SSP, from the SSP to the Ad Server, and from the Ad Server to the user’s device.

All of this occurs while the user’s page is loading.

You can see why the SSP plays such an important role in the sequence. It is the intermediary between the publisher and the entire system. And without the SSP, this chain breaks.

Direct SSP/DSP Communication

The world of programmatic online advertising can seem extremely complicated. That’s because it is. So don’t think that there aren’t other steps involved or exceptions!

For example, an advertiser can, but usually doesn’t, buy ads directly from the Exchange. Likewise, SSPs and DSPs can communicate and bid directly with one another without an Ad Exchange intermediary.

Either way, Real-Time Bidding is still utilized – with or without an Exchange.

Powered by Real-Time Bidding

Real-Time Bidding is the system that is used when the impressions are being auctioned off. When the Ad Exchange or SSP sends out a bid request, and the bids are returned (generally in under 120 milliseconds), this is Real-Time Bidding. That is to say, bidding… in real time!

Now, the actual data exchange protocol used is generally OpenRTB. This standardized protocol allows all of the different Exchanges, SSPs, and DSPs to communicate with one another.

If you want to learn more about it, check out our extensive article on Real-Time Bidding here.

Protect that brand

Another critical feature that SSPs include is brand protection. Reputations can take years to build, but only seconds to lose.

Because of this, publishers are generally a little bit concerned about just selling space on their sites to the highest bidder. A news site, for example, does not want to find out that their ad space has been used to sell firearm accessories or adult content.

But sometimes it’s not so clear cut. Publishers also don’t want to find out that they have been advertising scams or low-quality products on their sites or in their apps.

Badly matched ads can quickly damage a publisher’s reputation. So to avoid placing these kinds of damaging ads, SSPs almost always have built-in brand protection tools.

Brand protection is an essential part of maintaining publisher confidence in programmatic ad placement.

How do Publishers choose an SSP

So now that you know what an SSP is, how would you choose one as a publisher?

There are generally two ways that SSPs specialize. The first is by the kinds of ads sold. The second is by geographic location or linguistic sphere. For example, if one of the sites in your portfolio has a predominantly Chinese audience, you’re probably going to want to use one of the major SSPs that specialize in the Chinese market.

Likewise, if you’re in Japan or an Arab country, your options could look a lot different than they would if your site had a primarily American or British audience.

You’d also look at what kind of ad formats they offer. If you’re only interested in video or native, that could limit the number of SSPs with which you could work.

Matching ad format to the publisher

Different publishers generally want to serve certain kinds of ads in a limited range of formats.

Certain ad formats may convert extremely well, but they may also be annoying on certain sites or in certain apps. Judging not only the content of ads, but what kind is also a crucial part of brand protection.

While a streaming site can generally use a wide range of ads, from video to popup to push, native text ads (sponsored articles) rarely work.

News sites, likewise, can have a really hard time integrating video ads because the news online is generally presented in article form. Some try to get around this via autoplaying, but that can risk upsetting the audience.

Likewise, popups on a video site can seriously upset the audience.

So while a given site might have the space for a wide variety of ads, publishers need the SSP to parse potential ads for both brand-damaging content and unsuitable formats.


Supply-Side Platforms allow publishers to fill unsold ad space on an open market. They give big publishers the chance to sell space they couldn’t sell on their own and small publishers the opportunity to monetize.

Through Real-Time Bidding, the SSP can sell each impression for its highest potential market value.

The SSP software has built-in protections that ensure that the ad format and content won’t be a risk to the publishers’ brands.

SSPs provide a one-stop, easy-to-use gateway to a much larger ad ecosystem, allowing publishers of all kinds to make better returns on their audience.

Quick Recap

A Supply-Side Platform (SSP) is a an online tool that allows publishers of various forms of content to sell their inventory to advertisers. The publisher sets certain parameters regarding ad format and content, then the SSP sells the inventory on a per-impression basis. This is either done via an Ad Exchange or by directly proposing impressions to the Demand-Side Platforms.

This entire process occurs every time a new page is loaded and generally in under 200 milliseconds.

Whereas we’ve been discussing Supply Side Platforms, here at Mobinner, we run a High-Performance Demand Side Platform. We connect advertisers to many different SSPs at once so they can maximize conversions. Come check us out!

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