DSP (demand-side platform)
A demand-side platform is the buyer’s side of programmatic advertising. It connects an advertiser to many sources of inventory at once and decides, impression by impression, what to bid and on whom.
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Before programmatic buying, an advertiser who wanted to reach users across hundreds of apps and websites had to sign deals with each seller or ad network separately. A DSP replaces that with a single interface: the advertiser sets budgets, targeting and bids, and the platform evaluates incoming impressions from connected exchanges and buys the ones that fit.
How a DSP works
When a user opens an app or page with an ad slot, the publisher’s side announces that impression to one or more ad exchanges. Each exchange sends a bid request to connected DSPs, describing the placement, the device, the country and whatever other signals the publisher shares. The DSP scores the request against every active campaign, decides whether to bid and how much, and returns a bid within a fraction of a second. The highest eligible bid wins and its creative is shown.
- The publisher’s supply-side platform (SSP) offers the impression to exchanges.
- Exchanges send bid requests to DSPs.
- The DSP matches the request to campaigns and prices a bid.
- The exchange runs the auction and the winning ad is served.
- The DSP records the impression, and later any click, install or post-install event it can attribute.
DSPs typically support buying in open real-time auctions and in private marketplaces, where a publisher invites selected buyers to inventory on agreed terms.
How app advertisers use DSPs
Mobile DSPs buy in-app inventory: banners, interstitials, rewarded video and native placements inside other apps. App marketers use them for two jobs.
- User acquisition. Bidding on impressions likely to lead to an install, then optimizing toward later events such as a trial start or purchase once enough data exists.
- Re-engagement. Showing ads to people who already installed the app, for example lapsed users or trial users who did not convert, to bring them back. This depends on having an identifier or audience signal the platform is allowed to use.
On iOS, privacy rules limit user-level tracking across apps, so DSP campaigns increasingly rely on contextual signals and aggregated attribution rather than individual device histories. That makes it harder to see exactly which impressions produced a subscriber, and it is the main reason a subscription app should judge a DSP on downstream results, not on installs alone.
DSP vs ad network vs SSP
| Player | Works for | What it does |
|---|---|---|
| DSP | Advertisers | Bids on individual impressions across many exchanges from one account |
| SSP | Publishers | Offers the publisher’s impressions to exchanges and DSPs to get the best price |
| Ad exchange | Both sides | Runs the auction that matches bid requests with bids |
| Ad network | Mostly publishers, sells to advertisers | Aggregates inventory from its own publisher pool and sells it, often as packaged campaigns |
The lines blur in practice: many ad networks run their own exchange, and some companies operate both a DSP and an SSP. The useful distinction is control. A DSP gives the buyer impression-level bidding across supply sources; a network sells its own pool of inventory on its own terms.
Where a DSP fits next to Apple Ads
Apple Ads is not bought through DSPs. It is a closed auction inside the App Store, sold on Apple’s own platform, where users are already searching for apps. A DSP reaches people inside other apps who were not looking for yours. The two channels are complementary, but the traffic behaves differently, so compare them on the same downstream metrics: cost per trial, cost per subscription and cohort revenue, not cost per impression or cost per install.