Published November 7, 2026 · By Ailumic # What is a DSP, or demand-side platform? A demand-side platform, or DSP, is software that buys ad space for advertisers: it sees each slot that comes up for sale, decides in a fraction of a second whether to bid and how much, and places the ad if it wins. It sits on the advertiser’s side of the auction; the publisher’s side is a supply-side platform, and an ad exchange runs the auction between them. Ailumic is a DSP designed for small businesses to use directly. ## The three parts of an ad auction - **The demand-side platform (DSP)** works for the advertiser. It looks at each slot that comes up and bids for the ones worth having. - **The supply-side platform (SSP)** works for the app or the website. It offers each slot for sale to many buyers at once. - **The ad exchange** is the marketplace in between, where the auction runs and the best bid wins. Some supply-side platforms run an exchange of their own. The words “demand” and “supply” are the economist’s: advertisers want the space, publishers have it. Our guide on [how real-time ad auctions work](https://www.ailumic.com/guides/how-real-time-ad-auctions-work/) follows one slot through all three. ## What a DSP decides For every slot that comes up, in a fraction of a second, a DSP works out: - whether the slot is in the place, on the days and in the shape the advertiser asked for; - whether the advertiser still has budget left to spend; - what the viewing is worth to the advertiser, and so what to bid. If the bid wins, the DSP delivers the ad to be drawn in the slot, and it records the result for the report. ## A DSP is not an ad network An ad network buys space in bulk and resells it to advertisers as a package. A DSP buys one slot at a time, in auctions, for the advertiser it is working for. The first is a wholesaler; the second is an agent at the auction. ## Why most advertisers never meet one Most DSPs are used by agencies, who run campaigns for many advertisers every day, and are built for that work. A small business seldom has a reason or a way to use one directly, so it buys through an agency or through a service that keeps the buying out of sight. ## Where Ailumic fits Ailumic is a DSP designed for small businesses to use directly. You do not operate it. You set an amount, an area and the days, and it does the bidding and writes the report in plain words. How the pieces fit is on the page about [how Ailumic works](https://www.ailumic.com/platform/). Example A game app has a banner slot. Its supply-side platform offers the slot to an exchange. The exchange asks the DSPs what they will pay. A bakery’s DSP, which knows the bakery wants to be seen near its shop on weekends, bids; the best bid wins; the bakery’s banner is drawn in the app. All of it takes a fraction of a second. Read next - [What is programmatic advertising?](https://www.ailumic.com/guides/what-is-programmatic-advertising/) - [How do real-time ad auctions work?](https://www.ailumic.com/guides/how-real-time-ad-auctions-work/) - [How Ailumic works](https://www.ailumic.com/platform/) Ready to try it? Ailumic is opening to its first advertisers in the United States. [Get early access](https://www.ailumic.com/start/) Guides ## More questions, answered first. - ### [How do real-time ad auctions work?](https://www.ailumic.com/guides/how-real-time-ad-auctions-work/) Every ad slot is sold in an auction that lasts a fraction of a second. Who bids, what decides the winner, who pays, and what it means for a small budget. Updated November 1, 2026 - ### [What is a CPM in advertising?](https://www.ailumic.com/guides/what-is-a-cpm/) CPM is the price of showing an ad one thousand times. Why ad space is priced per viewing, what moves the price, and why Ailumic publishes no price list. Updated November 1, 2026 - ### [Banner, native or full-screen: which ad format should a small business choose?](https://www.ailumic.com/guides/banner-native-or-full-screen/) A banner runs beside the content, a native ad sits in the feed, a full-screen ad fills an app between pages. How to pick one for the ad you have. Updated November 1, 2026 - ### [How much should a small business spend on ads to start?](https://www.ailumic.com/guides/how-much-to-spend-on-ads/) Size a first ad budget by what you can afford to learn from, not by a rule of thumb: enough to run a full week, small enough that a lesson with no sale is fine. Updated November 1, 2026 - ### [How do I read an ad report?](https://www.ailumic.com/guides/how-to-read-an-ad-report/) Read an ad report in order: times shown, clicks, cost, then where and when it ran. What the click-through rate tells you, and what to change next. Updated November 4, 2026 - ### [How long should an ad campaign run?](https://www.ailumic.com/guides/how-long-should-an-ad-run/) Run a first ad for a full week and no longer than it takes to learn one thing. Why a week, why not months, when to stop early and when to add budget. Updated November 1, 2026 - ### [What is programmatic advertising?](https://www.ailumic.com/guides/what-is-programmatic-advertising/) Programmatic advertising is ad space bought by software, one viewing at a time, in an auction. What it replaced and what it means for a small business. Updated November 7, 2026 - ### [How do ads in mobile apps work?](https://www.ailumic.com/guides/how-mobile-app-ads-work/) An app sets aside ad slots, sells each one in an auction as it is about to appear, and draws the winning ad. What an advertiser chooses and sees afterwards. Updated November 7, 2026 - ### [How do I write an ad for my small business?](https://www.ailumic.com/guides/how-to-write-an-ad/) Write one message for one kind of person, say what to do next, and cut the rest. How to fit it to a banner, native or full-screen ad, and when to rewrite. Updated November 7, 2026