What is a DSP (Demand-Side Platform)?

A DSP (Demand-Side Platform) is software advertisers or agencies use to buy impressions across many publishers from one interface. The DSP connects to SSPs and ad exchanges, receives bid requests for an impression, decides whether to compete, and submits a bid. It is a programmatic role, not a brand: DV360, The Trade Desk, and Moloco are examples of DSPs, not the subject of this page.

Before DSPs, a buyer opened a campaign in each network. A DSP folds display, video, in-app, and often CTV inventory into one seat: creatives, audiences, GEO, frequency caps, domain filters, and bid strategy live in one place. Buyer billing is usually CPM (sometimes CPC/CPA goals on top of a CPM auction). A DSP seat is access and billing, not “another ad network”: inventory arrives from outside, through connected SSPs and exchanges.

What a DSP does on each impression

A bid request arrives: URL or app bundle, slot size, GEO, device type, deal ID, sometimes an audience signal.
The DSP checks the request against campaign rules (whitelist/blacklist, brand safety, viewability, frequency, budget).
If the impression fits, it computes a bid and replies in milliseconds (often over OpenRTB).
On a win it returns the creative; the click goes to a landing page or through a tracker.

The bid / no-bid decision is the product. Algorithms may optimize to CPA/ROAS, but the exchange still bills won impressions. Buyers watch eCPM, CPC, and ROI in the tracker, not only win rate in the DSP.

Place in the chain

Demand side: advertiser and DSP. Supply side: publisher and SSP. Between them sits an ad exchange (sometimes built into the SSP). The auction for one impression is RTB; invite-only deals with chosen publishers are PMPs (deal ID); fixed volume and price is programmatic guaranteed. A DSP can sit in all three when the seat and inventory allow it.

Targeting signals: first-party (own pixels and CRM), platform segments, and third-party providers where they still sell. Retargeting and frequency caps depend on cookies, mobile IDs, or alternative IDs; after ITP/ATT those audiences shrink.

Examples are not the article

DV360 is Google Marketing Platform’s DSP, stronger on Google inventory and the enterprise stack. The Trade Desk is an independent DSP, often used for open web and CTV. Moloco and other mobile DSPs skew to in-app and app UA. Large networks ship in-house DSPs; agencies use white-label seats. Brand pages describe a product; this page describes the role: demand, bid, won impression.

DSPs in arbitrage

A solo affiliate rarely holds an enterprise DSP seat: budget floors, KYC, vertical bans. More often the buyer uses a network DSP UI, an agency seat, or a self-serve DSP with a lower minimum. Typical formats are display, video, and in-app when you need scale and placement filters rather than one walled garden.

Without a postback and sub-source marks, the DSP optimizes to its own conversions (pixel, view-through) while the affiliate network pays for different events. Domain spoofing, bots, and non-viewable impressions inflate spend: buyers check viewability, fraud scores, and app/domain whitelists.

What a DSP is not

Not an SSP. An SSP sells publisher inventory. A DSP buys. One company may ship both products; the roles stay distinct.
Not a Direct or Google Ads account. Those are walled-garden PPC; in the CIS they fall under contextual advertising, not “DSP.” The exception is a separate programmatic product such as DV360 beside Google Ads.
Not an ad network with a fixed CPM card. A network sells its own pool from a UI. A DSP bids on external inventory request by request.
Not RTB. RTB is the auction rule for an impression. A DSP is the buyer that enters that auction — or takes a PMP/guarantee with no open auction.