Real-Time Bidding (RTB)

Unlike traditional bulk ad buying, RTB operates on a per-impression basis. Each single ad slot on a webpage triggers an independent auction. This granularity allows advertisers to value every user uniquely based on their data profile, ensuring they only pay for the specific individuals they want to reach rather than broad, undefined audiences.

The entire RTB transaction must complete in under 100 milliseconds from the ad request to ad serving. This includes:

• User data passing to a Supply-Side Platform (SSP)
• Bid request broadcast to multiple Demand-Side Platforms (DSPs)
• DSP evaluation against advertiser criteria
• Bid response and auction winner selection
• Ad creative retrieval and rendering Any delay beyond this window results in a default or blank ad, losing revenue.

Most RTB exchanges use a second-price auction model. The highest bidder wins but pays $0.01 more than the second-highest bid. This encourages truthful bidding, as the winner pays the market-clearing price rather than their maximum willingness to pay. Some exchanges have shifted to first-price auctions, where the winner pays exactly what they bid, requiring bid-shading algorithms to avoid overpayment.

Communication between SSPs and DSPs is standardized by the OpenRTB protocol, maintained by the IAB Tech Lab. This specification defines the JSON-based request and response objects, including:

• BidRequest: Contains site, user, device, and impression details
• BidResponse: Returns bid price, ad markup, and tracking URLs This standardization enables interoperability across hundreds of ad tech vendors without custom integrations.

DSPs evaluate each bid request by applying proprietary CTR prediction models and conversion rate models to calculate an expected value per mille (eCPM). The bid price is derived from:

• Predicted probability of a click or conversion
• Advertiser's target cost-per-action (CPA) or return on ad spend (ROAS)
• User segmentation data (demographics, browsing history, purchase intent) This valuation must occur in single-digit milliseconds to stay within the total latency budget.

Before an auction can occur, the SSP and DSP must map their respective user identifiers through a cookie sync process. When a user visits a publisher site, the SSP redirects to the DSP's sync URL, passing its user ID. The DSP maps this to its own ID and stores the match table. This identity resolution is critical for applying audience data and frequency capping during the bid evaluation.

A structured data packet broadcast by a Supply-Side Platform (SSP) to multiple Demand-Side Platforms (DSPs) when an ad impression becomes available. It contains critical contextual signals for valuation:

• User Data: Cookie ID, device type, IP-derived geolocation, browser language.
• Context Data: Page URL, content category, IAB taxonomy classification.
• Inventory Data: Ad slot position, accepted creative sizes, minimum bid floor.
• Privacy Signals: GDPR consent string, CCPA opt-out status. The DSP must parse this payload and return a bid response within a strict timeout window, typically 100-150 milliseconds.

A technology platform used by digital publishers to manage, sell, and optimize their available ad inventory. The SSP acts as a yield-maximization engine:

• Header Bidding Wrapper: Orchestrates a pre-auction among multiple demand sources before calling the primary ad server.
• Floor Price Optimization: Dynamically adjusts the minimum acceptable bid based on historical demand patterns and current fill rates.
• Channel Management: Segments inventory into direct deals, private marketplaces (PMPs), and the open exchange.
• Ad Quality Screening: Filters malicious creatives and enforces competitive separation rules before rendering.

A digital marketplace that facilitates the real-time transactional connection between DSPs and SSPs. It operates as a neutral auctioneer:

• Auction Mechanics: Typically runs a second-price auction (the winner pays $0.01 more than the second-highest bid), though many have shifted to first-price auctions.
• Traffic Shaping: Filters low-quality bid requests to reduce infrastructure load on DSPs.
• Fee Structure: Extracts a transparent "take rate" from the clearing price, usually 5-20%.
• Identity Resolution: Maps various user identifiers (cookies, MAIDs, UID2.0 tokens) to a common namespace for cross-platform targeting.

The post-auction workflow that finalizes the transaction and delivers the creative. After the exchange declares a winner:

• Win Notice URL: The DSP receives a ping confirming the auction win and the final clearing price.
• Creative CDN Retrieval: The user's browser is redirected to the advertiser's Content Delivery Network (CDN) to fetch the HTML5 or video creative asset.
• Client-Side Rendering: The creative executes in-browser, firing an impression tracker to confirm viewability.
• Bid Loss Feedback: Some exchanges provide a loss reason code (e.g.,

A unique identifier that facilitates non-open-auction transactions between a specific buyer and seller. This bypasses the fully competitive RTB environment for guaranteed access:

• Preferred Deals: The seller offers inventory at a fixed price before it goes to open auction; the buyer gets a "first look."
• Private Auctions: A closed group of invited buyers compete in a real-time auction for premium inventory.
• Programmatic Guaranteed: A direct reservation buy executed programmatically, guaranteeing a fixed volume of impressions at a fixed CPM.
• Deal ID Transparency: Both parties use the ID to reconcile billing and delivery reports in their respective platforms.