What Is RTB? How Real-Time Bidding Works

What Is RTB?

RTB (Real-Time Bidding) is the protocol that enables the ad impression opportunity created the moment a user opens a web page or mobile app to be bought and sold through an instantaneous auction between buy-side and sell-side software — all within milliseconds.

The auction process is run entirely by automated algorithms and completes within roughly 100 milliseconds (0.1 seconds) — a window imperceptible to the human eye — between the user clicking through to the page and the browser rendering the ad slot on screen.

Sample Latency Budget and Real-World Integration Constraints

In programmatic auctions, “100 milliseconds” is not a universal protocol requirement. Under the OpenRTB specification, the permitted response time is set dynamically by the tmax parameter within the bid request. Depending on the publisher’s latency tolerance and geographic server distances, this value typically ranges between 80 ms and 250 ms in standard integrations.

The 100-millisecond timeline below is a sample engineering latency budget (engineering SLA benchmark) scenario applied by tier-1 global ad exchanges:

[User Click]
  │  0 - 20 ms : Browser Ad Tag / Prebid.js client-side auction
  ▼
[SSP / Ad Exchange]
  │ 20 - 50 ms : Bid Request packaging & parallel broadcast to DSP networks
  ▼
[DSP Bidding Engine]
  │ 50 - 80 ms : Targeting validation, Valuation (ML), Bid Shading & Response
  ▼
[Clearing & Render]
  │ 80 - 100 ms: Highest bid (First-Price) selection, iframe render & Win Beacon
  ▼
[Ad Live]

(The flow above is a conceptual SLA allocation illustration for high-performance ad-server integrations.)

1. 0 – 20 ms (Client Request & Prebid): The user loads the page. The header bidding script (Prebid.js) or Google Publisher Tag (GPT) collects the on-screen slot sizes, the page URL, and user identity signals.
2. 20 – 50 ms (SSP & Ad Exchange Transmission): The SSP (Supply-Side Platform) packages every variable related to the ad slot according to the standard OpenRTB protocol and transmits it to dozens of contracted DSPs (Demand-Side Platforms) simultaneously over socket connections.
3. 50 – 80 ms (DSP Bidding Engine): The DSP’s bidding algorithms evaluate the incoming request:
   • Has this user visited our site before (Retargeting)?
   • Are the campaign budget and frequency cap (Frequency Capping) within limits?
   • What is the likelihood this impression will produce a click or conversion (CTR / CVR prediction)?
   • If the DSP decides to bid, it prepares the BidResponse JSON object within milliseconds.
4. 80 – 100 ms (Auction Clearing & Render): The Ad Exchange or SSP collects the incoming bids. The DSP submitting the highest bid wins the auction. The corresponding ad creative code (adm) is delivered to the user’s browser, and the win notification (nurl) is fired.

The OpenRTB 2.6 Protocol: Bid Request and Bid Response Architecture (IAB Tech Lab)

The common language of the programmatic ecosystem is the OpenRTB protocol, standardized by the IAB Tech Lab.

(Important Architectural Note: The JSON examples below are simplified illustrative templates based on the OpenRTB 2.6 specification, the most widely deployed production standard in the industry. They should not be confused with the layered AdCOM object structure introduced in OpenRTB 3.0.)

Sample OpenRTB 2.6 Bid Request (SSP → DSP – Illustrative Template)

The simplified JSON object below shows the bid call that the SSP sends to the DSP via the ad exchange:

{
  "id": "req-9842105-tr",
  "imp": [
    {
      "id": "1",
      "banner": {
        "w": 300,
        "h": 250,
        "pos": 1
      },
      "bidfloor": 1.20,
      "bidfloorcur": "USD"
    }
  ],
  "site": {
    "id": "pub-gazete-101",
    "name": "Ekonomi Portalı",
    "domain": "ekonomiportali.com",
    "cat": ["IAB13", "IAB13-1"]
  },
  "device": {
    "ip": "88.245.xxx.xxx",
    "ua": "Mozilla/5.0 (Windows NT 10.0; Win64; x64)...",
    "geo": {
      "country": "TUR",
      "city": "Istanbul"
    }
  },
  "user": {
    "id": "buyer-cookie-uid2-hash-8871"
  },
  "bcat": ["IAB25", "IAB26"],
  "tmax": 120
}

• bidfloor: The minimum eCPM floor price the publisher will accept for this slot ($1.20).
• cat: IAB content taxonomy (Real Estate / Finance).
• tmax: The maximum timeout within which the DSP must respond (120 ms in this request).

Sample OpenRTB Bid Response (DSP → SSP)

When the DSP wants to purchase this impression, it returns the following response:

{
  "id": "req-9842105-tr",
  "bidid": "bid-dsp-55102",
  "seatbid": [
    {
      "bid": [
        {
          "id": "b1",
          "impid": "1",
          "price": 2.45,
          "adid": "ad-luxury-villas-300x250",
          "nurl": "https://dsp.adtech.com/win?price=${AUCTION_PRICE}",
          "adm": "<a href=\"https://proje.com\"><img src=\"https://cdn.proje.com/300x250.webp\"/></a>",
          "crid": "cr-9021"
        }
      ]
    }
  ],
  "cur": "USD"
}

• price: The CPM amount bid by the DSP ($2.45).
• nurl: The notification URL fired when the auction is won (Win Notice Beacon).
• adm: The HTML/JS ad markup to be injected into the browser iframe.

Auction Models: The Shift from Second-Price to First-Price

Until 2019, the dominant model in digital advertising was the Second-Price Auction. Under this model, the highest bidder won but paid only 1 cent ($0.01) more than the second-highest bid.

What Is Bid Shading?

Because advertisers pay the full amount of their bid under the First-Price model, DSPs developed Bid Shading algorithms to prevent the risk of overpaying. AI analyzes the publisher’s historical clearing prices and lowers the bid to the minimum level sufficient to win (e.g., bidding $2.30 instead of $3.50 and still winning the auction).

The Difference Between RTB and Programmatic

These two concepts, often used interchangeably in the industry, are hierarchically distinct:

• Programmatic Advertising (Umbrella Concept): All digital ad buying and selling processes executed automatically through software.
• RTB (Buying Method): Just one of the programmatic buying methods. The programmatic landscape consists of 4 distinct models:
  1. Open Auction (RTB): A real-time auction open to all buyers.
  2. Private Marketplace (PMP): An invitation-only auction in which the publisher offers select buyers a custom floor price via a Deal ID.
  3. Preferred Deals: A model offering first-look bidding rights at a fixed CPM, without an inventory guarantee.
  4. Programmatic Guaranteed (PG): Direct contracts in which a specific impression volume and fixed price are guaranteed in advance.

Applying RTB in a Real Estate Investment Scenario

Let’s examine how a high-budget residential development project bids in RTB auctions:

• User: An investor reading an article on the currency/real estate market on Bloomberg or Fortune Türkiye.
• Bid Request: The publisher’s SSP passes the user’s historical cookie signals and content category (Finance) to the Ad Exchange.
• DSP Valuation:
  • Company A (Fast-Moving Consumer Goods): Bids $0.45 as a general impression eCPM for this user.
  • Company B (Luxury Real Estate Developer): Verifies through its CRM/DMP data layer that the user has previously browsed villa launch pages for Cyprus or Bodrum. Due to the high intent score (High Purchase Intent), it raises its bid to $2.85.
• Outcome: Company B wins the auction. As the user scrolls the page, they see precisely the targeted villa promotion creative.

Citation

Yalçın, K. (2026). What Is RTB? How Real-Time Bidding Works. KorayYalcin.org Publications & Research.

Related Articles

• What Is Programmatic Advertising?
• What Is a DSP? How Demand-Side Platforms Work
• What Is an SSP? A Guide to Supply-Side Platforms
• The Differences Between DSPs, SSPs, and Ad Exchanges