What the Addition of DOOH to the OpenRTB Protocol Means for AdTech

Since its inception in November 2010, real-time bidding (RTB) has become one of the most significant advancements in programmatic advertising, allowing advertisers to bid on and purchase individual impressions across thousands of publishers simultaneously.

RTB started in web advertising and gradually expanded into other digital channels — most notably in-app mobile. More recently, RTB has been adopted in an emerging channel: digital out-of-home (DOOH) advertising.

This article explains what RTB and the OpenRTB protocol are, the unique challenges DOOH presents, and what the formal addition of DOOH to OpenRTB 2.x means for AdTech platforms and the companies that operate in this space.

Key Points

• The IAB Tech Lab has added support for DOOH advertising in the release of OpenRTB 2.x.
• Various companies contributed to the addition of DOOH in the OpenRTB protocol, including trade organizations like the Out of Home Advertising Association of America (OAAA) and Out of Home Advertising Association of United Kingdom (Outsmart), as well as AdTech companies and media owners including Broadsign, Centro, Clear Channel, Global, Hivestack, JCDecaux, Lamar, Ocean Outdoor, Place Exchange, TheTradeDesk, Triton, Vistar Media, VIOOH, and Yahoo.
• The introduction of OpenRTB standards for DOOH addresses many of the challenges companies faced when buying, selling, and measuring digital out-of-home ads — including the one-impression-to-many-viewers problem, reporting discrepancies around auction win notifications and ad views, and geolocation ambiguity.
• The new objects in OpenRTB 2.x give companies a standardized way to communicate and transact when buying, selling, and measuring DOOH inventory.

What Is the OpenRTB Protocol?

Real-time bidding is a media-buying process that allows advertisers to bid on and purchase individual impressions across thousands of publishers, rather than buying a fixed block of impressions from a single publisher or a small group of them (e.g., 10,000 impressions across 15 publishers).

The technical standard that powers this auction-based process is the OpenRTB protocol, developed by 6 pilot companies back in 2010.

Since then, the IAB Tech Lab and its members have been responsible for developing and releasing updates to the protocol.

The goal of OpenRTB is to give advertising technology platforms a common language for buying and selling digital media programmatically — regardless of which vendor's stack is involved on either side of the transaction.

What Is Digital Out-of-Home (DOOH) Advertising?

Digital out-of-home advertising is a digital advertising channel where ads are displayed on digital signage: billboards, screens inside and on top of vehicles, bus shelters, and similar placements in public spaces. It is the digital evolution of the traditional out-of-home (OOH) advertising channel.

Some examples of OOH and DOOH advertising in the public space:

The Main Challenges With DOOH Advertising

Not all digital advertising is delivered and measured in the same way. DOOH faces a distinct set of challenges that simply don't exist in web or in-app mobile advertising.

For instance, web advertising is delivered in real-time — the entire buying and selling process happens as the page loads. With DOOH, it can take up to 2 hours for an ad to be displayed from the time it was purchased. The gap between transaction and delivery has downstream consequences for reporting, measurement, and ad quality management.

Internet Connectivity Issues

DOOH panels are often located in high-traffic areas where thousands of people may be connecting to the same cell tower simultaneously. That congestion regularly causes connectivity problems for the panels themselves.

To work around this, many DOOH display networks pre-sell ad inventory and store the creatives locally on the panel — typically in a queue or playlist. This approach resolves the connectivity problem but introduces delivery delays, which is why the up-to-2-hour lag between purchase and display is common.

Because win notifications and billing events can't be reliably synchronized under these conditions, the IAB Tech Lab recommends that AdTech companies send win and billing events separately.

Displaying Multiple Impressions at Once

DOOH ads are shown in public spaces where multiple people are present at the same time. This creates an inherent discrepancy: one ad display event can represent many impression-equivalents, and media buyers and sellers historically reported these numbers differently.

The IAB Tech Lab addressed this by expanding the OpenRTB protocol with new properties that enable an impression multiplier dimension, making reported impression counts more precise and consistent across platforms.

Geolocation and Location Targeting

To protect displays from security threats, publishers (i.e., digital display owners) route display content over private IP networks. Ad delivery and reporting — including latitude/longitude positions and geo information such as address, postal code, and region — are handled through first-party ad servers and/or CMS systems.

Because publishers use their own private networks for this, DSPs cannot identify where ads are being displayed using standard IP-based geolocation techniques. The updated OpenRTB guidelines address this directly: DOOH transactions are now required to include the latitude/longitude field.

Different Ad Sizes

DOOH displays vary enormously in physical size — from a 32" digital sign inside a shopping mall to a display covering an entire building wall. They also differ in resolution and aspect ratio, both of which affect how an ad renders and how many people it reaches.

The larger the advertising surface, the greater the potential audience for a given impression — but screen dimensions are only one factor. Accurate reporting requires capturing resolution and aspect ratio alongside physical size.

Ad Quality and Approval

A single poorly targeted or inappropriate ad served to one browser user is a limited problem. The same ad displayed on a large public screen reaches many people simultaneously, creating significant brand and contractual risk for media owners.

As a result, ad approval for DOOH is maintained manually and can take several days to complete. The stakes are simply higher when a bad ad is visible to hundreds or thousands of people at once.

Different Digital Display Manufacturers

Unlike the TV and mobile device markets — where a handful of major brands dominate the hardware landscape — there are no worldwide leading brands selling DOOH screen technology. Media owners and publishers source their screens from a wide variety of manufacturers, meaning each network ends up with its own proprietary device types, IDs, and user agent strings.

This fragmentation makes it difficult to reliably identify displays, which in turn creates challenges in detecting bot traffic and ad fraud.

What Has Been Added to the OpenRTB Protocol for DOOH Advertising?

AdTech companies and media owners have been transacting DOOH inventory over OpenRTB for several years, but without any standardization. Every party had to build custom integrations to facilitate the RTB process — an approach that required additional technical resources, cost time and money, and produced a fragmented ecosystem where interoperability was never guaranteed.

The formal addition of DOOH to the OpenRTB protocol changes that. Companies now have a standardized set of objects and fields for communicating and transacting DOOH inventory.

Below are the key objects for DOOH advertising in OpenRTB 2.x, as documented in the IAB Tech Lab's implementation notes:

What the Addition of DOOH to OpenRTB Means for AdTech

The overarching goal of the OpenRTB protocol is to improve how AdTech platforms communicate when buying and selling digital media programmatically. Extending it to cover DOOH gives all parties involved in these transactions a common framework for addressing the challenges described above.

Specifically, the standardized objects and fields now allow platforms to:

• Receive a more accurate count of available impressions.
• Identify the approximate position of DOOH devices and digital displays via the required latitude/longitude field.
• Receive more accurate reports on when an auction was won and when the ad was actually displayed.
• Easily identify DOOH devices within reporting systems.
• Calculate screen dimensions.
• Apply frequency capping to DOOH campaigns.
• Distinguish between publisher-provided and exchange-provided device IDs.
• Define the approximate time window when an ad will be displayed.

The practical impact falls into two areas: better targeting and improved measurement.

Better Ad Targeting

Before DOOH was formally integrated into the OpenRTB protocol, ad targeting in this channel was approximate and often inaccurate.

DOOH is not a channel suited to individual-level targeting. Depending on the context and data available, the ad will typically target a specific demographic group at a specific moment — that's a core characteristic of out-of-home advertising that won't change regardless of how sophisticated the underlying technology becomes.

Data used for DOOH targeting and analytics typically comes from:

• Cultural and sporting events.
• Smart sensors and cameras.
• Measurement data from third-party companies.
• Mobile location data from ad exchanges and data brokers.

With specific objects now embedded in the OpenRTB protocol, it's more straightforward for marketers and platforms to plan and analyze a broader range of campaign parameters — including frequency capping and the time and place of ad display.

Improved Measurement

As smart cities deploy more IoT sensors, advertisers, media sellers, and AdTech companies gain access to richer data streams. Measuring DOOH campaign performance increasingly relies on mobile data, particularly location and event-based signals.

The new objects in the OpenRTB protocol make measurement data more accurate and more actionable. Based on IoT sensor and mobile data points, advertisers can now:

• Obtain more precise location information about the DOOH device where an ad was displayed.
• Isolate DOOH devices from other advertising touchpoints — useful when running omnichannel campaigns.
• Estimate the screen size of displays that served an ad.

How the OpenRTB Protocol Works in Practice

The OpenRTB protocol is a JSON-based standard that allows two applications to communicate with each other in a common language. Adding RTB capabilities to an AdTech platform or digital display system requires a solid understanding of how the protocol is structured and what each object represents.

The standardization brought by DOOH's inclusion in OpenRTB 2.x reduces the custom integration burden considerably — platforms that already support OpenRTB can extend their existing implementation rather than building DOOH support from scratch. For new entrants, the documented spec provides a clear foundation to build from, rather than negotiating proprietary integrations with each counterparty separately.