The Basics of Getting Ads on the Page

Not a lot of people outside of ad ops can tell you how exactly an ad is served on a webpage, but what if we said that ad serving is kind of like staying at a friend’s place and ordering pizza? Bear with us here.

When you visit a publisher’s website, your browser is given HTML code. This code tells the browser where to get content for the site and how to format it, like how a friend shows you around their place, points to the clean towels and helps you figure out the TV setup. An ad tag is included in the code, and this tag orders an ad for your browser — not unlike the way your friend gives you the number to order pizza from their go-to place.

When the ad tag loads, it begins a conversation with the ad server and the browser. The browser gives the server basic info: cookie ID, the browser/OS, IP address and the URL it’s making the call from. The ad server uses this information to select an ad (more on this below), and tells the browser where to find the ad — like if you told the pizza place your food preferences (overshare much?) and they picked your pizza for you. All this takes around 200 milliseconds.

Fun Fact: Servers are always the life of the party.


After the server gathers the data it has on the browser, the impression is then shopped to other parties either systematically (this is called the Waterfall) or all at once (this is called Header Bidding). These other parties receive the data from the impression and check it against their own parameters and data to determine if they want to purchase the impression.

They then either accept the impression, decline it or bid on it depending on their agreement with the website. The server either chooses the highest-priority party that accepts (Waterfall), or the highest-bidding party (Header Bidding) to serve an ad to the impression.

Header bidding is gaining popularity as it allows more competition for bidding, which tends to lead to an increased CPM (Cost Per Thousand Impressions). However, header bidding has latency issues — there’s a strong correlation between the number of bidders and longer loading times. The CPM rises with more bidders, but so does the time it takes to load an ad.

How popular is header bidding? 43 percent of publishers in the UK use it and continue to use it. 46 percent of publishers don’t plan on using it.