When I meet people (outside of our industry) and after they learn what I do, I frequently get the same question: “How do online suppliers I have been to follow me around the Internet?”

One friend explained a scenario where he had attempted to buy a diamond ring for his wife, as an anniversary present, from an online supplier.  At the last moment he got cold feet and backed out of the process.  Thereafter the supplier haunted him as he moved from website to website, making him feel guilty for reneging on the gift.

In most cases a high level explanation of retargeting suffices, but in this case (as my friend has a reasonable technical understanding) it didn’t.  The issue that stumped my friend,was more the breadth of websites that subsequently displayed ads for diamond rings and how they had gained a common understanding of him.

OK, to try and get this down once and for all and to give me the opportunity to be less boring at parties, I will try to explain the process.

My friend (to hide his identity I will call him Gary) visited “Diamonds Online”.  At a point in the process, after he decided not to make the purchase, Diamonds Online decided to retarget Gary, hoping to bring him back to the website and complete the sale.

Diamonds Online have a small image on their page, which called out to a demand side platform (DSP), when Gary loaded the page.  This enabled the DSP to drop a unique cookie onto Gary’s PC, which I will refer to as “DSP cookie 1” later.

The DSP is a company and platform that manages the advertiser’s (Diamonds Online) advertising requests.  In this case, retargeting potential buyers.

When Gary moved on to “Sports Online” he was retargeted.  Sports Online sell their advertising inventory through a supply side platform (SSP).  The SSP makes the inventory available for the DSPs to bid on in real time.  The SSP also dropped a cookie onto Gary’s PC, which I will refer to as “SSP cookie 9”.

As I previously said, Gary is technically savvy and immediately said “but, the SSP cannot get access to the DSPs cookie as it was not issued by them; therefore how does the DSP know it was me on the Sports site?”

“Ah”, I said, “That is were the magic comes in!”  The SSP caused Gary to run a script, which calls known DSP bidders, passing on the reference “SSP cookie 9”.   This in turn enabled the DSP to collect their cookie reference from Gary’s machine “DSP cookie 1”.  “Gotcha”, the link was established.  This process is known as piggybacking.

Whenever Gary visits a website that deals with the SSP, the DSP will know that it is Gary, he is a potential buyer of diamond rings and is interested in sports.  They are now able to bid in real time for inventory that the SSP makes available, in an informed manner.

In reality, the retargeting would probably take place on a site that is more closely related to diamond rings (such as a lifestyle site) than a sports site, but this explains the principle.

For those who are really interested, some SSPs work the other way around.  Instead of the DSP storing the match, the SSPs store the match, which is a result of a redirect from the DSP, essentially achieving the same thing.

Good, glad I got that one off my chest!

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