Passbacks

A "passback" setup can be used to have a third party have a look at an impression and decide in realtime whether to use it (serve an ad) or pass it back. If passed back, we need a mechanism to put the impression to use.

In ASX, two features are used to facilitate passbacks.

Keyword Targeting

Assign a keyword such as "passback" to the campaigns that should only be available in a zone if it has been passed back to. The flow would be:

1. Zone is invoked without any keyword targets. 
2. A campaign containing ads that are tags from a third party is selected according to its priority
3. The third party either uses the impression and serves an ad, or serves an ASX passback tag that has been prepared.
4. The passback tag invokes the same zone, but with the keyword=passback parameter.
5. A campaign assigned to the zone that has the passback keyword is selected according to its priority

Passback Zone field and macro

Since several zones might traffic the campaign from the third party, we need to be able to specify in real time to the third party what zone to pass the impression back to. This is done via the {passback_zone} macro. The macro will be replaced with the id of the zone selected as the Passback Zone field in Inventory / Direct Supply / Zones.