This year, there was a dramatic rise in adtech “stacks,” with Facebook’s relaunch of Atlas and the expansion of Google’s DSP business, but WPP wants to support “an independent ad tech ecosystem where technology and media companies remain separate. It is this direction that aligns with the recently announced alliance with AppNexus, explains Brian Lesser, CEO of Xaxis, the programmatic agency unit of WPP, in this interview with Beet.TV