I think it's worth adding how DSPs and ADXs fit together. There are only a handful of ad exchanges out there -- Google ADX, OpenX, AppNexus, etc. Some brands an

I think it's worth adding how DSPs and ADXs fit together. There are only a handful of ad exchanges out there -- Google ADX, OpenX, AppNexus, etc. Some brands and agencies are large enough to buy inventory directly through these but for most brands and agencies, it's too expensive and cumbersome to do so. This is where DSPs fit in. DSPs buy large batches of inventory from the ad exchanges and resell them to brands and agencies and try to add value where they can.