I want to use Google Adsense in my chain of networks. I use BurstMedia ads on my site, but a lot of times, especially for international users, public service ads show up. I looked at using Google Adsense ads in place of Burst public service ads, but Burst only has a spot for a url, which will be shown in an i-frame if they cannot serve paid ads. So is Adsense in i-frame Okay? I don't think so, because that i-frame will have nothing but the Adsense ads, and I don't think thats in compliance. My question is, how do I put Adsense second in my ad chain and still follow Adsense polices/TOS when BurstMedia uses i-frames to display ads that are not being serevd by them?