How does 'Project Shield' work?

Allo Logan,

I just read about Google successfully testing what they call 'Project Shield' (sounds like a Marvel tie-in to me :p) in various 'trusted' networks. I understand that they are somehow using the Google infrastructure to pull off this DDoS protection, but how exactly?

Pyromethious

 

Note: Yes, I'm sure someone else on the forums is 'in the know' enough to answer this, but it's something 'new and exciting' for those who may have a delicate infrastructure (versus a DDoS attack) and worth having in the Tek.