Very simple. It was in english and they asked me about my experience with networks, carriers and UNIX system. I detailed my experience as independent consultant implementing Cisco equipments. I told I had no experience directly with carriers. Regarding my UNIX experience, I told I had 15 years implementing and managing UNIX systems as support System Engineers around the world.

It's called the gantlet for a reason. It's painful, long and scary. expect 8 or more people to interview you, possibly a panel. They will take you to the labs in which you will work if they like you expect to be taken out to eat.