Warframe uses Peer to Peer networking for lobbies, where one player is the host (in the upper right, you will see the number "1" next to their name). Everyone else in the lobby would be called clients and they are all connected to each other through the Host. A side effect of this is that Hosts tend to experience fewer bugs, and the game sometimes runs better for them than for clients (the game feels more responsive as a host to me even for certain things like transference which is supposed to work client side now) .

*One last thing about hosts in endless missions like defense. In the end of rotation screen the Host's avatar will have a small crown identifying them (it may be a little hard to see). You can also hover your cursor over everyone in that screen and a box will show up if you are hovering the Host.

Most of the time, if there is a host migration, the next person to host is number "2", on rare occasions it will pick someone else and I'm honestly not sure why. After a migration numbers are reassigned by who has been in the lobby the longest, reflecting the order of future host migrations.

As nice as fulmin is, its gated by ammo and is only a MR 8 or so weapon. Maybe the prime version will be stronger, but there are tons of weapon options at MR17 that will do 3-4X the damage.