HALO 4 Multiplayer Co-op on one Console?

Hi guys!

I wanted to know, if there’s a possibilty to play with one account co-op online? Yesterday i think I saw a Character XYZ and another one was called XYZ(1), like in Modern Warfare 3.

I tried it several times (like in MW3 with second controller as “guest”, but it always said that one account doesn’t have the permission to play.

So, am I wrong or can I play with a colleague with just one account?