PC Co-op Difficulties

I have tried doing Co-op with my roomie, we have been unable to join each other after 30 tries. I put down the sign, waited 30 seconds and lifted the sign. Rince & repeat. I even tried closing the game and opening it again to repeat the given methods, had no luck. Even removed him from my friends list, but it still wouldn't work. I heard some people have really good luck joining each other, I'm not sure to why I can't have said luck. :b Yes, my friend and I are in the same level range and we are both on the same amount of progress.

Does anybody have any ideas to how it functions on the PC version? I know it would be about the same in general. I'd mostly like specific details like how many servers are there, what are they called, and is there any way to switch between them or what prevents you to Co-op with a friend, and is it linked to the saved game data.

I have been looking at how things function with Co-Op on the PC version, it feels like it runs on one specific server or set of players per Gamer Tag. I looked in the save game file information and it had a large list of gamer tags, can anyone explain what these are for? Are these relevant to who you can connect with? If so, I'm hoping someone can figure out a efficient way to better our chances to connect to friends or even make LAN for the game.

I think you need to keep it down longer. Summon Signs take a while to appear in others worlds. Funnily enough, it usually takes 30 seconds to appear XD

as above - wait longer

I had a crack @ co-op the other night after installing and I did have issues getting people summoned into my game as there were so many people in the area I assume I was being invaded a lot also as the doorways were constantly closed.

as for me being summoned - I would put my sign down and I wold be called for duty very quickly indeed without issues