improve steam internet connection

[HipoH]

I have been playing coop with a friend via steam and it kicks him out without any warning he says he doesnt lag but from time to time the game kicks him out and shows him the connection lost message when we started to play this wasnt a big problem but we have entered hard mode and it happens more frecuently, im afraid that with the time it will become more and more frecuent

Thanks and Sorry for the bad english