I was watching an older episode of SG1 where O'Neill has the Ancient computer downloaded into his head. So Carter and Teal'c go through to another planet to try to find help for him and they can't dial out. So Stargate Command dials them and talks to them, but they can't come through unless they dial in. So was the gate always a "one way street" or was it changed later on and in the other series? I always assumed that if the gates were connected you could travel in either direction.