pcanywhere remote connection problem

pcanywhere was installed on both computers and within the same network, i can remotely maintain the other pc without any problem. Now the problem is that when i going out of the country (not within the same network), i could not use computer name to connect the other pc while, within the same network, i can do it. do i need to use ip address to connect instead or others? if use ip address, i also have the problem. the users on the other end, turns off the router every day which causes ip address changed. Please tell me how to deal with this situation. thanks in advance!