Ichat Av 2.1, User Did Not Respond


I cannot video conference my family who has G4 OS 10.3.9 like myself running iChat 2.1. Either of us initiate the video conf results in a other party did not respond message.
Both our firewall is turned off
Both have sucessfully video chat with mutual friend on G4 OS 10.4.1 iChat 3.0.

Both me and my family has ADSL on Dlink modem 302G.

I suspect modem settings is problem.

what can I do? short of changing modems?