Error 628: The port is disconnected or The connection was terminated by the remote computer before it could be completed. This is most likely a modem or phone line noise issue or blocking port issue.
1) make sure you have good phone line.
2) Upgrade the modem/router firmware
3) Make sure you logon using the correct username or password or try different username.
4) Reinstall the modem.
5) Re-enable RAS
6) Check the router/firewall settings.
7) Make sure the router is VPN pass through or GRE is enabled.