Sorry, error in my first message!
I am looking for the model of router which is able to answer to this specification.(see diagram)
We would like to implement a VPN between two sites, based on 2 ADSL lines connected to Internet. If the mail line (ADSL) is down, the router we start the ISDN link to continue the communication between the 2 sites. When the main line and the VPN are up we come back on the ADSL line. If you have an example of the configuration it should be great. Thank you.