Two Isp Fault Tollerance Help

[Alessandro Coppelli]

Hi to all.

One of my clients has got an Internet connection with a no much affidable 
provider. He reports continual disconnection and so on. I would like to do 
a second connection with another provider to obtain a sort of redundancy, a 
fault tollerance. What I have to do to obtain the automatic connection with 
both of the providers and to shift to the one that is connected when the 
other is in trouble? (  without problems for the client).

Ale