After switching from DSL to Cable modem my system is dropping the internet connection

if there is no 'traffic' for 10 min or so.

This never happened with DSL.

I have to re-boot to re-establish connection.

There is no router.

After disabling Firewall the connection is not dropped - but I don't want to

disable firewall (mcafee)

Running XP

 

Does anyone have a suggestion as to what setting needs changing?

 

Much Thanks