[sf-lug] keep alive time for an ssh connection

[Alex Kleider]

I have found that when using PuTTy as an ssh client from my office computer to log onto (via the internet) one of my linux computers the connection seems to remain established indefinitely. When I log onto that same computer from another site using a linux computer, the connection seems to time out after a period of inactivity. I've found nothing in the ssh_config file that might control this behavior. 
Does anyone know how this behavior is controlled?
i.e. how is it decided how long an ssh connection will remain established during inactivity? 
alex