Web Server Time-outs
The IIS and Apache web servers have default time-outs—a period of time when a user is automatically disconnected from the server if the server does not detect user activity for the period equal to the time-out period.
You may find you need to change the time-out period for your site and users. These time-out defaults are modifiable through the appropriate server administration tool.
See your web server software documentation for information on time-outs, and how and when to change them.