Session Time Out?

I work remotely from our iSeries.
I connect to the LAN through a Nokia VPN device then use Client Access
Express to get on the iSeries.

My problem is that if my iSeries session is inactive for about 20 minutes,
when I go back and try anything it disconnects me.  I can set up my Client
Access session to automatically reconnect and signon but I would rather it
not disconnected me so quickly.
The session job log gives me a CPF5140 error saying the Session stopped by a
request from device.
Cause . . The request shutdown was caused by either the user turning the
power off, be a device error, or the ASCII controller inactivity timer.

I did not power the session off.
I do not know of any device error happening (perhaps my Nokia VPN device is
disconnecting me by my network guy says it is set for over 1 hour before it
disconnects and besides I do not have to reconnect to the VPN device only
the iSeries),
What is the ASCII controller inactivity timer?

My system value QINACTITV is set at 240 (4 hours).

Any help is greatly appreciated.

Regards,
Bob Kohlndorfer