Session terminates automatically

Hi Am using unix Aix
Am facing an issue with my login.
When i enter user_id and password i can able to login and can able to work on it.

When i keep this session idle then again started accesing then i cant able to acesss giving error message "session terminated" everytime am reset my password and acessing the applications.

Is there be any network issue .Can anybody knows what is the issue ?

A network issue doesn't politely inform you that it's terminating your session for you before it does so...

Timeouts have probably been set on your shell via the TMOUT variable. You may need the cooperation of your sysadmin to change it.