Change 'Idle Time before Hanging-up'


I’m new in Wavecom modem world, and i want to know if it’s possible to change this parameter (‘Idle Time before Hanging-up’) automatically.
I know I can change directly this option in the properties, but in my case I must to do it automatically, because I have many modems to configure. (60 in a first time and more over 1000 after).
In fact, I want to pass this value to never, because I use a GPRS connection and i don’t want to be disconnected after a delay of inactivity.

I have already searched some solutions on my side, but i didn’t find any keys in the registry base or in a configuration file.
I try to find an AT command to do this unsuccessfully.

Is there a way to change this parameter?

Thanks for your help.