Why PDP connection turns off if udhcpc not called?

Hi, I have a EM7455 module running on ARM Linux board. I used AT!SCACT=1,1 to start the PDP connection and then call udhcpc to acquire an IP address for the cell port. AT!SCACT? command shows the PDP connection is active. All seems ok.

However, I did notice that if I didn’t call udhcpc to acquire an IP address for the cell port, the AT!SCACT? command will initially show the PCP connection is active, but then it becomes inactive after a while. Why is this happening?

Does it mean that if I have an active PDP connection, and then I lose cell network connectivity for a while, the PDP connection will turn itself off after a while? My app needs to constantly be polling the PDP connection state to detect such a case, and to issue a AT!SCACT=1,1 command whenever it sees that the connection has been inactivated?

Thanks