Unable to make PSTN calls in Google Compute Engine


I installed and configured Asterisk in Google compute engine (GCE). I am facing the below issues:

  1. Unable to login to Asterisk CLI by using asterisk -rvvvvv command (But, I am able to login using asterisk -vvvvvc
  2. I am able to make calls between the extensions. But, unable to make/receive PSTN calls.

Is there any modifications that I need to do in Google Compute Engine (GCE) environment?

Please note that I deployed my same server in different other environments like Amazon ec2 and working successfully. But, the same configured server is not working on GCE.

Thanks in advance.