kamalamohan Hello...
In Gcloud you need to add a few lines to your sip.conf, remember, Google cloud managed 2 IP's, external and internal, this will work for you:
nat=force_rport,comedia
localnet=local/255.0.0.0
externip=
media_address=
externaddr=
Were say's "local" you add your internal ip address and then you add your public ip address to the other fields.
And that's it.
