Android Question Firebase Messaging TCP time-out/keep-alive


Receiving Firebase messages instantly relies on an idle TCP connection to port 5228 (or 5229 or 5230) that is alive for at least 30 minutes.

Problem is: Some ISP (or local routers) cut NATed idle TCP connections in much shorter time periods. My observation is, that FCM still works, but it needs several minutes (worst case 30 minutes ?) for the client to "notice" that the connection isn't alive any more and establish a new one. THEN the message arrives.

So my question is: Is there any way to reduce the time period for the FCM client to send keep-alive packages ? Is there any way to force the client to use IPv6 (which has no NAT)