Calls not Working in Local Network when device is connected with Public IP.

[E2-Sterlin]

Hi Everyone,
To handle background call , I tried to integrate Flexisip as frontend SIP Proxy server and Asterisk as backend SIP Register server.
It is working well by sending Voip notification.
Calls were working fine with 2 way audio in local network and public network in transport TCP.

But I am facing only two issues:
1.calls in Public network to Public network (i.e) both the device registered with Public IP and connected to public network (for example cellular network) is getting disconnected after 32 seconds when the transport is in UDP(especially in UDP Transport).

2.When the two devices registered with Public IP and connected to the Local network either in TCP or UDP transport and trying to call,
the call is not even getting connected,
but it is working when it is connected to cellular network .

Kindly help me regarding this or share your thoughts which may helps me resolve the issue.

Thanks in Advance