I had previously mentioned that VoIP worked only when I made BSNLs default VoIP gateway as the default route on my Pi. This barred me from having internet access on Pi. I solved the issue by adding a static route to BSNLs default VoIP gateway like so:
Using tcpdump I observed that BSNL uses multiple VoIP servers and all servers are on 10.0.0.0/8 network.
I'm not using NAT as siproxd does proxying that is similar to NAT
ip route add 10.0.0.0/8 via 10.81.104.1
Using tcpdump I observed that BSNL uses multiple VoIP servers and all servers are on 10.0.0.0/8 network.
I'm not using NAT as siproxd does proxying that is similar to NAT