Hi,
OnionCat provides a public overlay network. If a SIP-proxy ist put on
top of OnionCat any dumb hardware-/software SIP-phone in the LAN can be
used.
On the OnionCat-interface I suggest to use
1. DTLS/SRTP with self-signed certificate created from the Tor Hidden
Service hostname/private key for authentication and encryption
2. OPUS audio codec with forward error correction enabled as it is the
most robust audio codec and adjusts bandwidth automagically
3. Use speed dialing capable proxy for hardware phones top map decimal
numbers to SIP-URIs (blockchain as long-term goal, see
https://forum.namecoin.info/viewtopic.php?f=2&t=1858)
I also suggest to consider RTCWeb as Tor pluggable transport for
OnionCat as it is encrypted by default, can multiplex multiple streams
and ordered mode/congestion control can be switched on/off per stream.
Best regards,
Renne