a part of my study work is the behaviour of asterisk with calls in dual stack
calls from ipv4 to ipv6 are working, but it would be nice to see how it works exactly.
when i examine the network traffic it seems that the asterisk server is a proxy between the two telephone clients and is forwarding the speech data
now i am searching for some more detailed information how it works
would be nice if somebody could give me some infos about it
Asterisk is a back to back user agent, with certain, optional, optimisations for RTP based traffic. It is not a SIP proxy. Please read asteriskdocs.org/ for that level of detail.
As to exactly how it works, that is well outside the scope of an end user forum. I mostly had to learn it by studying the source code, although the documentation may have improved slightly, since.
Note that IPv4 to IPv6 is, in principle, easy compared with IPv4 to ISDN. Any of the complications will be in the optimisations, not in the basic function.