As you've noted, the direct media thing is great but doesn't really work reliably with phones behind NAT unless there's special processing at the NAT side. And

As you've noted, the direct media thing is great but doesn't really work reliably with phones behind NAT unless there's special processing at the NAT side. And of course most NAT devices that offer said processing get it wrong and usually make things worse. I've been working in VoIP for years. We do direct media when we can, but we bounce it through the server fairly often because NAT sucks. RIPT seems to built primarily with cloud hosted applications in mind, which need to scale and are likely being connected to by clients behind NAT. It's explicitly not like SIP, where every user agent is equal and would theoretically communicate directly where possible. This is why I wish IPv6 had a real killer app to make it catch on, it'd make life so much easier for me and SIP would work how it's supposed to.