I understand now.
There's a SIPconnect group and others standards groups trying to make a standard but it doesn't work well imho.
I hooked up an ip pbx to a certain clec's sip trunks which are certified on that pbx, and they are SIPconnect members.
Everything works fine except one little thing, they can't dial their DIDs internally. They're being cheap by pointing our pbx to its own rtp stream for the calls audio (which doesn't work with calls that go out and come back to itself that way. I guess both are to blame, the pbx for not being advanced enough and the provider for being cheap on bandwidth or processing). If using ni2 one could always call their own DIDs with no problem.
The great thing about standards is there are so many to choose from! - Tanenbaum