Hi,

>UAC sends INVITE and then INFO. INFO can be sent before receiving 1xx or 200
>response or sending ACK.

It CAN be sent before you have received 1xx, but I am not sure it's a
very good thing to do so. 

>UAS on receiving INFO should check the call state. If the UAS has received
>INVITE and sent 200 or 1xx then handle INFO properly. If have received
>INVITE but not processed it, then sent 481.

I don't understand what you mean by "received INVITE but not processed
it". I think it's an IMPLEMENTATION issue when you consider that you
have some kind of call state. If you don't have it - no matter what you
have sent or received - you send 481.
 
>Issue is that when UAC will receive 481, it should realize this situation
>and retransmit the INFO message. Also if multiple INFO are send, then
>sequencing and reordering of INFO messages will come in place?

This is also an implementation issue. And, if you wait for the 1xx
before sending the INFO it shouldn't happen.
 
>I think INFO RFC says that INFO must only be sent in session ESTABLISHED
>state.

That is because the RFC was released before it was realized that INFOs
may be usable also before the session is fully established.

>SO I feel 409 is the right message. 

I don't think so. Also, there is a discussion on if 409 should remain in
the bis in the first place.

>481 is not becoz call leg do exist.

So, in that case, why would you send 481??? If you have call state, and
accept the INFO, you send 200.

>What 409 says is that "the request could not be completed due to
>conflict with the current state of the resource". I interpret resource here
>as call state.

Again, if you have call state you should accept the INFO - no matter
what the INFO RFC says.
 
>What do others say?

I have spoken :)

Regards,

Christer Holmberg
Ericsson Finland
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