Hold
A B
----invite------------>
<------------200Ok----
-----ACK------------->
Invite: sendonly
uncondition transfer
A B C
----refer----------------------------------à
ß-----------------202 ------------------
<---------------------notify---------------
-----------200 ok-----------------------à
-----------bye--------------------------à
ß-------------------------200 OK-------
------------invite---------------------------à
<--------------------------180----------------
ß-----------------------200 ok-----------------
--------------ACK----------------------------
ß--------------------------notify----------
-------------200 ok------------------------à
A transfer B to C,then A disconnect with B.B establish the session to C then report the success back to A in the notify.If the transfer fails,B can send a new invite back to A to re-establish the session.
Conference
A B C
--------invite-------------------à
ß-------------------180--------
ß-----------------200 ok--------
----------ACK--------------------
ß------------------invite----------
----------180-----------------------
ß--------------------Ack----------
--------invite-------------------à
ß-------------------180--------
ß-----------------200 ok--------
----------ACK--------------------
A and B are in a 2-party call when B wished to add C into the conversation.B is capable of media mixing in a 3-party call.B first send a re-invite to A changing Contact URIs to one that indicates B’mixer and acts like a focus.B tben invite C using the same Contact URI.
