First of all, to answer your question, I would need to know what 3pcc scenario you are striving for. There are basically two options: centralized using B2BUA and distributed using REFER. I personally think that use of b2bua (as proposed in a J. Rosenberg's draft) is pretty bloated. I do not know why IETF decided to call it _best_ current practice. In case you like it anyway, http://www.iptel.org/info/players/ietf/callprocessing/#draft-ietf-sipping-d… is a method for learning dialog state. I doubt however, that anyone has implemented it. A way I like much better is using REFER. There is already a (very) experimental Bourne-shell script on CVS in examples, which makes one phone call another one using REFER. A NOTIFY tells the "controller" (which is actually not a controller at all) how the INVITE went. Unfortunately, not every UA today implements REFER. It worked for Cisco and Mitel, it didn't work for Windows Mesenger which does not implement REFER. -Jiri At 07:32 PM 2/10/2003, Karsten Knuettel wrote: -- Jiri Kuthan http://iptel.org/~jiri/