I empathize with you, Bill. It's a common question. It's a good question. There's no quick answer. One could say the B2BUA is a concatenation of two user agents and thus can do whatever it feels like, but I suspect you already knew that and that answer won't really help you. My advice is thus:
1. As I said, it's a common question, so review past discussions of the topic. Google is your friend here: I recommend various incantations of "proxy," "B2BUA", "differences," "call stateful proxy," "transparent B2BUA" and maybe filter it with a "sip-implementors" or "sipping" 2. Don't expect definitive answers. Simply put, there aren't any. There do seem to be lots of opinions, however. Study the protocol long enough and you'll begin to form opinions of your own. 3. One opinion that stuck in my mind was a message Dean Willis posted to the SIPPING list a while back. If I were to paraphrase, he argues that maybe the important thing isn't to classify a node as being a "stateful proxy," "call stateful proxy," "B2BUA," or "transparent B2BUA," but rather to understand that there's great flexibility in what headers and fields a node will manipulate as it forwards a SIP message on. Nodes that manipulate less of the message are more "transparent" than others. And so there's really a sort of continuum of transparency. Here's a link to his post: http://www1.ietf.org/mail-archive/web/sipping/current/msg01855.html For the record, the message was titled "Transparency Top 10 List" and was dated May 14, 2002. I'm sorry for the "meta" answer to your question. I do hope that it's helpful on some level. -- Gary Cote www.awardsolutions.com _______________________________________________ Sip-implementors mailing list [email protected] https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors
