B2BUA can be viewed as virtual UAS/UAC connected back to back. It implements
server state machine for receiving SIP requests and client state machine for
generating outgoing SIP requests. In essence it must be capable of
controlling both the signalling paths. From implementation perspective B2BUA
can be used as a 3pcc service execution controller.
Also, unlike a proxy that does not originate SIP requests (other than ACK and
CANCEL) B2BUA can send INVITE/RE-INVITESs to communicating end points for
session establishment/codec negotiations. While the proxy is normally
associated with pure routing and lookup logic the B2BUA is expected to
provide interface to call/service control logic eg. to an external
media/application server. However all of these proxy, redirect, registrar and
B2BUA are SIP enabled logical entities that may/may not reside on the same
physical node.
For details refer to drafts "draft-rosenberg-sip-3pcc-01.txt"&
"draft-mahy-sip-peer-3pcc-00.txt" at IETF website.
-Gaurav
Victor Kueh wrote:
> Dear all,
>
> I am new to this sip-implementors list. I have come across the
> term 'B2BUA' many times, but am not very sure with the exact
> definition. Can someone please clarify that for me?
>
> Also what is the difference in behaviour of B2BUA with the other types of
> servers (proxy, redirect, registrar)?
>
> Thanks
>
> Victor
>
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