Hi Karthik, Lets say A supports certain codecs like G711ulaw and G711alaw. B supports G729 and G726. since both does not have common codec session establishment always fail. Here comes B2BUA importance, this receives invite from A and sends to B which B supports. Hence A and B will establish session. There are so many other instances like both A and B may not supports common DTMF techniques.
And another most useful scenario is if A is a H323 endpoint and B is a SIP endpoint, then also call establishment happens because of B2BUA. Hope this clarify your doubt. -Bhanu -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Paul Kyzivat (pkyzivat) Sent: Tuesday, September 23, 2008 10:11 PM To: karthik karthik Cc: sip-implementors@lists.cs.columbia.edu Subject: Re: [Sip-implementors] why do we need b2bua? karthik, B2BUA is a very general mechanism that may be used for a multitude of purposes, some good, some evil. Some things that are B2BUAs that you might not think of as such: - a conference focus - a presence server The kind of B2BUA you seem to be talking about is probably an SBC, or maybe a sip-pbx implemented as a B2BUA. The SBC is typically there explicitly to interfere in / obfuscate the signaling. Sip pbxs are often implemented as B2BUAs because it gives a lot of flexibility to the controller in the middle to handle the call "legs" independently. Its often easier to deal with "dumb" phones that way. In some cases a device that might otherwise be just a proxy must be a B2BUA instead because it wants the option to inject messages into the message stream between the two ends. For instance it may want to force the termination of a call by sending BYE. A proxy cannot do that. Thanks, Paul karthik karthik wrote: > Hello, > Here is a question which I have for long time. > What is the prupose of having B2BUA? > I know that the B2BUA changes from tag, callid and maintains a > seperate dialog when to tag is received. > > But why it does change in these headers? > Some say it is for security reasons? > If yes how is it used for security. We also have NAT for security. > > Some say it is for manipulation of supplementary services. If yes, > cant a statefull proxy handle the services without changing call-id, > from tag and to tag? > > Thanks Karthik Prabhu > _______________________________________________ > Sip-implementors mailing list > Sip-implementors@lists.cs.columbia.edu > https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors > _______________________________________________ Sip-implementors mailing list Sip-implementors@lists.cs.columbia.edu https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors _______________________________________________ Sip-implementors mailing list Sip-implementors@lists.cs.columbia.edu https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors
