Bhanu K S (bhks) wrote:
> 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.
This is one way to handle the codec matching issues, but not the only
one. The endpoints can also take the responsibility to invite in a
transcoder if needed. Of course, in that case the UA that does so is
acting as a B2BUA.
Paul
> 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
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