Hi, the only reference to B2BUA concept I find in RFC 3261 is:
Back-to-Back User Agent: A back-to-back user agent (B2BUA) is a
logical entity that receives a request and processes it as a
user agent server (UAS). In order to determine how the request
should be answered, it acts as a user agent client (UAC) and
generates requests. Unlike a proxy server, it maintains dialog
state and must participate in all requests sent on the dialogs
it has established. Since it is a concatenation of a UAC and
UAS, no explicit definitions are needed for its behavior.
Well, the fact is that the real world uses B2BUA's and session border
controllers and not just proxies to communicate with others. For
example, Company_A and Company_B use SIP internally and the same SIP
provider for PSTN calls. If an user in Company_A calls Company_B PSTN
number the call will do:
[EMAIL PROTECTED] B2BUA_A SIP_PROVIDER B2BUA_B [EMAIL PROTECTED]
INVITE B_PSTN ----------> -----------> -----------> --------->
So I really don't understand why all the SIP related RFC's imagine a
happy world plenty of proxies that is (and will be) false forever.
However, I don't find any documentation or references about the
behaviour of a B2BUA. For example:
- Is legal for a B2BUA to change completely the "From" in the second leg?:
User1 B2BUA User2
INVITE --->
From: user_1
INVITE --->
From: bob
- Should a B2BUA allow unknown headers from leg 1 to leg 2? or should
it create a completely new request from scratch?
- Can be problems if B2BUA copies in leg 2 the same "Call-Id" and "From_tag"?
Thanks.
--
Iñaki Baz Castillo
<[EMAIL PROTECTED]>
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