Subject: [dispatch] About B2BUA and e2e features:

From: [email-masked]
Date: Fri, 30 Jul 2010 22:43:02 +0800

For people care about B2BUA,

There has been a quit long discussion for the Session-ID and B2BUA topic. 
There are some people want to make "session-id" to UPDATE current 
normative RFCs, at least *potentially*.

I think the more general question behind this is about B2BUA and e2e 
feature, or in other words, do we need to *modify* e2e features for B2BUA 
use cases. IMO, I do not want to see any normative modification for B2BUA 
use cases.

Any SIP equipment should handle it's B2BUA behavior carefully. By my 
experience in IMS, if AS want to behave as B2BUA, it MUST modify the 
Replaces header's dialog information to make the Replaces header's 
dialog-id can be handled OK by the receiver(UAS for the request with 
replaces header), this is defined in 24.229. And the AS should also 
guarantee itself would be trigger for the subsequent request with replaces 
header, by modifying iFC.

And about SBC, if it want to behave as B2BUA, it also should modify the 
Replaces header's dialog information to make the Replaces header's 
dialog-id can be handled OK by the receiver(UAS for the request with 
replaces header). And we usually deployed SBC at the edge of the IMS Core, 
so the subsequent request with replaces header alway pass the same logical 
SBC. If there are more than one physical SBCs deployed in the network, 
they should share the dialog information when handle Replaces header.

So, B2BUA should regulate it's behavior for e2e features, while not 
*modifying* e2e features for B2BUA use cases.

Thanks,

Gao

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