[Asterisk-Users] * as sip b2bua?

[Thilo Salmon]

Olle,

On Fri, 2004-01-09 at 22:28, Olle E. Johansson wrote:
> Isn't the definition of a b2bua that the media streams pass it?
> back-to-back-user-agent.

Frankly, I am really not sure. My understanding has been that a b2bua
would act as a UAC to both endpoints - meaning it engages in some sort
of offer/answer dialog when it comes to media. I am not sure, if  that
implies to reroute a media stream through a local proxy. So far I have
been assuming it does not.

> Anyway, not to be picky, Asterisk by default wants to be in the media
> path. There are ways to release the signalling and media path
> back to the clients, with canreinvite=yes, but that's not the default behaviour.

Afaik, in that case asterisk would act as a user agent server and
redirect the calling party another URI. Imagine the following scenario:

UAC A -----> * --------> UAC B

Assume * wants to rewrite the callerid (the SIP "To:" header field in
this case) without touching the media stream. Forcing UAC A to re-INVITE
UAC B would not help in this case. Forcing the media stream through the
* box however does add the known zoo of problems (latency, bandwith
costs, scalability, ...).

> A SIP proxy like SIP express router from iptel.org fits your
> description better. And yes, SER works together with Asterisk.

On the SER list I learned, that (unlike asterisk) SER is stateless 
with regards to a call. However, if you stick with the example from 
above, state appears to be a prerequisite for rewriting the SIP 
header, because SER would need to map back any responses from the
called party to the original "To:" header before forwarding them 
back to the calling party. 

Thilo