[OpenSIPS-Users] Transfer issue

[Iñaki Baz Castillo]

El Sábado, 24 de Octubre de 2009, Jeff Kronlage escribió:
> I follow this, but -and please correct me where I'm misunderstanding- isn't
>  the point of using a Proxy versus a B2BUA is that it's more lightweight
>  and scalable?

Of course, but if you want PBX features you need a B2BUA. Also, trasferring a 
call from a SIP PSTN provider does require *always* a B2BUA (in fact the user 
doesn't transfer the provider, but the B2BUA which will accept such REFER).



>  It seems with this setup every call ends up routed through
>  Asterisk on the initial INVITE, simply so that when a REFER potentially
>  comes later in the dialog, it can handle it.

If you need a proxy use a proxy. If you need a PBX you need a PBX/B2BUA. If 
you need a very scalable system with high load you can scale it with a proxy 
in front of various PBX's (of course, most probably the PBXs won't share 
dialog inforamtion between them...).


>  Our setup has been initially
>  engineered for thousands of concurrent calls, and we're hoping to avoid
>  having a dozen Asterisk machines :)

What you are looking for is the dream all want: a scalable SIP B2BUA (no media 
handling), so a cluster of these B2BUA's would be located behind a proxy 
(which does load balancing and failover). And it would be greater if the B2BUA 
share information (about current dialogs and so) in some way (memcache? common 
database?...).

You could implement it with SipServlets (see Sailin SIP application server or 
others), or FreeSwitch which allows calls without handling the media...
Of course, Asterisk is not the most suitable solution: it involves media 
handling ("canreinvite" is a hack), it has a very poor SIP stack... and 
basically it's designed to be a single PBX box.


> Our goal is to design something like:
> 
> UA <--> Opensips <--> Our PSTN gateways
> 
> That could dynamically turn into, on the fly:
> 
> UA <--> Opensips <--> B2BUA <--> Our PSTN Gateway
> 
> We haven't found a clean way of doing this, unfortunately...  It may just
>  end up being a hack on Opensips 1.6 if that might work.

You shouldn't expect that OpenSIPS could behave as a PBX because it's a proxy. 
And what you need is a PBX, you MUST assume it. A proxy is very scalable, fast 
and so, but it will NEVER provide PBX features (as transferring a call coming 
from a PSTN provider to other user).
IMHO OpenSIPS b2bua module will be useful for some limited tasks (topology 
hidding and others) but not for replacing a PBX.



Regards.



-- 
Iñaki Baz Castillo <ibc at aliax.net>