[OpenSBC] OpenSER and OpenSCB as outbound proxy

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What I would like to do is have OpenSCB act as an Outbound proxy NAT traversal solution in front of OpenSER (OpenSER acts as the Registrar and main proxy). 
Clients who need NAT traversal can set the "outbound proxy" on their SIP UA. 

The documentation for OSBC is pretty poor, I'm putting this down partly to help others and partly to get some answers to problems. 
Please give comments/advise. I didn't do much testing other than this, so there could be heaps of other issues. 

The setup is as follows 

UA---------------  OSCB  ------------------------------------ OSER ----------------------------  PSTN 
               [http://oscb.dn.com]                [http://oser.dn.com]              [http://pstn.dn.com]

The UA is setup as follows 
username:123 
domain:oser.dn.com
outbound proxy:oscb.dn.com

There are no changes to OpenSER configuration to make this work, if you want you can register directly and make/recieve calls by omitting the "outbound proxy:oscb.dn.com" section on the UA config.

REGISTRATION 
============
(note: the usr/psw are configured on OpenSER)
OpenSBC's configuration
SBC mode: B2BUpperReg
Always Proxy Media: Yes 
(that's it, for registration, the rest is as default - don't even have Upper Registration Routes as oser.dn.com does not need translation(I guess)) 

The UA registers with no problem, 

Here's a simplified snip from the register message 

REGISTER sip:oser.dn.com SIP/2.0. &lt;-- Request URI 
From: "123"   
To: .   

As you cans see neither "Request URI" nor "To URI" are resolved to SBC's IP hence it's sent to the upper registration routes. 

When I check OpenSBC registration status, there are two entries (with same call-id)
uri=123@213.224.224.7(ip of SBC) aor=sip:123@78.16.113.195:5065
ur...@os... aor=sip:123@78.16.113.195:5065

When I check OpenSER there is one contact in location DB 
sip:123@213.224.224.7:65086 (why port 65086 ??)

You can see here, as expected, that the client registered with IP 78.16.113.195, this was then stored then masqueraded by OpenSBC and sent to OpenSER where the Contact IP is stored as 213.224.224.7 (The IP of OpenSBC). 

Any INVITES to OpenSER looking for 12...@os... will resolve it to sip:123@213.224.224.7:65086 (OpenSBC) and openSBC should then proxy it to the UA.

INVITE, BASIC OUTGOING UA TEST CALL 
================================
To be able to accept an INVITE you need to make sure the domain used in the 'From URI' appears in the 'Trusted Domain' section. 
SBC config 
Trusted Domains oser.dn.com &gt; add 

I then made a call to an echo test which is running on an Asterisk box. 
OpenSER handles the routing so no special routing needed to be configured on OpenSBC 

snip from invite 
INVITE sip:77...@os... SIP/2.0.
From: "123" 
To: .
Contact: .

Since 'To URI' was not 'local' it's sent off to openser which then proxies to the Asterisk echo test. 

Resource Counters (during call)
ICT=1 (what are these ? )  NICT=0  IST=0  NIST=0
CallSession=2  Connection=1  Registration=0  RTPSession=2
EventQueue=0  Cache=5 Garbage=3

INVITE, BASIC UA-UA CALL 
=====================
I made a call from UA to UA, both using 'outbound proxy' (ie. through SBC) 

No problem call worked 2 way voice

Resource Counters (during call)
ICT=6  NICT=0  IST=0  NIST=0
CallSession=4  Connection=2  Registration=0  RTPSession=4
EventQueue=0  Cache=9 Garbage=6

PSTN INCOMING ** PROBLEM ** 
=========================
The PSTN sends calls with from URI=pstn.dn.com so this had to be set to allowed 
Trusted Domains pstn.dn.com &gt; add 

Ok, so this was where I hit the first snag, perhaps someone can help on this one 

snip from INVITE 
INVITE sip:123@213.224.224.7:65086 SIP/2.0.
From: "0860111345" 
To: 
Contact: .

To explain what happens before this INVITE arrived 
An INVITE is sent from pstn.dn.com to oser.pn.com, as you can see the INVITE is to sip:35...@os..., we use the alias function in OpenSER to allow a UA have multiple numbers (this is equaly true for other text aliases, the 'to uri' could be jo...@os...). OpenSER performs an internal lookup on this sip:35...@os..., translates it to 12...@os... then a lookup is performed to find the contact sip:123@213.224.224.7:65086 and this is sent to the SBC 

As you can see the request URI (sip:123@213.224.224.7:65086) is correct, it matches the IP of the SBC. 
I would think this would be considered local and do a lookup in the local SBC registar and it would then be proxied to the UA, but alas no. 
It seems the SBC will only lookup the "to URI" which can't be found in the SBC and worse is sent back to OpenSER which sends it back to the SBC etc.. 

** IS THERE A SOLUTION TO THIS ??? ** (no, we will not re-write the 'to uri' in OpenSER)

Other problems 
SBC crashed several times 

one example 
2007/11/17 15:45:42.544    HTTP Service:8945460 Error   Accept failed for HTTP: Too many open files
2007/11/17 15:45:42.545    HTTP Service:8945460 Message Assertion fail: Operating System error, file tlibthrd.cxx, line 833, Error=24
get the message on the terminal  "got here" alot 
Some segmentation faults also 

"OpenSBC" v1.1.4