[asterisk-dev] pjsip / asterisk 14+: Sometimes outbound calls are forbidden by provider

[Joshua C. Colp]

On Fri, May 24, 2019, at 7:24 AM, Michael Maier wrote:
> On 24.05.19 at 13:14 Joshua C. Colp wrote:
> > On Fri, May 24, 2019, at 6:02 AM, Michael Maier wrote:
> >> Hello!
> >>
> >> some people are facing a problem regarding forbidden outbound calls to 
> >> the ISP. They start an outbound call, which is rejected by the
> >> provider. Debugging revealed the reason: The IP used for the outbound 
> >> INVITE is different from the IP used for the REGISTER. That's why the
> >> ISP forbids the outbound call.
> >>
> >>
> >>
> >> Background:
> >>
> >> A SRV lookup gives 3 hosts each with different priority. At the start 
> >> time, Asterisk takes the IP with the highest priority for the
> >> REGISTER. REGISTER timeout is 660s.
> >>
> >> Some time later, lets say 300s, an outbound call is started, which is 
> >> rejected by ISP (forbidden), because of wrong destination (REGISTER IP
> >> != INVITE IP).
> >>
> >> My question:
> >> Is it possible, that asterisk performs a DNS lookup before it sends the 
> >> INVITE to the ISP for the outgoing call? At this moment, the DNS
> >> reports changed priorities or the REGISTERed IP isn't there at all any 
> >> more and therefore, Asterisk uses another IP for the outgoing INVITE?
> > 
> > Yes, this is how it works. The outbound registration and calling aren't associated at all. When an INVITE is done then another resolution occurs along with picking an IP address.
> 
> Unfortunately, this doesn't work, if the REGISTER to the existing old 
> IP isn't re-registered to the new IP before the INVITE is performed.
> 
> I forgot to mention one more difficulty: There is more than one number 
> registered to the same destination which may have differing
> reREGISTER point of times.
> 
> Therefore, the process should be like this?
> 
> - Outbound call is started
> - DNS lookup is performed
> - Check for difference of REGISTER IP (of this dedicated outgoing 
> number) and INVITE IP
>   -> Difference detected? Yes:
> 	-> Stop REGISTER for this number (or leave it if there is an ongoing 
> call using this
>            number)
> 	-> Start REGISTER for this number with new IP
> - Start INVITE to new IP

There's nothing built in to do this, and honestly I'm not quite sure of the orchestration internally required to do such a thing. With code changes it may be possible but I don't even know if the foundations required are there.

-- 
Joshua C. Colp
Digium - A Sangoma Company | Senior Software Developer
445 Jan Davis Drive NW - Huntsville, AL 35806 - US
Check us out at: www.digium.com & www.asterisk.org