[asterisk-users] Forwarding a call "off pbx"

[Antony Stone]

On Tuesday 23 January 2018 at 14:43:21, Tech Support wrote:

> All;
> 
>     I had someone ask me if they received an incoming phone call and it was
> forwarded "off pbx" to their cell phone, would the call be strictly between
> the caller and the cell phone, or would it between the caller, the pbx, and
> the cell phone where the VoIP minutes continue to be charged. Rather than
> pull an answer out of my butt, I tested it and found that it's a
> three-legged call which really surprised me. So my question is, is that the
> correct behavior?

Yes.

Think about the call flow:

1. You have an account with a VoIP provider, and some incoming numbers which, 
if someone in the world dials them, will result in a SIP call from the 
provider to your PBX.

2. Your PBX knows that this particular user wants their calls to be forwarded 
to their mobile number, and they've told you what that number is.

3. Your PBX can make calls to the PSTN over some connection or other - it 
might be with the same provider as in (1) or it might be with a different 
provider.  If you do Least Cost Routing, you'll have several providers you can 
make calls over.

4. So, a call comes in to your PBX, which then forwards it out over the PSTN 
to the mobile phone.  There's no way your PBX can tell the inbound VoIP 
provider to forward that call instead, and anyway, why would they do this - it 
then costs them money to place the call to the PSTN instead of you.

So, the VoIP provider doesn't know what your user's mobile phone number is, 
and isn't going to pay to place calls to it anyway.  They have a contract with 
you to send calls to your PBX.  That's all they do.


Hope that helps,


Antony.

-- 
"If I've told you once, I've told you a million times - stop exaggerating!"

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