[asterisk-users] OT - How does the blind transfer function work on Snom-870?

James B. Byrne byrnejb at harte-lyne.ca
Thu Mar 5 09:43:45 CST 2015

On Thu, March 5, 2015 09:56, Ruben Rögels wrote:

> Hi again,
> I'm glad to hear that I provided a somehow useful answer.
> Unfortunatelly, I don't know these details.
> If you wasn't lucky consulting the snom docs, maybe the snom support
> can be helpful with information about the exact implementation
> details.
> You also could use "sip debug" on asterisk to check what's going on
> when pressing the transfer button vs. what's happening when using
> "##" via DTMF.
> Are you forced to get the transfer information from the SIP
> signalling, or can you use AMI events for example? I think
> this would be possible if asterisk is configured to stay in
> the media path, so re-inviting is handled over asterisk itself
> and therefore detectable with AMI events.

I am working with a FreePBX12/Asterisk11 setup.  Asterisk stays on the
path (B2B) and there are no peer-to-peer re-invites.

What I am trying to do is to get our Snom870s to use a distinctive
ring tone when external calls are transferred internally.  I have an
extension context override that detects the origin of calls and
assigns a distinctive ring to each based on "${CallerIDNum}".

But when a call is transferred then the tone does not change since the
CallerIDNum does not.  An external original call always rings as if it
were coming from the outside (which it is but transferred calls have a
different handling procedure than unanswered calls).  I need some way
to distinguish when the call has already been answered at least once
without changing the CallerID.

I am not worried about attended transfers since then the internal ring
tone is what should be used and that is what happens now.  I just need
to deal with blind transfers.

What I have now is:

1. Outside call => ring1
2. Internal call => ring2
3. Transferred call => ring1 || ring2 (depending on 1 or 2)

What I want is:

1. Outside call => ring1
2. Internal call => ring2
3. Transferred call => ring3 (regardless of 1 or 2)

If everything went though ## then that would be simple enough.  The
trick is that most (all) users employ the transfer button and the
touch screen to forward calls using blind transfer.  But whatever
method they use to transfer I want the transfer ring tone to be the
same, albeit different from the one used for a new incoming call.

If the transfer is done using a sip message then that should be doable
as well.  I just have to discover what the message is.  If someone
already knows and would care to share the information then that would
be helpful.  Otherwise wireshark and debug will eventually reveal it.

I may not know what I am doing. But, at least I know that I do not
know what I am doing.

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James B. Byrne                mailto:ByrneJB at Harte-Lyne.ca
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