[Asterisk-Users] Individual call-forwarding on ISDN

[Peter Svensson]

On Wed, 25 Aug 2004, Stefan Neufeind wrote:

> > > Can I detect if the phone I'm trying to redirect to is maybe unavailable
> > > and itself wants to redirect me (unavailable mobile phone, which would
> > > redirect the call again - e.g. to the voice-mail)?
> > 
> > Probably. I think all the isdn channels give you the isdn cause code in a 
> > variable after a failed dial or a hangup.
> 
> Do I really have a failed dial? Asterisk would dial my mobile - and that would 
> recirect to it's voicemail-box. But what I intend to do is detect the 
> additional redirect and cancel the try to reach my mobile phone (and instead 
> divert to another phone from Asterisk directly). Is that possible? I'm quite 
> sure that I can detect a failed dial - but this is about detecting (and 
> avoiding) another redirect.

I doubt this. It may work if the mobile operator supports the connected
line presentation. Even if they do I believe this information is not
available in the asterisk. It may be possible to make this work but it may 
be quite a bit of work.

> > > Can I give the caller a message like "please stay tuned" while Asterisk 
> > > searches for me?
> > 
> > Well, kindof. You can play a message before you attempt to dial the 
> > outgoing leg. You can play the message without answering the line if you 
> > are on isdn (the reverce audio path is opened before the call is answered. 
> > I do not think the Dial app allows playing anything but ringtones while 
> > you wait.
> 
> Really? Didn't know that - cool. So the caller is not yet charged but you can 
> play out something for him while waiting? How can I set up something like that?
> When I play something to the caller, I can dial in background (and not have the 
> caller hear ring-tones), can't I?

Yes, this is possible in isdn lines. Do not put an Answer() before the 
Playback command and then pass the parameter "noanswer" to the Playback 
function. This allows you to play audio without initiatin a charge to the 
A subscriber. The Dial() application in asterisk does not have an option 
to play audio to the A subscriber while it attempts to connect to the B 
subscriber it is dialing. It can generate ring signals so it should not be 
too difficult to add sound file playback to Dial.

> > > Can I try multiple destination-phonenumbers at once? E.g. ring three phones
> > > - if I pickup one, divert incoming call to that destination.
> > 
> > Do you want to dial first and, if that person answers, push the loop to 
> > your pstn provider thus freeing two b channels? That may be more tricky. 
> > I am not sure if that is possible or not. It may even depend on your 
> > operator.
> 
> Kind of, yes. Otherwise I'd need e.g. one channel for incoming caller, three 
> for outgoing (trying) calls. And if the outgoing call is active I'd 
> interconnect the caller with the outgoing call and free the other two 
> additional, not needed lines, right? That would mean I need four channels and 
> would occupy two channels during the call though I don't need that after having 
> connected the two call-participants.

As far as I know you need to allocate B channels for each SETUP message 
you send. In order for you to be able to dial three numbers 
simultaneous you will have to use three B channels. After you know which 
one has answered you may be able to hand over the loop to your operator, 
thus freeing the two B channels that are left. I doubt this functionallity 
is in Asterisk.

I believe the Call Deflection implemented by Junghanns works as a call 
forward. I am not too sure about this though.

Peter