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New Member

Redirecting an inbound ISDN call?

Is the following scenario even possible?

1) Inbound calls terminate on a T1/E1 trunk of a UC520 (ie. Voice IOS router)

2) Rotuer matches the call on an inbound dial-peer, answers it

3) Somehow, the router now decides to redirect the caller.  Instead of setting up a new call leg, it uses an ISDN-level signal to tell the incoming leg (from the Telco's switch) to instead dial a different number.

The goal of doing it this way is so that:

1) the calling-number of the original inbound leg is presented to the redirectee

2) hey, we save ourselves a call

If it's feasible-from-a-signalling-perspective, is a TclIVR script required?  Or is there a way of configuring the dial-peers on the Voice router to do it?  For example, the initial out-bound leg of the call is a SIP dial-peer, and the router receives a SIP REDIRECT from it ... how to tell the router to 'forward the redirect to the inbound leg', rather than looking for a new outbound peer?



Hall of Fame Super Silver

Redirecting an inbound ISDN call?

So, you basically don't want the call to be hairpinned on your GW? This would be possible feature such as takeback-and-transfer which is offered by some telco providers at a fee.



New Member

Redirecting an inbound ISDN call?

Yes, that would do.  The main point is not so much avoiding tying up the channels, but making sure that the eventual transferee has the original caller's number show up on caller-line-id.  (Although avoiding call redirection charges and 2 channels is a bonus).

How does one typically invoke the TNT feature?  Is a TclIVR script indicated here, or is there some fancy things one can do with dial-peers?



Hall of Fame Super Silver

Redirecting an inbound ISDN call?

Original caller-ID should be preserved fine on PRI circuit as long as the provider does not do ANI screening, which you can always ask to have disabled.

TNT is invoked by sending inband DTMF code, i.e. *8, so with UC520/CME deployment a TCL script would be needed.

HTH, please rate all useful posts!


New Member

Redirecting an inbound ISDN call?

Hmm, won't the original caller hear the DTMF sounds on the line?  Apart from that, I like this solution.

Alternatively, I have located a whole bunch of information on doing redirects with TCBT (Two B-Channel Transfer) .  In that scenario, you can apparently tell the teclo switch to connect two call legs on the same ISDN trunk, even if the 2nd one is outbound (and even when the 2nd one is in the 'ringing' state, which is nice).  But it's not clear which Caller-ID will be presented to the eventual recipient of the call.  Do you have any experience with this?

I'm asking around in the TclIVR community for some specifics on how to practically access this functionality in a script.



Redirecting an inbound ISDN call?

Hello David,

Please do keep in mind that to use TBCT, the following conditions must be met:-

-PRI interface is subscribed to TBCT service from ISDN service provider.

-Both calls are voice calls.

-Both calls use the same PRI or both PRIs are part of the same trunk


-Incoming call is answered.

-Transfer-to number is placed as a separate call.

-To support TBCT, the switch type must conform to the NI-2 standard.

Hope the above conditions are met .


Karthik Sivaram

New Member

Redirecting an inbound ISDN call?

Thanks Karthik.  Hi, yes all of the above are true, I believe.  The telco is Telstra, and the product is their ISDN10, which I believe uses an NI-2 type switch.  Their literature suggests that it is possible to subscribe to an ISDN-delivered transfer service like this.  (I will check all of this with them soon).

But I would really like to know if it is feasible to instruct the NI-2 compliant switch to present the caller-ID of the transferee to the tranfer-to party?

Hall of Fame Super Gold

Re: Redirecting an inbound ISDN call?

If (and that seems unlikely to me, because I have never seen it working), you can have the forward to be telco based, then yes the calling number would be the original calling number.

Anway, before woryiing about caller ID, you should find out if your telco supports TBCT, honestly I think they don't.    

By the way, ISDN in Australia uses Euro ISDN, not NI-2, that is an American only standard.