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I'm curious if anyone got TBCT (Two B-Channel Transfer) feature working on H.323 IOS gateway. I see the "isdn supp-service tbct" command on the D-Channel Ser0:23 interface, but my research indicates that I must also have a TCL script to make TBCT work. I got one Cisco 2821 H.323 gateway with one PRI, one Cisco CallManager 8, one UCCX 8. The call flow:

PSTN >>(1st b-channel)>> 2821 >>> CUCM-UCCX-IVR >>> 2821 >>(2nd b-channel)>> PSTN >>(3rd b-channel)>> 2821 >>> CUCM >>> IP Phone = 3 B-channels in use

and sometimes

PSTN >>(1st b-channel)>> 2821 >>> CUCM-UCCX-IVR >>> 2821 >>(2nd b-channel)>> PSTN >>(3rd b-channel)>> 2821 >>> CUCM >>> 2821 >>(4th b-channel)>> PSTN = 4 B-channels in use

Customer calls into IVR, the call is transferred to an outside on-call service PSTN number, on-call service person picks up and eventually transfers the call to a DID extension. In some situations, that DID extension forwards to an outside PSTN cell number.

I would like to disconnect unnecessary channels.

Found this:

PRI switch type must be NI-2, provider would need to support TBCT, and IOS gateway would subscribe to TBCT service. In my example, when IVR blind transfers the call to the PSTN, TBCT would disconnect b-channel 1 and b-channel 2 effectively handing off the call to PSTN. At that moment the call no longer exists on the internal systems and PRI has no channels in use.

When the outside on-call service transfers the call back into DID extension, it will go to an IP Phone. If the call happens to transfer to an outside PSTN number, TBCT would again hand off the call to the PSTN provider and disconnect both b channels.

Does anyone have this working? Is TCL necessary?


Hall of Fame Super Gold


I doubt it is possible without TCL. Actually, just the knowledge necessary to build the necessary message to activate the feature, is quite elusive in TCL/IVR.

Community Member


Yes, I have it setup from h323 gateway to CVP using tcl scripts. I am now trying to get it to work from UCM.

I was told that H323 can't play with CCM. But MCGP can't play with H323! So I am trying to find out if I can setup this up using 2 trunking protocols.... Anyone know?

Hall of Fame Super Gold


Sorry, can you be more clear? "play" what ?

Community Member


In other words, that when UCM is trunked to a H323 GW, tcbt isn't supported.

I would like to know what trunking protocol will support TBCT, for UCM. I would need it to support CVP if possible.

Hall of Fame Super Gold


None likely. It's quite an exotic feature in which very little people is interested.

However, if you can have TBCT working on router with TCL/IVR, you can have it working with UCM / H.323.

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