Two B-Channel Transfer (TBCT)
The Release Link Trunk (RLT) feature utilizes the Two-Bearer Channel Transfer (TBCT) technique for ISDN NI2 to off load two B-Channels which are bridged or looped on the IMG 2020. If there are two calls active on the IMG 2020 and they are bridged or looped together the resources on the IMG 2020 are being used inefficiently. The TBCT feature has the ability to send specific facility messages back to the Stored Program Control Switch (SPCS) on the PBX or TDM switch and tell the PBX/TDM switch to connect these two calls together so they are no longer active on the IMG 2020. This would effectively open up two B-Channels that were initially being utilized. Below is information on how TBCT is utilized and configured.
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Two calls are in progress. The SIP side sends a REFER message to the notifying the IMG 2020 to connect the two calls together.
After the call is bridged, the SIP leg is no longer connected. Call A and Call B are now routed through the IMG 2020 as displayed below.
With Two Bearer Channel Transfer Enabled, the IMG 2020 will recognize that the call does not need to be routed through it. The bridged call is using resources on the IMG 2020 that could be used for other functions. The IMG 2020 would then send a request to the SPCS/Switch B (Stored Program Control Switch) that the two independent calls be bridged together as shown below.
Configuration
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