IMG 1010 - Two B-Channel Transfer (TBCT)

Overview:

Feature F-1638 Release Link Trunk utilizes the Two-Bearer Channel Transfer technique for ISDN NI2 to off load two b-channels which are bridged or looped on the IMG. If there are two calls active on the IMG and they are bridged or looped together the resources on the IMG are being used inefficiently. With this feature the IMG 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Switch (SPCS) on the PBX or TDM switch and tell the PBX/TDM switch to connect these two calls together so they are no longer active on the IMG. This would effectively open up two b-channels on the IMG that were initially being utilized. TCBT is initiated from a SIP Refer message and is supported from ISDN to SIP only. Below is information on how TCBT is utilized and configured on the IMG.

Feature F-0858 Explicit Call Transfer Support is also now supported on the IMG. All functionality for ECT is the same as that for TBCT. Explicit Call Transfer is supported in E1 where TCBT is supported for T1. ECT is configured and operates the same as TCBT.

Call Flow Diagram: (ISDN to SIP)

Call Flow Diagram: (SIP to ISDN)

Diagram:

Below is diagram explaining how TBCT would operate in an ISDN to SIP network.

1. Two calls are in progress. The SIP side sends a REFER message to the IMG telling the IMG to connect the two calls together.

   

2. After the call is bridged in the IMG, the SIP leg is no longer connected. Call A and Call B are now routed through IMG as shown below.
   

   

3. With F-1638 Two Bearer Channel Transfer “Enabled”, the IMG will recognize that the call does not need to be routed through it. The bridged call is using resources on the IMG that could be used for other functions. The IMG 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.
   

   

4. At this point, the call is being routed through Switch B and the IMG has released the call thereby freeing resources on both the IMG and the SPCS.  

Configuration:

Initial Configuration:

The procedure below explains how to configure the IMG for TBCT. Verify the following entities are configured before proceeding:

•  IMG 1010 - Logical IMG

• IMG 1010 - Physical IMG

• IMG 1010 - Configuring T1 or E1 Bearer Profile - 10.5.x

• IMG 1010 - Configuring IP Bearer Profiles

• IMG 1010 - IP Network (Interface)

• IMG 1010 - Configuring T1 or E1 Bearer Spans - 10.5.x

• IMG 1010 - VoIP Resource

Configure these initial objects before proceeding to the procedure below.

Feature Configuration:

• Right click on the Physical IMG node and select New Signaling. A Signaling object will get created. This is a placeholder for multiple signaling objects. No configuration is needed here. For more information, see IMG 1010 - Signaling Object .

• Right Click on the Signaling object created and select New ISDN.  An ISDN D Channels object will get created.  This is a placeholder for multiple signaling objects. No configuration is needed here. For more information see IMG 1010 - ISDN Signaling Pane .

• Right Click on ISDN D Channels object and select New ISDN D Channel. Select which Interface and Channel to configure the D-Channel on. See IMG 1010 - Configuring ISDN Signaling and IMG 1010 - ISDN D Channel for more information on configuring this object and other ISDN configuration.

• Right Click on Dialogic IMG EMS and select New Routing Configuration. The routing configuration object will appear. This object is a placeholder object and no configuration is accomplished within this object. See IMG 1010 - Routing Configuration Object for more information.

• Right Click on Routing Configuration and select New Channel Groups. The channel group object will appear. This object is a placeholder object and no configuration is accomplished within this object. See IMG 1010 - Channel Groups for more information.

• Right Click on the Channel Groups object just created and select New Channel Group. Enter a name for the channel group and select ISDN as the signaling type. By selecting ISDN, the Channel Transfer field can now be enabled or disabled.

• To enable the Two Bearer Channel Transfer feature, select ‘enable’ from the drop down menu in the ‘Channel Transfer’ field. See screen capture below. For more information on Channel Group pane see IMG 1010 - Channel Group .
  

  

• Once the Two Bearer Channel Transfer has been enabled, complete the ISDN Channel group by configuring the D-Channel created earlier into the ISDN Channel Group. Right Click on Ch_Grp_ISDN_2BCT – ID:0  and select New ISDN Group. See IMG 1010 - ISDN Group for more information on configuring this object.

• At this point the feature has been enabled and can now be added to a Route Table, Route List, or Translation Table.

• Below is screen capture of tree within ClientView once the above procedure has been configured
  

  

Additional Information:

• TBCT supports ISDN NI2 only

• IMG will take on the role as the controller.

• The IMG will not support/process a TBCT request. The request will be discarded.

• In order for TBCT to be invoked following a SIP Refer, both ISDN B-Channels must be terminated on the same remote switch.

• TBCT will be available only if the initial call was established between ISDN and a SIP device. The direction of the call is irrelevant.

• TBCT is triggered from the SIP call leg via the REFER method.

• Both channel groups must have the TBCT feature enabled for the feature to be invoked. Feature will not be available if one of the channel groups does not have TBCT enabled.

• The IMG will invoke a TBCT request only when both ISDN call legs are answered.

• If TBCT is unsuccessful, the two calls will remain in the same state they were in prior to the request. IMG will not initiate clearing of the call.

Related Topics:

IMG 1010 - Channel Group