ISUP Explicit Call Transfer
- Kelli Higdon
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The ISUP Explicit Call Transfer (ECT) feature effectively utilizes the IMG 2020 resources during a SIP call transfer scenario. An inefficient utilization of resources is depicted in the following diagrams.
After the call transfer, the only role the IMG 2020 serves is to bridge the two TDM call legs.
The ISUP ECT feature allows the IMG 2020 to request that switch B bridges the call. Doing so will remove the IMG 2020 from the call and free up the TDM resources.
For ISUP ECT, there are several types of ECT scenarios:
Services platform redirect and transfer
Third-party interaction
Service platform-initiates call back
Re-origination scenario with bridging at the originating switch
Re-origination scenario with bridging not at the originating services platform
This feature implements the "Services platform redirect and transfer" scenario.
In the "Services platform redirect and transfer" scenario, the IMG 2020 will interwork the SIP REFER to the SS7 side with two FAR messages, requesting the SS7 Switch (Switch B) to bridge the call.
If SS7 Switch cannot bridge the call due to congestion, the IMG 2020 will be notified by the FRJ message and the IMG 2020 will establish the terminating leg and will bridge the call.
Call Flow Diagram
The ECT request is accepted by the SS7 switch, the IMG 2020 is release from the originating leg.
If the ISUP ECT request is rejected by the SS7 switch with cause "Switching Equipment Congestion", the IMG 2020 establishes the terminating leg and will bridge the call.
If the cause has some other value, the IMG 2020 will notify the SIP Device that the call transfer cannot be performed with a NOTIFY (5xx) method.
Configuration
Initial Configuration
The procedure below explains how to configure the IMG 2020 for ISUP ECT. Verify the following entities are configured before proceeding. Refer to the Configuration topic for information on configuring the basic functionality.
Configure SS7
Configure SS7 Signaling and SS7 Network
Configure SS7 Stack
Configure SS7 Link
Configure SS7 Routes
Configure the ISUP Group and Circuit Group (CICs)Â
Configure SS7 Channel Group
Right click on the Dialogic object and select New Routing Configuration. The Routing Configuration object is a parent or container object and no configuration is needed here. Refer to the Routing Configuration topic for more information on this object.
Right click on the Routing Configuration object and select New Channel Groups. The Channel Groups object is a parent or container object and no configuration is needed here either. Refer to the Channel Groups topic for more information on this object.
Right click on the Channel Groups object and select New Channel Group. In the Name field, enter a Name that will identify this channel group or accept the default entry.
In the Signaling Type field select SS7_ISUP from the drop down menu. By selecting SS7_ISUP, the Channel Transfer field can now be modified.
To enable the ISUP Explicit Channel Transfer feature, select Enabled from the drop down menu in the Channel Transfer field. See screen capture below.
Click on the Channel Groups object again. The Channel Groups object will have a yellow exclamation point in place of the icon indicating the configuration has not been sent to the IMG 2020. Click on the Download Resource Tables button and the new configuration will be sent to the IMG 2020.
Refer to the Channel Group object for more information on configuring the individual fields.
 Additional Information
ISUP ECT supports SS7 ITU97 only.
The IMG 2020 only support the "Service Platform Redirect and Transfer" scenario.
The IMG 2020 will only take on the role of the controller; the equipment requesting the ECT.
The IMG 2020 will not process ECT request from the SS7 side. They will be discarded.
ECT will be available only if the initial call was established between SS7 and a SIP device. The direction of the call is irrelevant.
ECT is triggered from the SIP call leg via the REFER method.
Related Topics
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