IMG 1010 - Release Link Trunk (RLT)

Overview:

Feature F-1648 Release Link Trunk is a technique for the Nortel DMS Variant where 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specific facility messages back to the Nortel DMS and tell the switch to connect these two calls together so they are no longer active on the IMG.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. Release Link Trunk supports a portion of specification (NISA211_V801_NI-1, chapter 5-12 (Issue, August 98)). See links under Related Topics below for more information on what is supported and how to configure

Call Flow Diagram:

Diagram:

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

Two calls are in progress. The SIP side sends a REFER message to the IMG telling the IMG to connect the two calls together.
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.
With F-1648 Release Link Trunk “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 Switch B (Nortel DMS) that the two independent calls be bridged together as shown below.
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 Switch B.

Configuration:

Initial Configuration:

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

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. Also select the Northern Tel DMS-100 Variant as shown in screen capture below. 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 Release Link Trunk 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 Release Link Trunk 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_RLT – 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:

RLT supports Northern Telecom DMS-100 and DMS-250 only
IMG will take on the role as the User Switched.
The IMG will not support/process an RLT request. The request will be discarded
In order for RLT to be invoked following a SIP Refer, both ISDN B-Channels must be terminated on the same remote switch
RLT will be available only if the initial call was established between ISDN and a SIP device. The direction of the call is irrelevant.
RLT is triggered from the SIP call leg via the REFER method.
Both channel groups must have the RLT feature enabled for the feature to be invoked. Feature will not be available if one of the channel groups does not have RLT enabled.
Two b-Channels can be controlled by one d-channel or they can be controlled by separate d-channels.
The IMG will invoke an RLT request only when both ISDN call legs are answered.
If RLT 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.