SIP Redirect - Initiated 302 Response

1 SIP Redirect Diagram
2 Configuration

The Initiated 302 response feature allows the IMG 2020 to initiate a SIP Redirect by sending a 302 message back to an originating gateway with IP information of other gateways or devices to send the call to. Referring to the diagram below, before the Redirect feature was added if a call came in on SIP GhGrp1 and the TDM resources on that IMG 2020 were all busy, the IMG 2020 would send out a 486 Busy Here message and the call would be dropped. With the SIP Redirect feature the call will get passed on to the second and possibly third gateway or IP device.

SIP Redirect is in response to an INVITE message from a SIP gateway. Using the diagram below, the Originating Gateway sends an INVITE message to the IMG 2020 0. The call signaling then gets passed to the TDM side. If the resources on the TDM side of the IMG 2020 0 are all being utilized, the IMG 2020 0 will send a 302 response back to the originating gateway with contact information to communicate with a second gateway (Displayed below as IMG 2020). The originating gateway then sends the INVITE message to the second gateway. The second gateway accepts the INVITE and routes the call out the TDM channel group and the call is eventually processed.

The Redirect feature can be configured by creating a route list along with a Route List Entry. Within each Route List Entry there is a field labeled Channel Group Type. This field will enable the redirect feature for that channel group within the route list. The procedures below describe configuration of SIP Redirect.

In the diagram below, the IMG 2020 can act as the Originating Gateway and accept the 302 to reroute the call (Refer to the SIP Redirect topic for information on this). It also can act as the IMG 2020 0 that will receive the INVITE and reject the call if the TDM side is busy. The procedure below describes how to configure the IMG 2020 0 which will receive the call.

SIP Redirect Diagram

The procedure below configures the IMG 2020 0 for the redirect feature.

Configuration

The procedure below explains how to configure the IMG 2020 to function using the SIP Redirect 302 Initiated response message. Before configuring, the IMG 2020 labeled IMG 2020 0 that will be a redirect server must have an initial configuration created on it. Follow the Basic Configurations procedure before proceeding. Once all initial steps have been achieved, the IMG 2020 can be configured for the SIP Redirect 302 Initiated response feature.

Configure SS7 Signaling on each of the nodes

Since the call will be routed to the TDM SS7 side, an SS7 Stack will need to be configured on the IMG 2020 0. Refer to the Configure SS7 topic for a procedure describing the steps needed to configure the SS7 functionality. Create an SS7 stack along with its CIC groups on IMG 2020 0 (refer to diagram to view which node is IMG 2020 0).

Create SIP Profile (SGP)

Create a SIP Profile that has the SIP redirect functionality enabled

Right click on the Profiles object and select New SIP Profiles. The SIP Profiles object is a parent or container object. No configuration is needed here. Refer to the SIP Profiles topic for more information on this object.
Right click on the SIP Profiles object and select New SIP Profile. The first profile that gets created is a Default SIP Profile and cannot be modified. Disregard this profile.
Right click on the SIP Profiles object and select New SIP Profile again. In the SIP Profile object that appears, either enter a name that identifies this SIP Profile or accept the default name already entered. In this example the SIP Profile was labeled SIP_Redirect_Profile.
Verify the 3xx Redirect Support field is set to Enable (Default). For more information on the SIP Profile object refer to the SIP Profile - SGP topic.

Create TDM Channel Group

Create a TDM Channel Group that will be used to route the incoming SIP call to. This will be done on the node labeled IMG 2020 0 in diagram above.

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.
Right click on Routing Configuration and select New Channel Groups. The Channel Groups object is a container object also and no configuration is needed. Refer to the Channel Groups topic for more information.
Right click on the Channel Groups object and select New Channel Group. Either enter a name that identifies this channel group or accept the default entry. In this example the Channel Group was labeled ChGrp0_SS7.
Select SS7_ISUP from the drop down menu of the Signaling Type field. Refer to the Channel Group topic for more information on configuring the remaining fields in this object.
Right click on ChGrp0_SS7 just created and select New Circuit Group. Select the starting and ending DS-1's and DS-0's for this ISUP Group.

Create an External SIP Gateway

Create an External SIP Gateway. The gateway created will be given an IP address. This IP address is sent back to the originating gateway in the 302 message when the SS7 circuits are busy. The originating gateway will then send a re-invite to all the gateways on this list. Follow the procedure below to create these gateways.

Right click on the Dialogic object and select New External Network Elements. The External Network Elements object is a container object and no configuration is needed. Refer to the External Network Elements object for more information on this object.
Right click on the External Network Elements object and select New External Gateways. The External Gateways object is a container object and no configuration is needed here. Refer to the External Gateways topic for more information on this object.
Right click on the External Gateways object and select New External Gateway. Refer to the screen capture below

Enter a name that describes this gateway. In this example the Name given was Redirect_Gateway.
Enter the IP address of the external Gateway in the IP Address field.
In the SIP Profile field, select from the drop down menu the SIP Profile created that has the SIP Redirect enabled. This was created earlier in the procedure.

Refer to the External Gateway topic for more information on configuring the remaining fields in this object.

Configure SIP Signaling

The configuration above displays how to configure the SIP Profile and External SIP Gateway so that the SIP Redirect functionality on the SIP leg is configured. The next step is to configure the SIP signaling stack. Refer to the Configure SIP (Single SIP IP) topic for a procedure on how to configure the SIP Signaling stack.

In the Configure SIP topic referenced above, the procedure describes how to create the SIP Stack, External SIP Gateway, and SIP Channel Group. Disregard configuring the SIP Channel Group from this procedure and use the configuration described below instead.

Create SIP Channel Groups

Create a SIP channel group along with its IP Network element. Each IP Network Element will have an IP address associated with it. This will be the IP address of the gateway that the call will be redirected to. Follow procedure below.

Right click on the Channel Groups object and select New Channel Group. Enter a name for this channel group. In this example the channel group was named ChGrp1_SIP.
Select SIP from the Signaling Type field drop down menu. For more information, refer to the Channel Group topic.
Right click on the Channel Group just created and select New IP Network Element. Select the external gateway created above. In this example, the gateway selected was labeled Redirect_Gateway.
Repeat steps 1 through 3 to create as many channel groups required and link them to each of the gateways created above.

Create Route List

The next few steps are to create a Route List with the SIP Channel Groups that the call will be routed to.

Right click on the Routing Configuration object and select New Route Lists. The Route Lists is a container or parent object and no configuration is needed here. Refer to the Route Lists topic for more information on this object.
Right click on Route Lists object in object tree and select New Route List. Enter a name that identifies this Route List. In this example, Route_List_SIP_Redirect was entered. Refer to Route List topic for more information on configuring the remaining fields in this object.
Right click on the Route List object and select New Route List Element. In the Channel Group Type field select Normal and in the Channel Group field select the outgoing SS7 channel group. Refer to screen capture below.

Right click on the Route List object again and select New Route List Element. The SIP channel groups will now be added. Refer to the screen capture below.

In the Channel Group Type field, select Redirect from the drop down menu.
In the Channel Group field select from the SIP channel group created earlier.
The Network Element field will be automatically populated with correct IP Network Element.

Refer to the topic for more information on the Route List Element object.

Create Route Table and route call to SS7 Channel Group

Right click on the Routing Configuration object and select New Routing Tables. The Routing Tables object is a container object and no configuration is needed here. Refer to the Routing Tables topic for more information on this object.
Right click on the Route Tables object and select New Route Table. Refer to the Route Table topic for information on configuring the fields in this object.
Right click on the Route Table object and select New Route Element. Select the Routing Criteria Type from drop down menu. In this exampleChannel Groupwas selected.
In theIn Channel Groupfield, select the incoming SIP Channel Group that is communicating with the Originating gateway. This would have been the first SIP channel group created above.
In the Route Action Type field select Route List.
In the Outgoing Route List select the Route List created above. Refer to the screen capture below.

Click back on the Channel Groups object. It will have a yellow exclamation point for the icon in the configuration tree indicating the configuration needs to be sent to the IMG 2020. Click on the Download Resource Tables button and the configuration will be sent. Do the same for the Route Table entry that has the yellow exclamation point for an icon in the configuration tree.

Dialogic Integrated Media Gateways