SIP Proxy - Overview / Configuration

SIP Proxies and SIP Session Border Controllers are used as intermediate routes between domains. The IMG 2020 can route traffic to these entities and also have a knowledge of the calls final destination (Remote SIP User Agents). The SIP Proxy feature allows the IMG 2020 to successfully request or respond to a SIP Proxy which includes the handling of the following SIP concepts.

• Outbound Proxy - A proxy that receives SIP requests from a client, even though it may not be the server resolved by the Request-URI.

• Loose Routing -  A proxy is said to be loose routing if it follows the procedures defined in RFC 3261 for processing of the Route header field. These procedures separate the destination of the request (present in the Request-URI) from the set of proxies that need to be visited along the way (present in the Route header field).  

• Strict Routing - A proxy is said to be strict routing if it follows the Route processing rules of RFC 2543 and many prior work in progress versions of this RFC. That rule caused proxies to destroy the contents of the Request-URI when a Route header field was present.  Strict routing behavior is not used in RFC 3261, in favor of a loose routing behavior. Proxies that perform strict routing are also known as strict routers. 

Diagram - SIP Proxy

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Call Flow

A SIP request uses a transport layer destination IP address different from the other URI values.

Open

Configuration

The procedure below explains how to configure the IMG 2020 for SIP Proxy support feature. Before configuring the SIP Proxy feature, the IMG 2020 must have an initial configuration created on it. Follow the Basic Configurations procedure before proceeding onto configuring the SIP Session Timer feature.

 Create a SIP Profile (SGP) for SIP Proxy Support Feature

• 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 Proxy_Support_Profile.

Create an External Gateway and associate to SIP Profile

Create and configure an External Gateway object. This object can be used to configure an External SIP Gateway as a SIP Proxy.

• Right click on the Dialogic object and select New External Network Elements. The External Network Elements object is a container or parent object and no configuration is needed here. Refer to the External Network Elements topic 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 or parent object also and no configuration is needed here. Refer to the External Gateways topic for more information on the External Gateways object.

• Right click on the External Gateways object and select New External Gateway. Enter a Name that identifies the gateway being created. In this procedure the External Gateway was labeled Ext_Proxy_GW.

• In the IP Address field, enter the IP address given to the proxy.

• In the Profile field, select from the drop down menu the SIP Profile created in the section above. Refer to the External Gateway topic for more information on this object.

• Right click on the SIP Profile created above (labeled Proxy_Support_Profile) and select New SIP Proxy. Select from the drop down menu of either the Gateway field or the Hostname field the External Gateway that was configured as the SIP Proxy server. Once the selected, the IP address field will automatically be populated with the IP address of the SIP Proxy. Refer to the SIP Profile - Proxy topic for more information on the SIP Proxy topic.

Create a SIP Signaling Stack

• Right click on the IMG 2020 physical node and select New Signaling.  The Signaling object is a parent or container object and no configuration is needed here. Refer to the Signaling topic for more information on this object.

• Right click on the Signaling object created and select New SIP. In the IP Operation Mode field, select Single IP from drop down menu if the SIP Stack will service only one IP address. Select Multiple IP if the SIP stack will service more than one IP address. In this procedure, Multiple IP was selected. Refer to IMG 1010 - SIP Signaling Object topic for more information.

• Right click on the SIP signaling object just created and select New SIP IP Address. Select from the drop down menu of the IP Address field the IP address that will be used to pass the SIP signaling messaging to the SIP stack. The IP addresses in the drop down menu will be both the IP address given to the IMG 2020 during the bootup process and any IP Addresses configured to be Service IP address.

• Select the Transport Type from drop down menu and modify the Port field as required. Refer to the SIP Signaling - IP Address topic for more information on configuring the remaining fields.

Create SIP Channel Groups

• 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 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 Name given to this Channel Group was Proxy_Support_ChGrp.

• Select SIP from the drop down menu of the Signaling Type field. Refer to Channel Group topic for more information on configuring this object.

Insert SIP External Network Element into SIP Channel Group

• Right click on the SIP Channel group created earlier and select New IP Network Element. Within the IP Network Element field, select from the drop down menu, the gateway created. Refer to the screen capture below.

• Right click on the IP Network Element just configured and select New Node Association. The Node Association object defines the SIP IP and Packet Facility that are associated to the Channel Group/IP Network Element. Select the Node that will be communicating with the remote external gateway from the drop down menu.

• Select the IP address from the drop down menu of the Service IP Address field. The Service IP is the IP of the SIP Signaling stack that will be communicating with the remote external gateway/proxy server.

• Select the packet facility from the drop down menu of the Media Packet Facility field. This will be the IP channels / Packet Facility that will be streaming the RTP data between the IMG 2020 and the external gateway / proxy server. Refer to the SIP Signaling - Node Association topic for more information on this object.

• 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.

• The SIP Proxy Support feature is now configured.

SIP Call Trace - Using an Outbound Proxy

Example of UAC sending a SIP Request to an outbound proxy:

Additional Information

• The IMG 2020 allows a SIP request intended for a remote User Agent, to be sent to a configured Outbound Proxy Server.

• There is only one SIP Outbound Proxy Server configured per external SIP gateway, therefore no support for redundancy.

• Supports loose routing which follows the procedures defined in RFC 3261 for processing of the Route header field.

• Supports strict route processing rules of RFC 2543 (backward compatibility requirement imposed by RFC 3261).

• The IP Profile is to remain associated with the remote UA (gateway), and not the configured outbound proxy.

• The IMG 2020 will detect an Inbound SIP request if the SIP method was forwarded by a proxy or sent by a remote User Agent. The relevant IP address is to be used to retrieve the associated gateway profiles.

• The IMG 2020's dialog route list is not be updated based on RR headers received in the ACK or in subsequent transactions within the same dialog.

• An option to send outbound REGISTER methods to the Outbound Proxy, instead of the external gateway, shall be configurable in each SGP object. By default, the IMG 2020 is to send REGISTER methods to the Outbound Proxy.

• Re-invite and 3xx Redirect to outbound proxy are supported.