The solution to the problem of multiple router dialects is to have the IMS AAA Server translate policy server requests into VSAs that the router understands. To do this, the IMS AAA Server needs a mechanism for translating policy server requests so that the router can understand and implement them. Our solution is to use XML for specifying initial authorization, activation, deactivation, and abort session requests.
Juniper Networks provides XML-based templates for Juniper Networks and Cisco router communication with the policy server. If you want to add a router from another vendor, you must write a custom template so that the policy server can communicate properly with your new router.
The policy server in our solution is called the Service Resource Controller (SRC). This document uses policy server and SRC interchangeably.
Figure 116 shows the overall structure of the network with an upstream router.
The downstream AAA handles authentication methods not supported by the IMS AAA Server. In our solution, the downstream AAA is known as Steel-Belted Radius (SBR).
The IMS AAA Server generates dynamic RADIUS authorization requests on SRC request. Because the SRC does not communicate directly with your router, translations between SRC, IMS AAA, and your router must take place. This translation process is called rendering. The SRC provides parameters for the rendering. The rendering process is shown in Figure 117.
The rendering process takes three inputs and produces one output. Inputs are:
- The data the policy server sends
- XML templates from the IMS AAA Server
- Data that returns with the authentication response from the downstream AAA Server
The templates for rendering are in an XML file, called
deviceModels.xml, located in the root directory of the IMS AAA Server. A default version of this file includes sample service templates for Juniper Networks and Cisco routers. The next section explains how to add templates for other routers to this file. After that, the Juniper Networks and Cisco router XML files are discussed as concrete examples.