During the authorization process, the IMS AAA Server uses user-defined Profile Selection Rule Sets to select the local profile used to authorize the request. To select the correct local profile, the server compares the HSS or downstream server response, with the Profile Selection Rule Sets in the order in which the sets are defined. A match is declared when everything in a Profile Selection Rule Set is included in the HSS or downstream server response. If a match is found, the local profile associated with the Profile Selection Rule Set, is merged with the HSS or downstream server response, to form a complete profile used to authorize that subscriber's requests.
The merged profile is cached in the IMS AAA Server and used to authorize all future requests from that subscriber. The cached profile in the IMS AAA Server and the HSS stay synchronized through the Push Profile Request (PPR) process, which notifies the IMS AAA Server through a PPR message whenever a profile is modified. If there is a conflict between the two databases, the HSS profile data takes precedent.
A specific profile can be configured for processing requests with no matching rules, or you can configure the server to reject all requests for which no match is found.
The IMS AAA Server can also provide backup support for the HSS by continuing to process requests in the event the HSS is unavailable. A specific profile can be defined for processing requests in this situation, or you have the option to reject all requests when the HSS is unavailable.
A Profile Selection Rules Set consists of ordered lists of user defined attributes and/or I-WLAN parameters. To create a Profile Selection Rule Set, first you select the profile for which you want to create the selection rule set. You then add the user defined attributes and I-WLAN parameters. You select each attribute from a predefined list and are then prompted to enter a value for the attribute. The I-WLAN parameters are selected from a predefined list, and where required, you enter specific values.
Figure 56 presents a conceptual view of profiles and the profile selection process.