Local IMS Policy
In 3GPP networks, authorization is based on subscriber data provided by the HSS (Home Subscriber Server). The IMS AAA Server can provide additional authorization policy using Local Profiles.
The IMS AAA Server can enforce fine-grained authorization policy by using Local Profiles. Local profiles are used in combination with the subscriber profile stored in the HSS to provide additional security for subscriber authorization. A Local profile is configured in the IMS AAA Server Administrator by defining ordered lists of attributes and an I-WLAN policy. You can define as many local profiles as you require.
Each profile consists of six configurations, one for each 3GPP WLAN service scenario supported by the IMS AAA Server as shown in Table 11.
One way a mobile operator might use profiles, would be to create a profile for each wireless plan they offer. For example, you might offer a voice only plan, as well as a voice and data plan. A profile could be defined for each plan and customized for the specific requirements of the 3GPP WLAN access scenarios supported in the plan.
To create a profile, you configure lists of attributes and an I-WLAN policy for each 3GPP WLAN service scenario. The attribute lists specify attribute values that are placed in the response to the requestor, and are typically used to provide additional parameters needed to complete the authorization. The I-WLAN policy is a list of rules governing authorization. The order of the attribute lists is user-defined.
Local Profile Selection
During the authorization process, the IMS AAA Server uses 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. 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.
A Profile Selection Rules Set consists of ordered lists of user defined attributes and/or I-WLAN parameters.
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.