1. Configuration Guide
  2. External Policy Servers
  3. AAR Message Optimization

AAR Message Optimization

Currently, upon receiving an INVITE with a Proxy-Authorization header, the P-CSCF sends an Authorization-Authentication Request (AAR) message when the values of the optimize-aar and the reserve-incomplete parameters in the ext-policy-server configuration element are set to enabled. If the INVITE does not contain a Proxy-Authorization header then an AAR message is not sent. However, for mobile VoLTE, because IMS AKA is used for security there is no need to authenticate requests, so all INVITE messages are sent without Proxy-Authorization headers. This enhancement allows the P-CSCF to generate an AAR message when the INVITE is identified as coming from an IMS AKA user.

When the Oracle Communications Session Border Controller acts as a P-CSCF, the Diameter Rx interface updates bandwidth and addressing changes during a session. Many transactions between the P-CSCF and a PCRF server trigger a new SDP offer resulting in the transmission of an P-CSCF-initiated AA-Request (AAR) sent to the PCRF for the purpose of updating bearer parameters. However, not all transactions need to be reported to the PCRF, for example transactions that do no carry any bandwidth or addressing changes. In such instances, the issuance of an AAR is unnecessary and wasteful.

AAR message optimization (the suppression of unnecessary AARs) is activated by setting the optimize-aar parameter in the ext-policy-server configuration element to enabled.

If optimization is enabled, AARs are suppressed when:

  • the originating INVITE does not contain a proxy-authorization header, except for INVITE messages coming from IMS AKA users
  • the codec & bandwidth provided in the m-line of an SDP response, and media IP address and port have not changed since the last SDP message
  • In the MTC scenario, AAR is suppressed on reception of the originating non-IMS-AKA INVITE with no NPLI configured

AAR Optimization for Supplementary Services

In some call flows, a reINVITE or UPDATE request or response is sent to the P-CSCF and neither the bandwidth nor codec has changed. Such reINVITEs or UPDATES may include SDP offers/answers with new a=sendonly, a=recvonly, or a=inactive. These SDP parameters are directly related to the provision of Supplementary Services such as Call Hold. By default the Oracle Communications Session Border Controller does not send an AAR to the PCRF for these changes.

The Oracle Communications Session Border Controller can be configured to allow the generation of an AAR in these cases by adding the optimized-aar=supplementary-service option to the ext-policy-server configuration element. (You may also configure the option as optimized-aar= supplementry resulting in identical behavior.) The following call flow reflects this optimized behavior.