Section: 16.2 RADIUS Accounting
Content: RADIUS Accounting shall be used according to IETF RFC 2866 [39] , IETF RFC 2869 [116], IETF RFC 3162 [50] and IETF RFC 4818 [97]. The RADIUS accounting client function may reside in a GGSN/P-GW. The RADIUS accounting client may send information to an accounting server, which is identified during the APN provisioning. The accounting server may store this information and use it to automatically identify the user. This information can be trusted because the Packet Domain network has authenticated the subscriber (i.e. SIM card and possibly other authentication methods). The GGSN/P-GW may use the RADIUS Accounting-Request Start and Stop messages during IP-CAN bearer (e.g. primary and secondary PDP context, default and dedicated bearer) activations and deactivations procedures, respectively. For EPC based Packet domain, if the P-GW is not aware of the IP-CAN bearers, e.g. in case of PMIP-based S5/S8, the P-GW may use the RADIUS Accounting-Request Start and Stop messages per IP-CAN session as it would be one IP-CAN bearer. The use of Accounting-Request STOP and in addition the Accounting ON and Accounting OFF messages may be used to ensure that information stored in the accounting server is synchronised with the GGSN/P-GW information. If the AAA server is used for IPv4 address and/or IPv6 prefix assignment, then, upon reception of a RADIUS Accounting-Request STOP message for all IP-CAN bearers associated to an IP-CAN session defined by APN and IMSI or MSISDN, the AAA server may make the associated IPv4 address and/or IPv6 prefix available for assignment. For PDN/PDP type IPv4v6 and deferred IPv4 address allocation, when the IPv4 address is allocated or re-allocated, the accounting session that was established for the IPv6 prefix allocation shall be used to inform the accounting server about the allocated IPv4 address by sending RADIUS Accounting-Request Interim-Update with Framed-IP-Address attribute and its value field containing the allocated IPv4 address. Similarly, the release of IPv4 address shall be indicated to the accounting server by sending RADIUS Accounting-Request Interim-Update without the Framed-IP-Address attribute. In order to avoid race conditions, the GGSN/P-GW shall include a 3GPP Vendor-Specific sub-attribute "Session Stop indicator" when it sends the Accounting-Request STOP for the last IP-CAN bearer of an IP-CAN session and the IP-CAN session is terminated (i.e. the IPv4 address and/or IPv6 prefix and any associated GTP tunnels or PMIP tunnel can be released). The AAA server shall not assume the IP-CAN session terminated until an Accounting-Request STOP with the Session Stop indicator is received.