Section: 16a.3a.2 Accounting Update
Content: During the life of a bearer some information related to this bearer may change. Upon occurrence of the following events the P-GW may send an Accounting Request (Interim) to the Diameter server: RAT change, S-GW address change and QoS change. Interim updates are also used when the IPv4 address is allocated/released/re-allocated for deferred IPv4 addressing for the PDN type IPv4v6. When the P-GW receives a signalling request (e.g. Modify Bearer Request in case of GTP-based S5/S8) that indicates the occurrence of one of these chargeable events, the P-GW may send an Accounting Request (Interim) to the Diameter server to update the necessary information related to this bearer. The P-GW need not wait for the Diameter Accounting Answer message from the Diameter server before sending the response for the triggering signalling message (e.g. Modify Bearer Response). The P-GW may delete the bearer if the Accounting Answer is not received from the Diameter server. The P-GW may also send interim updates at the expiry of an operator configured time limit. The message flow in figure 25d.2 provides an example for Diameter Accounting Update procedure on Sgi interface, which is applicable for GTP based S5/S8: Figure 25d.2: Diameter accounting update for bearer modification