Section: 16a.3.3 Accounting Update
Content: During the life of a PDP context some information related to this PDP context may change (i.e. SGSN address if an Inter-SGSN RA update occurs). Upon reception of an UpdatePDPContextRequest from the SGSN, the GGSN may send an Accounting Request (Interim) to the Diameter server to update the necessary information related to this PDP context (see figure 25c). Interim updates are also used when the IPv4 address is allocated/released/re-allocated for deferred IPv4 addressing for the PDP type IPv4v6. If the GGSN receives an UpdatePDPContextRequest from the SGSN that specifically indicates a direct tunnel establishment or a direct tunnel teardown (switching the user plane tunnel end back to the SGSN), and only the GTP user plane address or the GTP-U TEID have changed, then the GGSN should not send the Accounting Request (Interim) message to the Diameter server. In such cases, the GGSN need not wait for the Diameter Accounting Answer from the Diameter server message before sending the UpdatePDPContextResponse to the SGSN. The GGSN may delete the PDP context if the Accounting Answer is not received from the Diameter server. NOTE: As shown the GGSN need not wait for the Diameter Accounting Answer message from the Diameter server to send the UpdatePDPContextResponse to the SGSN. The GGSN may delete the PDP context if the Accounting Answer is not received from the Diameter server. Figure 25c: Diameter for PDP context Update