Section: 6.1.3.11 Handling of APN based congestion control
Content: The network may detect and start performing the APN based congestion control when one or more APN congestion criteria as specified in 3GPP TS 23.060[ General Packet Radio Service (GPRS); Service description; Stage 2 ]  [74] are met. The network may store an APN congestion back-off time on a per MS and congested APN basis. If the MS does not provide an APN for the PDP context activation, then the SGSN uses the APN which is used in GGSN/PDN GW selection procedure as congested APN. When APN based congestion control is active, the network may reject session management requests except the modify PDP context requests from UEs or deactivate existing PDP contexts with SM cause value #26 "insufficient resources". In the MS, session management timers T3396 for APN based congestion control are started and stopped on a per APN basis. The APN associated with T3396 is the APN sent by the MS when the PDN connection is established. If no APN is included in the ACTIVATE PDP CONTEXT REQUEST message, then T3396 is associated with no APN. For this purpose the MS shall memorize the APN provided to the network during the PDP context activation. The timer T3396 associated with no APN will never be started due to any SM procedure related to an emergency PDN connection. If the timer T3396 associated with no APN is running, it does not affect the ability of the MS to request an emergency PDN connection. If timer T3396 is running or is deactivated, and the MS is an MS configured to use AC11 – 15 in selected PLMN, then the MS is allowed to initiate any session management procedure for the respective APN.