Section: 6.3.5 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 23.401[ General Packet Radio Service (GPRS) enhancements for Evolved Universal Terrestrial Radio Access Network (E-UTRAN) access ]  [10] are met. The network may store an APN congestion back-off time on a per UE and congested APN basis. If the UE does not provide an APN for a non-emergency PDN connection, then the MME uses the APN which is used in PDN GW selection procedure as congested APN. When APN based congestion control is active, the network may reject session management requests except the modification of bearer resources requests from UEs or disconnect existing PDN connections with ESM cause value #26 "insufficient resources". In the UE, EPS 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 provided by the UE when the PDN connection is established. If no APN is included in the PDN CONNECTIVITY REQUEST or, when applicable, in the ESM INFORMATION RESPONSE message, then T3396 is associated with no APN. For this purpose the UE shall memorize the APN provided to the network during the PDN connection establishment. The timer T3396 associated with no APN will never be started due to any ESM procedure related to an emergency PDN connection. If the timer T3396 associated with no APN is running or is deactivated, it does not affect the ability of the UE to request an emergency PDN connection. If timer T3396 is running or is deactivated, the UE is allowed to indicate change of the 3GPP PS data off UE status, initiate PDN disconnection procedure, initiate bearer resource modification procedure to release of bearer resources for the respective APN, and if the UE is a UE configured to use AC11 – 15 in selected PLMN, then the UE is allowed to initiate an attach procedure or any EPS session management procedure for the respective APN.