Section: 6.3.6 Handling of network rejection not due to based congestion control
Content: The network may include a back-off timer value in an EPS session management reject message to regulate the time interval at which the UE may retry the same procedure. For ESM cause values other than #26 "insufficient resources", the network may also include the re-attempt indicator to indicate whether the UE is allowed to re-attempt the corresponding session management procedure for the same in A/Gb or Iu mode or N1 mode after inter-system change. NOTE 1: If the network includes this back-off timer value, then the UE is blocked from sending another ESM request for the same procedure for the same PLMN and combination for the specified duration. Therefore, the operator needs to exercise caution in determining the use of this timer value. NOTE 2: If the re-attempt indicator is not provided by the network, a UE registered in its HPLMN or in an EHPLMN (if the EHPLMN list is present) can use the configured SM_RetryAtRATChange value specified in the NAS configuration MO or in the USIM NASCONFIG file to derive the re-attempt indicator as specified in clauses 6.5.1.4.3, 6.5.3.4.3, and 6.5.4.4.3. If re-attempt in A/Gb or Iu mode or N1 mode is allowed, the UE shall consider the back-off timer to be applicable only to the EPS session management in S1 mode for the rejected EPS session management procedure and the given PLMN and combination. If re-attempt in A/Gb and Iu mode and N1 mode is not allowed, the UE shall consider the back-off timer to be applicable to all three NAS protocols, i.e. applicable to the EPS session management in S1 mode for the rejected EPS session management procedure, to the GPRS session management in A/Gb and Iu mode for the corresponding session management procedure and the given PLMN and combination and to the 5GS session management in N1 mode for the corresponding session management procedure and the given PLMN and APN combination. NOTE 3: In the present clause the terms APN and DNN are referring to the same parameter. The APN of the PLMN and APN combination associated with the back-off timer 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 the back-off timer is associated with the combination of the PLMN and no APN. For this purpose the UE shall memorize the APN provided to the network during the PDN connection establishment. The back-off timer associated with the combination of a PLMN with no APN will never be started due to any ESM procedure related to an emergency PDN connection. If the back-off timer associated with the combination of a PLMN with no APN is running, it does not affect the ability of the UE to request an emergency PDN connection. The network may additionally indicate in the re-attempt indicator that a command to back-off is applicable not only for the PLMN in which the UE received the EPS session management reject message, but for each PLMN included in the equivalent PLMN list at the time when the EPS session management reject message was received. If the back-off timer is running or is deactivated for a given PLMN and APN combination, and 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 this PLMN and APN combination.