Section: 6.3.2.5 Abnormal cases on the network side
Content: The following abnormal cases can be identified: a) Expiry of timer T3591. On the first expiry of the timer T3591, the SMF shall resend the PDU SESSION MODIFICATION COMMAND message and shall reset and restart timer T3591. This retransmission is repeated four times, i.e. on the fifth expiry of timer T3591, the SMF shall abort the procedure and enter the state PDU SESSION ACTIVE. The SMF may continue to use the previous configuration of the PDU session or initiate the network-requested PDU session release procedure. If the SMF decides to continue to use the previous configuration of the PDU session and i) the Authorized QoS rules IE is included in the PDU SESSION MODIFICATION COMMAND message, the SMF may mark the corresponding authorized QoS rule(s) of the PDU session as to be synchronised with the UE; and ii) the Authorized QoS flow descriptions IE is included in the PDU SESSION MODIFICATION COMMAND message, the SMF may mark the corresponding authorized QoS flow description(s) of the PDU session as to be synchronised with the UE. b) Void. c) Collision of UE-requested PDU session release procedure and network-requested PDU session modification procedure. If the SMF receives a PDU SESSION RELEASE REQUEST message during the network-requested PDU session modification procedure, and the PDU session indicated in the PDU SESSION RELEASE REQUEST message is the PDU session that the SMF had requested to modify, the SMF shall abort the PDU session modification procedure and proceed with the UE-requested PDU session release procedure. d) Collision of UE-requested PDU session modification procedure and network-requested PDU session modification procedure. If the network receives a PDU SESSION MODIFICATION REQUEST message during the network-requested PDU session modification procedure, and the PDU session indicated in the PDU SESSION MODIFICATION REQUEST message is the PDU session that the network had requested to modify, the network shall: i) if the PDU SESSION MODIFICATION REQUEST message includes connection capabilities, ignore the PDU SESSION MODIFICATION REQUEST message received in the state PDU SESSION MODIFICATION PENDING except for the connection capabilities and proceed with the network-requested PDU session modification procedure; or ii) otherwise, ignore the PDU SESSION MODIFICATION REQUEST message received in the state PDU SESSION MODIFICATION PENDING and proceed with the network-requested PDU session modification procedure as if no PDU SESSION MODIFICATION REQUEST message was received from the UE. e) 5G access network cannot forward the message. If the SMF determines based on content of the n2SmInfo attribute specified in 3GPP TS 29.502[ 5G System; Session Management Services; Stage 3 ]  [20A] that the DL NAS TRANSPORT message carrying the PDU SESSION MODIFICATION COMMAND message was not forwarded to the UE by the 5G access network, then the SMF shall abort the procedure and enter the state PDU SESSION ACTIVE. f) 5G access network cannot forward the message due to handover. If the SMF determines based on content of the n2SmInfo attribute specified in 3GPP TS 29.502[ 5G System; Session Management Services; Stage 3 ]  [20A] that the DL NAS TRANSPORT message carrying the PDU SESSION MODIFICATION COMMAND message was not forwarded to the UE by the 5G access network due to handover, then the SMF shall abort the procedure and enter the state PDU SESSION ACTIVE. The SMF may re-initiate, up to a pre-configured number of times, the network-requested PDU session modification procedure when the SMF detects that the handover is completed successfully or has failed or at the expiry of the configured guard timer as specified in 3GPP TS 23.502[ Procedures for the 5G System (5GS) ]  [9]. g) Collision of re-establishment of the user-plane resources and network-requested PDU session modification procedure for the same PDU session. If the SMF receives an indication from the AMF to re-establish the user-plane resources during the network-requested PDU session modification procedure for the same PDU session, the network shall abort the network-requested PDU session modification procedure and proceed with re-establishment of the user-plane resources for the PDU session as specified in 3GPP TS 29.502[ 5G System; Session Management Services; Stage 3 ]  [20A] subclause 5.2.2.3.2.2. NOTE: After the completion of re-establishment of the user-plane resources for the PDU session, the SMF can re-initiate the network-requested PDU session modification procedure for the PDU session. h) Collision of UE-requested PDU session establishment procedure and network-requested PDU session modification procedure. If the network receives a PDU SESSION ESTABLISHMENT REQUEST message with request type set to "existing PDU session" or "existing emergency PDU session" during the network-requested PDU session modification procedure, and the PDU session ID indicated in the PDU SESSION ESTABLISHMENT REQUEST message is the PDU session that the network had requested to modify, the network shall abort the network-requested PDU session modification procedure and proceed with the UE-requested PDU session establishment procedure.