6.4.2.4.1 General

Upon receipt of a PDU SESSION MODIFICATION REQUEST message, if the SMF does not accepts the request to modify the PDU session, the SMF shall create a PDU SESSION MODIFICATION REJECT message.

The SMF shall set the 5GSM cause IE of the PDU SESSION MODIFICATION REJECT message to indicate the reason for rejecting the PDU session modification.

The 5GSM cause IE typically indicates one of the following SM cause values:

#26 insufficient resources;

#29 user authentication or authorization failed;

#31 request rejected, unspecified;

#32 service option not supported;

#33 requested service option not subscribed;

#35 PTI already in use;

#37 5GS QoS not accepted;

#43 Invalid PDU session identity;

#44 Semantic errors in packet filter(s);

#45 Syntactical error in packet filter(s);

#46 out of LADN service area;

#59 unsupported 5QI value;

#67 insufficient resources for specific slice and DNN;

#69 insufficient resources for specific slice;

#83 Semantic error in the QoS operation;

#84 Syntactical error in the QoS operation;

#87 QoS differentiation for non-3GPP device identifier(s) not available;

#95 – 111 protocol errors.

If the UE requests a PDU session modification for an LADN when the UE is located outside of the LADN service area, the SMF shall include the 5GSM cause value #46 "out of LADN service area" in the 5GSM cause IE of the PDU SESSION MODIFICATION REJECT message.

If the UE initiates the UE-requested PDU session modification procedure to modify or delete the packet filter(s) which were created by the network without a request from the UE, the SMF shall include the 5GSM cause value #44 "semantic errors in packet filter(s)" in the 5GSM cause IE of the PDU SESSION MODIFICATION REJECT message.

If the Extended protocol configuration options IE of the PDU SESSION MODIFICATION REQUEST message indicates 3GPP PS data off UE status and the SMF detects the change of the 3GPP PS data off UE status, the SMF shall not include the 5GSM cause value #26 "insufficient resources", the 5GSM cause value #67 "insufficient resources for specific slice and DNN", the 5GSM cause value #69 "insufficient resources for specific slice" and the 5GSM cause value #46 "out of LADN service area" in the 5GSM cause IE of the PDU SESSION MODIFICATION REJECT message.

If the UE initiates UE-requested PDU session modification procedure to modify the PDU session transferred from EPS to an MA PDU session with the Request type IE set to "MA PDU request" in the UL NAS TRANSPORT message as specified in 3GPP TS 24.193 [13B] and the SMF determines, based on operator policy and subscription information, that the PDU SESSION MODIFICATION REQUEST message is to be rejected, the SMF shall include the 5GSM cause value #33 "requested service option not subscribed" in the 5GSM cause IE of the PDU SESSION MODIFICATION REJECT message.

NOTE: If the SMF determines, based on operator policy and subscription information, that the PDU SESSION MODIFICATION REQUEST message is to be accepted as single access PDU session, the ATSSS container IE cannot be included in the PDU SESSION MODIFICATION COMMAND message.

If the PDU SESSION MODIFICATION REQUEST message includes a Non-3GPP device information IE and one or more of the non-3GPP device identifiers included in the Non-3GPP device information IE are not available for the UE, the SMF shall include the 5GSM cause value #87 "QoS differentiation for non-3GPP device identifier(s) not available" in the 5GSM cause IE of the PDU SESSION MODIFICATION REJECT message.

The network may include a Back-off timer value IE in the PDU SESSION MODIFICATION REJECT message.

If the 5GSM cause value is #26"insufficient resources", #67 "insufficient resources for specific slice and DNN", or #69 "insufficient resources for specific slice" and the PDU SESSION MODIFICATION REQUEST message was received from a UE configured for high priority access in selected PLMN or SNPN or the request type provided during the PDU session establishment is set to "initial emergency request" or "existing emergency PDU session", the network shall not include a Back-off timer value IE.

The SMF shall send the PDU SESSION MODIFICATION REJECT message.

Upon receipt of a PDU SESSION MODIFICATION REJECT message and a PDU session ID, using the NAS transport procedure as specified in clause 5.4.5, the UE shall stop timer T3581, release the allocated PTI value, and enter the state PROCEDURE TRANSACTION INACTIVE.

If the PDU SESSION MODIFICATION REQUEST message was sent with the Requested MBS container IE included and the MBS operation set to "Join MBS session", and the UE receives a PDU SESSION MODIFICATION REJECT message, then the UE shall consider the requested MBS join as rejected.

If the PDU SESSION MODIFICATION REQUEST message was sent with the Requested MBS container IE included and the MBS operation set to "Leave MBS session", and the UE receives a PDU SESSION MODIFICATION REJECT message, then the UE shall locally leave the multicast MBS session(s) corresponding to the TMGI(s) in the Requested MBS container IE of the PDU SESSION MODIFICATION REQUEST message.

If the PDU SESSION MODIFICATION REJECT message includes 5GSM cause #87 "QoS differentiation for non-3GPP device identifier(s) not available", the UE behaves as specified in clause 6.4.2.4.3.