3GPP 24.501 v20.0.0 — the document's own text

6.4.2.1 General

Taught in 6. Getting on the network, and getting a connection through it (CT1 — the group that writes what your phone says, in depth), 4. Inside TS 24.501, the document at the centre (CT1 — the group that writes what your phone says, overview).

The purpose of the UE-requested PDU session modification procedure is:

to enable the UE to request modification of a PDU session;
to indicate a change of 3GPP PS data off UE status for a PDU session;
to revoke the previously indicated support for reflective QoS;
to request specific QoS handling and segregation of service data flows;
to indicate to the network the relevant 5GSM parameters and capabilities (e.g. the UE's 5GSM capabilities, whether the UE supports more than 16 packet filters, the maximum data rate per UE for user-plane integrity protection supported by the UE for uplink, the maximum data rate per UE for user-plane integrity protection supported by the UE for downlink and whether the UE requests the PDU session to be an always-on PDU session in the 5GS) for a PDN connection established when in S1 mode, after an inter-system change from S1 mode to N1 mode, if the UE is a UE operating in single-registration mode in a network supporting N26 interface and the UE has not previously successfully performed the UE-requested PDU session modification to indicate to the network the relevant 5GSM parameters and capabilities;
to delete one or more mapped EPS bearer contexts;
to convey a port management information container;
to re-negotiate header compression configuration associated to a PDU session using control plane CIoT 5GS optimization;
to enable the UE to request to join or leave one or more multicast MBS sessions associated with a PDU session;
to send the URSP rule enforcement report to the network associated to:

an established PDU session; or
a PDN connection, after an inter-system change from S1 mode to N1 mode, if the UE is a UE operating in single-registration mode in a network supporting N26 interface; or

to request QoS differentiation of traffic or to request suspend of QoS differentiation of traffic from one or more non-3GPP devices connecting through the UE.

NOTE 1: The case c), d), e), f) and g) do not apply to PDU sessions associated with the control plane only indication.

NOTE 2: For case e), the procedure is attempted after the first inter-system change from S1 mode to N1 mode.

When the UE-requested PDU session modification procedure is used to indicate a change of 3GPP PS data off UE status for a PDU session (see clause 6.2.10), the UE shall initiate the UE-requested PDU session modification procedure even if the UE is outside the LADN service area or the timer T3396, T3584, T3585 or the back-off timer is running or is deactivated.

If the UE needs to revoke the previously indicated support for reflective QoS for a PDU session and timer T3396, T3584, T3585 or the back-off timer is running or is deactivated, the UE shall not initiate the UE-requested PDU session modification procedure and shall instead initiate the UE-requested PDU session release procedure.

If the UE needs to initiate the UE-requested PDU session modification procedure to indicate to the network the relevant 5GSM parameters and capabilities (e.g. the UE's 5GSM capabilities, whether the UE supports more than 16 packet filters, the maximum data rate per UE for user-plane integrity protection supported by the UE for uplink, the maximum data rate per UE for user-plane integrity protection supported by the UE for downlink and whether the UE requests the PDU session to be an always-on PDU session in the 5GS) for a PDN connection established when in S1 mode, after an inter-system change from S1 mode to N1 mode, the UE is a UE operating in single-registration mode in the network supporting N26 interface, the UE has not previously successfully performed the UE-requested PDU session modification to indicate to the network the relevant 5GSM parameters and capabilities, and:

timer T3396, T3584, T3585 or the back-off timer is running, the UE shall initiate the UE-requested PDU session modification procedure after expiry of timer T3396, T3584 or T3585 or after expiry of the back-off timer; or
the UE is in substate 5GMM-REGISTERED.NON-ALLOWED-SERVICE and has not performed the the UE-requested PDU session modification procedure (see clause 5.3.5), the UE shall initiate the UE-requested PDU session modification procedure after entering substate 5GMM-REGISTERED.NORMAL-SERVICE.