6.4.1.5A Handling the maximum number of allowed active user-plane resources for PDU sessions of UEs in NB-N1 mode

For a UE in NB-N1 mode, the UE's maximum number of supported user-plane resources is two (as defined in 3GPP TS 36.300 [25B]) when the UE sets the Multiple user-plane resources support bit to "Multiple user-plane resources supported" during the registration procedure for initial registration or for mobility and periodic registration update, and one otherwise.

For a UE operating in NB-N1 mode, if:

• the UE's maximum number of supported user-plane resources is one, then only one PDU session can have active user-plane resources even though that UE might have established more than one PDU session; or
• the UE's maximum number of supported user-plane resources is two, then only two PDU sessions can have active user-plane resources even though that UE might have established more than two PDU sessions.

When the maximum number of active user-plane resources is reached and upper layers request for more user-plane resources for PDU sessions other than the PDU sessions with those active user-plane resources, the UE can choose to release one or more of the PDU sessions with active user-plane resources to cater for the upper layer request. The choice of which PDU sessions to be released is implementation specific. However if there is a PDU session with an active user-plane that is used for exception data reporting (see clause 6.2.13), that PDU session shall not be released.

If the maximum number of active user-plane resources is reached and the upper layers of the UE request user-plane resources for exception data reporting (see clause 6.2.13), the UE shall release a PDU session that has user-plane resources to cater for the request for exception data reporting. The choice of which PDU session to be released is implementation specific.

If the UE decides to release one or more active user-plane resources to cater for upper layer request, the UE shall release the PDU session via explicit 5GSM signalling.