3GPP 23.501 v20.2.0 — the document's own text
5.15.18.1 General
Taught in 17. One network, many networks (The 5G system architecture, in depth), 6. One network behaving like several (The 5G system architecture, overview).
The network support for a Network Slice is defined on a per Tracking Area granularity. It may be beneficial to deploy some Network Slices such that the Network Slice have a limited geographical availability that is not matching existing Tracking Area boundaries.
The operator can in this case decide to change the topology of the Tracking Areas so they match the boundaries of the Network Slice, or the operator may configure resources for the Network Slices in the cells of TAs where the Network Slices are to be available and in cells of the TAs where the network slice is defined to be not available the cells are configured with zero resources. If a Network Slice is considered available in a cell, the Network Slice is also supported by the TA comprising the cell.
The AMF receives from the OAM the information on availability of a network slice when the granularity is smaller than TA, i.e. if the NS-AoS includes TAs where the network slice is not available in some cells of the TA.
In order to optimize the end-to-end behaviour, the AMF can, based on NS-AoS information received from OAM, configure supporting UEs with S-NSSAI location availability information and the network may need to monitor the S-NSSAI usage and enforce the NS-AoS e.g. if the UE does not support the S-NSSAI location availability information.