I 2 Figure 1.18 Slice selection and identifiers [55]. to the NSIs serving a UE. The selection of the set of NSIs for a UE is triggered by the first associated AMF during the registration procedure typically by interacting with the network slice selection function (NSSF), which may lead to change of AMF. A network slice is identified by an identifier known as single-network slice selection assis- tance information (S-NSSAI). The S-NSSAI identity consists of a slice/service type (SST), which refers to the expected network slice behavior in terms of features and services and a slice differentiator (SD), which is an optional information element that complements the SST(s) to differentiate among multiple network slices of the same SST. The support of all standardized SST values by a public land mobile network (PLMN)2 29 is not required. The S- NSSAI can have standard values or PLMN-specific values. The S-NSSAI identifiers with PLMN-specific values are associated with the PLMN ID of the PLMN that assigns them. An S-NSSAI cannot be used by the UE in AS procedures in any PLMN other than the one to which the S-NSSAI is associated. Standardized SST values provide a way for establish- ing global interoperability for slicing SO that PLMNs can support the roaming use case more efficiently for the most commonly used SSTs. Currently, the SST values of 1, 2, and 3 are associated with eMBB, URLLC, and mMTC slice types [16]. The NSSAI is a collection of S-NSSAI. There can be at most eight S-NSSAIs in the NSSAI sent in signaling messages between the UE and the network. Each S-NSSAI assists the network in selecting a particular NSI. The same NSI may be selected via different S-NSSAIs. NSSAI includes one or more S-NSSAIs. Each network slice is uniquely identified by an S-NSSAI [3] (see Fig. 1.18). Public land mobile network is a mobile wireless network that is centrally operated and administrated by an organization and uses land-based RF transceivers or base stations as network hubs. This term is generally used to refer to an operato