1. A communication method performed by a network slice selection function (NSSF) device in a network, the method comprising:receiving a network slice selection request for a network slice with a Single Network Slice Selection Assistance Information (S-NSSAI) from an access and mobility management function (AMF) device;
selecting a network slice instance; and
responding to the AMF for the network slice selection request,
wherein the network slice instance is served to a user equipment (UE) in the network,
wherein the S-NSSAI comprises a slice/service type (SST) or the slice/service type and a slice differentiator (SD),
wherein the SST is an expected network behavior in terms of features and services, and
wherein the SD is information that complements the SST.