Section: 4.3.8.4 SGSN selection function
Content: The SGSN selection function selects an available SGSN to serve a UE. The selection is based on network topology, i.e. the selected SGSN serves the UE's location and for overlapping SGSN service areas, the selection may prefer SGSNs with service areas that reduce the probability of changing the SGSN. When a MME/SGSN selects a target SGSN, the selection function performs a simple load balancing between the possible target SGSNs. In networks that deploy dedicated MMEs/SGSNs for UEs configured for low access priority, the possible target SGSN selected by source MME/SGSN is typically restricted to SGSNs with the same dedication. When a MME/SGSN supporting DCNs selects a target SGSN, the selected target SGSN should be restricted to SGSNs that belong to the same CN. The DNS procedure may be used by the source CN node to select the target SGSN from a given DCN. If both low access priority and UE Usage Type parameter are used for SGSN selection, selection based on UE Usage type parameter overrides selection based on the low access priority indication.