4G to 5G – What Is Included, Interworking
Shahab Lavasani, Zhu Fenqin · Wiley 5G Ref · 2021
Abstract This article describes the method to support the interworking between the 5GS and EPS networks. Two types of mechanisms, i.e. RAN‐ and CN‐based interworking, are introduced. For the CN‐based interworking mechanism, the UE may operate in single‐ or dual‐registration mode, and the network may support the interworking with or without N26 configuration. The relation between the UE operation mode and the network configuration case is clarified. The mobility and the PDU Session handling in different network configurations are described. The mobility handling includes GUTI mapping, registration or TAU procedure selection, and network sharing specific consideration. The PDU Session handling includes the method to do the parameter mapping between the PDU Session and PDN Connection, EBI management, QoS flow status synchronization, multiple PGW‐C + SMF selection, APN rate and small data rate handling, and buffered data forwarding. Network slice is one important feature supported in 5GS network but not in EPS network. Thus, the method to support one PDN Connection move to 5GS network associated with the suitable slice is discussed. Finally, the service exposure due to the interworking is also mentioned.