Feature Description
Important | The PGW-C term used in this chapter denotes the EPS interworking functionality supported by SMF and must not be assumed as a standalone P-GW that is used in the LTE network. |
EPS Interworking through 5G Core Network
The SMF implements the 3GPP recommendations for interworking of Evolved Packet System (EPS) and 5G Core Network (5GC).
The UEs capable of supporting both 4G and 5G NAS connect to the Evolved Terrestrial Radio Access Network (E-UTRAN) and the 5GC network. The SMF with the EPS interworking capability acts as a SMF and uses the S5 or S8 interface with S-GW to receive the 4G Session Creation Request. All the other interfaces involved in the 4G Session Creation (for example, Gx, Gy, Gz, and so on) are replaced by the corresponding 5GC Service Based Interfaces (for example, Npcf and Nchf).
After a PDU session is created on the SMF with E-UTRAN, Mobility Management Entity (MME) and Serving Gateway (S-GW), the UE can hand over E-UTRAN to 5G New Radio (NR) and conversely.
The SMF uses the N26 interface to interwork with EPS. This interface is an inter-CN interface between the MME and AMF and supports a subset of the functionalities over S10 interface to enable interworking.
The UE uses EPC NAS or 5GC NAS procedures depending on the core network by which it's served.
SMF Interworking with Diameter Interfaces
The Converged Core deployment allows signaling from a 4G subscriber. The SMF implements the 3GPP recommendations for interworking of Evolved Packet System (EPS) and Diameter Interfaces such as Gx for Policy, Gy for OCS, and Gz for offline charging. It also supports RADIUS authentication and accounting for subscribers. The signaling call flows and Pod level communications along with communication over various 3GPP interfaces is limited with only E-UTRAN access types.
Following are the SMF Diameter Interface call flow procedures for E-UTRAN access types:
Note | It should not be assumed that the Diameter interface features available on the SMF have full feature parity and functionality with StarOS or CUPS product. Furthermore, it should not be assumed that any constructs (including, but not limited to, commands, statistics, attributes, MIB objects, alarms, logs, services) referenced in this document imply functional parity with StarOS legacy or CUPS products. Please contact your Cisco Account or Support representative for any questions about parity between this product and any StarOS legacy or CUPS products. |
Alternate RAT Tunnel Creation for 4G
SMF creates an alternate RAT tunnel during 4G sessions for 4G attach and dedicated bearer procedures. This tunnel is reused when a subscriber moves to another RAT during handover.
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