5G • Core Network
SMF
Session Management Function
The 5GC control plane entity that creates, modifies, and terminates PDU Sessions, allocates IP addresses, and controls User Plane Functions (UPF).
Technical Explanation
The SMF manages the lifecycle of end-to-end Packet Data Unit (PDU) Sessions. It translates service requests into user plane rules (Packet Detection Rules - PDR, Forwarding Action Rules - FAR, QoS Enforcement Rules - QER) and programs the UPF via the N4 interface using Packet Forwarding Control Protocol (PFCP). It allocates IP addresses or IPv6 prefixes to UEs, selects appropriate UPFs (including anchor and intermediate UPFs for Edge Computing), and negotiates QoS policies with the PCF.
Key Functions
- PDU Session establishment, modification, and release
- IP address allocation and DHCP management for UEs
- Selection and control of UPF instances via PFCP over the N4 interface
- Enforcement of QoS policies received from the PCF
- Charging data collection and roaming session coordination
Specifications
3GPP TS 23.501, TS 23.502, TS 29.244 (PFCP)
Interfaces
N4 (UPF - PFCP)N7 (PCF)N10 (UDM)N11 (AMF)Nsmf (SBI)
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