What is SMF?
The SMF is the 5G Core control-plane function responsible for the complete lifecycle management of PDU (Protocol Data Unit) sessions. It establishes, modifies, and releases data sessions, allocates IP addresses, selects and controls UPF instances, and enforces QoS and charging policies — replacing the combined functions of the 4G MME (session parts), S-GW-C, and P-GW-C.
How Does SMF Work?
The SMF communicates via: N11 (with AMF — session-related NAS signalling), N4 (with UPF — PFCP protocol to program forwarding and QoS rules), N7 (with PCF — policy and charging rules), N10 (with UDM — subscription data), and N40 (with CHF — charging). For MEC deployments, the SMF uses ULCL (Uplink Classifier) or IPv6 Multi-Homing to steer selected traffic to an edge UPF.
Use Cases
Every 5G data session: IP address assignment, QoS flow creation, MEC traffic steering, roaming data session management (visited/home network), lawful intercept session control.
3GPP / Standards Reference
3GPP TS 29.502 (Nsmf Service Definition), TS 29.244 (N4 Interface — PFCP Protocol)
Related Terms
AMF | UPF | PCF | UDM | CUPS | Network Slicing | MEC
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This glossary entry is part of the 5GWorldPro Complete 5G Glossary. To go deeper into 5G architecture and technology, explore our 5G Training courses.
