Every PDU session on a 5G Standalone network is set up, modified, and torn down by the SMF. It allocates IP addresses, selects the UPF, and applies policy from the PCF. In a 4G core, this work sat inside the PGW. In 5G SA, it splits into a control plane and a data plane joined over N4.
In a 4G core, session management lives inside the PGW: one element handles both the control decisions and the data forwarding. 5G Standalone separates them. The control plane becomes the SMF. The data plane becomes the UPF. They are different network functions, connected over N4.
Operators moving from LTE to 5G SA face that split as a procurement question. A packet core that cannot decompose into SMF and UPF means a full replacement at 5G launch: a new vendor, a new integration, and another migration event at the point when engineering teams are already committed to the 5G rollout.
AMF passes the request — SMF creates the session
When a 5G device establishes a data session, the AMF passes the request to the SMF over N11. The SMF creates the PDU session, allocates the IP address, selects a UPF to carry the traffic, and programs that UPF over N4 using PFCP. It retrieves the subscription from the UDM over N10 and the policy rules from the PCF over N7. For the duration of the session, the SMF is the control point: it modifies bearers, applies QoS changes, and tears the session down when the device detaches.
Gateway continuity: PGW-C becomes the SMF
The Ouroboros SMF is the control-plane half of the gateway that already runs as GGSN for 2G/3G and PDN-GW for LTE. Operators moving to 5G SA extend that platform into the SMF/UPF split rather than procuring a separate 5G data core. The session logic, the charging integration, and the policy interfaces carry forward.
Charging, slicing, and QoS in one control point
Charging events report to the converged charging system over N40. The SMF supports session and slice selection, so traffic for different network slices is mapped to the appropriate UPF and policy set.
5G SA migration, greenfield launch, network slicing, private networks — one session control plane.
LTE-to-5G SA migration on the existing gateway
An operator running the Ouroboros PDN-GW for LTE turns up the SMF/UPF split at 5G launch, with session control handled by the SMF and no separate 5G packet core to procure.
5G Standalone greenfield
An operator with new 5G spectrum deploys the SMF alongside the UPF and the 5G core to manage PDU sessions from first attach. Session management, IP allocation, and UPF control run from one platform.
Network slicing
The SMF maps PDU sessions to the correct UPF and policy profile per slice. An operator offering differentiated slices for enterprise, IoT, or consumer traffic controls session placement at the SMF.
Private 5G networks
A campus, industrial, or utility private 5G network runs the SMF on local infrastructure to manage on-site sessions, with UPF placement controlled for low-latency local breakout.
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CTO · Major MNO
Control-plane continuity from PGW to SMF
The same platform that runs GGSN and PDN-GW provides the SMF control plane in 5G SA. Operators extend the gateway into 5G rather than replacing it. The session logic carries forward.
N4 control of the UPF
The SMF programs forwarding, QoS, and charging rules on the UPF over PFCP. Control and data planes scale independently. Add UPF capacity at the edge without touching the control plane.
Per-slice session management
PDU sessions map to the correct UPF and policy profile for their network slice. Enterprise, IoT, and consumer slices run with isolated session handling on one SMF.
Policy integration over N7
The SMF applies PCF policy decisions per session at setup and on modification. The same policy platform serving LTE extends to 5G SA without a separate policy stack.
Dual-stack IP allocation
IPv4, IPv6, and dual-stack address assignment per PDU session. Operators running IPv6 or mixed addressing need no separate configuration path.
Converged charging over N40
Session charging events report to the converged charging function. 5G sessions bill through the same charging path as earlier generations.
The SMF is one half of a split that only matters if the operator is moving a real network to 5G SA. Ouroboros has carried that network through 2G, 3G, and 4G already. The gateway that runs as GGSN and PDN-GW becomes the SMF and UPF in 5G SA, so the move is an extension of a known platform, not a new vendor relationship at the riskiest point in the rollout.
The platform is carrier-grade and in production since 2004. The same deployment flexibility applies: bare metal, VMware, KVM, Docker, Kubernetes, or public cloud.
OPEX rental is available, so 5G control-plane capacity can be added as the network turns up rather than committed ahead of subscriber demand.
What PGW are you running, and when does 5G SA land on the roadmap? We'll confirm how the platform extends into the SMF/UPF split and what the migration sequence looks like.