PDU Session
A logical connection between UE and a data network through the UPF, providing end-to-end user-plane connectivity with associated QoS flows.
A PDU session is the unit of connectivity in 5G — it's what gives a UE an actual path to a data network, with an IP address (or an Ethernet or unstructured payload) and a defined QoS treatment. The SMF sets it up, assigns the address, picks the UPF, and the traffic flows over N3 to that UPF and out N6 to the data network.
Inside a session, traffic is split into QoS Flows, each marked with a QFI and treated according to its 5QI — that flow-level granularity is the 5G replacement for LTE's per-bearer model, and it's finer-grained. A single UE can hold several PDU sessions at once: one to the internet, one to an enterprise network, one to an IMS slice for voice. Each session is tied to a single S-NSSAI and DNN, which is exactly how a device ends up using different slices for different traffic simultaneously.
Frequently asked questions
- How is a PDU session different from an LTE EPS bearer?
- An EPS bearer was the basic QoS unit in 4G — you got a default bearer plus dedicated bearers, each with its own QoS. 5G restructures this: the PDU session is the connectivity container, and QoS differentiation happens inside it via QoS Flows (each with a QFI), not via separate bearers. It's more flexible — you can have many flows with distinct treatment under one session without standing up new bearers.
Related terms
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