PDU session type — IPv4, IPv6, IPv4v6, Ethernet, Unstructured

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Sessions, flows and slices

Where it sits

Sits atLevel 4 of the hierarchy · Sessions, flows and slices · explained
The 5 of them
IPv4 — an IPv4 address, the ordinary case
IPv6 — an IPv6 prefix, delegated to the device
IPv4v6 — both at once, on one session
Ethernet — frames, not packets — the session is a wire, and 5G is the LAN
Unstructured — no header the network understands; the payload is opaque
Learn firstPDU session — 6 concepts in the full chain, see the paths
UnlocksNothing else depends on it directly.
Primary clauseTS 23.501 §5.6.1
Used inref-session 22 · index 1
Scanned from the notes at page load and joined with terms.json; nothing on this card is typed by hand.

What it is

What it is. What kind of protocol data unit the session carries, fixed at establishment. TS 23.501 §5.6.1 defines five: IPv4, IPv6, IPv4v6, Ethernet, Unstructured.

Type What the device gets Used for
IPv4 an IPv4 address the ordinary case
IPv6 an IPv6 prefix, delegated the ordinary case, done properly
IPv4v6 both, on one session dual-stack without two sessions
Ethernet no address at all — the session carries frames the device is on a LAN, and 5G is the wire
Unstructured no header the network parses anything with its own framing

The last two are the reason 5G is pitched at factories, and they are genuinely new. LTE offered IP and little else. An Ethernet PDU session means the 5G system behaves as a layer-2 segment: the device sends Ethernet frames, the UPF bridges them onto a real LAN at N6, and everything on that LAN sees the device as an ordinary host on the same broadcast domain.

That matters because industrial protocols are frequently not IP. PROFINET, EtherCAT and their relatives are Ethernet protocols. Under an IP-only system they would need a gateway at both ends; under an Ethernet PDU session they simply run, and the radio link becomes a cable replacement.

It also explains two odd lines in the function lists. Both the SMF (§6.2.2) and the UPF (§6.2.3) carry "Functionality to respond to Address Resolution Protocol (ARP) requests and / or IPv6 Neighbour Solicitation requests based on local cache information for the Ethernet PDUs". A radio link is expensive and broadcast traffic is constant, so the network answers ARP on the device's behalf rather than flooding it over the air. That is a piece of layer-2 emulation sitting in a mobile core specification, and it is there entirely because of this session type.

Unstructured is the escape hatch: the payload is opaque, the network applies no interpretation, and it is used where the application supplies its own framing entirely.

Read on

This concept is read as part of one argument in ref-session, alongside the rest of its group.

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Before this concept, the hierarchy says to learn the following — the full chain, in order:

To understand PDU session type (level 4) you first need 6 other concepts. Read them in this order — everything on one line can be read in any order, but no line before the one above it:
Level Learn these
0 5G Core
1 DNN · Network function · Reference point
2 SMF
3 PDU session
Immediately before PDU session type: PDU session.
Keep going — where this sits on the route
◀NF servicestep 38 · level 4
Step 39 of 118level 4 · Sessions, flows and slices
SSC modestep 40 · level 4▶
Nothing depends on this one directly
It is a leaf of the graph — follow the route rather than the branch.
↳ all 14 concepts at level 5 · level 4 in full · the whole route
The route is every concept in the folder ordered by level, so nothing here needs anything after it. Computed at page load from terms.json; the same numbering as the route page.
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