Network Slicing.
The feature that lets one physical 5G network pretend to be a thousand private ones. A slice is a complete logical network — radio, transport and core — carved from shared infrastructure and named by an S-NSSAI. This module builds the whole picture: the SST and SD, the confusing NSSAI family untangled, the NSSF and slice selection, what is shared versus isolated, and the two guardians NSSAA and NSAC — narrated and fully animated, with real slice-topology diagrams.
One network, carved into many private ones
The player screen is a live animation stage with real slice diagrams — packets flow through parallel slice pipes, the selection call-flow fires, and the isolation layers light up exactly as the narration reaches them. Karaoke subtitles in English, two subtitle modes, fullscreen.
Every slicing structure in the module
Each slicing structure the video opens — its interface, direction, purpose and clause. Click any row to open its full breakdown. Filter to find any of them.
| Structure | Interface | Dir | What it does | Clause |
|---|
Network Slicing, at protocol depth
Everything the video animates, as reference you can scan: the S-NSSAI structure, the standardised SST values, the confusing NSSAI family untangled, the NSSF and slice selection, what is shared versus isolated, and the two guardians — NSSAA and NSAC. All cited to TS 23.501 V19.6.0 §5.15.
SST — Slice/Service Type (8 bits)
- The KIND of slice — its expected behaviour.
- Standardised values 1–7 are globally interpretable.
SD — Slice Differentiator (24 bits)
- Optional — separates multiple slices of the same SST.
- An SD (or a non-standard SST) makes the S-NSSAI local to its own PLMN.
| SST | Type | Characteristics |
|---|---|---|
| 1 | eMBB | Slice suitable for the handling of 5G enhanced Mobile Broadband. |
| 2 | URLLC | Slice suitable for ultra-reliable low latency communications. |
| 3 | MIoT | Slice suitable for the handling of massive IoT. |
| 4 | V2X | Slice suitable for the handling of V2X services. |
| 5 | HMTC | Slice suitable for High-Performance Machine-Type Communications. |
| 6 | HDLLC | Slice suitable for High Data rate and Low Latency Communications. |
| 7 | GBRSS | Slice suitable for Guaranteed Bit Rate Streaming Service. |
| NSSAI | Lives in | Meaning | Limit |
|---|---|---|---|
| Subscribed S-NSSAIs | UDM | what you are entitled to (≥1 marked default) | ≤ 16 |
| Configured NSSAI | device | what the device may use in a given PLMN | 1 per PLMN |
| Default Configured NSSAI | device | HPLMN-set fallback for any PLMN with no specific one | — |
| Requested NSSAI | UE→network | what the device asks for now (the wish) | ≤ 8 |
| Allowed NSSAI | network→UE | what the network grants (in Registration Accept) | ≤ 8 |
| Rejected S-NSSAIs | network→UE | refused slices, each with a cause | — |
| Partially Allowed NSSAI | network→UE | allowed only in part of the registration area | ≤ 7 |
The conversation: Configured (may ask) → Requested (do ask) → Allowed (get) · Rejected (the no). Subscribed is your entitlement in the UDM. Master these five and half of slicing is clear.
| Step | Who | What |
|---|---|---|
| 1 | UE → (R)AN → AMF | Requested NSSAI in RRC (for AMF selection) and in the NAS Registration Request |
| 2 | (R)AN | uses the Requested NSSAI to pick an initial AMF — a best guess |
| 3 | AMF ⇄ UDM | check the Requested NSSAI against the subscription |
| 4 | AMF | can it serve all allowed slices? yes → proceed · no → ask the NSSF |
| 5–6 | AMF ⇄ NSSF | NSSF returns the Allowed NSSAI + the target AMF Set |
| 7 | network | AMF re-allocation (direct or via (R)AN) if the initial AMF isn’t in the target set |
| 8 | AMF → UE | Registration Accept carrying the Allowed NSSAI |
Shared
- AMF (often one, across slices).
- NSSF · NRF — the common control plane.
Dedicated per slice
- SMF · UPF · PCF.
- The user plane is the most strongly isolated.
End-to-end isolation
- Radio: reserved resource blocks + slice-aware scheduling.
- Transport: reserved bandwidth (segment routing / FlexE).
- Core: dedicated functions. All three, or it is an illusion.
NSSAA — the slice owner’s gate
- For S-NSSAIs flagged as subject to slice-specific auth.
- EAP over NAS: UE ⇄ AMF ⇄ NSSAAF ⇄ external AAA server.
- Keyed to the GPSI (public id), not the SUPI.
- The owner can revoke authorization mid-session.
NSAC — the capacity bouncer
- Enforces max UEs and max PDU sessions per slice.
- The NSACF keeps the count and admits or denies.
- Non-hierarchical · hierarchical · centralised.
- Checked early (registration) or later (PDU session).
Filter by name or clause — IDENTITY · NSSAI · FUNCTION · PROCEDURE · CONTROL.
| Element | Family | Where | Clause | What it is |
|---|
The rule to remember: a slice is a complete logical network, named by an S-NSSAI, selected by the NSSF, and kept honest by isolation, authentication, and admission control. One physical network, carved into many private ones — the deepest trick in the 5G core, and the way an operator sells the same infrastructure a hundred times over.
Built from ETSI TS 123 501 V19.6.0 §5.15Network Slicing mastery check
Questions and answers reshuffle every load. 70%+ to consider Module 8 done.