SST

SST is the part of an S-NSSAI that classifies what a slice is for. It's an 8-bit value, and 3GPP standardises a handful of these so that slices of the same type interwork consistently across operators:

• 1 — eMBB (enhanced mobile broadband: high throughput, the classic consumer slice)
• 2 — URLLC (ultra-reliable low-latency: control loops, automation)
• 3 — mMTC (massive machine-type comms: huge fleets of low-rate IoT devices)
• 4 — V2X (vehicle-to-everything)

Values below 128 are reserved for these standardised types; the rest of the range is operator-specific, so a carrier can define its own slice categories. Two things to keep straight: SST on its own only describes the type of behaviour, not a unique slice — pair it with an SD when you need to distinguish instances; and a standardised SST is an interworking convenience, not a guarantee that any given operator has actually deployed that slice.