Registration,
Mobility & CM.
Watch a stranger become a trusted, tracked, reachable subscriber — message by message. The full General Registration flow, 5G-AKA, Service Request, paging, Xn and N2 handover, deregistration — narrated and fully animated, explained like an expert.
Registration, Mobility & Connection Management — the full flow
The player screen is a live animation stage — 58 scenes fire exactly as the narration reaches them, message by message. Karaoke subtitles in English, two subtitle modes, and fullscreen.
Every message in the module
Each NAS, N2/NGAP, Xn and service-based message the video walks through — interface, direction, purpose and clause. Click any message to open its full Information-Element breakdown. Filter to find any of them.
| Message | Interface | Dir | What it does | Clause |
|---|
The state machines, at protocol depth
Registration is long-term, connection is momentary, the radio has its own life — and inside 5GMM each has a set of substates the AMF and UE actually run. Read these together and no trace will surprise you.
Registration Management (RM / 5GMM)
- RM-DEREGISTERED — AMF holds no valid location; UE not reachable.
- RM-REGISTERED — context held, TAI-list valid, UE pageable.
- Enter REGISTERED on Registration Accept; leave on Dereg / implicit timeout.
- TS 23.501 §5.3.2 · substates TS 24.501 §5.1.3
Connection Management (CM / 5GMM)
- CM-IDLE (5GMM-IDLE) — no N1 NAS signalling connection, no N2, no N3.
- CM-CONNECTED (5GMM-CONNECTED) — active N1/N2; may pair with RRC_INACTIVE.
- IDLE→CONNECTED on Service Request / paging; CONNECTED→IDLE on AN Release.
- Independent per access (3GPP vs non-3GPP). TS 23.501 §5.3.3
RRC (radio, per access)
- RRC_IDLE — cell reselection, monitors paging; no UE context in RAN.
- RRC_INACTIVE — context kept in gNB, RNA registered, RRC Resume in ms.
- RRC_CONNECTED — SRBs/DRBs active, HO possible.
- CM-CONNECTED maps to RRC_CONNECTED or RRC_INACTIVE. TS 38.331 · TS 38.300
5GMM-DEREGISTERED substates
- NORMAL-SERVICE · LIMITED-SERVICE (no allowed PLMN)
- ATTEMPTING-REGISTRATION · PLMN-SEARCH
- NO-SUPI · NO-CELL-AVAILABLE
- eCALL-INACTIVE · INITIAL-REGISTRATION-NEEDED
5GMM-REGISTERED substates
- NORMAL-SERVICE · NON-ALLOWED-SERVICE
- ATTEMPTING-REGISTRATION-UPDATE
- LIMITED-SERVICE · PLMN-SEARCH
- NO-CELL-AVAILABLE · UPDATE-NEEDED
| From → To | Trigger | Machine |
|---|---|---|
| DEREGISTERED → REGISTERED | Registration Accept (initial / mobility) | RM |
| REGISTERED → DEREGISTERED | Deregistration, or implicit dereg (T3512 + implicit timer expire) | RM |
| CM-IDLE → CM-CONNECTED | Service Request / Registration / paging response (N2 setup) | CM |
| CM-CONNECTED → CM-IDLE | AN Release (UE Context Release on N2) | CM |
| RRC_CONNECTED → RRC_INACTIVE | gNB suspends (RRC Release with suspend); core stays CM-CONNECTED | RRC |
| RRC_INACTIVE → RRC_CONNECTED | RRC Resume (UL data / RAN paging) | RRC |
| RRC_INACTIVE → RRC_IDLE | context relocation fails / periodic RNAU expiry | RRC |
| Timer | Side | Default | What it guards |
|---|---|---|---|
| T3512 | UE | 54 min | periodic registration update — the reachability heartbeat |
| Implicit dereg | AMF | T3512+4 min | silent removal when the heartbeat stops |
| T3502 | UE | 12 min | wait before re-attempting registration after failure |
| T3510 | UE | 15 s | Registration Request sent → awaiting Accept/Reject |
| T3517 | UE | 15 s | Service Request sent → awaiting Accept/Reject |
| T3550 | AMF | 6 s | Registration Accept sent → awaiting Registration Complete |
| T3555 | AMF | 6 s | Configuration Update Command → awaiting Complete |
| T3560 | AMF | 6 s | Authentication Request / Security Mode Command → awaiting response |
| T3346 | UE | ≤ 30 min | mobility-management back-off (congestion control) |
The trap to avoid: CM-IDLE is not RM-DEREGISTERED. A sleeping phone is still a registered subscriber (RM-REGISTERED, 5GMM-REGISTERED.NORMAL-SERVICE) — it has simply released its N2 connection, not checked out of the hotel. And CM-CONNECTED does not imply an active radio link — the UE may be sitting in RRC_INACTIVE.
TS 23.501 §5.3.2/5.3.3 · TS 24.501 §5.1.3 & §10.2 · TS 38.331 · TS 38.300Registration & mobility mastery check
Questions and answers reshuffle every load. 70%+ to consider Module 2 done.