Registration
5G registration and 4G tracking area update
NAS mobility management: registration in 5GS, tracking area update in EPS, and the reject causes.
Overview
In 5GS, the Registration Request carries a 5GS registration type. TS 24.501 covers initial registration (5.5.1.2) separately from the registration procedure for mobility and periodic registration update (5.5.1.3). In EPS the equivalent is the normal and periodic tracking area updating procedure (TS 24.301 clause 5.5.3.2).
The network answers with an accept message or a reject carrying a cause. Cause values are listed below, as defined in TS 24.501 for 5GMM and TS 24.301 for EMM.
Call flow
- 1UEtogNB / eNB
RRC setup carrying a NAS message
Registration Request (5G) or Tracking Area Update Request (4G).
- 2gNB / eNBtoAMF / MME
Initial UE Message (N2 / S1)
- 3AMF / MMEtoUE
Registration Accept / TAU Accept
Or a reject with a cause value.
Timers and parameters
| Name | Where | Role |
|---|---|---|
| T3512 | UE (5GMM) | Periodic registration update timer. TS 24.501 gives a default of 54 minutes. |
| T3412 | UE (EMM) | Periodic tracking area update timer. TS 24.301 gives a default of 54 minutes. An extended value IE (T3412 extended value) also exists. |
| T3430 | UE (EMM) | Supervises the tracking area update request. TS 24.301 gives 15 s. |
Specifications
| Spec | What it covers |
|---|---|
| TS 24.501 | Registration for mobility and periodic registration update (initial registration is 5.5.1.2).(see clause 5.5.1.3) |
| TS 24.301 | Normal and periodic tracking area updating.(see clause 5.5.3.2) |
| TS 23.502 | General Registration procedure at the core-network level.(see clause 4.2.2.2.2) |
Failure behaviour in the specs
- 5GMM cause values (TS 24.501): #3 Illegal UE, #7 5GS services not allowed, #9 UE identity cannot be derived by the network, #10 Implicitly de-registered, #11 PLMN not allowed, #12 Tracking area not allowed, #13 Roaming not allowed in this tracking area, #15 No suitable cells in tracking area, #22 Congestion.
- EMM causes #11 PLMN not allowed, #12 Tracking area not allowed, #13 Roaming not allowed in this tracking area, and #15 No suitable cells in tracking area exist in TS 24.301 with the same names.
Related procedures
Idle mode
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How an idle or inactive UE selects a cell by the S-criterion and keeps the best one by priority and ranking.
IoT power saving
NB-IoT and LTE-M power saving: PSM and eDRX
Power Saving Mode and extended idle-mode DRX, and what they mean for reachability.
NTN
NR-NTN mobility and satellite switch
Satellite assistance in SIB19 and how NR uses it for synchronisation, measurement initiation, conditional handover and satellite switch.