Procedure-first reference

Mobility procedures

Start from what the network and device do, then jump to the exact specifications. Each page has the call flow, the timers that matter, the specs with clause numbers, release-tagged changes where the specs confirm them, and the failure behaviour the specs define.

Checked against the Rel-19 specifications named on each page. Older releases can differ, so confirm against the version you work with.

Connected mode

5G Xn-based handover

Inter-gNB handover prepared over the Xn interface, with an NG path switch toward the core.

Connected mode

5G NG-based (N2) handover

Handover whose preparation is signalled through the AMF over N2 instead of directly between gNBs.

Connected mode

LTE handover

LTE connected-mode handover: RRCConnectionReconfiguration with mobilityControlInfo and timer T304.

Connected mode

Conditional handover (CHO)

The network pre-configures candidate target cells with execution conditions and the UE moves when a condition is met.

5GNTN

Idle mode

Cell selection and reselection

How an idle or inactive UE selects a cell by the S-criterion and keeps the best one by priority and ranking.

4G5GNTNIoT

Inactive state

RRC_INACTIVE: resume and RNA update

How an NR UE in RRC_INACTIVE resumes a connection or updates its RAN-based notification area, with UE context retrieval over Xn.

Registration

5G registration and 4G tracking area update

NAS mobility management: registration in 5GS, tracking area update in EPS, and the reject causes.

4G5G

Failure handling

Radio link failure and RRC re-establishment

Out-of-sync handling with N310, N311 and T310, then re-establishment supervised by T311 and T301.

4G5G

Optimisation

Mobility robustness optimisation (MRO)

How NG-RAN detects too-late, too-early and wrong-cell handovers from RLF reports and successful handover reports.

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.

5GNTN

NTN

IoT-NTN: NB-IoT and LTE-M over satellite

Satellite assistance information in LTE system information for NB-IoT and eMTC, and how the UE uses it in idle mode.

IoTNTN4G

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.

IoT4G