3GPP mobility, explained and traceable
Handover, reselection, registration, radio link failure, NTN and NB-IoT power saving: call flows, timers and release changes, each linked to the specifications behind it.
Mobility-focused catalog: Rel-15–Rel-20 LTE, NR, NTN and IoT specifications from the official FTP archive (2G/3G retired).
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Procedure-first
Start from what happens
Call flows, timers and release changes for the procedures engineers ask about most.
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.
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.
Registration
5G registration and 4G tracking area update
NAS mobility management: registration in 5GS, tracking area update in EPS, and the reject causes.
Technology briefings
Browse by Technology
Explore specifications organized by technology area
4G/5G
Mobility
Idle- and connected-mode mobility across LTE and NR: cell selection and reselection, handover, conditional handover, RLF and re-establishment, registration and tracking-area updates.
36 specs
4G
LTE
The foundational 4G radio access technology built around OFDMA/SC-FDMA and the flat E-UTRAN architecture.
13 specs
5G
5G NR
The 5G air interface, supporting both non-standalone and standalone deployments across FR1 and FR2.
140 specs
4G
LTE-Advanced Pro
Extends LTE toward 5G-like capabilities with NB-IoT, LAA, and massive MIMO enhancements.
109 specs
5G
5G-Advanced
The evolution of 5G NR starting at Rel-18, adding AI/ML-native features, NTN, and RedCap enhancements.
143 specs
5G
5GC
The service-based, cloud-native core network architecture underpinning 5G NR.
450 specs
5G
NTN
Satellite and other non-terrestrial access for NR and IoT, covering transparent and regenerative payloads, feeder links, and NTN-capable UE/RAN procedures.
24 specs
4G
IoT-NTN
NB-IoT and eMTC operation over satellite access, using satellite assistance information in SIB31, SIB32 and SIB33 of TS 36.331.
3 specs
4G
NB-IoT
LTE-based IoT operation with its own RRC messages (the -NB variants), idle-mode mobility, and PSM and eDRX power saving.
1 specs
4G
LTE-M
Bandwidth-reduced (BL) and coverage-enhanced (CE) LTE UE operation for IoT, with PSM and eDRX.
1 specs
5G
RedCap
Reduced-capability NR UEs (RedCap, and eRedCap defined in TS 38.306) that use the NR mobility procedures.
4 specs
6G
6G
Not yet tracked on this site. See the 6G mobility watch page for what the Rel-19 specifications already define for mobility.
3 specs
Latest
Recent Specifications
Recently added or updated documents
Service accessibility
Service
Service aspects; Service principles
Service
IP Multimedia Core Network Subsystem (IMS) Multimedia Telephony Service and supplementary services; Stage 1
Service
Service requirements for the 5G system
Service
Public Warning System (PWS) requirements
Service
Numbering, addressing and identification
Architecture
Non-Access-Stratum (NAS) functions related to Mobile Station (MS) in idle mode
Architecture
IP Multimedia Subsystem (IMS) emergency sessions
Architecture
Policy and charging control architecture
Physical Layer
Common API Framework for 3GPP Northbound APIs
Architecture