Description
Mobile Initiated Connection Only (MICO) is a power-saving feature defined in 3GPP standards, primarily for IoT and other battery-constrained devices. It fundamentally alters the traditional reachability model. In a standard 3GPP connection, the network can page a UE at any time during its registered state to deliver mobile-terminated data or signaling, requiring the UE to periodically listen for paging messages. MICO mode disables this network-side paging capability. When a UE registers with the network and indicates support for MICO, the network allocates it a MICO-specific Allowed NSSAI and configures the Access and Mobility Management Function (AMF) accordingly. After successful registration, the UE enters a deep sleep state. The AMF will reject any mobile-terminated requests (like Session Management or Data Notification messages from the SMF/UPF) with a cause indicating the UE is unreachable. The network may buffer or discard this downlink data based on policy. Reachability is restored only when the UE itself initiates a Service Request procedure, typically triggered by its own uplink data or periodic Registration Update timer expiry. This procedure moves the UE to a connected state, allowing any buffered downlink data to be delivered. The UE's Radio Resource Control (RRC) state in MICO mode is typically RRC_IDLE, but with the crucial difference that it does not monitor the paging channel, leading to substantial power savings. The feature is negotiated during the Registration procedure via the MICO indication in the UE's Registration Request and the network's MICO indication in the Registration Accept. Network parameters like the Active Time and Periodic Registration Timer are also configured to manage the UE's sleep cycles and mandatory check-ins.
Purpose & Motivation
MICO was created to address the critical challenge of battery life for massive Machine-Type Communication (mMTC) devices in 5G and beyond. Traditional cellular devices, even in idle mode, must wake up frequently to listen for paging messages, which consumes significant energy over time. For IoT sensors, meters, or trackers that send data infrequently (e.g., once per day) but are expected to operate for years on a single battery, this constant readiness for downlink traffic is wasteful and impractical. MICO solves this by shifting to a purely mobile-originated communication model, aligning the network's behavior with the typical traffic pattern of many IoT applications. It was motivated by the need to make 5G networks viable for ultra-low-power, wide-area IoT deployments, competing with and surpassing the energy efficiency of non-cellular LPWAN technologies like LoRaWAN or Sigfox. By eliminating the power drain from paging reception, MICO enables decade-long battery life, which is a key requirement for many industrial and smart city IoT use cases. It represents a paradigm shift from 'always reachable' to 'reachable on device terms,' optimizing the network for asymmetric, device-triggered traffic.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (230 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 15, the MICO (Mobile Initiated Connection Only) function was newly introduced with specific clarifications on its operation and interworking. The release defined the MICO indication and addressed its interworking with the Evolved Packet Core (EPC) to ensure seamless mobility. Furthermore, procedures were established for a UE in MICO mode to be allocated a registration area encompassing the entire PLMN, and a mechanism for the local deactivation of MICO for emergency services was introduced.
- Establishment of N1 NAS signalling connection due to change in the network slicing information TS 24.501CR0169
- Access attempt barred for the UE-initiated NAS transport procedure TS 24.501CR0194
- Sending of congested S-NSSAI during AN signalling connection Establishment TS 23.501CR0102
- MICO and interworking with EPC TS 23.501CR0110
- Mobile Terminated SMS over NAS: 5GS Access Selection TS 23.501CR0201
- Local deactivate MICO for emergency service TS 23.501CR0297
+ 38 more changes
In Release 16, the MICO function was enhanced with the introduction of an "Active Time" for the mode and the ability for the network to use analytics from the NWDAF to decide MICO parameters. Furthermore, the release provided clarifications and corrections on the interaction between MICO mode and eDRX, as well as the UE's strictly periodic registration timer behavior in relation to MICO.
- Use of NWDAF analytics for decision of MICO mode parameters TS 23.501CR0837
- Establishing UP connection during CP Data Transfer TS 23.501CR1101
- Corrections to MICO mode with Active Time TS 23.501CR1250
- Introduction of RRC Connection Re-Establishment for CP TS 23.501CR1667
- Interworking of Ethernet PDU session to Ethernet PDN connection TS 24.501CR0936
- Active Time for MICO mode TS 24.501CR1019
+ 59 more changes
In Release 17, the MICO function was enhanced with clarifications and specific handling rules for connection release during mobility and concurrent procedures. Key updates included clarifications on the MICO indication IE's SPRTI bit and detailed procedures for NAS signalling connection release triggered by events like receiving a CAG information list without an entry for the current PLMN. Furthermore, the release specified the UE's behavior regarding connection release and paging restriction during a mobility registration update when moving to a Tracking Area outside its current Registration Area.
- 5GS Connection release support for 5GC/NR TS 23.501CR3088
- Network shall not release the RRC connection for ProSe services TS 24.501CR3126
- NW initiated de-registration upon failure of ongoing UUAA-MM TS 24.501CR3406
- Collision between UUAA-MM and UE initiated deregistration TS 24.501CR3789
- On Connection Release and Paging Restriction during a Mobility Registration Update in a TA outside the current Registration Area TS 23.501CR3335
- Correct the MUSIM Connection Release feature TS 23.501CR3467
+ 41 more changes
In Release 18, the MICO function was enhanced to support multicast MBS sessions, allowing a UE in MICO mode to receive multicast traffic. Furthermore, the release specified procedures to deactivate MICO mode at the broadcast start time or activation times of a broadcast MBS session. These updates enable more efficient multimedia broadcast service delivery to UEs using the Mobile Initiated Connection Only mode.
- Introduction of Mobile Base Station Relay TS 23.501CR3813
- Support non-3GPP access leg of MA-PDU Session with PDN connection in EPC TS 23.501CR3937
- Common EAS re-discovery initiated by SMF TS 23.501CR4144
- Associating a QUIC connection with a QoS flow TS 23.501CR4459
- Equivalent SNPN usage for mobile identity selection TS 24.501CR4840
- UE initiated de-registration procedure for Unavailability Period TS 24.501CR4999
+ 46 more changes
In Release 19, key enhancements were made to the Mobile Initiated Connection Only (MICO) function, specifically defining the interaction for PSAP emergency callbacks with a UE in MICO mode. Furthermore, corrections were introduced to ensure proper handling of NAS timers during MICO mode and unavailability periods, and clarifications were added regarding the mobile reachable timer to prevent its expiry during these unavailability intervals.
- Adding support of Mobile Wireless Access Backhaul in 5GS TS 23.501CR5596
- Connection information for QoS differentiation in PDU session modification procedure, coding TS 24.501CR6960
- NW capability for multiple LCS-UPP connections per UE TS 24.501CR6953
- Definition of non-3GPP device connection information TS 23.501CR5963
- Clarification on N2 connection setup TS 23.501CR6365
- PSAP emergency callback interaction with MICO mode TS 23.501CR6413
+ 16 more changes
Explore further
Broader topics and technologies where MICO plays a role.
Defining Specifications
3GPP specifications that define or reference MICO, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 23.501 vk00 | 5G System Architecture Stage 2 | Rel-20 |
| TS 24.501 vj50 | 5G NAS Protocols Specification | Rel-19 |
| TS 24.890 vg00 | 5G NAS Protocol for 5GS Stage 3 | Rel-16 |
| TS 29.503 vj50 | UDM Service Based Interface Stage 3 | Rel-19 |
| TS 31.102 vj40 | USIM Application Specification | Rel-19 |
| TS 32.256 vj40 | 5G Connection & Mobility Charging Spec | Rel-19 |
| TS 38.300 vj00 | NG-RAN Overall Description | Rel-19 |
| TS 38.304 vj00 | UE RRC_IDLE and RRC_INACTIVE Procedures | Rel-19 |