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
Release Timeline
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (39 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) mode was introduced, allowing a UE to indicate a preference for this power-saving mode during registration, where it is only reachable for mobile-terminated data when in CM-CONNECTED state. The release specified procedures for enabling, disabling, and re-negotiating MICO mode, including its local deactivation for emergency services and clarifications on its interworking with EPC. It also defined that a UE in MICO mode need not listen to paging while in CM-IDLE and introduced considerations for the UICC interface during this mode.
- MICO and interworking with EPC TS 23.501CR0110
- Local deactivate MICO for emergency service TS 23.501CR0297
- Clarifications on MICO indication TS 24.501CR0008
- Removal of redundant MICO statement TS 24.501CR0064
- Clarification on MICO indication and LADN information via generic UE configuration update procedure TS 24.501CR0351
- Enabling use of and disabling use of MICO mode TS 24.501CR0528
+ 2 more changes
In Release 16, the MICO function was enhanced with the new "MICO mode with Active Time" feature, allowing a UE to remain reachable for mobile-terminated data for a defined period after going idle. Furthermore, Release 16 introduced "MICO mode and Periodic Registration Timer Control," providing mechanisms for the network to manage the strictly periodic registration timer for UEs in MICO mode. These enhancements, alongside clarifications on the interaction between MICO with Active Time and eDRX, aimed to improve power saving and mobile-terminated reachability, particularly for Cellular IoT (CIoT) use cases.
- Use of NWDAF analytics for decision of MICO mode parameters TS 23.501CR0837
- Corrections to MICO mode with Active Time TS 23.501CR1250
- Active Time for MICO mode TS 24.501CR1019
- Strictly periodic registration timer indication for MICO mode TS 24.501CR1030
- MICO mode and Periodic Registration Timer Control TS 23.501CR1047
- Clarification on MICO and eDRX during CN node changes TS 23.501CR1075
+ 11 more changes
In Release 17, the MICO function was enhanced with clarifications and corrections to its indication Information Element (IE), including the SPRTI bit. Furthermore, the release specified new MICO mode variants for power saving and improved Mobile Terminated reachability, namely "MICO mode with Active Time" and "MICO mode and Periodic Registration Timer Control," which can be combined with extended DRX.
In Release 18, the MICO function was enhanced to support multicast MBS sessions, allowing a UE in MICO mode to receive broadcast/multicast services. The release introduced mechanisms to deactivate MICO mode at the start of a broadcast MBS session and enabled MBS operation when MICO is combined with eDRX. Furthermore, Release 18 added clarifications and corrections for timer handling in MICO mode, including the Tsense timer and the slice deregistration timer, and introduced the capability for a UE to request a specific T3512 value during MICO negotiation.
- Supporting multicast MBS session for UE in MICO mode TS 24.501CR5318
- Deactivate MICO mode at the broadcast start time/activation times of a broadcast MBS session TS 24.501CR5814
- MBS operation with eDRX MICO TS 38.304CR0399
- Correction to timers handling in MICO mode TS 24.501CR6129
- Tsense timer handling for MICO mode TS 24.501CR6166
- The UE handling on the MICO mode TS 24.501CR6160
+ 2 more changes
In Release 19, the key enhancements for MICO mode focused on ensuring a UE remains reachable for a Public Safety Answering Point (PSAP) emergency callback. Specifically, the specifications were updated to define that after an emergency PDU session is released, the UE should wait for a UE implementation-specific duration (with a recommended value of 10 minutes) before requesting to re-enter MICO mode. This change, along with corrections to NAS timer handling during MICO unavailability, ensures the UE does not become unreachable for a critical callback from emergency services.
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 |
