Minimization of Service Interruption

Description

Minimization of Service Interruption (MINT) is a collection of mechanisms standardized in 3GPP to reduce the time during which a User Equipment (UE) cannot send or receive user plane data during mobility procedures. Service interruption typically occurs during the execution of a handover, where the UE switches its connection from a source network node (e.g., gNB, eNB) to a target node. MINT techniques work by optimizing the handover preparation, execution, and re-establishment phases at both the Radio Access Network (RAN) and Core Network (CN) levels.

Architecturally, MINT involves enhancements in several network functions. In the RAN, it includes features like early handover preparation, where the source node initiates context fetching and resource reservation at the target node well before the actual handover command is sent to the UE. This is specified in RAN protocols (e.g., NGAP, XnAP). Another key technique is "Make-Before-Break" handover, particularly relevant in multi-connectivity scenarios like Dual Connectivity (DC) or Carrier Aggregation (CA), where the UE establishes a connection with the target cell while maintaining the link with the source cell, thereby eliminating the break period. The core network supports MINT through procedures like the "Handover without TAU/RAU" optimization for idle mode mobility and enhancements to the N26 interface for inter-CN mobility between 5GC and EPC.

From an operational perspective, MINT works by minimizing the sequential steps in a handover. For example, in a typical LTE-to-NR handover, the UE measurement reporting, target cell preparation, security key derivation, and path switch in the core network all contribute to delay. MINT procedures parallelize these tasks where possible. Key components involved are the Access and Mobility Management Function (AMF) for coordinating core network aspects, the source and target gNBs for RAN-level coordination, and the UE itself, which must support the enhanced RRC procedures. Its role is critical in 5G networks to meet the stringent requirements of Ultra-Reliable Low-Latency Communications (URLLC) and to ensure seamless experience for real-time services like voice (VoNR) and industrial automation during cell changes.

Purpose & Motivation

MINT was created to address the inherent service disruption that occurs during cellular handovers, which becomes particularly problematic for 5G use cases demanding high reliability and low latency, such as autonomous vehicles, remote surgery, and augmented reality. Traditional handover procedures, while reliable, involved a series of sequential signaling steps that could result in interruptions of hundreds of milliseconds, unacceptable for these new services. The limitations of previous approaches were their reactive nature and lack of coordination between RAN and CN during the critical handover execution phase.

The motivation for standardizing MINT in Release 17 and beyond stems from the 5G design principle of supporting diverse service requirements. Prior to MINT, enhancements like Data Forwarding during handover in LTE helped, but did not fully eliminate the interruption time, especially in inter-gNB or inter-system handovers. MINT provides a systematic framework to analyze and reduce every component of handover delay. It solves problems like prolonged interruption during inter-radio access technology (IRAT) handover between 4G and 5G, and during handovers in high-frequency bands (mmWave) where cells are smaller and handovers more frequent. By minimizing interruption, it ensures service continuity, which is a key performance indicator for network operators and a fundamental requirement for the commercial success of 5G-enabled critical applications.