Isolated Operation for Public Safety Mode of Operation

Description

The IOPS mode of operation is a state in which a radio access network (typically comprising one or more eNodeBs) and a local core network (Local EPC) function autonomously to provide communication services to mission critical (MC) users when the backhaul link to the central core network is unavailable. This mode is defined in 3GPP specifications such as TS 23.180 and TR 23.700, with the primary goal of maintaining a minimum level of service for public safety personnel during incidents where the central infrastructure is unreachable.

When the backhaul connection is lost, the network detects the isolation and transitions into IOPS mode. In this mode, the Local EPC takes over the role of the central core, handling essential functions such as authentication, mobility management, session management, and policy control for the users attached to the local eNodeBs. The IOPS mode of operation ensures that MC services—voice, video, and data—can continue to be delivered, albeit possibly with reduced capabilities compared to normal operation. For example, group calls may be supported, but certain supplementary services or connectivity to external networks may be unavailable.

The transition into IOPS mode is typically triggered by the loss of the S1 interface between the eNodeB and the central EPC. The eNodeB and Local EPC are pre-configured with the necessary parameters to operate in isolation, including local subscriber profiles, group configurations, and security credentials. The system may also support a manual trigger for planned isolation, such as when a network slice is intentionally disconnected for maintenance.

While in IOPS mode, the network continues to serve users within its coverage area. It may also support limited inter-connection with other isolated networks if they are within range, enabling broader communication among first responders. The IOPS mode of operation is designed to be transparent to the user, who may not even notice the transition, except for potential limitations in service reachability.

When the backhaul connection is restored, the network exits IOPS mode and performs a synchronization procedure with the central core. This includes updating subscriber location, transferring charging records, and reconciling session states. The IOPS mode of operation is a critical enabler for resilient public safety communications, ensuring that mission critical users can rely on their networks even in the most challenging circumstances.

Purpose & Motivation

The IOPS mode of operation was created to address the vulnerability of cellular networks to backhaul failures, which can occur due to natural disasters, physical damage, or other emergencies. In such scenarios, public safety users need to communicate, but traditional networks would cease to provide service because all control and user plane functions reside in the central core. The IOPS mode allows a local network to continue operating independently, providing a lifeline for first responders.

Before IOPS, isolated operation was not standardized, and any local fallback would rely on proprietary solutions or limited functionality. The introduction of IOPS in 3GPP Rel-13 provided a standardized approach for LTE networks, enabling a Local EPC to serve eNodeBs when the backhaul is lost. This was a significant step forward, but it initially focused on basic connectivity and voice services. With the evolution of mission critical services, the IOPS mode of operation has been extended to support MC services, ensuring that the full suite of public safety applications remains available during isolation.

The IOPS mode of operation solves the problem of service continuity during backhaul loss by defining the procedures, architecture, and requirements for autonomous operation. It provides a clear set of rules for how the network should behave, what services can be offered, and how to recover once connectivity is restored. This standardization ensures interoperability between different vendors and enables public safety agencies to deploy resilient networks with confidence.