Public Land Mobile Network with Disaster Condition

Description

The term 'PLMN with Disaster Condition' refers to a Public Land Mobile Network that is experiencing a disaster condition, which is defined as a situation that causes a significant disruption to the normal operation of the network, such as a natural disaster (earthquake, flood, hurricane), a major power outage, or a cyber-attack. This concept was introduced in 3GPP Release 19 as part of ongoing efforts to improve disaster response and emergency communications. It is specified in 23.401 (for EPS) and 23.501 (for 5GS), indicating its applicability to both 4G and 5G core networks.

When a PLMN is in a disaster condition, it may have limited resources or connectivity, and it needs to prioritize certain services, particularly emergency calls and public safety communications. The network may also need to cooperate with other PLMNs to provide service to affected subscribers. The 'PLMN with Disaster Condition' concept allows the network to signal this state to UEs and to other network functions, enabling them to take appropriate actions. For example, a UE may be configured to attempt emergency calls on a PLMN with disaster condition even if it is not the home PLMN, or to use specific access classes for priority.

The disaster condition can be declared by the PLMN operator or by a regulatory authority. Once declared, the network may enter a special mode of operation where certain features are disabled or restricted to conserve resources, and where emergency services are given the highest priority. The network may also broadcast indicators in the system information to inform UEs about the disaster condition, so that UEs can adjust their behavior, such as by reducing non-essential signaling or by selecting a different PLMN if available.

In the 5G core network, the disaster condition handling involves the Access and Mobility Management Function (AMF) and the Policy Control Function (PCF), among others. The AMF may enforce access control for certain UEs, while the PCF may provide special policies for emergency services. The concept also relates to the Disaster Roaming feature, where a UE can roam onto a PLMN with disaster condition to make emergency calls even without a roaming agreement, as mandated by some regulators.

The introduction of this term in Release 19 reflects the growing importance of network resilience and emergency communications. It provides a standardized way for networks to indicate and handle disaster conditions, ensuring that critical communications can be maintained when they are most needed. This is part of a broader trend in 3GPP to enhance public safety and disaster response capabilities, building on features like Mission Critical Services (MCX) and the 5G Emergency Services framework.

Purpose & Motivation

The PLMN with Disaster Condition concept was created to address the need for standardized handling of network disruptions during emergencies. In the past, when a disaster struck, networks might become congested or partially unavailable, and there was no standardized way for the network to signal this condition to UEs or for UEs to know how to behave. This led to inefficient use of remaining resources and potential failure of emergency calls. The new term provides a clear definition and triggers specific behaviors in both the network and UEs.

The purpose is to ensure that during a disaster, emergency services remain accessible and that network resources are prioritized correctly. It allows a PLMN to declare a disaster condition and to take actions such as barring non-essential services, prioritizing emergency calls, and enabling disaster roaming so that subscribers of other networks can still make emergency calls. This is particularly important for public safety and for meeting regulatory requirements in many countries, where emergency calls must be possible even if the home network is unavailable.

Historically, disaster response in mobile networks relied on features like Access Class Barring (ACB) and Emergency Call handling, but these were not specifically designed for large-scale disasters. The PLMN with Disaster Condition concept, introduced in Release 19, provides a more holistic approach by formally defining the state and integrating it with roaming and policy frameworks. It builds on earlier work on Disaster Roaming and enhances the overall resilience of mobile networks.