eCall Only Mode

Description

eCall Only Mode is a UE configuration option introduced in 3GPP Release 14 that allows a User Equipment (UE) to attach to the Evolved Packet System (EPS) and register in the IP Multimedia Subsystem (IMS) solely for the purpose of performing eCall over IMS. In this mode, the UE is restricted from initiating or receiving any other services except for eCall and specific non-emergency calls for test and terminal reconfiguration. The mode is configured in the USIM, ensuring that the UE behaves according to regulatory requirements for eCall-only devices.

The primary behavior of a UE in eCall Only Mode is that it refrains from any signaling to the network except when necessary for eCall or the allowed test/reconfiguration calls. This means the UE does not perform periodic registrations, location updates, or other background signaling that could consume network resources or cause interference. However, the UE must remain reachable for a short period after an eCall or test call to allow the PSAP or HPLMN operator to call back. This callback window is essential for emergency services to contact the vehicle if needed.

The mode is designed for vehicles that are equipped with eCall but do not offer other telematics or infotainment services. By limiting the UE's functionality, it reduces complexity and ensures that the device is always available for emergency calls. The UE attaches to EPS and registers in IMS only when needed, and after the call, it may deregister or enter a dormant state. The USIM contains the configuration that indicates the UE should operate in eCall Only Mode.

From the network perspective, the UE in eCall Only Mode is treated as a normal UE for emergency calls, but the network may be aware of its restricted capabilities. The UE can still perform IMS registration to support eCall over IMS, which requires an IMS profile. The eCall over IMS uses the IMS emergency session procedures with additional eCall indicators. The MSD is transmitted either in-band or via an IMS data channel, depending on the network and UE capabilities.

Security and privacy are maintained as with regular eCall. The mode does not affect the authentication and authorization procedures. The UE must still be authenticated by the network and authorized for eCall. The eCall Only Mode is particularly important for aftermarket eCall devices or vehicles that only have eCall functionality. It ensures compliance with the eCall mandate without requiring full telematics capabilities.

Purpose & Motivation

eCall Only Mode was introduced to address the need for a simplified UE configuration that supports only eCall services. Many vehicles are equipped with eCall but do not have other connectivity features. Without this mode, such UEs would need to support full network signaling, which increases complexity and cost. The mode also prevents unnecessary network signaling that could congest the network or drain the vehicle's battery. It ensures that the UE is always ready for an eCall and complies with regulatory requirements. The mode was standardized in Release 14 to support the deployment of eCall over IMS and to facilitate the certification of eCall-only devices.