As the name suggests, eCall stands for Emergency Call and is used during emergency situations. The following topics are covered in this article:

1. What is eCall ?

2. Triggers for eCall

3. eCall ECO System

4. eCall Sequence

5. MSD and its contents

6. Technical Requirements for eCall

7. eCall Regulations

8. Conclusion

What is eCall and why Is It needed ?

As mentioned in the introduction section, eCall is used in emergency situations.

Assume a vehicle is being driven in a remote area where there are very few people around. Unfortunately, the vehicle gets into an accident, and the passengers are fighting for their lives. Since there are no people nearby, there is no one available to help. The main purpose of eCall is to provide assistance during such emergencies, even when no one is around.

Once eCall is triggered, a voice communication session is established with the PSAP (Public Safety Answering Point) or call center so that the driver or passengers can speak with the police or a call center operator. Additionally, vehicle and passenger information is uploaded to the server. This information alone is sufficient to trigger rescue services, even when the driver or passengers are unable to speak.

The established voice communication can continue for a long time and can only be ended by the call center. Even after the eCall session ends, the call center team can call back the vehicle to provide further assistance. This waiting period for a callback is known as the "CALLBACK period" in eCall terminology.

Types of eCall

eCall is classified into two categories:

1. Automatic eCall

2. Manual eCall

Basically, eCall can be triggered either automatically or manually. In most cases, eCall is triggered automatically when the vehicle airbag is deployed. This is known as Automatic eCall.

In situations where passengers require emergency assistance without an accident, or when the airbag is not deployed after an accident, eCall can be triggered manually by pressing the SOS button in the overhead compartment. This is known as Manual eCall.

eCall Ecosystem

The following infrastructure is required to fully realize the eCall system:

1. Vehicle equipped with an Airbag and Button

2. TCU or DCM

3. GNSS Satellite

4. Cellular Provider (MNO)

5. Server and Call Center

6. Rescue Services

Vehicle equipped with Airbag and Button

To support eCall, the vehicle must be equipped with an airbag and an SOS button located in the overhead compartment.

The airbag output is directly connected to the TCU/DCM to monitor airbag deployment. Depending on vehicle architecture, the Airbag ECU may provide a dedicated trigger signal (often PWM-based or equivalent) to the TCU/DCM. When the airbag is deployed, the Airbag ECU sends a dedicated trigger signal (for example, a PWM pattern) to the TCU/DCM for a predefined period. If this setup is not working, the driver or passengers can manually press the SOS button to trigger the call.

TCU or DCM

The DCM/TCU is primarily used for eCall and requires only a 2G/3G/4G/5G voice connection. The TCU is equipped with both GNSS and cellular antennas. The GNSS antenna is used to retrieve the vehicle's location at the time of the accident. The cellular antenna is used to establish the emergency call and upload the MSD (Minimum Set of Data)

GNSS Satellite

GNSS satellites provide the precise location (latitude and longitude) required to determine the accurate position of a vehicle. Various GNSS constellations can be used, such as GPS (USA), GLONASS (Russia), Galileo (Europe), BeiDou (China), and NavIC (India). Depending on the vehicle's location, any available constellation can be used to obtain an accurate position.

Cellular Provider (MNO)

For the TCU/DCM to have network connectivity (4G/5G), a contract must be established with an MNO. This service typically involves a three-party agreement between the ECU manufacturer (Tier-1), the OEM (vehicle manufacturer), and the MNO.

Server & Call Center

Basically, a Public Safety Answering Point (PSAP) is managed either by the government or a private organization to provide eCall services. The server receives vehicle and driver information through the MSD (Minimum Set of Data), and the call center provides support by communicating with the driver or passengers to offer immediate assistance.

Rescue Services

Rescue services include emergency response units such as fire trucks, ambulances, and police. These services provide immediate emergency assistance. Rescue services are activated by the call center after confirming the vehicle's location and the condition of the driver and passengers.

eCall Sequence

The following is the sequence of events from the moment eCall is triggered until rescue services are provided:

1. A collision occurs, or an emergency situation arises.

2. The airbag is deployed, or the manual emergency button is pressed.

3. Vehicle data (MSD) is uploaded to the server.

4. Upon successful upload of the MSD, voice communication is established.

5. The call center dispatches the rescue services.

The high-level sequence is shown below.

After the eCall session ends, the TCU/DCM starts the callback timer and remains available to automatically answer callback requests from the call center. This is useful when the call center requires the latest vehicle location information or needs further clarification from the driver or passengers. In many regulatory implementations, the vehicle remains available for automatic callback for minimum 60 minutes after the eCall session ends.

End-to-End eCall Flow

MSD Contents

The Minimum Set of Data (MSD) is important for understanding details about the vehicle, driver, and passengers. Depending on the regulatory region (e.g., Europe, Japan, or other countries), the contents of the MSD may vary. The following are the common contents of an MSD:

1. Precise location (latitude and longitude)

2. Precise time

3. VIN - Vehicle Identifier (to identify the vehicle)

4. Vehicle type (car, truck, bus, etc.)

5. Vehicle propulsion type (Diesel, Petrol, EV, Hybrid, etc.)

6. Number of passengers (optional, not available in all vehicles)

7. Last recorded vehicle positions (useful for estimating the vehicle's location if a valid position is not available at the accident site)

he method used to transmit the MSD to the server varies depending on the type of eCall. Refer to below section that captures different type of MSD transmission method per eCall type.

eCall types per region

Different eCall implementations are used depending on the region in which the service is deployed.. Below are the major categories of eCall based on the region.

• Legacy eCall

• NG-eCall

• Hybrid eCall

• Helpnet

• Private Call

Legacy eCall or ERA-GLONASS call

Legacy eCall is used in European regions, while ERA-GLONASS is a more stringent variant used in Russia. Basically, voice is established with 2G or 3G voice channel and MSD is transmitted as part of voice channel (in-band MSD). It is called "in-band Modem". In other words, data is transmitted by embedding it within the audio voice channel.

NG-eCall (Latest Pan European Call)

It is the next generation of Legacy eCall and is widely deployed in Europe and parts of the Middle East. Instead of using a legacy voice channel, it uses packet data to transmit the MSD using SIP (Session Initiation Protocol).

Legacy eCall Vs NGeCall

Hybrid eCall

Hybrid eCall is designed to support both Legacy eCall and NG eCall. It combines the capabilities of both systems to ensure compatibility across different network infrastructures. When an emergency call is triggered, the system first attempts to establish an NG eCall session. If NG eCall is not available or the connection fails, it automatically falls back to Legacy eCall.

Helpnet (Japan)

Japan uses VoLTE or VoNR to establish the eCall and it transmit the MSD to server using HTTP protocol aligned with server. MSD contents are transmitted per Helpnet standards.

Private Call (all other regions)

Typically, private eCall uses VoLTE, VoNR, or other communication technologies depending on the country and server infrastructure. The MSD is transmitted to the respective server based on server defined protocols (e.g HTTPS or MQTT).

Technical Requirements for the TCU/DCM

To support eCall, the TCU/DCM must be equipped with the following hardware and software components:

1. Antennas (GNSS and Cellular)

   • These provide connectivity to the outside world, enabling precise location tracking and cellular connectivity for voice communication.

2. BUB (Backup Battery)

   • This provides sufficient power to the TCU when the main vehicle battery is disconnected during an accident.

   • In many regulatory regions, the BUB capacity must support at least 10 minutes of eCall operation and 1 hour of callback waiting time.

3. Audio Subsystem (Speaker and Microphone)

   • In most cases, the TCU/DCM uses the vehicle's existing speakers and microphone.

   • In some regulatory regions, a dedicated speaker may be installed in addition to the existing vehicle speakers.

4. PWM Signal

   • This is required to detect airbag deployment.

   • A direct physical PWM signal connection is established between the Airbag ECU and the TCU/DCM.

5. ADC (Analog-to-Digital Converter Interface)

   • This is used to connect the SOS button in the overhead compartment to the TCU.

   • It is also used to indicate the status of the eCall system to end users via LEDs

6. CAN/Ethernet

   • This is used to collect vehicle information (e.g., number of passengers, propulsion type, etc.).

eCall Regulations

eCall is a mandatory feature in several countries. The following regions have regulations that require vehicles to support eCall. This means that vehicles cannot be launched in these regions without eCall functionality.

1. European Union

2. Russia

3. Saudi Arabia and UAE

4. Turkey

5. Japan

Since eCall is mandated in these regions, many regulatory requirements must be met to ensure reliable operation of the system. In addition, the respective governments provide support through call centers and rescue services.

Although eCall is not mandatory in some regions, similar services may be provided through private call centers. These services are referred to as Private eCall.

The following regulatory standards apply to different regions:

Regulatory Legacy eCall

Regulatory Legacy eCall is also known as Pan-European eCall. These regulations are applied in all European countries, as well as Saudi Arabia, UAE, and Turkey.

• EN 16072: Defines the core operating requirements, trigger mechanisms, and general service handling for Pan-European eCall.

• EN 15722: Specifies the data structure and content of the Minimum Set of Data (MSD) sent to emergency services (e.g., GPS coordinates, vehicle VIN, and direction of travel).

• EN 16454: Standardizes end-to-end conformance testing for in-vehicle eCall systems.

NG eCall

Next Generation eCall (NG eCall) is the successor to Regulatory Legacy eCall. It moves toward LTE-based voice communication instead of legacy 2G or 3G circuit-switched eCall. The following standards apply to NG eCall:

• CEN/TS 17184: Defines the High-Level Application Protocol (HLAP) for IMS-based NG eCall systems.

• CEN/TS 17240: Defines end-to-end conformance testing for packet-switched/IMS-based NG eCall systems.

Hybrid eCall

All above mentioned regulations for both Legacy and NGeCall are applicable to Hybrid call. On top of that, following requirements to be adapted for hybrid eCall

• EN 18052: Defines the end-to-end conformance testing protocols for eCall High-Level Application Protocols (HLAP) operating within hybrid network environments

Helpnet

The following regulations are commonly associated with Helpnet. Helpnet is primarily used in the Japanese market.

• UN Regulation No. 144 (UN R144): Establishes uniform provisions for the approval of Accident Emergency Call Systems (AECS). It defines how in-vehicle devices must operate during crashes and how they connect to public and private emergency centers.

• UN Regulation No. 10 (UN R10): Focuses on electromagnetic compatibility (EMC), ensuring that eCall devices do not interfere with other critical vehicle electronics and are resistant to external electromagnetic interference.

ERA-GLONASS

ERA-GLONASS is applied in Russia. Compared to Pan-European eCall and Helpnet, ERA-GLONASS has more stringent regulatory requirements.

• GOST 33467: Defines the general technical requirements for emergency call systems in vehicles.

• GOST 33464: Specifies the technical requirements for the navigation module, including support for GLONASS and GPS.

• GOST 33468: Defines standards and test methods for hands-free audio quality.

• GOST 33471: Defines the test methods for the navigation module to ensure compliance with ERA-GLONASS requirements.

Private Call

In regions where eCall is not mandated by regulations, eCall can still be supported based on custom requirements. For example, regions such as North America, Australia, and many others offer eCall services without specific regulatory requirements.

In such cases, the TCU/DCM implements the eCall functionality according to custom requirements defined by the OEM, together with a private call center and server infrastructure.

Conclusion

eCall is a life-saving emergency communication system designed to provide rapid assistance during accidents and other emergency situations. By automatically or manually establishing a connection with a call center, transmitting critical vehicle information through the Minimum Set of Data (MSD), and enabling voice communication with emergency operators, eCall helps reduce response time and improve the chances of timely rescue.

Although the implementation details and regulations may differ across regions, the fundamental objective of eCall remains the same: to ensure that help can reach vehicle occupants as quickly as possible when an emergency occurs. As connected vehicle technologies continue to evolve, eCall remains one of the most important safety features in modern vehicles.

I hope this article has provided a clear understanding of the eCall ecosystem, its architecture, operational sequence, technical requirements, and regulatory landscape.

Thank you for reading!

If you have any questions, suggestions, or feedback, please feel free to leave a comment. I would be happy to discuss the topic further and answer any questions related to eCall, TCU/DCM systems, vehicle connectivity, or automotive telematics.