eCall is an emergency call system initiated by the European Union, designed for vehicles to dial the emergency services automatically in the event of a serious road accident or it can be manually activated by the vehicle occupant if needed. The aim is to reduce response times, which can be crucial in saving lives and minimizing the severity of injuries. Once activated, the system establishes a voice connection with the nearest emergency center or Public Safety Answering Point (PSAP) and sends a Minimum Set of Data (MSD) which contains the vehicle’s location, the time of the accident, the type of vehicle, the number of passengers and other relevant information.
eCall system leverages two existing infrastructures in its operation: The Global Navigation Satellite System (GNSS) and telecommunication network. The GNSS provides accurate location data of the vehicle. When an accident occurs, the eCall system uses GNSS to pinpoint the exact geographical coordinates of the incident. The location data obtained from GNSS is integrated into MSD. The vehicle’s position is continuously updated to ensure the most accurate location data is available. The telecommunication network provides the communication channel through which the eCall is made. It enables the transmission of the MSD and facilitates voice communication between the vehicle’s occupants and the PSAP. Following the transmission of the MSD, the system automatically establishes a voice call between the vehicle and the PSAP operator, allowing two-way communication. This is crucial for assessing the situation and providing immediate assistance.
Figure 1: eCall system
The eCall concept was introduced in the early 2000s, with standardization beginning around 2004 when 2G was prevalent and 3G networks were being deployed. Since 2G and 3G are circuit-switched (CS) networks, the MSD is encoded into a series of audio tones using an in-band modem within the In-Vehicle System (IVS), allowing it to be transmitted over the voice channel. IVS is a module within the vehicle which triggers an emergency call to the PSAP. Once the voice call is established between the vehicle and the PSAP, the IVS sends the encoded MSD data as audio signals over the call. The PSAP then decodes these audio signals back into digital data, reconstructing the MSD.
Mobile network operators (MNOs) worldwide are currently shutting down 2G / 3G networks as these technologies sunset, aiming to reclaim those frequency spectrums for 4G and 5G networks. Therefore, there is a need to transition the eCall system to 4G / 5G networks, referred to as Next Generation eCall (NG-eCall). It is important for vehicle manufactures and their suppliers to move forward and ensure that the next generation of vehicles is compatible with the NG-eCall system.
4G and 5G is a packet switches networks, therefore the cornerstone of NG-eCall is the IP Multimedia Subsystem (IMS), a framework that facilitates the delivery of IP-based multimedia services. It utilizes text-based protocols like Session Initiation Protocol (SIP) and Session Description Protocol (SDP) for initiating and managing emergency calls. The SIP is responsible for initiating the emergency call and ensuring it is directed to the appropriate emergency service and terminating the session. Complementing SIP, the SDP provides a standardized format for describing the multimedia content of the communication session such as the type of media and its properties. Traditional emergency call numbers 112, 911 and 999 are replaced in the NG-eCall with Emergency Uniform Resource Name (URNs). The UNRs used in NG-eCall include:
- urn:service:sos.ecall.automatic
- urn:service:sos.ecall.manual
- urn:service:test.sos.ecall
As I explained earlier in eCall systems, the MSD transfer relies on in-band modem communication, which can often be unreliable. NG-eCall addresses this issue by including the initial MSD in the SIP INVITE message as text, ensuring that essential data is conveyed right at the start of the call as shown in Diagram 1 below.
Diagram 1: Standard NG-eCall SIP flows. The initial MSD is included in the INVITE message.
This diagram illustrates the SIP signaling messages exchanged during an NG-eCall. When an emergency call is triggered, the IVS module or DUT (Device Under Test) sends an INVITE message to the IMS SIP Server, which includes the MSD. The IMS Server forwards the INVITE message to the PSAP. The PSAP acknowledges receipt of the INVITE by sending a “100 Trying” response. It then sends a “180 Ringing” response to indicate that the call is being alerted. Next, the PSAP sends a “200 OK” response to indicate that the INVITE has been accepted and the MSD acknowledged. The DUT responds with an ACK message to confirm receipt of the “200 OK” response. The call is then established, and communication between the DUT and PSAP is in progress. Either the PSAP or DUT can end the call by sending a BYE message, which is acknowledged with a “200 OK” response. Figure 2 below is an example of MSD content in the INVITE message. As you can see, it is a string of data that the PSAP will decode into human-readable text.
Figure 2: Example of MSD content in INVITE message
During the ongoing SIP call, if there is new information or update to the MSD, the DUT needs to send this update data to the PSAP, or the PSAP can request the updated MSD from the DUT. These updates are transmitted using SIP INFO message as text, allowing for continuous communication of critical data such as changes in the vehicle’s status or location. This is a mechanism in the NG-eCall for updating the MSD in real time to further enhance the reliability of MSD transmission. The SIP flow with MSD update is shown in the diagram below.
Diagram 2: Standard NG-eCall with MSD update included in INFO message
eCall and NG-eCall need to be co-exist before the industry fully transitions to NG-eCall. The migration occurs in several phases: initially dominated by eCall, then a mix of eCall and NG-eCall, followed by NG-eCall with some circuit-switched fallback, and finally achieving universal NG-eCall implementation. The key differences between eCall and NG-eCall are summarized in the table below.
Testing of NG-eCall
Vehicle manufacturers must adopt a comprehensive approach in the development and integration of NG-eCall into their vehicles to ensure compliance with all relevant regulations and standards such as CEN/TS 17184, CEN/TS 17240, ETSI TS 103683 and EN 15722. Testing of these standards and requirements in the real-world environments can be hard, yield inconsistent results and present various challenges. To address this, Keysight has developed a comprehensive testing solution in the lab environment, ensuring more cost-effective and repeatable test results.
Figure 3: Keysight NG-eCall test solution
Keysight NG-eCall test solution setup consists of five key components, as illustrated in Figure 3 above:
- 4G IVS Module –This module, essentially a Device Under Test (DUT), resides within the vehicle and is tasked with collecting the vehicle’s information and initiating communication with emergency services. The call can be triggered automatically or manually.
- N5172B EXG – This Keysight signal generator serves a GNSS emulator, replicating signals and data from Global Navigation Satellite Systems like GPS, GLONASS, Galileo and Beidou. It provides GNSS coordinates or location information such as latitude and longitude of the accident site required by the IVS to compile the MSD.
- E7515B UXM – This is a cellular base station emulator equipped with LTE Test Application software, designed to simulate a real-world 4G LTE network environment, particularly in the context of NG-eCall.
- IMS Server – It is software that can be installed in any reachable network. It handles the VoLTE call between the IVS and PSAP.
- PSAP software – This is Public Safety Answering Point software that emulates emergency services, decoded the MSD data.
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