# CarTwin--Development of a Digital Twin for a Real-World In-Vehicle CAN Network
## 3 Topology of the Real-World In-Vehicle CAN
### The In-Vehicle Subsystems  
The vehicle network used as the basis for the digital twin is one of the OBD-accessible CAN networks from the vehicle we analyzed. By checking its Wiring Diagram Handbook, we found that there were seven nodes communicating on the CAN network connected to the Data-Link Connector (DLC): the Accessory Protocol Interface Module (APIM), Power Steering Control Module (PSCM), Instrument Panel Cluster (IPC), Remote Function Actuator (RFA), Restraints Control Module (RCM), Anti-lock Brake System (ABS) and Powertrain Control Module (PCM).  
The Accessory Protocol Interface Module (APIM), also called SYNC module, is an entertainment and multimedia system that allows the driver or passenger to connect the phone to the car for hands-free phone calls, control the music inside the car and perform voice commands. More information regarding the APIM ECU is provided by authors in [37], which details the supported features for each version of the module.  
The Power Steering Control Module (PSCM) adjusts the column angle with the use of a motor to provide the wheel steering, having as inputs the steering wheel angle, driver torque and road disturbance. Power steering system modules are analyzed by authors in [38], with detailed block diagrams for the controller, feedback loops and simulations for different system configurations.  
The Instrument Panel Cluster (IPC) receives inputs from other ECUs (directly or via gateways) and provides that information to the driver using gauges or warning lamps (these are simulated on digital screens on newer vehicles). Additional details and more instrument panel cluster functionalities together with a risk assessment on attacks for IPC functionalities are presented by authors in [39]. A similar analysis is presented for in-vehicle Body Control Modules (BCM) in [40].  
The Remote Function Actuator (RFA) is a system paired with a remote function receiver, which provides information on the vehicle bus related to intelligent key access on cars that have the remote keyless entry (RKE) feature. Most remote keyless access systems are considered vulnerable and prone to attacks since the security of keyless entry and keyless engine start has received little to no interest from manufacturers in the last decade until it was emphasized as insecure by various research works [41; 42; 43; 44].  
The Restraints Control Module (RCM) is a passive safety system that checks the seat-belt buckle switch and seat position. In case of a vehicle crash, it controls airbag firing and seat-belt pretension. The RCM detects that a vehicle is crashing by using acceleration and pressure information from multiple sensors placed in multiple areas inside the vehicle. Security evaluation of restraint control modules is analyzed by authors in [45], who proposed counter-measures and security tests to mitigate analyzed threats and attack paths.  
The Anti-lock Brake System (ABS) module prevents the vehicle tires from skidding and reacts when the tires lose traction due to heavy braking or if the brakes are not applied but there is ice, snow, sand or gravel on the road that causes the loss of tire-to-road friction. Sensors provide individual tire speed to the ABS ECU, which commands a hydraulic pump to control the break pressure whenever any of the tires loses grip. Vulnerabilities and proposals for enhancing the security of anti-lock brake systems were analyzed by recent works [46; 47].  
The Powertrain Control Module (PCM) from vehicles with a manual transmission manages and monitors the engine and transmission functions and controls the injection of fuel in the engine, control of emissions and the gear change using sensor data. Security of powertrain systems from hybrid and electric vehicles was analyzed by authors in recent papers [48; 49].