# A Perspective on Ethernet in Automotive Communications--Current Status and Future Trends
## 2 Current In-Car Network Architectures and Technologies
### Legacy In-Car Networking Technologies  
Traditional in-car networking technologies include:  
* _LIN_[12]. The Local Interconnect Network (LIN) is a low-cost, low-speed broadcast serial communication system on a single wire, widely used in production cars. LIN is simple, cheap and it is typically found in body and comfort subsystems. LIN adopts a bus topology, with a maximum total length of 40 m. It is based on a shared medium and follows a Master-Slave transmission protocol, with one master and up to 16 slaves forming a LIN cluster. A LIN Description File is used in the design phase to configure \begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Functional Domain** & **Description** & **Networking Technologies** \\ \hline Powertrain & Control of engine and transmission & CAN, CAN FD, FlexRay \\ \hline \multirow{3}{*}{Chassis} & Control of the vehicle stability and dynamics according to steering/braking solicitations and driving conditions (e.g., ground surface, wind, etc.) & CAN, CAN FD, FlexRay \\ \hline Body and Comfort & Control of doors, windows, roof, and seats, climate control, etc. & LIN, CAN, CAN FD \\ \hline Multimedia/ Infotainment & Audio CD, DVD players, MP3 players, TV, Rear Seat Entertainment, navigation information services, etc. & MOST, CAN \\ \hline Human Machine Interface & Advanced display technologies & MOST, CAN \\ \hline \multirow{3}{*}{ADAS} & Lane Departure Warning, Traffic Sign Recognition, Night vision, Pedestrian detection, Parking assistant, etc. & CAN, FlexRay \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The traditional automotive functional domains. the scheduling behavior of the LIN cluster. LIN offers services to put nodes into a sleep mode (go-to-sleep command) and to wake them up before new data is sent on the bus, in order to optimize energy consumption. * _CAN_[13]. The Controller Area Network (CAN) is the most widely used in-car network technology [14]. It is found in many functional domains, i.e., powertrain, body and comfort, and multimedia (to send control messages). CAN is a multimaster serial bus that implements Carrier Sense Multiple Access with Bitwise Arbitration (CSMA/BA) to access the shared channel. Each CAN message has a maximum payload of 8 bytes and starts with an Arbitration field that includes the message identifier (11 bits in the CAN 2.0A version, 29 in the CAN 2.0B one) plus another bit (called the Remote Transmission Request bit). The Identifier field gives the message priority. If multiple messages begin to be transmitted at the same time, an arbitration phase starts. At the end of this phase, the highest priority message goes through unaffected, while the others are stopped. CAN offers several speeds, i.e., 125 Kbps, 250 Kbps, 500 Kbps, and up to 1 Mbps, but the higher the speed, the shorter the maximum bus length (e.g., 1 Mbps works for bus lengths up to 40 m). This is because the CAN arbitration procedure relies on the fact that a sending node monitors the bus while transmitting. Therefore, the signal must be able to propagate to the most remote node and return back before the bit value is decided. This requires the bit time (i.e., the time between two consecutive bits of the same frame) to be at least twice as long as the propagation delay, which limits the data rate. For in-car usage, the typical maximum CAN speed is 500 Kbps. CAN provides error detection and recovery mechanisms and fault-confinement mechanisms to identify permanent failures. CAN is able to offer predictability in real-time communications, but may introduce transmission jitter, i.e., the channel access time instant of a periodic message is not deterministic, but may vary, depending on the presence of ongoing transmissions on the shared channel. _CAN FD_[13] introduces improvements in terms of longer payloads than traditional CAN (0-8, 12, 16, 20, 24, 32, 48, and 64 bytes) and higher transmissions speeds (2 Mbps, 5 Mbps). The longer payload helps reduce segmentation of long messages and add security features.