Understanding The Controller Area Network (CAN)

You are requested to research one of the technologies listed below and produce a report that will inform and educate your fellow students:

• Body-Area-Networking
• Zigbee / Zwave networking
• Bluetooth networking
• Controller Area networking (CAN Bus)
• Any other topic agreed upon with the tutor

Knowing that the above technologies are not immune and hence using these types of network technologies inherent all vulnerabilities. The research requires exploration of potential advantages and disadvantages of the chosen network technology. Your report should demonstrate understanding and evaluation of your chosen topic in various areas, such as security, architecture/technology and potential use.

You are required to research one of above technologies and produce a report covering the issues related to the underlying networking technology. You should use online open-source materials, together with the subscription-only resources available to you via the University’s electronic library. Select and explain one of the listed technologies, explaining the fundamental method by which it operates, exploring the underlying networking principles. Explore and investigate the strengths, weaknesses and potential risks.

The Standard of CAN

Robert Bosch GmbH developed the controller area network for applications that are automotive in nature as early as 1980s and then it was released to the public in 1986. The specification of Bosch CAN was then made an ISO standard, that is, (ISO 11898), in the year 1993 (CAN 2.0A). In 1995, it was extended to allow for longer identifiers of devices (CAN 2.0B). Basically, controller area network links together a network of modules through the use of a twisted pair cable made up of two wires. A huge number of companies utilize devices controller area network. The controller area network device is referred to as the TouCAN module in the Freescale MPC 5xx processors’ series while it’s referred to as the FlexCAN in the seires of MPC 55xx. Controller.

Controller area network is a multicast protocol, multimaster, serial which implies that when the bus is free, the multimaster that can be any node, transfers a message whereby all the nodes present receive the multicast which is the message and then act on it. The transmitter is the node which triggers the message while the receiver is every node that does not send any message. Static priorities are assigned to the messages while the node transmitting remains as the transmitter until the time the bus gets idle or up to the time the node transmitting is suspended by a higher priority message node. This is achieved in a process referred to as the arbitration. A controller message may comprise of up to data of 8 bytes.

The Standard of CAN

The CAN is an ISO defined serial bus of communication. It was first created in order to be used in the automotive industry so as to eliminate the harness of wiring that was complex with a bus of two-wire. The communication devices are connected by a physical medium and the communication is defined by the model’s physical layer.

The OSI/ISO model has seven layers and the two bottom model layers are defined by the ISO 11898 architecture as illustrated in figure 1 below. They are the physical layer and the data link layer.

                                                     The Standard Architecture of ISO 11898

In the figure above, the link of communication is established in the application layer to a specific protocol of the upper-level application like the CANopen™ protocol that is vendor-independent. The protocol has the support of CiA (CAN in Automation), which is the manufactures group, and the international users (Chen and Tian, 2009).

Standard and Extended CAN

The protocol of communication of CAN is a multiple-access protocol sense of carrier with arbitration and detection collision on message priority.

The CAN standards first version, ISO 11519 which is the CAN with speed that is low is meant for applications that uses up to 125 kbps with 11-bit identifier standard.

ISO 11898 is the second version that that uses 11-bit identifiers as well offers rates of signaling from 125kbps to 1 Mbps.

Standard and Extended CAN

The extended CAN standard was introduced in 1995 which is the ISO 11898 that was amended. It has the 29-bit identifier.

The standard CAN offers services for 2048 or 211 message identifiers while the extended CAN offers for 537 or 229 million identifiers (Nolte, Hansson and Norstrom, 2013).

CAN Fundamentals

CAN frames or messages are divided into four categories which are Error Frame, Data Frame, Overload Frame and Remote Frame.

• The Error Frame can be transmitted by a node that identifies the error of the bus.
• The Data Frame is the CAN message standard that broadcasts the data to the nodes from the transmitter on the bus.
• The Overload Frame is applied in bringing about delay that is additional between remote frames or data.
• The Remote Frame requests data from a unique node after being broadcast by the transmitter (Zuberi and Shin, 2015).
• Fault Confinement and Error Checking

The protocol of CAN incorporates uses five methods to check errors. Two of the methods are utilized at the bit level and the rest are utilized at the message level. An error fragmented is created by the receiving nodes when a message failure occurs with the methods of detecting error. As a result, the node keeps on resending the message until it’s correctly received.

At the level of message, a form check, ACK and CRC slots are found. The ACK comprises of the checksum of the application that is preceding for detecting the errors while the ACK comprises of the bit acknowledge delimiter and the acknowledge bit. The form check checks for the message fields. An error is generated on detection of a dominant bit.

At the level of the bit, the message transmitter monitors the bit transmitted. An error is generated if the opposite of a data bit written on the bus is read (Barranco et al., 2011).

The CAN Bus

The physical signaling and data link layers are basically transparent to an operator of the system. They are located in all the kinds of controllers that utilizes the protocol of CAN. A line transceiver is used to implement a connection to the medium that is physical to create an electronic control unit. CAN is able to tolerate fault and become immune to noise as signaling is differential. Differential signaling that is balanced reduces coupling of noise and enables rates of high signaling over cable of twisted pair. CAN bus high immunity of noise and rejection of common-mode are enhanced by the cabling of twisted pair and usage of balanced differential receivers.

The ISO 11898 standard high speed specifications are provided for maximum rate of signaling of 1 Mbps with a 40 m length of the bus and 30 nodes in maximum. An unterminated maximum stub length of 0.3 m is also recommended. The cable can either be shielded or the unshielded twisted-pair that has 120-Ω impedance characteristic (Zo). The network topology is defined by the ISO 11898 standard as a twisted-pair cable of a single line as indicated in figure 2 below.

The cable is terminated with 120-Ω resistors at both ends that matches the impedance characteristic of the line to avoid reflections of the signal. Placement of R_L on a node ought to be prevented since the lines of the bus loses termination when the node is terminated from the bus. The two signal lines of the bus, that is, CANL and CANH, in the state that is recessive and quiescent, are biased passively to ? 2.5 V.

A network of communication that connects the nodes linked to a bus is defined by the CAN standard and allows them to communicate with each other. A central node may not be there but it can be introduced while the network is in operation (Pazul, 2010).

Merits of CAN

• CAN helps in wiring reduction as it is a control that is distributed and this enables enhancement of the performance of the system.
• Development and coding becomes easier as the manufactures of the CAN chip offer the physical and the data link layer interfaced to the chips and what is required from the developer is just developing the coding application.
• It enables working in various electrical environment and also that the transmission is free from noise.
• It enables elimination of traffic congestion since the transmission of the messages is based on the priority and also enables meeting of time constraints in the network.
• During transmission, every node checks for the errors and the sends the frame of the error. This enables transmission that is error free (Lee and Lee, 2014).

Demerits of CAN

• The software expenditure of the software is high.
• There is likely to arise undesirable interaction (Zuberi and Shin, 2010).

Applications of CAN

The following are some of the applications of CAN:

• It is used for antilock braking, transmission airbags and power steering among others.
• It’s applied in systems of video and audio.
• It is also applied in escalators and lifts, automatic doors and sport cameras.
• It is also applied in coffee machines and telescope.
• It is applied in aircraft as well with systems of navigation, state sensors and analysis of flight data to control systems of the aircraft engine like the pumps, fuel systems and linear actuators.
• It can also be applied in mirror, windows and doors adjustment.
• It is also applied in applications of the railway like the trams, light railways, undergrounds and street cars (Johansson, Törngren and Nielsen, 2015).

Conclusion

Controller area network is best utilized in applications that require a numerous number of short messages in a short time period. It has reliability that is high in operation environments that are rugged. It is best also when the data is required by many locations since it is message based.  Its data consistency system wide is mandatory. It has a huge merits such as fault confinement whereby the nodes that are faulty are dropped automatically from the bus. This is essential as it helps to prevent the node from failing the network and ensures that the bandwidth is available at all times in case of transmission of critical messages. This containment of error enables addition of the nodes while the system is still working. This is referred to as hot-plugging.

CAN has brought improvements in trains, automobiles, busses, trucks, marine vehicles, airplanes, construction, mining and agriculture.

Control systems that are CAN-based are applied in domestic appliances, building and factory automation and medical services among others.

References

Barranco, M., Proenza, J., Rodríguez-Navas, G. and Almeida, L., 2011. An active star topology for improving fault confinement in CAN networks. IEEE transactions on industrial informatics, 2(2), pp.78-85.

Chen, H. and Tian, J., 2009, May. Research on the controller area network. In Networking and Digital Society, 2009. ICNDS'09. International Conference on (Vol. 2, pp. 251-254). IEEE.

Johansson, K.H., Törngren, M. and Nielsen, L., 2015. Vehicle applications of controller area network. In Handbook of networked and embedded control systems (pp. 741-765). Birkhäuser Boston.

Lee, K.C. and Lee, H.H., 2014. Network-based fire-detection system via controller area network for smart home automation. IEEE Transactions on Consumer Electronics, 50(4), pp.1093-1100.

Nolte, T., Hansson, H. and Norstrom, C., 2013, May. Probabilistic worst-case response-time analysis for the controller area network. In Real-Time and Embedded Technology and Applications Symposium, 2013. Proceedings. The 9th IEEE (pp. 200-207). IEEE.

Pazul, K., 2010. Controller area network (can) basics. Microchip Technology Inc, 1.

Zuberi, K.M. and Shin, K.G., 2010. Design and implementation of efficient message scheduling for controller area network. IEEE transactions on computers, 49(2), pp.182-188.

Zuberi, K.M. and Shin, K.G., 2015. Scheduling messages on controller area network for real-time CIM applications. IEEE Transactions on Robotics and Automation, 13(2), pp.310-316.