Computer-CAN(Campus Area Network)

CAN

CAN stands for Campus Area Network. It is network composed of multiple inter-connected LAN in limited coverage area. CAN network type is smaller in comparison with MAN and WAN as described below. 

Examples of CAN based network: 
• SUNet network of Stanford University 
• Project Athena of MIT 

It has following benefits: 

• It is cost effective. 

• It enables multi-department network access.
• It supports single and shared data transfer.

1. CAN History

Bosch originally developed the Controller Area Network (CAN) in 1985 for in-vehicle networks. In the past, automotive manufacturers connected electronic devices in vehicles using point-to-point wiring systems. Manufacturers began using more and more electronics in vehicles, which resulted in bulky wire harnesses that were heavy and expensive. They then replaced dedicated wiring with in-vehicle networks, which reduced wiring cost, complexity, and weight. CAN, a high-integrity serial bus system for networking intelligent devices, emerged as the standard in-vehicle network. The automotive industry quickly adopted CAN and, in 1993, it became the international standard known as ISO 11898. Since 1994, several higher-level protocols have been standardized on CAN, such as CANopen and DeviceNet. Other markets have widely adopted these additional protocols, which are now standards for industrial communications. This white paper focuses on CAN as an in-vehicle network.

2. CAN Benefits

CAN provides an inexpensive, durable network that helps multiple CAN devices communicate with one another. An advantage to this is that electronic control units (ECUs) can have a single CAN interface rather than analog and digital inputs to every device in the system. This decreases overall cost and weight in automobiles.  

Broadcast Communication

Each of the devices on the network has a CAN controller chip and is therefore intelligent. All devices on the network see all transmitted messages. Each device can decide if a message is relevant or if it should be filtered.  This structure allows modifications to CAN networks with minimal impact.  Additional non-transmitting nodes can be added without modification to the network.

Priority

Every message has a priority, so if two nodes try to send messages simultaneously, the one with the higher priority gets transmitted and the one with the lower priority gets postponed.  This arbitration is non-destructive and results in non-interrupted transmission of the highest priority message.  This also allows networks to meet deterministic timing constraints.

Error Capabilities

The CAN specification includes a Cyclic Redundancy Code (CRC) to perform error checking on each frame's contents.  Frames with errors are disregarded by all nodes, and an error frame can be transmitted to signal the error to the network.  Global and local errors are differentiated by the controller, and if too many errors are detected, individual nodes can stop transmitting errors or disconnect itself from the network completely.