CAN protocol basic information

CAN - Control Area Network protocol
Multi-master & multicast/ broadcast type system
2 wire interface (Differential signal) CANH CANL

Reliable communication protocol compared to Ethernet. Its better than Ethernet because, in Ethernet when multiple nodes are sending data over the network collision is detected and jamming signal is sent on the line. This causes loss of Bandwidth.
Whereas in CAN, there is a concept called arbitration and hence there is loss of Bandwidth. This makes it reliable and real-time, best suitable for industries where real-time is of utmost priority.

Multiple CAN standards like CiADS301 (CAN in Autoamtion Data Structure) are defined based on

1. Framework of application
2. Device profile 
3. Application profile

CANOpen is a protocol built over CAN. It consist of software part and application

In terms of OSI model task can be divided as

1. Physical layer: bit transmit and receive
2. Data link layer: synchronization at start of packet
3. Network layer: arbitration, addressing
4. Transport layer: segmentation of large data into small packets
5. Session layer: handles complete communication cycle. like in case of SDO request to response
6. Presentation layer: Object dictionary (OD) data handling
7. Application layer: Requirement specific

Physical layer: CAN Transceiver

Data, Network: CAN Controller

Transport, Session, Presentation & Application layer: Software running on Microcontroller

Why TCP/IP cant be used instead ?

1. It takes lot of resources of CPU and memory to implement
2. Cost of HW and SW will be more
3. TCP/IP is not developed for this purpose. Each packet is 1500 bytes with overhead of 24bytes. Hence if actual data is 1 or 2 bytes then unnecessarily redundancy is introduced.
4. Jamming signal on collision problem. Hence cant be used for real-time critical applications.

Criteria for deciding on any protocol to use

1. Performance provided
2. Price
3. Resources need