What is a physical layer, object layer, transfer layer in CAN?

01. The Physical Layer defines how signals are actually transmitted. Within this specification, the physical layer is not defined so as to allow transmission medium and signal level implementations to be optimized for their application.
02. The Transfer Layer represents the kernel of the CAN protocol. It presents messages received to the object layer and accepts messages to be transmitted from the object layer. The transfer layer is responsible for bit timing and synchronization, message framing, arbitration, acknowledgment, error detection, and signaling, and fault confinement.
03. The Object Layer is concerned with message filtering as well as status and message handling.