According to the "computer network and communication" suggested communication protocol is divided into five layers architecture, physical layer, Data link layer, network layer, transport layer and application layer, and the general agreement on each floor frame structure has a Header and the Data,
Apply to the EtherCAT, data link layer is responsible for the data frame forwarding and processing, the corresponding Ethernet and EtherCAT head, the network layer is responsible for the communication between master station and slave station, corresponding ZiBao Datagram, the transport layer is responsible for providing communication channels with the application layer, corresponding to the Mailbox, the application layer is responsible for the direct manipulation from the stand of the servo function or other function, corresponding to the COE, SOE, such as
However, the official agreement is three layer structure, physical layer, data link layer and application layer, data link layer including the above to remove all the work of the physical layer and application layer, isn't it strange?

As a novice BBS, said no how many points can provide, just as a opinions hoping to discuss with you,