The core handles all protocol-related functions to communicate with the PCS and Ethernet MAC interface of another device. This includes handshaking, synchronizing and error checking. You provide packet data through the AXI4-Stream TX interface, and receive packet data from the AXI4-Stream RX interface. A detailed description is given in AXI4-Stream Interface.
The 40G/50G High Speed Ethernet Subsystem is designed to be as flexible as possible and can be used in many different applications. The RX path does not perform any buffering other than the pipelining required to perform the required operations. Received data is passed directly to the user interface in a cut-through manner, allowing you the flexibility to implement any required buffering scheme. Also, the core TX path consists of a single pipeline with minimal buffering to provide reliable cut-through operation.