Low Latency Ethernet 10G MAC Intel® FPGA IP User Guide

ID 683426
Date 3/01/2022
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4.6. Flow Control

The MAC IP core implements the following flow control mechanisms:

  • IEEE 802.3 flow control—implements the IEEE 802.3 Annex 31B standard to manage congestion. When the MAC IP core experiences congestion, the core sends a pause frame to request its link partner to suspend transmission for a given period of time. This flow control is a mechanism to manage congestion at the local or remote partner. When the receiving device experiences congestion, it sends an XOFF pause frame to the emitting device to instruct the emitting device to stop sending data for a duration specified by the congested receiver. Data transmission resumes when the emitting device receives an XON pause frame (pause quanta = zero) or when the timer expires.
  • Priority-based flow control (PFC)—implements the IEEE 802.1Qbb standard. PFC manages congestion based on priority levels. It supports up to 8 priority queues. When the receiving device experiences congestion on a priority queue, it sends a PFC frame requesting the emitting device to stop transmission on the priority queue for a duration specified by the congested receiver. When the receiving device is ready to receive transmission on the priority queue again, it sends a PFC frame instructing the emitting device to resume transmission on the priority queue.
Note: Intel recommends that you enable only one type of flow control at any one time.