What is 802.3x Flow Control?

Flow Control is a standard defined by IEEE 802.3x that manages data transmission to prevent packet loss during network congestion. It uses pause frames to temporarily stop the sending of data, allowing the receiving device to process information without overflow. This is particularly useful in full-duplex Ethernet networks, where both devices send and receive data simultaneously. Flow control ensures smooth communication, reducing dropped packets and improving reliability.

Example Scenario: Flow Control with HMI, PLC, and Switch:

A Maple Systems HMI and a Maple Systems PLC are connected to a switch that supports IEEE 802.3x Flow Control. During regular operation, both the HMI and PLC send and receive data at the same time using full-duplex communication.

If the PLC becomes overwhelmed with incoming data (for example, due to a sudden surge in commands or updates), it may not be able to process all the packets in time. When the switch detects congestion it sends a pause frame to the HMI telling it to temporarily stop sending data. This pause allows the PLC to process the incoming data without losing packets. Once the PLC is ready, the switch sends a signal to resume normal data transmission.

This process helps prevent packet loss and ensures smooth communication between the devices.

Content created by Mike Day