AT-FS708LE Installation Guide
end-node to stop transmitting data to allow the slower end-node to catch up. An example of this would be when a server operating at 100 Mbps is sending data to a workstation operating at only 10 Mbps.
How a switch signals an end-node to stop transmitting data differs depending on the speed and duplex mode of the end-node and switch port. A twisted pair port operating at 100 Mbps port and half-duplex mode stops an end-node from transmitting data by forcing a collision. A collision on an Ethernet network occurs when two end-nodes attempt to transmit data using the same data link at the same time. A collision causes end-nodes to stop sending data. When the switch needs to stop a 100 Mbps, half-duplex end-node from transmitting data, it forces a collision on the data link, which stops the end-node. Once the switch is ready to receive data again, the switch stops forcing collisions. This is referred to as back pressure.
A port operating at 100 Mbps and full-duplex mode uses PAUSE frames, as specified in the IEEE 802.3x standard, to stop the transmission of data from an end-node. Whenever the switch wants an end-node to stop transmitting data, it issues this frame. The frame instructs the end- node to cease transmission. The switch continues to issue PAUSE frames until it is ready again to receive data from the end-node. This is referred to as flow control.