Allied Telesis AT-8350GB - Manual (Page 47)

AT-8350GB Installation Guide
47
between the nodes, might need to instruct the faster 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 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 backpressure.
A twisted pair 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.