Allied Telesis AT-8016F/MT Installation Manual page 45

AT-8000 Series Fast Ethernet Switches Installation Guide
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 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.
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