Allied Telesis AT FS708LE AT-FS708LE AT-FS708LE Installation Manual page 17

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.
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