Allied Telesis AT-S20 - Manual (Page 53)

AT-S20 User’s Guide
4-23
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This feature is available for the XL versions only. For backpressure to
be implemented, the ports must be in half-duplex mode.
Backpressure is useful when a port’s input buffer is running low on of
memory resources. For example, outbound packets are traversing a
single uplink port. When backpressure is enabled, the switch
simulates a collision when its input buffers are nearly filled so that
sending devices will defer transmissions. These sending devices will
retry transmissions according to the Ethernet back-off algorithm.
Once switch resources are available again, the switch stops sending
the collision signals and devices can freely transmit again. Figure 4-2
shows backpressure enabled.
Figure 4-2 Enabling Backpressure