Allied Telesis AlliedWare Plus Operating System Version 5.4.4C (x310-26FT,x310-26FP,x310-50FT,x310-50FP) - Manual (Page 364)

Switching Commands
Software Reference for x310 Series Switches
15.2 AlliedWare Plus TM Operating System - Version 5.4.4C C613-50046-01 REV A
Command List
This chapter provides an alphabetical reference of commands used to configure
switching. For more information see
Chapter 14, Switching Introduction .
backpressure
This command provides a method of applying flow control to ports running in half duplex
mode. The setting will only apply when the link is in the half-duplex state.
You can disable backpressure on an interface using the off parameter or the no variant of
this command.
Syntax backpressure {on|off}
no backpressure
Default Backpressure is turned off by default. You can determine whether an interface has
backpressure enabled by viewing the running-config output; backpressure on is shown
for interfaces if this feature is enabled.
Mode Interface Configuration
Usage The backpressure feature enables half duplex Ethernet ports to control traffic flow during
congestion by preventing further packets arriving. Back pressure utilizes a pre-802.3x
mechanism in order to apply ethernet flow control to switch ports that are configured in
the half duplex mode.
The flow control applied by the flowcontrol (switch port) command on page 15.11
operates only on full-duplex links, whereas back pressure operates only on half-duplex
links.
If a port has insufficient capacity to receive further frames, the switch will simulate a
collision by transmitting a CSMACD jamming signal from this port until the buffer empties.
The jamming signal causes the sending switch to stop transmitting and wait a random
period of time, before retransmitting its data, thus providing time for the buffer to clear.
Although this command is only valid for switch ports operating in half-duplex mode the
remote switch (the one sending the data) can be operating in the full duplex mode.
To see the currently-negotiated duplex mode for ports whose links are up, use the
command
show interface . To see the configured duplex mode (when different from the
default), use the command show running-config .
Examples To enable back pressure flow control on interfaces port1.0.1-port1.0.2 enter the
following commands:
Parameters Description
on Enables half-duplex flow control.
off Disables half-duplex flow control.
awplus# configure terminal
awplus(config)# interface port1.0.1-port1.0.2
awplus(config-if)# backpressure on