Flow Control; Back Pressure - GE MultiLink ML1200 Instruction Manual

CHAPTER 9: PORT MIRRORING AND SETUP
9.3.2

Flow Control

Note
9.3.3

Back Pressure

MULTILINK ML1200 MANAGED FIELD SWITCH – INSTRUCTION MANUAL
The setting is disabled by default. In this case, the port will not generate flow control
flow
packets and drops received flow control packets. If the
uses 802.3x Link Layer Flow Control, generates flow control packets, and processes
received flow control packets.
With the port speed set to auto (the default) and flow control set to enabled; the switch
negotiates flow control on the indicated port. If the port speed is not set to auto, or if flow
control is disabled on the port, then flow control is not used.
Use the command to set flow control:
flowcontrol
flowcontrol xonlimit=<value> xofflimit=<value>
where can be from 3 to 127 (default value is 4) and
xonlimit
127 (default value is 6).
The command disables/enables back pressure based flow control
backpressure
mechanisms. The default state is disabled. When enabled, the port uses 802.3 Layer 2 back
off algorithms. Back pressure based congestion control is possible only on half-duplex, 10-
Mbps Ethernet ports. Other technologies are not supported on the MultiLink ML1200
Managed Field Switch.
backpressure rxthreshold=<value>
where the value can be from 4 to 30 (default is 28).
rxthreshold
Back pressure and flow control are used in networks where all devices and switches can
participate in the flow control and back pressure recognition. In most networks, these
techniques are not used as not all devices can participate in the flow control methods and
notifications. Alternately, QoS and other techniques are widely used today.
In the example below, the MultiLink ML1200 Managed Field Switch is set up with flow
control and back pressure.
Example 9-2: Back pressure and flow control
ML1200#
device
ML1200(device)##
show flowcontrol
XOnLimit : 4
XOffLimit : 6
ML1200(device)##
flowcontrol xonlimit=10 xofflimit=15
XOn Limit set successfully
XOff Limit set successfully
ML1200(device)##
show flowcontrol
XOnLimit : 10
XOffLimit : 15
ML1200(device)##
show backpressure
Rx Buffer Threshold : 28
(continued on next page)
PORT MIRRORING AND SETUP
setting is enabled, the port
flow
ranges from 3 to
xofflimit
9–5