GE ML1200 Flow Control, Back Pressure, Flowcontrol xonlimit=value xofflimit=value

CHAPTER 9: PORT MIRRORING AND SETUP PORT MIRRORING AND SETUP

9.3.2Flow Control

The flow setting is disabled by default. In this case, the port will not generate flow control packets and drops received flow control packets. If the flow setting is enabled, the port 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 flowcontrol command to set flow control:

flowcontrol xonlimit=<value> xofflimit=<value>

where xonlimit can be from 3 to 127 (default value is 4) and xofflimit ranges from 3 to 127 (default value is 6).

9.3.3Back Pressure

The backpressure command disables/enables back pressure based flow control 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 rxthreshold value can be from 4 to 30 (default is 28).

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

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MULTILINK ML1200 MANAGED FIELD SWITCH – INSTRUCTION MANUAL 9–5