Flow Control; Back Pressure - GE MULTILINK ML2400 Instruction Manual

CHAPTER 9: PORT MIRRORING AND SETUP
Note
9.3.2

Flow Control

Note
9.3.3

Back Pressure

MULTILINK ML2400 ETHERNET COMMUNICATIONS SWITCH – INSTRUCTION MANUAL
To change the port speed on a transceiver port, it is required to reboot the switch.
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 family of
switches.
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 family of switches are setup with flow control and back
pressure.
PORT MIRRORING AND SETUP
setting is enabled, the port
flow
ranges from 3 to
xofflimit
9–5