Cabletron Systems SmartSTACK ELS100-24TXM, Инструкция по установке и эксплуатации

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9032785 Flow Control 87
APPENDIX C. FLOW CONTROL
Flow control is a mechanism which allows you to protect the switch from
overload conditions and to keep additional traffic off the network when
excessive congestion will result. Figure C-1 illustrates flow control for
both half and full duplex applications.
Figure C-1. Flow Control for Full and Half Duplex Applications
Each port of the switch has a transmit queue which buffers frames to be
sent out on that port. In this example, large amounts of data are being
sent from Workstation A (connected to port X) and other ports on the
switch to Workstation B (connected to port Y).The queue on port Y starts
filling up with data until it reaches a determined threshold. The packet
which causes the threshold to be exceeded triggers the Flow Control
function on the port from which the packet entered the switch, in this case
port X.
Since port X is configured with Flow Control set to Enabled, the switch
responds by initiating a pause frame (full duplex applications) or back-
pressure mechanism (half duplex applications). The pause frame causes
Workstation A to stop sending packets. After a certain amount of time has
elapsed, determined by a value in the pause frame, Workstation A will
resume sending data. Similarly, the back-pressure mechanism forces
Workstation A to stop sending packets by inducing collisions on port X.
The pause frame flow control mechanism supported by the
ELS100-24TXM switch conforms with the IEEE 802.3x specification for
full duplex flow control.