Cabletron Systems SmartSTACK ELS100-S24TX2M User Manual

Also see for SmartSTACK ELS100-S24TX2M: Quick installation guide Quick installation guide Management guide

Contents

9033260-01 Flow Control 35APPENDIX B. FLOW CONTROLFlow control is a mechanism which allows you to protect the switch fromoverload conditions and to keep additional traffic off the network whenexcessive congestion will result. Figure B-1 illustrates flow control for bothhalf and full duplex applications.Figure B-1. Flow Control for Full and Half Duplex ApplicationsEach port of the switch has a transmit queue which buffers frames to besent out on that port. In this example, large amounts of data are beingsent from Workstation A (connected to port X) and other ports on theswitch to Workstation B (connected to port Y).The queue on port Y startsfilling up with data until it reaches a determined threshold. The packetwhich causes the threshold to be exceeded triggers the Flow Controlfunction on the port from which the packet entered the switch, in this caseport X.Since port X is configured with Flow Control set to Enabled, the switchresponds by initiating a pause frame (full duplex applications) or back-pressure mechanism (half duplex applications). The pause frame causesWorkstation A to stop sending packets. After a certain amount of time haselapsed, determined by a value in the pause frame, Workstation A willresume sending data. Similarly, the back-pressure mechanism forcesWorkstation A to stop sending packets by inducing collisions on port X.The pause frame flow control mechanism supported by theELS100-S24TX2M switch conforms with the IEEE 802.3x specification forfull duplex flow control.For the full duplex pause frame mechanism to work, the device connectedto the switch port must also support IEEE 802.3x flow control. FlowControl is configurable per port in the Port Configuration Menu of theconsole menus, using the on-board Web agent, or via SNMP.