Cabletron Systems ELS100-8TXUF2 manual Appendix B. Flow Control

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APPENDIX B. FLOW CONTROL

Flow control is a mechanism that controls the flow of data in both directions to prevent data loss, buffer deadlock, overload conditions and minimizing communications overhead during transmission. Figure B-1 illustrates flow control for both half and full duplex applications.

Figure B-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 buffer on port Y starts filling up with data until it reaches a pre-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. Note that for the full duplex pause frame mechanism to work, the device connected to the switch port must also support IEEE 802.3x flow control.

The pause frame flow control mechanism supported by the ELS100- 8TXUF2 switch conforms with the IEEE 802.3x specification for full duplex flow control.

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Contents Installation User Guide ELS100-8TXUF2 Fast Ethernet SwitchPage FCC Notice Industry Canada Notice Cabletron SYSTEMS, INC Program License Agreement 9033029 9033029 9033029 Cabletron Systems Limited Program License Agreement Viii 9033029 Declaration of Conformity 9033029 Table of Contents ELS100-8TXUF2 Conventions PrefacePurpose AudienceXiv Preface Description FeaturesProduct Overview Name Function Front PanelPort LEDs Defined Rear PanelAuto-negotiation Feature SummariesIeee 802.1D Bridge Frame Buffering and Frame LatencyFlow Control Full Duplex ModeApplication Examples LEDsClient/Server Network Application Client/Server Network ApplicationSite Requirements InstallationInspecting Your Shipment Mounting the Switch on a Table or Shelf Mounting the Switch on a Wall Mounting the Switch on a WallPower-Up Verification Powering the SwitchFiber Network Cable RequirementsCopper 10Base-T/100Base-TX Ports Inserting an RJ-45 Connector into a Port100Base-FX Fiber Ports Inserting a Dual SC Connector into a PortELS100-8TXUF2 General Appendix A. Technical SpecificationsMemory Port SpecificationsMDI/MDI-X Crossover Cable Wiring PhysicalTable A-2. Power Adapter Requirements Power Adapter RequirementsELS100-8TXUF2 Appendix B. Flow Control ELS100-8TXUF2 Term Definition Appendix C.ACRONYMS AbbreviationsELS100-8TXFU2 Index ELS100-8TXUF2
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