28 CHAPTER 2: OPTIMIZING BANDWIDTHa link do not support auto-negotiation, both ends must be manually setto full duplex or half duplex accordingly.Ports operating at 1000 Mbps support full duplex mode only.Flow Control All Switch ports support flow control, which is a mechanism that preventspacket loss during periods of congestion on the network. Packet loss iscaused by one or more devices sending traffic to an already overloadedport on the Switch. Flow control prevents packet loss by inhibiting thetransmitting port from generating more packets until the period ofcongestion ends.Flow control is implemented using the IEEE Std 802.3-2002(incorporating 802.3x) for ports operating in full duplex mode, andIntelligent Flow Management (IFM) for ports operating in half duplexmode.Auto-negotiation Auto-negotiation allows ports to automatically determine the best portspeed, duplex-mode (only at 10 Mbps and 100 Mbps) and flow control.When auto-negotiation is enabled (default), a port “advertises” itsmaximum capabilities — these capabilities are by default the parametersthat provide the highest performance supported by the port.You can modify the capabilities that a port “advertises” on a per portbasis, dependant on the type of port.You can disable auto-negotiation for the whole Switch, or per port. Youcan also modify the capabilities that a port “advertises” on a per portbasis, dependant on the type of port.1000BASE-SX and GBIC ports do not support auto-negotiation of portspeed.Ports operating at 1000 Mbps support full duplex mode only.If auto-negotiation is disabled, the auto-MDIX feature does not operateon the ports. Therefore the correct cables, that is, cross-over orstraight-through need to be used. For more information, see the GettingStarted Guide that accompanies your Switch.Conditions that affect auto-negotiation: Ports at both ends of the link must be set to auto-negotiate.
