3Com 3c17300 Implementation Guide - Page 15
Auto-negotiation, Multicast Filtering, Optimizing Bandwidth
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Switch Features Explained 17 Auto-negotiation Auto-negotiation allows ports to auto-negotiate port speed, duplex-mode (only at 10 Mbps and 100 Mbps) and flow control. When auto-negotiation is enabled (default), a port "advertises" its maximum capabilities - these capabilities are by default the parameters that provide the highest performance supported by the port. For details of the auto-negotiation features supported by your Switch, please refer to the Management Quick Reference Guide that accompanies your Switch. Ports operating at 1000 Mbps only support full duplex mode. Duplex Full duplex mode allows packets to be transmitted and received simultaneously and, in effect, doubles the potential throughput of a link. Flow Control All Switch ports support flow control, which is a mechanism that minimizes packet loss during periods of congestion on the network. Flow control is supported on ports operating in half duplex mode, and is implemented using the IEEE 802.3x standard on ports operating in full duplex mode. Smart Auto-sensing Smart auto-sensing allows auto-negotiating multi-speed ports, such as 10/100 Mbps or 10/100/1000 Mbps, to monitor and detect high error rates, or problems in the "physical" interconnection to another port. The port reacts accordingly by tuning the link from its higher speed to the lower supported speed to provide an error-free connection to the network. For more information about auto-negotiation and port capabilities, see Chapter 2 "Optimizing Bandwidth". Multicast Filtering Multicast filtering allows the Switch to forward multicast traffic to only the endstations that are part of a predefined multicast group, rather than broadcasting the traffic to the whole network. The multicast filtering system supported by your Switch uses IGMP (Internet Group Management Protocol) snooping to detect the