Setting Up the Switch Unit 4-9Setting Up the Switch UnitWith the Switch Management screen displayed,choose the management level Unit, then select theSETUP button.The Unit Setup screen is displayed as shown inFigure 4-10. The screen shows the following:Unit Name This read-only field shows the type ofdevice.sysName This field takes its name from the MIB IISystem Group object. You can edit the first 30 char-acters of this field to make the name more mean-ingful. This name is displayed on the Main Bannerwhen you first access the VT100 screens, and is alsoaccessible to an SNMP Network Manager.Forwarding Mode Fast Forward / Fragment Free /Store and Forward / Intelligent This field allows youto set the forwarding mode for the Switch:n Fast Forward — Frames are forwarded as soonas the destination address is received and verified.The forwarding delay, or latency, for all frames inthis mode is just 40μs but with the lack of check-ing time, error frames are propagated onto thenetwork.n Fragment Free — A minimum of 512 bits of thereceived frame is buffered prior to the framebeing forwarded. This ensures that collision frag-ments are not propagated through the network.The forwarding delay, or latency, for all frames inthis mode is 64μs.Figure 4-10 Unit Setup screen (3C16900A)n Store and Forward — Received packets are buff-ered in their entirety prior to forwarding. Thisensures that only good frames are passed to theirdestination. The forwarding delay for this modevaries between 64μs and 1.2ms, depending onframe length. In this mode the latency, measuredas the time between receiving the last bit of theframe and transmitting the first bit, is 8μs.n Intelligent — The Switch monitors the amountof error traffic on the network and changes theforwarding mode accordingly. If the Switchdetects less than 18 errors a second, it operatesin Fast Forward mode. If the Switch detectsmore than 18 errors a second, it operates inStore and Forward mode until the number oferrors returns to zero.Intelligent Forwarding Fast Forward / Store andForward This read-only field shows the forwardingstate if the Forwarding Mode is set to Intelligent.
