106 Chapter 4: EIU maintenance297-8991-910 Standard 03.01 August 1999Table 27 summarizes the preset bucket parameters for reported LAN faults.EIU overload controlIn an overload situation, the EIU overload control discards packets at theinterrupt level rather than at the process level.The feedback scheme is devised such that packets received either from theEthernet interface or F-bus interface are discarded when the EIU resourcesreach critical condition. The EIU can withstand a broadcast storm or ababbling node due to overload controls that have been implemented. This levelof robustness follows standard DMS maintenance philosophy: a node must bemaintainable even under overload conditions.Lab tests show that a moderately loaded LAN with broadcast messagesresulted in the workstation and the router locking up while the EIU remainedfunctional. The workstations were overloaded to the point that all activitywithin the operating system stopped:• the on-screen clock stopped ticking• the cursor did not respond to mouse movements• keystrokes were ignored• outgoing LAN activity stopped• programs were not aware that a period of time had elapsed• the router stopped routing packetsTable 27 EIU LAN fault leaky bucket parametersBucket name Bucket size Thresholdset levelThresholdclear levelError eventcount valueGood eventcount valueReceiveframing error3000 3000 2970 1000 1Receiveroverflow3000 3000 2970 1000 1Receive CRC 3000 3000 2970 1000 1TransmitDeferred60 30 15 1 1Loss of carrier 30000 30000 29940 10000 1Late collision 300 300 270 10 1Transmitretriesexceeded300 300 270 10 1
