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106 Chapter 4: EIU maintenance
297-8991-910 Standard 03.01 August 1999
Table 27 summarizes the preset bucket parameters for reported LAN faults.
EIU overload control
In an overload situation, the EIU overload control discards packets at the
interrupt level rather than at the process level.
The feedback scheme is devised such that packets received either from the
Ethernet interface or F-bus interface are discarded when the EIU resources
reach critical condition. The EIU can withstand a broadcast storm or a
babbling node due to overload controls that have been implemented. This level
of robustness follows standard DMS maintenance philosophy: a node must be
maintainable even under overload conditions.
Lab tests show that a moderately loaded LAN with broadcast messages
resulted in the workstation and the router locking up while the EIU remained
functional. The workstations were overloaded to the point that all activity
within 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 packets
Table 27 EIU LAN fault leaky bucket parameters
Bucket name Bucket size Threshold
set level
Threshold
clear level
Error event
count value
Good event
count value
Receive
framing error
3000 3000 2970 1000 1
Receiver
overflow
3000 3000 2970 1000 1
Receive CRC 3000 3000 2970 1000 1
Transmit
Deferred
60 30 15 1 1
Loss of carrier 30000 30000 29940 10000 1
Late collision 300 300 270 10 1
Transmit
retries
exceeded
300 300 270 10 1