Cabletron Systems DMS-100 manual EIU overload control

106Chapter 4: EIU maintenance

Table 27 summarizes the preset bucket parameters for reported LAN faults.

Table 27 EIU LAN fault leaky bucket parameters

Bucket name	Bucket size	Threshold	Threshold	Error event	Good event
		set level	clear level	count value	count value
Receive	3000	3000	2970	1000	1
framing error
Receiver	3000	3000	2970	1000	1
overflow
Receive CRC	3000	3000	2970	1000	1
Transmit	60	30	15	1	1
Deferred
Loss of carrier	30000	30000	29940	10000	1
Late collision	300	300	270	10	1
Transmit	300	300	270	10	1
retries
exceeded

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

297-8991-910 Standard 03.01 August 1999