Cabletron Systems SmartCell 6A000 manual EFCI, EPD, and RM Thresholds

Switch Administration Traffic Management

Class of Service Queue Allocation Guidelines

The following are recommended settings for the Min and Max thresholds for the class of service queues under specific sustained traffic conditions. Use these settings as guidelines for threshold settings:

•CBR — fewer than 100 connections on a port: Min = 50, Max = 1000

•CBR — more than 100 connections on a port: Min = 100, Max = 1000

•rt-VBR — bandwidth utilization less than 20%: Min = 10, Max = 1000*

•rt-VBR — bandwidth utilization more than 20 %: Min = 100, Max = 4000*

•Nrt-VBR — for port B4 (CPU): Min = 100, Max = 4000

•Nrt-VBR — for all other ports: Min = 10, Max = 1000

•UBR — Min = 32, Max = 16,000

* Use the show cacstats command to view bandwidth utilization.

4.6.4EFCI, EPD, and RM Thresholds

To control switch congestion, the SmartCell 6A000 implements standard resource management cell (RM-cell) marking, explicit forward congestion indicator cell marking (with backward RM cell marking), and early packet discard (EPD). These congestion control schemes are triggered when the number of cells within shared memory reaches user definable thresholds. Use the switchtrafficcongestion command to view and set these thresholds.

For example, enter the show switchtrafficcongestion command.

SmartCell ZX # show switchtrafficcongestion

Switch Traffic Congestion Parameters

============================================================================

Queue 1	EFCI	Threshold	: 4096 cells
Queue 2	EFCI	Threshold	: 4096 cells
Queue 3	EFCI	Threshold	: 4096 cells
Queue 4	EFCI	Threshold	: 4096 cells
Low EPD	Threshold		: 10922 cells
High EPD Threshold			: 21845 cells
Switch Discard Threshold			: 30508 cells
RM Cell	Marking Enable		: ON
EFCI Cell Marking Enable			: ON
SmartCell ZX		#

EFCI thresholds are set on a per class of service queue basis, while EPD thresholds are set with respect to the total amount of shared buffer space being used by all classes of service.

For most types of traffic, EPD triggering is tied to the low EPD threshold. Signaling traffic, however, is tied to the high EPD threshold to assure that signaling packets are discarded only when congestion is most severe.

Use the set switchtrafficcongestion command to change thresholds for EFCI and EPD and to enable or disable RM and EFCI cell marking.

Along with EFCI and backward RM cell marking, the SmartCell 6A000 uses standard RM cell marking. The switch discard threshold (show switchtrafficcongestion) corresponds to total shared buffer utilization and represents the point at which the switch considers itself congested and starts marking RM cells.

The switch discard threshold is not user configurable and is shown only for information.

For information on troubleshooting congestion problems, see Chapter 5, "Troubleshooting."

SmartCell 6A000 User Guide 4-23