Cabletron Systems ZX-250 manual EFCI, EPD, and RM Thresholds, QoS Queue Recommended Settings

Traffic Management Switch Administration

Quality of Service Queue Allocation Guidelines

The following values are recommended settings for the Min and Max thresholds for the QoS queues under specific sustained traffic conditions. Use the settings in Table 4-3as guidelines for threshold settings.

Table 4-3 Settings for QoS queues

QoS Queue	Recommended 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.

4.6.3EFCI, EPD, and RM Thresholds

To control switch congestion, the SmartCell ZX-250 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 commands 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-QoS-queue basis, while EPD thresholds are set with respect to the total amount of shared buffer 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; this assures 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.

4-22 SmartCell ZX-250 User Guide