Congestion Control; Overview - Cisco ASR 5500 System Administration Manual

Congestion Control

This chapter describes the Congestion Control feature. It covers the following topics:
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Overview

Congestion Control monitors the system for conditions that could potentially degrade performance when the
system is under heavy load. Typically, these conditions are temporary (for example, high CPU or memory
utilization) and are quickly resolved. However, continuous or large numbers of these conditions within a
specific time interval may impact the system's ability to service subscriber sessions. Congestion control helps
identify such conditions and invokes policies for addressing the situation.
Congestion control operation is based on configuring the following:
• Congestion Condition Thresholds: Thresholds dictate the conditions for which congestion control is
• Service Congestion Policies: Congestion policies are configurable for each service. These policies
Overview, page 201
Configuring Congestion Control, page 202
enabled and establishes limits for defining the state of the system (congested or clear). These thresholds
function in a way similar to operation thresholds that are configured for the system as described in the
Thresholding Configuration Guide. The primary difference is that when congestion thresholds are
reached, a service congestion policy and an SNMP trap (starCongestion) are generated.
A threshold tolerance dictates the percentage under the configured threshold that must be reached in
order for the condition to be cleared. An SNMP trap, starCongestionClear, is then triggered.
◦ Port Utilization Thresholds: If you set a port utilization threshold, when the average utilization
of all ports in the system reaches the specified threshold, congestion control is enabled.
◦ Port-specific Thresholds: If you set port-specific thresholds, when any individual port-specific
threshold is reached, congestion control is enabled system-wide.
dictate how services respond when the system detects that a congestion condition threshold has been
crossed.
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