QoS Management

To manage the network quality of service it is necessary to create and install a QoS policy. The QoS policy consists of a list of up to 15 classes of service. Each class is assigned certain traffic characteristics and DSCP values.

The QoS policy is managed using the cpqos command.

Class of Service Definitions

The definition of a class of service includes the following:

• Name. The class name is a unique identifier which identifies the class during configuration and when presenting statistics
• Type. There are two types of classes, LLQ and regular classes. Regular classes are non-LLQ classes which can be assigned a weight value.
• Priority. Each class is assigned a unique priority value between 1 and 15. The priority value is effective in prioritizing LLQ classes and during congestion, when drops occur.
• Weight value. Each class is assigned a specific weight value
• One or more DSCP values. The Differentiated Services code point

Priority and LLQs

If there are multiple LLQ classes, packets are handled in a strict priority-based manner. Packets from a class with a higher priority are handled before packets with a lower priority class.

Priority and Drop Precedence

Priority also determines the probability of drops. A class with a lower priority has a higher drop precedence during times of congestion.

The class priority is not the only factor that determines if drops occur. Other factors affect drops, for example if the class is LLQ or if the class exceeds its assigned resource allocation.

LLQ's are not immune to drops. Although LLQ's are processed as soon as they arrive (and thus have a lower drop rate), drops may occur if there are many LLQ classes or if a large portion of the incoming traffic is LLQ.