Technical data
Optimizing VSX
Check Point VSX Administration Guide NGX R67 | 155
QoS Features
Two main features of QoS are:
Resource allocation
Latency control
Resource Allocation
System resources are allocated by assigning different weights to different classes of service. A weight is the
relative portion of the available resources allocated to a class. Allocating resources according to weights
ensures full utilization of the line even if a specific class is not using all of its resources. In such a case, the
remaining resources are divided among the remaining classes in accordance with their relative weights.
Latency
For some types of traffic, such as voice and video, it is necessary to minimize the latency (delay) of packets.
Latency is controlled by defining special LLQ (low-latency queueing) classes. These classes are handled in
a strict priority manner. LLQ packets are handled immediately upon arrival, and before packets that do not
belong to LLQ classes.
QoS supports multiple LLQ classes. In some cases, it may be necessary to define more than one Low
Latency class, for example when different types of traffic have a different sensitivity to delays. In such cases,
a class with the higher sensitivity to delay receives a higher priority than a class with the lower sensitivity.
Note - When LLQ classes are used, it is assumed that the expected
traffic will not exceed a relatively small amount of the available
resources. Although QoS does not allow LLQ traffic to starve non-LLQ
traffic, too much LLQ traffic reduces overall network quality of service
and prevents efficient management of weighted resources.
WRED
RED (Random Early Drop) is a congestion avoidance mechanism for detecting and preventing congestions.
It takes advantage of TCP's congestion control mechanism by randomly dropping packets during periods of
congestion. This causes TCP senders to slow down their transmission, thus preventing high congestion.
QoS implements WRED (Weighted RED) in which packets are dropped according to their priority. WRED
mostly affects traffic which is of low priority and which exceeds its weight.
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 ("The cpqos Command" on page 156) 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