Samsung Ubigate iBG3026, Configuration Manual

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CHAPTER 19. QoS
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© SAMSUNG Electronics Co., Ltd.
Egress Queuing, Shaping and Scheduling
The CBQ along with congestion detection & avoidance and scheduling
algorithm forms full fledged class-based packet queuing and scheduling
method in the iBG3026 platform. Shaping of egress traffic to a configured
‘peak rate’ is also supported as part of CBQ. The following sub-sections
provide details on design, implementation and configuration & management.
The CBQ feature works closely with the hierarchical MF classifier. As a first
step, traffic classes should be configured in a hierarchical fashion in the
outbound direction on an interface. The leaf-classes are of greater significance
since they actually represent the traffic flows for which QoS needs to be
configured. When CBQ is enabled, each leaf-class will have a queue(‘class-
queue’) associated with it. Hence the term Class Based Queuing. CBQ service
parameters can be configured for each leaf-class.
These parameters are Committed Rate(CR), Peak Rate(PR) and Priority.
After the destination look-up, the outgoing interface is identified and the
packet is taken through the hierarchical MF classification configured on that
interface. After the packet is classified into a leaf traffic class, it is placed in
its class-queue. The CBQ scheduler periodically services the class-queues of
all leaf traffic classes on each interface. The service that each class queue
receives depends on the service parameters(CR, PR, Priority) assigned to it.
Eight priority levels will be supported. Priority 1 is the highest and 8 is lowest.
CBQ Scheduler Operation
This section explains the scheduler operation and algorithm.
The scheduler lists are part of CBQ structure. As you see, the scheduler list
contains only leaf classes of egress classification tree in given interface.
There are eight prioritized individual scheduling lists numbering from 1
through 8, where 1 being the highest, and 8 being the lowest priority.
Each scheduling list is formed as circular linked list of same priority classes.
In each list head points to leaf class from where scheduling starts with.
The rest of the section explains about scheduling operation, excess bandwidth
list formation, fairness for classes in the same priority.