Understanding HQoS
The traditional Quality of Service (QoS) technology schedules packets based on interfaces. An interface, however, can identify priorities of different services but cannot identify services of different users. Packets of the same priority are placed into the same queue on an interface, and compete for the same queue resource. Therefore, the traditional QoS technology is unable to provide differentiated services based on traffic types and users.
Currently, more and more enterprises construct their own intranets by leasing dedicated lines from carriers. Enterprises may focus on different services and need differentiated QoS. Enterprises are required to provide different scheduling policies and QoS guarantee based on enterprises' services. Traditional QoS technology cannot provide differentiated services because it cannot identify users.
As users increase continuously and services develop, users require differentiated services so that better QoS is provided at less cost. Hierarchical Quality of Service (HQoS) implements hierarchical scheduling based on queues and differentiates services and users. It provides QoS guarantee and saves network operation and maintenance costs.
Queues Supported by HQoS
As shown in Figure 6-1, the device supports three levels of queues, that is, level-3 flow queue (FQ), level-2 subscriber queue (SQ), and level-1 port queue. The HQoS hierarchy is a tree structure. A flow queue is taken as a leaf and a port queue is taken as the root. When packets pass through an interface configured with HQoS, the packets are classified so that they traverse the branches of the tree. Packets arrive at the top of the tree and are classified on one of the leaves. Packets then traverse down the tree until they are transmitted out the interface at the root.
Flow queue
The same type of services of a user is taken as a service flow. HQoS schedules queues based on service flows. A flow queue including EF, AF, and BE queues corresponds to a service type. You can configure scheduling modes for flow queues.
Subscriber queue
All services of a user are taken as a subscriber queue. HQoS allows all services in the subscriber queue to share bandwidth.
Port queue
Each port corresponds to a queue and port queues are scheduled in RR mode. You can only configure interface-based traffic shaping, and cannot configure scheduling modes.
HQoS Scheduler
HQoS implements hierarchical scheduling and provides good service support.
The device provides three levels of schedulers, that is, flow queue scheduler, subscriber queue scheduler, and port queue scheduler. The flow queue scheduler and subscriber queue scheduler support PQ scheduling, WFQ scheduling, and PQ+WFQ scheduling. The port queue scheduler uses RR scheduling.
- Controlling traffic scheduling among the three types of services of a single enterprise user
- Controlling total bandwidth of the three types of services of a single enterprise user
- Controlling bandwidth allocation between multiple enterprise users
- Controlling total bandwidth of multiple enterprise users
HQoS Shaper
HQoS shapers buffer packets and limit the packet rate. The device supports three levels of shapers, that is, flow queue shaper, subscriber queue shaper, and port queue shaper. After packets enter the device, the device buffers the packets in queues and sends the packets at the limited rate. Shapers can ensure the CIR and limit the rate of packets by using the rate limit algorithm.
HQoS Dropper
Port queue: tail drop
Subscriber queue: tail drop
Flow queue: tail drop and WRED