D-Link DGS-6600-48TS Configuration Guide - Page 384

Volume 6-QOS / Chapter 36-Quality of Service (QoS) QoS Configuration Commands The purpose of QoS is to make traffic delivery more predictable to meet different user's requirement and make more effective use of the bandwidth. This functionality is achieved by the following major functional components: classification, marking, policing, and congestion avoidance. To utilize the network bandwidth more efficiently, normally the aggregated guarantee bandwidth needs to be within the available bandwidth, but the aggregate of non-guarantee service can be overprovisioned. Normally, when user traffic enters the edge node, they will be classified based on the fields of the packet and polices based on the service agreement in terms of Committed Information Rate (CIR), or size of burst. The result of classification or policing will mark the packet with an appropriate QoS label. With this marked QoS label, the internal node can simply trust it and provide the QoS treatment accordingly. The QoS can be either labeled via IEEE 802.1p priority tag or the DSCP field for IP packets. Since different packets may have different latency requirements, and the traffic from a user normally comes in bursts, the packet will be put in different transmit queues of the egress port. The packet with different QoS labels can have different drop probability during the transmit link's congestion. Thus, the QoS label of a packet will affect how the transmit queue is selected, and how the packet is handled during congestion. Policing and Color Markers Policing is the monitoring of the data rates for a particular class of traffic. When the data rate exceeds user-configured values, marking or dropping of packets occurs immediately. When traffic exceeds the data rate, you instruct the system to either drop the packets or mark QoS fields in them. You can define single-rate, dual-rate, and color-aware policers. Single-rate policers monitor the committed information rate (CIR) of traffic. Dual-rate policers monitor both CIR and peak information rate (PIR) of traffic. In addition, the system monitors associated burst sizes. IP packet stream are metered and it's packets are marked based on two rates, Peak Information Rate (PIR) and Committed Information Rate (CIR), and their associated burst sizes to be either green, yellow, or red. A packet is marked red if it exceeds the PIR. Otherwise it is marked either yellow or green depending on whether it exceeds or doesn't exceed the CIR. Color-aware policers assume that traffic has been previously marked with a color. This information is then used in the actions taken by this type of policer. QoS Configuration Commands Defining the Queuing Criteria One of the most important factors when configuring QoS on the Switch is to determine the transmit queue. The first step in determining the transit queue is to determine the trust state of the interface. The next step is to configure the CoS mapping to a queue. Finally, the DCSP needs to be mapped to CoS. DGS-6600 Configuration Guide 384