H3C S5120-EI series Configuration Manual

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H3C S5120-EI series Configuration Manual Manual pdf 26 page image

16QoS overviewIn data communications, Quality of Service (QoS) is a network’s ability to provide differentiated serviceguarantees for diversified traffic in terms of bandwidth, delay, jitter, and drop rate.Network resources are scarce. The contention for resources requires that QoS prioritize important trafficflows over trivial ones. For example, in the case of fixed bandwidth, if a traffic flow gets more bandwidth,the other traffic flows will get less bandwidth and may be affected. When making a QoS scheme, youmust consider the characteristics of various applications to balance the interests of diversified users andto utilize network resources.The following section describes some typical QoS service models and widely used, mature QoStechniques.QoS service modelsBest-effort service modelThe best-effort model is a single-service model and also the simplest service model. In this service model,the network does its best to deliver packets, but does not guarantee delivery or control delay.The best-effort service model is the default model in the Internet and applies to most network applications.It uses the first in first out (FIFO) queuing mechanism.IntServ modelThe integrated service (IntServ) model is a multiple-service model that can accommodate diverse QoSrequirements. This service model provides the most granularly differentiated QoS by identifying andguaranteeing definite QoS for each data flow.In the IntServ model, an application must request service from the network before it sends data. IntServsignals the service request with the Resource Reservation Protocol (RSVP). All nodes receiving the requestreserve resources as requested and maintain state information for the application flow.The IntServ model demands high storage and processing capabilities because it requires all nodes alongthe transmission path to maintain resource state information for each flow. This model is suitable forsmall-sized or edge networks, but not large-sized networks, for example, the core layer of the Internet,where billions of flows are present.DiffServ modelThe differentiated service (DiffServ) model is a multiple-service model that can satisfy diverse QoSrequirements. It is easy to implement and extend. DiffServ does not signal the network to reserveresources before sending data, as IntServ does.All QoS techniques in this document are based on the DiffServ model.