QoS - Quality of Service

If we are downloading a file from the network or browsing a web page, we don't even notice the many problems that occur during the transfer. These are, for example, various delays in packet delivery or delivery in a different order than the transmission. The communication protocol handles these problems and corrects everything. The problem occurs with operations where we need the result immediately, such as VoIP and streaming audio/video. Then these problems will manifest themselves in the failure of video and audio. The technology that solves these problems is called Quality of Service.

This section of Quality of Service articles focusing on Cisco focuses on the first action we need to take when applying QoS. This involves examining the traffic and classifying it into classes - classification and then marking each packet with that class - marking.

In the last episode we dealt with sorting traffic into classes. We also covered the Modular QoS CLI, which is used to configure most QoS features on Cisco IOS. The commands for the properties that will be covered in this article were also briefly mentioned. These are bandwidth management - Traffic Rate Management, i.e. setting the maximum rate that a certain traffic (for example, a user) can consume. We will use the method of policing (rate limiting) and shaping.

In this section we will focus on the area of Congestion Management. Different queues are used for this purpose. In practice, it means that we can define a certain bandwidth for some communication, i.e. guarantee the bandwidth. And possibly to ensure express clearance (i.e. low latency) - to prioritize traffic. In the second part I will only lightly mention a similar area, Congestion Avoidance, which is solved by intelligent dropping.

The configurations that were described in the previous parts were primarily intended for routers, although they can also be used (sometimes in a more limited form) on switches. In this article, I'll cover the special commands and configurations designed for switches. Due to the principle of operation, when a switch often connects end clients, it needs to handle different operations than a router.

The last part of the series on Quality of Service focuses on simple practical examples. For those who have read the previous parts, it shows more complex configurations. But it is also suitable for those who have not read the previous articles. In my opinion, we can configure various properties without knowing the principle by which they will be implemented. The biggest focus is on the various options for limiting the speed (throughput) of the port.

This article contains various additional information regarding Quality of Service (very briefly) that I needed when I was preparing for the Cisco 642-845 test. Besides the minor additions, it talks about Link Efficiency Management, QoS pre-classification, Control Plane Policing, Cisco Router and Security Device Manager, and the addition of Auto QoS.