Introduction

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0.0. Introduction

Why QoS (Quality of Service) need to be applied? Well, the answer could be that perhaps you have some problems with your networks. Perhaps you have them but you don't know. Or perhaps you know you have them because user and customer complaints are very frequent.

For inquiring about QoS problems first thing you have to do is listening to your users and customers. Are they happy? Are there problems? What kind of problems do they report more frequently? Are those problems related to service availability, reduced bandwidth, poor and slow application response behavior, frequent timeouts and delays, corrupted data, etc.

If you have this kind of complaints you have to pay attention and figure out what's happening. In front of theses problems almost everyone will tell you that your network need, urgently, a deep upgrade including new equipments and connections. Faster routers and switches, higher rate cables, new high capability servers and workstations and higher speed wan links. Redesign your topology and spend a lot of money to try to resolve the problem.

You can do that or you better have a cup of coffee and analize problems carefully. Perhaps what people are saying is true or perhaps it's not. Having the right answer requires that before spending money take first some time to study the network behavior to get a better understanding about what is ocurring.

To begin with it's absolutely necessary to be sure that your network infrastructure is viable or sustainable. If your network infrastructure is not sustainable problems are not going to be resolved applying QoS knowledge and tools; instead you have to think about a network redesign and reengineer process. These approaches are out of the scope of this document.

How do you know if your network infrastructure is sustainable? First you have to check that load is manageable with actual infrastructure or at least making some minor changes to it. If load is manageable problems could be resolved improving the topology, checking if it is possible to balance better the load moving some pieces from here to there and some from there to here, or applying policy routing, or perhaps spending a limited quantity of money to replace some old equipment, especially hubs for switches that is a method that pays better and faster the money to be invested.

After making the "petite" reengineer process indicated above QoS can be applied to fine tune the network behavior, increasing the utilization factor and prioritizing traffic to make your users and customers very happy.

On the contrary, if load is not manageable because resources are very limited to support it, prepare yourself to the idea of spending some -considerable?- amount of time and money to get a reasonable solution.

By the way and before continuing it´s very important to leave clearly affirmed that QoS is not a miracle solution and can only be successfully applied when following premises are previously fulfilled: load is manageable and networks are well designed. Trying to apply QoS not resolving first these problems is like trying to cure a cancer using an aspirine based treatment. As I said before is out of the scope of this document to focus these problems; we are going to limit ourself to the approach of applying QoS to a well behave network.

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