What is QoS?

[anand]

Hi,

I just wanted to the what is QoS & in what way that is going to improve the network performance. thanks in advance.

[scottmac]

QOS = Quality of Service ... it's a method for marking packets & frames (COS = Class of Service) such that, if the network infrastructure (all of it) is configured to watch for it, provides a mechanism to allow you to prioritize your traffic.

For example, VoIP& realtime video are sensitive to delay and variance of delay. By being able to mark VoIP and video traffic at a higher priority (and using a network that supports it), you provide a path that is likely to give better performance for those applications.

Most data traffic (web, database ...) is not time or delay sensitive, so it can be marked at a lower priority. Network infrastructure configured for QOS/COS will permit the higher priority traffic (voice, video) to pass ahead of lower priority (web, database) traffic.

Another part of it is which packets/frames are better to discard in the event that some congestion occurs. Along the path, if a congested queue is encountered, the infrasturcture device is given a clue as to which traffic is preferred to be lost ... saving the critical traffic.

Here's a link on the main Cisco site that discusses the various QOS types.

http://www.cisco.com/en/US/tech/tk543/tsd_technology_support_category_home.html

Good Luck

Scott

[johgill]

Remember that QoS, above all, does not give you any more bandwidth. In switching, you basically use a combination of queueing, scheduling, marking, policing, and congestion avoidance in order to give certain classes of traffic a higher or lower "quality" of service.

This is a very broad topic and is similar to asking what quality of life is. There are many factors, but you should start with what you want to accomplish, and sometimes QoS can get you there.

Regards