QoS encompasses many techniques for dealing with congestion. If there's never (ever) any congestion, there's no need to consider QoS. However, it's very rare to find networks that can't congest somewhere, yet statistically, such congestion might be acceptable for the traffic being congested. If not, the two solutions are either to increase bandwidth until the statistical results are acceptable or to deal with the congestion intelligently, i.e. QoS.
On LANs, where bandwidth is usually plentiful and relatively inexpensive, QoS might not be used at all or only in the most rudimentary fashion (e.g. only prioritize real-time traffic). On WANs, where bandwidth is often not as plentiful and relatively expensive, QoS techniques can be very beneficial.
Well,I see from the responses that it is clear that Qos will kick in only in case of congestion. I agree to this as far as queueing is concerned.
But if you consider features like policing/ shaping etc, there is no need for the link to be congested for these features to kick in. Again you could argue looking at the bigger picture... but for practical purposes, you have a fastethernet link to your SP. But you have bought only 2Mbps of bandwidth. Then you might want to shape the traffic and prioritize it so that imp. traffic is not dropped by the SP.
So yeah... "queueing" features only kick in when there is congestion. but not Qos if you consider policing/shaping etc. to be a part of it. :)
Hi everyone, I would like to thank you in advance for any help you can provide a newcomer like myself!
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