Re: DSCP values

paltel · ‎07-08-2005

We know that there are 4 classes for AF, AF1,AF2,AF3, and AFf. and for each class there is 3 Drop Probabilities. AF technique quarantees bandwidth for specific class and maybe use extra bandwidth if available. i have a question, AF4 has better teatment than 3,2,and 1. right? In other words, what is the difference between each one.

If we decide to use shaping, and the traffic marked a edge router, there is a benefit from traffic marking if we will use WRED as congestion avoidance at the core router, right? And also, we will apply shaping at the edge router and also at the output interface for this remote site and the core router, right?

Thanks in advance

Kevin Dorrell · ‎07-08-2005

The AF classes (and drop probabilities) do not have any inherrent traffic engineering. They are only tags that you can apply to your traffic. It is then up to your policies to decide how to handle each class of traffic based on the tag. But the point is that you decide the policy.

Having said that, the convention and the reccommendation, is that AF4 gets a better treatment than 3, 2, 1 etc, but it's only a convention. You could write a policy that give priority to AF13. It it would be a bit perverse, but quite possible.

You can apply your policies where you like, but they are really only useful where there are potentially congested links. And that is the other point - the traffic engineering is applied link by link. That is why Differentiated Services are also known as "PHB - Per Hop Behaviors".

Kevin Dorrell

Luxembourg

paltel · ‎07-08-2005

Thank you.

I have another question, if we would like to apply QoS for specific time only. I think time-based ACL will help us, , but if the time inactive, i think all the traffic will match class-default right? and this will be problem (all of the traffic will have a bandwidth apllied to the class-default). Is there is another solution to do that?

Thanks in advance

Kevin Dorrell · ‎07-09-2005

Sorry, I've never used time-based ACLs for QoS, so I don't know how they behave. Can anyone else help us out? I would be interested to hear the answers to this one too.

Kevin Dorrell

Luxembourg

paltel · ‎07-22-2005

Anyone help us about time based QoS?