Quality of Service

EildorEildor Member Posts: 444
in CCNP
I'm not knowledgeable with QoS (yet another thing I need to learn at some point).

How is QoS implemented for voice when you have a L2 access layer? From what I've been reading it sounds like you don't implement QoS at the access layer, you implement CoS instead. Is this correct?

What about at the distribution layer where routing takes place? Is QoS necessary there?
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  • EildorEildor Member Posts: 444
    Sorry, slightly confused. Does autoqos implement CoS? Because the access layer here is L2, with trunk links connecting to the distribution layer.
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  • networker050184networker050184 Mod Posts: 11,962 Mod
    I think you are a little confused on the terminology. QoS is just the Cisco way to describe implementing traffic management tools whether they be marking with DSCP at L3 or CoS bits at L2.
    An expert is a man who has made all the mistakes which can be made.
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  • EildorEildor Member Posts: 444
    Right, so it sounds like I need to implement CoS at the access layer, and DSCP at the distribution layer with some some sort of L2 to L3 QoS mapping... what does the autoqos command do exactly then? Does it configure CoS parameters as well as DSCP parameters? What about the mappings?
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  • networker050184networker050184 Mod Posts: 11,962 Mod
    You can configure your switches to map IP Prec/DSCP to CoS bits, vice versa, or what ever you need really. Auto QoS will set up all the basics of this for you with queueing, scheduling, policing etc. I think you'd be best set to do some reading on all the different L2 QoS technologies before diving into quto QoS. Auto QoS will do most of it for you, but it's better to have a good understanding of what's going on behind the scenes.
    An expert is a man who has made all the mistakes which can be made.
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  • aaron0011aaron0011 Member Posts: 330
    With AutoQOS I believe CoS bit 5 is mapped to the DSCP EF PHB, this is typically used for the audio stream (RTP traffic).

    I believe the call signaling by default is CoS 3 at the Layer 2 level and is mapped to the DSCP CS3 PHB at Layer 3.

    Depending on your scenario you may want to use a higher DSCP PHB for signaling.
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  • EildorEildor Member Posts: 444
    AutoQoS will do for now. This is for a university assignment, doesn't need to be complicated. But yeah, I will look into QoS properly at some point for sure. I remember there being some coverage of QoS in CCNP SWITCH OCG, maybe I'll have a read of that to start off... but I can't remember it being much. Thanks guys.
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